OpenUCT :: Browsing by Author "Randall, Dyllon"

Browsing by Author "Randall, Dyllon"

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Open Access
A technical and economic feasibility study on repurposing copper mine tailings via microbial induced calcium carbonate precipitation
(2021) De Oliveira, Daniel; Randall, Dyllon
The current manufacturing of clay-fired and cement bricks has contributed greatly to anthropogenic global emissions and environmental damages. A possible solution that could be used to alleviate such environmental pressures is through the adoption of carbon neutral, microbial induced calcium carbonate precipitation (MICP) bio-bricks as a replacement for traditional bricks. MICP produced bio-bricks are formed by exploiting the ability of the microorganism, Sporosarcina pasteurii, to produce a biocement capable of binding sand particles (or any aggregate) together into a solid. Furthermore, such bio-bricks can be grown from otherwise ‘waste' resources such as human urine. This significantly reduces energy inputs whilst creating value by ‘upcycling' waste streams, resulting in a product which is sustainable whilst promoting the modern ethos of implementing environmentally friendly circular economies. However, the environmental benefits of MICP bio-bricks are hindered by the use of sand in their production. Sand, after water, is by volume the worlds most exploited and traded raw material and as such the supply of sand is being rapidly depleted globally. Added to this, sand extraction processes are known to cause extensive environmental damages. A possible solution to this issue is to replace the sand aggregate used to grow bio-bricks with mine tailings. The increasing global demand for metal products has resulted in the concurrent production of vast volumes of waste mine tailings which, if left untreated, pose a potential risk of leaching toxins into surrounding populations and biota. As such it was postulated that this risk to surrounding populations and the environment could be mitigated by repurposing mine tailings, as a replacement for sand, into MICP bio-bricks. Both a technical and economic study was conducted to determine the feasibility of repurposing copper mine tailings into bio-bricks. As bio-bricks were resource intensive to produce (reagents, chemicals etc.), bio-columns were used as a proxy in studying the technical feasibility of such a process. The technical aspect of this study involved characterising copper mine tailings received from Columbia in terms of physiochemical make-up, particle size distribution and the development of a MICP submergent technique used in growing the bio-columns. This was necessitated by the fact that it was noted during the characterisation of the mine tailings that the cementation media could not be pumped through the columns filled with mine tailings aggregate, resulting in the traditional pumping method used to grow MICP bio-solids being impractical. The submergent technique was used to compare the MICP efficiency of growing biocolumns from either beach sand or copper mine tailings. In addition, the toxicity of copper to S. pasteurii was investigated and an attempt was made to acclimate a culture of S. pasteurii to the copper concentration found within copper mine tailings. Furthermore, the copper mine tailings were screened to determine if there were any indigenous, anaerobic and copper tolerant ureolytic extremophiles contained within, which had the potential to grow more robust bio-columns.
Open Access
Concentrating human urine by evaporation
(2021) Hislop, Amy; Randall, Dyllon
The current size of the global population was estimated to be 7.7 billion people in 2019. This is expected to increase to 9.7 billion people by the year 2030. To supply sufficient food for this growing population, the use of synthetic fertilizers has become a widely adopted agricultural practice. These fertilizers, rich in nitrogen, phosphorus and potassium (NPK) nutrients, ensure rapid and adequate food supply. However, the use of synthetic fertilizers is not sustainable. This is due to nitrogen (N) being derived from synthetic ammonia (NH3) produced via the energy intensive Haber-Bosch process. The phosphorus (P) in synthetic fertilizer is also mined from non-renewable phosphate rock. Similarly, a large population size leads to the inevitable generation of waste effluents collectively known as wastewater. Currently, wastewater is transported to and treated in traditional wastewater treatment facilities to ensure that nutrients in the wastewater are removed. This ensures that when the treatment plant effluent is released back into bodies of natural water, these bodies of water are not polluted. However, the cost associated with the treatment of wastewater and the maintenance of such facilities is high. As a result, less affluent countries have not been able to adequately maintain wastewater treatment facilities. One component of the wastewater that is treated in such facilities includes black water. This contains urine, faeces and other excreta that are flushed down the toilet. Although human urine contributes approximately 1% by volume, to the total wastewater generated, this urine contains approximately 80%, 56% and 63% of the total N, P and K found in domestic wastewater, respectively. In addition, traditionally black water is flushed down a toilet and enters the wastewater system, but a large portion of the global population do not have access to flushing toilets and clean drinking water. Furthermore, traditional flushing toilets use significant amounts of clean water, which in water scarce regions is a waste of an otherwise precious resource. These two ideas combined drives the need to rethink the current sanitation and wastewater practices. Rethinking current sanitation and traditional wastewater treatment practices encompasses a more wholistic approach towards achieving global sustainability – this approach considers resource recovery and reuse. As urine is rich in the same NPK nutrients required in synthetic fertilizers, it has been proposed to separate and collect this urine through source separating toilets, and more recently, waterless urinals. Before re-use, the urine should be treated and turned into a urine-based fertilizers or other products. The nutrients contained in the collected urine can be recycled back into the environment while simultaneously reducing the need for synthetic fertilizers. Separating urine from wastewater also lowers the N and P concentration entering the traditional wastewater treatment plants. This results in a wastewater stream that has a more favorable C:N:P nutrientratio for conventional wastewater treatment. Thislowers the volume requirement of the wastewater treatment plant, allowing for treatment with a relatively short sludge age. A shortened sludge age corresponds to a smaller requirement in plant volume, with lowered infrastructure and associated maintenance costs on the treatment plant. The use of waterless urinals not only allows for the removal of urine from wastewater, but also minimizes the clean water traditionally used when flushing urinals. From previous studies, it was shown 11 g of solid fertilizer could be harvested from 1 kg of urine collected in the urinal. The literature showed a diverse range of urine treatment and concentration options with evaporation being the most common. The experiments conducted in previous literature differed to the experiments in this thesis due to the chosen operating conditions (pH, temperature, humidity etc.) as well as the type of urine studied (fresh, hydrolyzed and stabilized). Furthermore, few studies focused on maximising the recovering of all key nutrients (N, P and K). Therefore, this study aimed to investigate these aspects through experiments and simulations. The purpose of this dissertation was to further understand the fertilizer produced from human urine. More specifically, this dissertation aimed to experimentally determine the urine stabilization technique that gave the highest N, P and K nutrient recoveries at a water removal interval of 100%. This dissertation also aimed to determine the effect of water removal on the solids formed when using the preferred urine stabilization method of calcium hydroxide dosing. From this, a comparison between experimental and theoretical results was presented. It was also desired to use theoretical simulations to determine the influence of urine composition on the preferred stabilization process and similarly, the influence of temperature on the preferred stabilization process. The final aim of this dissertation was to determine the energy consumed when evaporating water from urine stabilized through the preferred stabilization process. To further study the solid fertilizer produced from human urine, a series of experiments and simulations were conducted. Firstly, six synthetic urine solutions and three real urine solutions, each stabilized using different treatment techniques, were evaporated. The success of each stabilization treatment was assessed in terms of the measured NPK recovery in the urine solution. Once the preferred urine stabilization method was chosen from the NPK experiments, this urine stabilization method was used when evaporating urine solutions. Urine solutions were evaporated to water removals of 50%, 75% and 100% respectively. At each water removal percentage, the total mass of solids formed was measured, as well as the N, P and K concentrations in these resulting solids. Experimental results were compared to the theoretical results which were obtained from thermodynamic simulations. A further comparison was drawn by comparing the evaporation of synthetic and real Ca(OH)2 stabilized urine solutions. Ca(OH)2 stabilized synthetic urine solutions included both a solution with excess (unfiltered) Ca(OH)2 as well as a filtered synthetic urine solution. The reason an excess Ca(OH)2 stabilized synthetic urine solution was included in the comparison was to compare the influence of excess Ca(OH)2 on the pH of the urine solution. Thermodynamic simulations predicted that a urine solution with excess Ca(OH)2 was predicted to have a greater buffering capacity against CO2 compared to a filtered urine solution. A comparison was also drawn between the three urine solutions by studying the mass of remaining solution over time, as well as the scale formed in the synthetic and real urine solutions. A final experimental aspect considered urea hydrolysis in solution between temperatures of 40°C to 70°C, at a relative humidity of 40%. Urea solutions were evaporated at different temperature conditions in a climate chamber to determine the extent of urea hydrolysis . These experiments were evaporated for 95 hours. Urea hydrolysis experiments were repeated at 40°C and 70°C. However, these experiments were stopped once 100% of the water was removed from solution, shortening the evaporation time to 53 hours for the 70°C experimental run. Using a fixed urine composition, additional thermodynamic simulations were run. One set of simulations varied evaporation temperature and the second set of simulations varied stabilized urine composition by introducing four additional stabilized urine streams. From the simulated results, the total mass of solids as well as the mass of NPK solids were used to determine the influence of temperature and composition on the chosen stabilized urine solution. The results from the thermodynamic simulations were further processed using a basic mass and energy balance to develop a first estimate of the energy input associated with the evaporation process. This estimate was done independently for both varied temperature and varied composition conditions. From the experimental procedure, it was determined that Ca(OH)2 stabilized human urine was the preferred urine stabilization treatment as this urine solution had a nitrogen recovery of 109%. As P and K components of each urine solution were non-volatile, the preferred urine stabilized treatment was chosen by considering the solution with the highest N recovery. Although acetic acid and citric acid stabilized synthetic urine solutions has N recoveries of 103% and 93.5% respectively, it was decided that stabilizing with Ca(OH)2 power is a better stabilization method. This decision was made considering the precise dosing required when acidifying urine. This method would require additional equipment such as a dosing pump, compared to Ca(OH)2 stabilization which requires no dosing equipment. Urine stabilization with Ca(OH)2 required only the pre-addition of sufficient Ca(OH)2 powder to the urine solution. Using Ca(OH)2 stabilized synthetic urine, simulations were compared to experimental results at 50%, 75% and 100% water removal. It was found that the simulations did not compare well with experimental results. A total of 18.8 g of solids were predicted to form at 100% water removal. Experimentally 22 g solids were formed. Additionally, at 75% water removal a peak in N, P and K recovery was experimentally observed but this was not observed in the simulation results. Reasons for this deviation include the loss of ammonia to the atmosphere due to ammonia volatilization, which were not accounted for in thermodynamic simulations. The loss of urea due to urea hydrolysis was also not accounted for in OLI where experimentally 8.12% urea loss was observed at 70°C. When considering the influence of temperature on the solids formed in Ca(OH)2 stabilized urine, the simulations showed a decrease in solids with an increase in temperature. Furthermore, a change in urine composition showed that the mass of solids that formed depended on whether the quantity of ions that are present in major salts, increased or decreased in solution. Lastly, when using the simulation results to determine the input energy requirement associated with the process, it was seen that the overall input energy requirement increases with an increase in evaporating temperature. However, a changing urine composition did not have a significant effect on the overall energy input. When costing this energy requirement, a urine-based fertilizer could be produced via the evaporation process at a cost of 0.63 R kg-1 . When compared to available synthetic fertilizers, which are sold for between 13.17 and 24.53 R kg-1 , there appears to be a good business case for urine-based fertilizer production. Considering the information presented in this dissertation, it was recommended that future work consider investigating the rate of urea hydrolysis at further different operating temperatures and evaporation rates. Additionally, when considering Ca(OH)2 stabilized synthetic and real urine, Ca(OH)2 stabilized synthetic urine was a good proxy to Ca(OH)2 stabilized real urine. However, there were slight discrepancies, especially in terms of evaporation rates. Therefore, it is recommended that all the different stabilization methods used in this dissertation that were based on synthetic urine, be tested also with real urine. It was also recommended that the thermodynamic simulations account for urea hydrolysis, NH3 volatilization and the formation of CaCO3 during evaporation in future work. Finally, it was recommended that the solid fertilizer formed after complete water removal by evaporation be tested to determine its applicability to growing different crops, as well as to determine how this fertilizer compares to commercial and synthetic fertilizers.
Open Access
Development of novel fertilizer manufacturing processes using human urine
(2023) Courtney, Caitlin; Randall, Dyllon
Over 20 years of research on how to integrate and normalize urine as a resource has been conducted, including topics such as source-separation, fertilizer effectivity, public perception, and logistics. Another important aspect is the urine treatment method and how resources are recovered. This is because urine is 97% water, making the logistics of using urine as a fertilizer challenging. In addition, without treatment, the major nitrogen source in urine (urea) breaks down to ammonia and is lost to the atmosphere. This thesis investigated the technical feasibility of using different membrane and freezing techniques to concentrate and recover nutrients from human urine. It assessed different stabilization methods (to prevent urea breakdown), pre-treatment techniques, and process configurations to produce fertilizer products with different compositions. To prevent urea degradation and subsequent ammonia volatilization during the collection phase, urine was ‘stabilized' by adding an acid (citric acid) or a base (Ca(OH)2). The addition of Ca(OH)2 resulted in a saturated solution which would scale the RO membrane during concentration. Paper 1 and Paper 2 investigated two pre-treatment methods and showed that chemical addition (NaHCO3) and air bubbling can remove 85-98% of the excess calcium ions from the solution, thus significantly reducing potential RO membrane scaling during concentration. The calcium concentration in urine after stabilization varies based on urine composition. To minimize the addition of unwanted sodium ions, an equimolar dose of NaHCO3 is required. In Paper 1 it was determined that this dose (± 5%) could be determined by using conductivity as a proxy for calcium concentrations to help determine the required chemical dosage. In Paper 2, a model was developed to better understand the mechanisms of CO2 dissolution and CaCO3 precipitation. This model was used to optimize the time required to precipitate the maximum CaCO3 as well as the energy required to operate the air blower. In Paper 3, acid and base-stabilized urine were both concentrated using RO, and the two stabilization methods were compared. It was determined that membrane processes are not ideal for urine stabilized with an acid. This was due to the potential crystallization of uric acid dihydrate crystals which resulted in membrane scaling during concentration. Both pre-treatment methods for Ca(OH)2 stabilized urine were found to be equally effective at preventing membrane scaling and significantly improved flux and ion rejection. Air bubbling was chosen as the preferred pre-treatment method as it does not add additional ions (Na+ ), it reduces the urine pH to within the operating range of most common RO membranes (2-11), and it sequesters CO2 from the atmosphere. Reverse osmosis was successfully used to remove 60% of the water from real urine stabilized with Ca(OH)2 and pre-treated with air bubbling. The process recovered 85.5% of the urea and 98% of the potassium in the brine stream. Water removal was further improved to 70% with 79.5% of the urea and 98% of the potassium being recovered in the brine stream. This process produced a fertilizer with an N content of 1.9% and a K content of 0.5%. While RO is effective at concentrating stabilized urine, it also concentrates undesirable salts and pharmaceuticals together with desired fertilizer components. In Paper 4, the feasibility of nanofiltration (NF) as a pre-treatment to remove pharmaceuticals and salts was thus investigated. Two types of NF membranes were tested, a loose NF and a tight NF membrane. The NF permeate was then further concentrated with seawater RO membranes as described in Paper 3. A hybrid loose NF-RO configuration could remove 80% of water, more than 70% of the pharmaceuticals, 78% of the organics, and 44% of the total ions, however, urea recovery was only 56%. A tight NF-RO configuration could remove 80% of water, 90% of the organics, more than 99% of the pharmaceuticals, and 66% of the total ions, however, urea recovery was only 32.8%. Based on an economic analysis it is unlikely that the increased value of the product (due to increased purity) outweighs the additional cost of this pretreatment step. In Paper 5, eutectic freeze concentration (EFC) was investigated to further concentrate the RO brine (70% water removal), whilst simultaneously crystallizing undesirable salts, as this treatment method is not affected by membrane scaling. It was experimentally shown that at eutectic conditions, Na2SO4∙10H2O crystallizes simultaneously with ice. A theoretical mass balance of the RO-EFC process, including ice washing and recycle streams, showed that 77% of the urea and 96% of the potassium could be recovered with a 95% water removal. Over 98% of the phosphorus would be recovered as calcium phosphate during the urine stabilization step. The final liquid fertilizer would have a composition of 11.5% N and 3.5% K, and 3.5 kg of Na2SO4∙10H2O would theoretically be recovered from 1000 kg of urine. This research was the first to experimentally show that EFC can be used to concentrate human urine whilst simultaneously crystallizing salts. A high-level economic analysis showed that RO treatment processes have the lowest energy requirements (16 kWh m-3 , 70% water removal), followed by freeze concentration (119-162 kWh m-3 , 70-95% water removal), and lastly evaporative processes (154 -198 kWh m-3 , >95% water removal) which required the most energy. The fertilizer produced can either be sold as a niche (home gardening) or bulk (large agricultural) fertilizer. The size of the niche fertilizer market is important when determining a preferred treatment method. Assuming a feed supply of 7.5m3 urine per week, for a market size where only 0.14 m3 per week of niche fertilizer can be sold, RO-EFC produced the product with the highest value at R73 000. Alternatively, if the market size was 2 m3 per week, RO had the highest value product at R304 000. Treatment methods that produce a product with a higher nutrient content are preferred as bulk fertilizers. When selling fertilizers in bulk high density nutrient content is important to reduce transportation costs. For example, transport of the RO fertilizer, 75 km to farmland, would account for 3.2% of the gross fertilizer value whilst only 0.8% of the fertilizer value for the RO-EFC. The feed volume of urine required to make sufficient fertilizer for a small 20 ha wine farm using the alkaline dehydration treatment is 145 m3 which would take 19 weeks to collect from 8 shopping centers. This bulk fertilizer has a value of R76 000 compared to 0.14 m3 of niche RO-EFC fertilizer which has a potential value of R73 000. It would take less than a week to collect enough urine to produce the niche RO-EFC fertilizer. At this stage, focusing on the niche fertilizer market would be more profitable. It also indicates that urine collection and treatment need to become more mainstream and normalized before significant replacement of commercial synthetic fertilizers can be achieved. A membrane process with a variety of configurations can be used to concentrate human urine to produce a liquid fertilizer. Each configuration produces a product with a different composition and a commercial fertilizer with a comparable composition for each product could be found at a local garden center in Cape Town. However, the preferred treatment choice will be dependent on several factors such as process CAPEX and OPEX, fertilizer intended use (ornamental plants versus edible crops), the market size, the associated fertilizer regulations, and the scale at which urine collection is conducted. Overall, this work has shown that membrane processes can be used to concentrate stabilized urine whilst still achieving high urea (>79.5%) recovery and water removal (70%). This allows for significant scalability of urine treatment processes using RO membranes as this technology is already widely used to treat both brackish water and sea water at varying scales. However, not all urine stabilization methods are suitable for use before RO concentration. This research was the first to determine that acid stabilization results in the crystallization of uric acid dihydrate which would scale RO membranes and reduce efficiency. This research was also the first to show that EFC can be used to simultaneously crystallize ice and salts from real human urine that has been pre-concentrated with RO (70% water removal). The work also demonstrates how hybrid configurations, combining various urine concentration methods, can be used to produce products with different compositions and urea purity. Ultimately, this novel research makes a valuable contribution to the growing field of urine treatment and resource recovery.
Open Access
Feasibility of groundwater abstraction and treatment for urban water supply
(University of Cape Town, 2020) Blignault, Samantha Paige; Randall, Dyllon
Water is one of Earth's most valuable resources and one of Earth's most threatened resources. Continuously increasing population growth coupled with changing climate has resulted in the depletion of water sources. As a result, investigations into alternative water sources are being conducted worldwide. One such alternative water source is groundwater abstraction. Groundwater abstraction involves the abstraction of water from an underground source. The volume of water that can be sustainably abstracted is governed by legislation. Groundwater typically requires treatment before it can be distributed to the general population for use, and thus the implementation of large-scale groundwater abstraction projects involves large capital outlays, as well as monthly operational outlays. The feasibility into the implementation of large-scale groundwater abstraction projects is therefore of interest to stakeholders involved in the water supply industry. The lifecycle of a recently implemented large-scale groundwater abstraction project was analysed in order to determine its feasibility. The project was implemented by Drakenstein Municipality in the Western Cape in 2017. The project involved identifying groundwater abstraction points that could provide sustainable volumes of water. The water quality of each groundwater abstraction point was then investigated for any outlying parameters according to SANS 241-1:2015 guidelines for potable water. Groundwater abstraction water treatment plants were then designed in order to treat the combined sustainable flow rates of water at their specific water qualities. The treated water from each groundwater abstraction water treatment plant was then analysed in order to confirm compliance with the SANS 241- 1:2015 guidelines, before the booster pumps were commissioned and commenced with their continuous supply of potable water into the network. The capital expenditure associated with each of the groundwater abstraction water treatment plants was obtained from the Engineer, Aurecon. In addition, the estimated monthly operational expenditure was computed. These expenditures were used to determine the feasibility of the large-scale groundwater abstraction project by computing the payback period and comparing this period to the design life of each of the groundwater abstraction water treatment plants. In addition, the monthly savings applicable to the municipality as a result of the project's implementation was computed. Finally, the feasibility into varying flow rates of groundwater abstraction water treatment plants, and varying water quality of groundwater abstraction points was investigated. Two sites were identified within the municipal area, each with four groundwater abstraction points capable of delivering a combined 5.18 ML/day and 1.62 ML/day. These sites were identified as Boy Louw Sportsgrounds and Parys Sportsgrounds respectively. Although the sites were only 2.60 kilometres apart, the water quality of the combined flow rates indicated that the groundwater abstraction points were accessing two different water sources. The combined sustainable flow rate at Boy Louw Sportsgrounds required turbidity, iron and manganese removal, as well as disinfection. The combined sustainable flow rate at Parys Sportsgrounds required turbidity removal and disinfection. Groundwater abstraction water treatment plants were then designed to treat the water at Boy Louw Sportsgrounds and Parys Sportsgrounds. Boy Louw Sportsgrounds involved the distribution of equipment across seven shipping containers, whilst Parys Sportsgrounds involved the distribution of equipment across three shipping containers. It was found that the groundwater abstraction project was feasible with a payback period of three years. This payback period fell well within the 10-year design life of each groundwater abstraction water treatment plant. In addition, it was found that the municipality would be subject to a 72% monthly saving in water costs as a result of utilising the groundwater abstraction water treatment plants, as opposed to purchasing water in bulk from the City of Cape Town. It was found that the payback periods of Boy Louw Sportsgrounds and Parys Sportsgrounds were two and five years respectively. Although Boy Louw Sportsgrounds delivered almost three times the potable water flow rate than that of Parys Sportsgrounds, its payback period was three years sooner. In addition, it was found that the municipal savings as a result of Boy Louw Sportsgrounds was 8% more than that of Parys Sportsgrounds. It was therefore concluded that the larger the flow rate of water to be treated, the more financially feasible the project. In addition, it was determined that the more water quality parameters lying above the upper limits of SANS 241-1:2015 guidelines for potable water, the more treatment processes would need to be implemented resulting in additional capital and operational expenditure. It was therefore concluded that the more water quality parameters requiring treatment, the less financially feasible the project. Finally, it was determined that the feasibility of the large-scale groundwater abstraction project is limited by the rate at which the municipality purchases water in bulk from the City of Cape Town. As long as the bulk water purchase tariff remains above R 2.85/m³, the project will remain feasible. Should the bulk water purchase tariff fall below this value, the project no longer remains feasible as the payback period of the project exceeds the design life of the groundwater abstraction water treatment plants.
Open Access
Geo-tiles: manufacturing tiles from copper mine tailings using geopolymerisation
(2025) Makole, Karabo; Randall, Dyllon
Sustainability in ceramic tile manufacturing is constrained both by the substantial energy required to power the high temperature production process (>950°C) and its reliance on virgin raw material from natural reserves. Conventional solutions to manage the voluminous residue of the mining industry are also unsustainable as they do not comprehensively eliminate the hazards posed. This study investigated the technical feasibility of using aluminosilicate-rich mine waste, termed tailings, as the primary raw material to produce tiles using the low-energy geopolymerisation process. Traditional efforts to increase sustainability of ceramic tile manufacturing include waste valorisation to reduce virgin raw material consumption and optimisation of the manufacturing process to reduce energy demand. Despite adoption of best available techniques, the high temperatures required render the process energy intensive. Promising research is underway to produce tiles using the low-energy biomimetic processes of microbially induced calcite precipitation. An ecological limitation of and key improvement recommendation for this technique is to increase the quantity of waste material it repurposes as feedstock. Geopolymerisation presents a promising path to redress the ecological limitations of tile manufacturing as it both operates at low temperature (<210°C) and can utilise a feedstock comprising waste. The geopolymerisation reaction generally entails a fine-grained substance comprising reactive aluminosilicates being mixed with a high pH solution (the alkali activator). After mixing and being subjected to elevated temperatures (23°C – 210°C), the aluminosilicates dissolve and recombine into a gel that binds the non-reactive particles into a gel matrix called a geopolymer. Prior attempts at fabricating tiles by geopolymerisation have not simultaneously combined a low energy process that fully incorporates waste as feedstock. The large volumes of particulate waste with inhomogeneous mineralogy produced by the mining industry are ideal for geopolymerisation. Consisting of a combination of fine dust particles and residual processing fluid, mine tailings contribute to negative externalities affecting both atmospheric and terrestrial environments, in addition to endangering human life. Traditional tailings risk mitigation techniques often demand indefinite oversight, and do not completely eliminate hazards. The most comprehensive solution is to repurpose the entire volume of tailings as raw material for economically viable alternative uses or products. It was thus hypothesised that the sustainability of both the mining and ceramic tile industries could be ameliorated by valorising mine tailings as feedstock for production of geopolymerised tiles, referred to as geo- tiles in this study. This thesis investigated the technical feasibility of geo-tile production using copper (Cu) mine tailings as they accounted for the largest share of tailings generated globally (46% in 2016). The alkali activator solution they were mixed with was concentrated (15 M) aqueous sodium hydroxide. A custom stainless-steel mould was fabricated, and a novel manufacturing procedure developed to form and compress the moistened tailings into 100 mm × 100 mm × 10 mm geo- tiles. Geo-tiles were then benchmarked against standard certification criteria to validate performance relative to conventional tiles. Technical feasibility was assessed using mechanical strength parameters and tile testing techniques obtained from international, South African and American standard accreditation bodies. The primary mechanical strength parameter investigated was modulus of rupture (MOR), which depends on the tile's breaking strength. Water absorption test results needed to fall within a specified range to validate breaking strength and MOR targets. Additional quality assurance (QA) criteria of abrasion resistance and heavy metal encapsulation efficiency were investigated to indicate a further development direction should technical feasibility be established. Selecting a curing duration and temperature that minimised the process' energy intensiveness was the first step. Curing at 85°C, 95°C and 105°C respectively required 7-day, 4-day and 2-day curing durations. The curing regime selected for subsequent geo-tiles produced was 105°C for two days because this required 34 MJ of electrical energy, less than the 58 MJ and 92 MJ consumed by the other two regimes. Literature indicated that input factors with the potential to maximise mechanical strength of tailings-based geopolymers were forming pressure and particle size. The first of these variables was investigated by varying the pressure applied by a hydraulic press that shaped the moist geo-tiles between 0.1 MPa, 0.2 MPa, 0.3 MPa and 0.4 MPa for different tiles. To investigate the second variable, five batches of Cu tailings were prepared, each containing progressively larger proportions of fine material. This was achieved by passing each batch through one of five sieves: 150 μm, 212 μm, 300 μm, 425 μm and 600 μm. The sieve aperture size through which a given batch of tailings was passed defined the particle size distribution (PSD) classification of that batch. Thus, the batch that passed through the 600 μm sieve was assigned a PSD classification of 600 μm, the batch that passed through the 425 μm sieve was assigned a PSD classification of 425 μm and so on. The ranges of forming pressure and PSD classification selected were based on cylinders and cubes from literature. Since tiles have a differing form factor, the validity of forming geo-tiles over these inferred input factor ranges needed verification. Response surface methodology (RSM) achieved this, whilst also giving preliminary insights into how the two input predictor factors influenced the response variable (MOR). The RSM model validated the design space by indicating that geo-tiles had adequate strength over the entire design space. The RSM model also indicated that using finer grained tailings (reducing PSD classification) had a larger effect on increasing MOR than modifying forming pressure. This was quantified by the Pearson's correlation coefficient, which was −0.77 for PSD vs MOR whereas it was −0.06 for forming pressure vs MOR. The highly negative correlation between PSD and MOR aligns with literature. Finer grained tailings have a larger specific surface area, increasing the region upon which the geopolymerisation reaction can proceed, ultimately enhancing mechanical strength. A likely explanation for the low correlation between forming pressure and MOR was that prior to curing, the geo-tiles were too moist, with a solid to liquid ratio (SLR) between 4.3 and 4.7. When forming pressure variation significantly influenced mechanical strength, geopolymers with much stiffer rheology were used. Literature reports that such geopolymers were formed under similar conditions to geo-tiles but were characterised by SLRs ≈ 5.5 – 5.6. A design chart was developed to evaluate the breaking strength and MOR results for geo-tiles against limits dictated by International Organization for Standardization (ISO13006 (2018)) and South African National Standards (SANS1449 (2012)). The chart indicates a target performance region requiring breaking strengths >800 N and MOR results >16 MPa. Geo-tiles with the highest MOR were formed at 0.1 MPa pressure, using Cu tailings that had passed through a 150 μm sieve, i.e. had a PSD classification of 150 μm. The breaking strength and MOR of the geo-tile formed under these conditions were respectively 986 ± 151 N and 18.5 ± 0.7 MPa; exceeding the design chart limits. Water absorption of geo-tiles needed to fall within 6% and 11% for these targets to be valid. This QA condition was met as results ranged between 6.4% and 9.8%. Since it classifies flooring use cases, abrasion was used as the second QA criterion. Equipment constraints necessitated adoption of American Society for Testing and Materials (ASTM C418) standards to evaluate abrasion resistance. Of the classifications governed by the ASTM C418 equipment, the abrasion limits for interlocking paving units (IPUs) represent the most abrasively demanding service conditions. Selection of IPU requirements as the QA benchmark for geo-tiles was made under the assumption that meeting the most stringent abrasion targets would indicate suitability for less severe situations. Requirements for IPUs only allow 0.3 cm3/cm2 of volumetric abrasion loss, with a maximum allowable abrasive depth of 3 mm. Both requirements were met as the volumetric abrasion of geo-tiles with the highest MOR was 0.11 ± 0.01 cm3/cm2 with an abrasive depth of 1.1 ± 0.1 mm. These results suggest geo-tile applications could include domestic floors and patios as well as residential sidewalks and driveways. As with abrasion, equipment limitations necessitated a heavy metal test that exposed geo-tiles to conditions more severe than required for typical service conditions and standardised tests for tiles. Geopolymerisation of Cu tailings to form geo-tiles reduced leaching in 16 of the 17 heavy metals detected by X-ray fluorescence and inductively coupled plasma mass spectrometry analyses. However, encapsulation of heavy metals in geo-tiles occurred at lower efficiencies (≤37%) than those achieved by geopolymers in literature (>90%). Therefore, the final QA criterion pertaining to heavy metal encapsulation was not met. The likely cause of incomplete encapsulation was that the Si/Al ratio of the source Cu tailings (4.5) was higher than typically required for effectively complete heavy metal immobilisation (Si/Al ≈ 2). Concerningly, the 17th heavy metal detected, Hg, leached more after undergoing geopolymerisation. Relativistic effects inherent to Hg that affect its bonding behaviour were the most likely explanation, in addition to Hg's inability to form low solubility hydroxide solids, precluding its encapsulation using alkali cementation-based methods like geopolymerisation. Investigation of additives that can both reduce the Si/Al ratio of the tailings and promote encapsulation of Hg was recommended. One that has achieved the former is NaAlO2, whilst suggestions to address the latter from literature include Ca and Na2S. Additional considerations include observations by both scanning electron micrograph and energy dispersive spectroscopy indicating that geo-tiles comprised sodium aluminosilicate hydrate geopolymeric gel. Furthermore, the embodied specific energy of geo-tiles (10.86 kWh/m2) is lower than that for both porcelain (26.6 kWh/m2) and cement tiles (16.6 kWh/m2). Finally, decorative options operating below 950°C are required to prevent the geo-tiles melting. Overall, this dissertation shows that geopolymerisation of Cu mine tailings to produce tiles is technically feasible. Geo-tiles exceeded standards-based targets for breaking strength and MOR whilst meeting abrasion and water absorption QA criteria. Geo-tile production valorises harmful mining waste as a primary feedstock and respectively uses 59% and 35% less embodied energy than required to make conventional porcelain and cement tiles. Whilst heavy metal leaching criteria was not met, there is strong literature support that additives can significantly improve encapsulation efficiencies. Combining additives with standard testing that is both appropriately aggressive and representative of service conditions increases the likelihood of meeting the heavy metal benchmark. It is therefore suggested that geo-tiles be tested in compliance with the ISO standards outside the scope of this study, in addition to undertaking of an economic feasibility study to evaluate scalability beyond lab production.
Open Access
Investigating the feasibility and logistics of decentralized urine treatment for resource recovery
(2019) Chipako, Tinashe; Randall, Dyllon
Background Phosphorous levels around the world are decreasing rapidly, as urbanization increases. This is significant as phosphorus is a resource that is required by all living organisms and is a key ingredient in many fertilizers. Similar to the peak oil phenomenon, phosphorus will soon experience a peak in its production, and it is predicted that within the next century, naturally occurring phosphorous will be completely depleted. Moreover, methods of nitrogen production such as the Haber‐Bosch process contribute largely towards global energy expenditure and greenhouse gas emissions. Considering this, researchers have aimed to investigate methods of recovering phosphorus and nitrogen to help cope with the increasing global demand and promote environmental sustainability. Urine has been identified as a potential source of recoverable phosphorus and nitrogen. Urine accounts for approximately 1% of the total volume of domestic wastewater. Conversely, urine accounts for 80%, 60% and 63% of the nitrogen, phosphorus and potassium in domestic wastewater, respectively. Moreover, wastewater treatment plants specifically target the removal of nitrogen and phosphorus. This is because these substances can cause a toxic environment in surface water, which can have a negative effect on aquatic organisms. This research aimed to evaluate a novel mode of resource recovery, through the assessment of a decentralized approach to urine treatment. Methodology Two methodological approaches were adopted to evaluate this system. In the first, a thorough review of literature was conducted to assess current innovations pertaining to urine treatment technologies. Public perceptions regarding the collection and recycling of urine were also researched. This culminated in the creation of design charts depicting treatment sequences for fresh and hydrolyzed urine, aimed at maximum resource recovery. These charts were entirely based on values from published literature and basic calculations. Secondly, geographic information systems (GIS) were used to assess the transportation and logistics of a decentralized urine treatment system, using the City of Cape Town as an illustrative case study. In this model, existing urinals at frequently visited shopping centres are theoretically replaced with waterless nutrient recovery urinals. Within these urinals, urea hydrolysis is prevented from occurring in an attached urine collection container. This minimizes nitrogen losses and allows for a solid, phosphorous based fertilizer to form. The collected urine is retrieved from individual buildings and transported to a resource recovery facility (RRF) by truck. The collected urine is filtered to remove the solid fertilizer, while the remaining liquid is concentrated to produce a liquid fertilizer. Finally, the recovered material is then sold as fertilizers to wholesalers. The implication of transportation and logistics was also assessed through four scenarios of decentralization. In scenario one, one RRF was used. In scenarios two, three and four; two, four and eight RRFs were used, respectively. The economic and environmental implications of each scenario were then evaluated through standard engineering economics and potential greenhouse gas (GHG) emissions. Ideal treatment sequence It was deduced that the most promising treatment sequence for maximum resource recovery, based on nutrient recovery rates and operating conditions, incorporated a combination of alkaline stabilization and volume reduction. Calcium hydroxide and reverse osmosis (RO) were the chosen mediums for stabilization and volume reduction. If this sequence is used, almost all urine constituents can be recovered. Moreover, a liquid fertilizer with a 3.3 - 0 ‐ 0.8 NPK rating, and 11 grams of calcium phosphate, per litre of urine treated, can theoretically be produced. This was the chosen treatment sequence for the decentralized urine transportation system. Decentralized urine transportation treatment It was found that the main contributor to GHG emissions in the decentralized system was the truck. Driving distance decreased as the number of RRFs increased, which led to a decrease in the GHG emissions because of fuel consumption. However, warehouse rental costs were a large contributor to operating expenditure (OPEX) and increased proportionately as the degree of decentralization increased. Therefore, a globally optimal solution incorporating the minimum cost, minimum GHG emissions and shortest travel distance was not possible. From a financial perspective, increased decentralization was not appealing, meaning the use of one RRF was the most favourable scenario. Weight limitations of the truck were found to influence the travel route designations within the model road network. However, transportation had a small effect on the systems monetary cost, as it only accounted for 2% to 6% of the total OPEX across all design scenarios. This is likely due to the geographical configuration of Cape Town. Similar studies in larger areas with more dispersed collection locations may yield different results. It was found that a positive net present value was achieved if the recovered fertilizer was capable of being sold at prices in line with commercially available liquid fertilizers, with similar nitrogen content. However, it is likely overly optimistic to believe the recovered liquid fertilizer could break into the South African fertilizer market and immediately compete with established products. Although, it was shown that the liquid fertilizer produced would only need to be sold at R22.75/L to equate the total system expenditure to the total income, over a five‐year period. Conclusion and Outlook It was determined that the decentralized approach to urine treatment, investigated in this research, exhibited several advantages over biological nutrient removal at conventional wastewater treatment plants. These advantages included lower GHG emissions and energy expenditure for a similar operating cost. This study ultimately shows that the collection of source‐separated urine for the purposes of resource recovery holds significant potential from a monetary and an environmental perspective. Furthermore, the combination of transportation planning and waste management could play an important role in future studies aiming to improve decentralized sanitation systems.
Open Access
Investigating the feasibility of implementing microbially induced calcite precipitation to stabilize sand, clay and gold tailings
(2022) Hyde, Rhonda; Nolutshungu, Lita; Randall, Dyllon
Microbially Induced Calcite Precipitation (MICP) is an emerging bio-mediated technology which has been successfully applied in soil improvement research. MICP uses the enzyme urease produced from bacteria to breakdown urea into carbonate ions. These carbonate ions combine with free calcium ions to form calcium carbonate, which acts as a bio-cement. MICP presents a unique, sustainable soil improvement solution to the pressing issues resulting from tailings impoundment failures. It has shown potential through increasing shear strength and decreasing porosity in soils. However, MICP applications in soil improvement outside erosion mitigation in granular soils remain limited. This is similar to the limited use of injection treatment, in comparison to the more prevalent spraying and surface percolation in MICP applications. This research focused on the efficacy of the developed injection procedure for administering the MICP treatment to increase shear strength and decrease porosity in sand, clay and gold tailings at greater depths and evaluating its feasibility. By determining the efficacy and significance of the treatment in improving the geotechnical characteristics of the soil samples, the methodology can be evaluated for its application as a soil improvement technique. Results showed successful cementation of the particles of the soils tested with an increase in cohesion of 7.7% and 23.1% for clay, and tailings respectively and an infinite increase in the apparent cohesion of sand from 0 to 20kPa. The response to MICP treatment in terms of the angle of internal friction were inconclusive, where a decrease was observed across the board. This was attributed to complex stress-strain behaviour as well as the particle morphology. A decrease in porosity of approximately 26% in clay and 8% in tailings was observed, whilst sand had an increase of approximately 3%. The increase in porosity in sand was identified as a result of the erosion of the coarse uncemented particles during treatment. The results emphasised the greater success of MICP treatment in more granular soils, with sand achieving the greatest improvement with regard to the apparent cohesion and particle density. Characteristically, the particle sizes of the gold tailings fell between the fine clay and the coarse sand which was reflected in the response of the gold tailings to treatment. Overall, sand had the greatest increase in shear strength, followed by the gold tailings and lastly the clay. The gold tailings contained a higher percentage of fines than the sand, illustrating the limitation of MICP applications in fine grained soils. However, the predominant coarse fraction allowed for an overall increase in the shear strength parameters in the gold tailings. An evaluation of the feasibility shows that the methods provide a scalable soil improvement technique in stabilisation applications in contrast to existing MICP surface treatments in sands. In clays and tailings however, interactions of heavy metals with the microbial community as well as the particle size limit the efficacy of MICP. In conclusion, MICP is found to be a feasible soil improvement technique in stabilising gold tailings with the consideration of the impact of heavy metals and the particle size on the efficacy of the treatment.
Open Access
Investigating the feasibility of recovering urea from human urine
(2021) Marepula, Hlumelo; Randall, Dyllon
Background Urea is the most frequently used fertilizer by farmers globally and accounts for more than 50% of nitrogen-based fertilizer. It is produced indirectly through an energy intensive process known as the Haber-Bosch process. This process is often considered the most important invention in modern history because it contributed to the exponential growth in human population by providing food security. However, the process consumes 1 – 2% of the world's energy and contributes significantly to greenhouse emissions. The growth in human population has brought with it a multitude of challenges including waste management, resource depletion, greenhouse gas emissions and water scarcity. All these challenges are addressed in isolation and the synergistic benefits of integrating their solutions are not often realized. One way to integrate the solutions is to create a paradigm shift where ‘wastes', particularly human urine, are recognized as valuable resources, used to create value-added products. Human urine contains the key nutrients used in agriculture, nitrogen (N), phosphorous (P) and potassium, (K), of which N is the most dominant nutrient. Most of the N present in human urine is in the form of urea. Therefore, the aim of this work was to investigate the feasibility of recovering and purifying urea crystals from human urine using a novel ethanol evaporation and recrystallization process. This would be achieved by exploiting human urine for its N content to produce urea crystals in a sustainable way. In this investigation, it was hypothesized that urea can be recovered from urine by evaporating the water from it and dissolving the remaining solids in ethanol to purify the product. The impurities would then be isolated via filtration, resulting in a urea-ethanol solution that can be evaporated to isolate purer urea crystals. This is because most inorganic compounds found in urine are insoluble in ethanol while urea is highly soluble. The successful recovery of urea from human urine could potentially supplement the fertilizers produced from the Haber-Bosch process and address resource depletion. Challenges with waste management could also be addressed by introducing source separation of urine and faeces so that urine can be recycled for urea production. Because urine contains the highest nutrient load entering wastewater treatment plants (WWTPs), removing it from the wastewater flow could render the treatment process more energy efficient. Urea is a versatile product with uses spanning across different industries including agriculture, chemical, aviation, and automotive. Therefore, the success of this study has the potential to sustain urea production by manufacturing it in a responsible manner by utilizing a ‘waste' stream as a key input. Methodology Three objectives were investigated to recover urea from human urine using the solubility differences of urea and impurities in water and ethanol. The first objective involved conducting a series of thermodynamic simulations on five different urine compositions obtained fromliterature. The results of these simulations informed the conditions and parameters for the physical experiments that followed. Water removal from urine was simulated to determine at which point urea and other impurities would form. The simulation also predicted the potential yield and purity of the urea product. Thereafter, the addition of an intermediate filtration step at 99% and 95% water removal as a purification step was modelled to investigate whether the purity of urea improved. Following that, the solubility of pure urea in ethanol was simulated to determine the volume of ethanol required to dissolve and maximize the yield of urea. Physical experiments were then conducted to validate the results of the model. To improve the volume estimate of ethanol, the impact of the urine composition on the solubility of urea in ethanol was also investigated. From these results, the solubility of one of the compositions was chosen as a standard to conduct all physical experiments. The second objective involved recovering urea from different types of urine by operating within the parameters set by the thermodynamic model. Urea was recovered from a synthetic urine stream containing urea and inorganics (SI), a synthetic urine stream containing urea, organics, and inorganics (SO) and finally, a real urine stream (RU). The yields and purities of the three different experiments were compared and interrogated. In a final experiment, the solubility of urea in ethanol was investigated and compared to the thermodynamic model prediction. The model did not have the necessary database to model organics, other than urea. Therefore, another experiment was conducted to confirm the solubility of ethanol in urine containing organics. The final objective was the conceptual design of a small-scale urea recovery unit treating 1 m3 of urine per day. This was done to estimate the power requirements of such a system and the potential urea yield recovered per day. Finally, the profitability of the procedure was investigated by exploring different urea-based products. Key findings Thermodynamic modelling revealed that the point of crystallization of urea from urine was above approximately 99% water removal. Therefore, complete water removal was necessary to obtain the optimum amount of urea. An intermediate filtration step at 95% (58% purity) only improved the purity by 5% (from a purity of 53% at 100% water removed), while intermediate filtration at 99% (71% purity) improved the purity by 17%. An improvement of 5% was found to be insignificant relative to the final purity that could be achieved. In addition, intermediate filtration at 99% would not be practically feasible for the small volumes used in this study (1 L). Therefore, 100% water removal was used for these experiments. Based on this, a yield and purity of 100% and 53% was predicted by the model. The solubility of pure urea in ethanol was determined to be 40.98 g L-1 at 22°C, which was the average temperature in the laboratory. However, the impact of the urine composition on the solubility of urea in ethanol resulted in a higher solubility (50.05 g L-1 ). This value was therefore used for all physical experiments that followed and resulted in an ethanol volume requirement of ~232 mL. After complete water removal, yields of 91%, 84% and 93% and purities of 41%, 41%, and 43% were achieved for urea recovery from SO, SI and RU, respectively, which was lower that what the simulation predicted. After ethanol evaporation, yields decreased to 88%, 77% and 67% while the purities increased to 91%, 76% and 76% for SI, SO and RU, respectively. This demonstrated that the addition of ethanol improved the purity, but at a reduced yield. The loss in yield was likely due to a gradual decrease in pH during water removal, and prolonged evaporation times during ethanol evaporation, which could have resulted in enzymatic urea hydrolysis and loss of nitrogen as ammonia gas. To improve the solubility measurement, a physical experiment was conducted and revealed that the actual solubility of a typical urine stream containing organics is 56.7 g L-1 , demonstrating that the solubility increases with the presence of organics. Therefore, future work should use this higher solubility instead to further maximize the yield and purity. The conceptual design of a small-scale urea recovery system treating 1 m3 of urine per day had an estimated system power requirement of 8.4 kW m-3 . The potential recovery of urea per day was 15.61 kg (67% yield) at a purity of 76%. The system could be improved to recover 20.5 kg at 88% yield and 91% purity if the measures for improving the purity and yield are incorporated in the design. These measures include the selective removal of dissolved ions from the urea-ethanol solution via ion-exchange, increasing the temperature to speed up the evaporation process, and adding an intermediate filtration step at 99% water removal. Finally, through the analysis of different urea markets, the profitability of the procedure developed in this study was determined. It was concluded that a niche urea-rich liquid fertilizer would be the most valuable end-product to produce by redissolving the urea crystals in reclaimed water from the process. However, due to the small market of niche liquid fertilizers (~10% in the Cape Town region) it can only be produced in low volumes. Therefore, it was recommended that the remainder be used for diesel engine fluid production. The estimated profit per day (1 m3 of urine) from the production of 20 L of niche liquid urea fertilizer, 11.5 kg of solid calcium phosphate fertilizer and 44.6 L of diesel engine fluid was R3110. Conclusion and outlook This investigation demonstrated that the recovery of urea from human urine is achievable using the solubility differences in water and ethanol. All research objectives were fulfilled and the study described various opportunities for future work. This research developed an innovative method for recovering urea from human urine to potentially supplement the energy intensive Haber-Bosch process and discussed the possibility of producing alternative high-value products from human urine.
Open Access
Manufacturing bio-bricks using microbial induced calcium carbonate precipitation and human urine
(2019) Lambert, Suzanne; Randall, Dyllon
The production of building materials is a significant contributor to anthropogenic greenhouse gas emissions with conventional kiln brick production being one of the most energy intensive processes. In addition, phosphorus is a resource that is required by all living organisms and is a key ingredient in many fertilisers. The demand for building materials and global natural phosphate rock (phosphorous) are increasing and decreasing respectively as urbanization increases. Naturally occurring phosphorous is expected to experience a peak in the near future after which it will be completely depleted. Urine has been identified as a potential source of phosphorous for fertiliser production as well as urea for microbial induced calcium carbonate precipitation (MICP) applications. MICP is a natural process that has the ability to produce bio-building material. Urine accounts for a small percentage of the total volume of domestic wastewater but contains a large percentage of the nutrients wastewater treatment plants (WWTP) seek to remove before they adversely affect receiving water bodies. The unprecedented rate of climate change and the associated pressures, coupled with the increased awareness around the depletion of natural resources, presents a significant challenge for which innovative and sustainable solutions are required. The reason for engaging in this project was to investigate if the urea present in human urine could be used in the natural MICP for the production of bio-bricks while at the same time recovering phosphorus from urine. Firstly, a thorough review of literature was conducted to assess current innovations pertaining to the dissertation topic. The process of bio-brick production by MICP requires a urea rich solution which could be recovered from urine. However, the urea present in urine naturally degrades and this process needs to be delayed if urine is to be used as a urea source for MICP. This was achieved by “stabilising” the urine with calcium hydroxide. Sporosarcina pasteurii (S. pasteurii) was the bacteria strain used to help drive the MICP process. The bacteria degraded the urea present in the urine to form carbonate ions which then combined with the calcium ions present in the urine solution to produce calcium carbonate. This calcium carbonate was then used as a bio-cement to glue loose sand particles together in the shape of a brick. The cementation media was made by adding calcium chloride and nutrient broth to the stabilised urine, and lowering its pH to 11.2. The purpose of adding calcium chloride was to improve the efficiency of the process since the stabilised urine did not have enough calcium ions. Ordinary sand mixed with Greywacke aggregate and inoculated with S. pasteurii bacteria was used as the media for the MICP process. Bio-brick moulds were filled with the sand mixture and sealed. The cementation media was pumped through the bio-brick mould to fill its’ pore volume. The media was retained in the moulds for a defined retention time ranging from 1-8 hours. At the end of every retention time, new cementation media was pumped through the bio-brick to fill it’s pore volume again. iv To establish an optimal starting influent calcium concentration the influent calcium concentration changed between experiments. Additionally, in subsequent experiments, the calcium concentration was raised in a stepwise manner during an experiment to establish the maximum amount the influent calcium concentration could be raised to before the microbial community experienced adverse effects. Additionally, experiments explored the effects a range of retention times had on the bio-brick system in order to establish an optimal retention time. Another experiment was set up to investigate the relationship between the number of treatments and the resultant compressive strength. The findings from the above-mentioned experiments further guided subsequent experiments which singled out and tested certain factors thought to be affecting the bio-brick system. The factors tested include after treatment washing, ionic strength, pH and calcium concentration of the influent cementation media. Possible alternative nutrient medias (ANMs) were also investigated for a cheaper alternative to the laboratory grade growth media used to grow the bacteria. Lastly, an integrated system that produced both fertilisers and bio-bricks was developed. Its basic economics of raw material inputs and outputs were used to assess the financial implications of the proposed system, and the social and policy barriers likely to affect the implementation of an integrated urine treatment system were examined. Urine treated with calcium hydroxide offers a urea-rich solution that can be used for MICP processes. This resulted in the worlds’ first bio-brick “grown” from human urine. The starting influent calcium concentration reached a maximum of 0.09 M before adverse effects to the microbial community were experienced. Furthermore, in terms of a stepwise increase during the treatment cycle, the influent calcium concentration could be raised to 0.12 M without any adverse bacteria effects. The minimum retention time the bio-brick system could withstand was 2 hours which allowed the treatment cycle to be completed in a shorter time. The highest compressive strength obtained was equal to 2.7 MPa. To produce this strength about 31.2 L of stabilised urine was used. The relationship between the number of treatments and the compressive strength showed that an increase in the number of treatments increased the compressive strength. Both the pH and ionic strength of the urine were identified to have an inhibiting effect on the ureolytic activity and MICP process. Additionally, using an influent cementation media with an optimal pH for urea hydrolysis, improved the bacteria’s ability to operate at higher ionic strengths. However, when the stabilised urine was stored, urea hydrolysis occurred earlier likely because of external contamination by naturally occurring bacteria in the lab. LML (Lactose mother liquor) was identified as alternative growth media for S. pasteurii growth which could reduce raw material costs considerably. The bio-brick production process was found to be more cost-effective if it was incorporated into the integrated urine treatment process system. The integrated system included fertiliser production by recovering calcium phosphate fertilisers and ammonium sulphate fertilisers before and after the bio-brick production respectively. Producing 1000 bio-bricks a day would require 23% of Cape Towns’ population daily urine production and would incur a profit of ZAR 7330 per day between the raw material cost and the revenue from sales. For implementation in a South African context, certain policy barriers need to be overcome. Potential paths for implementation are reclassifying the urine for its use in an industrial process and obtaining an operating permit or seeking an exemption for a permit through the ECA (Environment Conservation Act). Research suggests that products from the integrated system are likely to be socially v accepted and that a combined appeal to people's environmental sensitivities and targeted marketing messages would enhance people’s acceptance. Finally, recommendations for further paths to take to build on the research established in this dissertation were made. It is recommended that additional characteristics of the bio-bricks should be tested, recycled material should be used as media for bio-bricks, the bacteria strain should be modified and methods for reducing the ionic strength of urine should be investigated. Additionally, it is recommended that consumers’ willingness to use urine-based products should be further studied, the legislative options for implementing bio-brick and fertiliser production should be investigated and a more detailed and expansive economic analysis should be performed.
Open Access
Manufacturing bio-tiles
(2025) Horn, Emma; Randall, Dyllon
Bio-tiles are a biobased alternative to conventional tiles that utilise a promising low energy technology called microbially induced calcium carbonate (CaCO3) precipitation (MICP). This work aimed to determine whether bio-tiles that meet the strength requirements of conventional ceramic tiles could be met using the ureolysis MICP pathway. The ureolytic activity of Sporosarcina pasteurii was controlled by centrifuging and dilution with fresh yeast extract media. Bio-tiles can be made with MICP using various methods, each with drawbacks and advantages. Three methods were tested: submersion, pumping and combining the benefits of both into a third that is more automated, modular and scalable: binder jet 3D printing. The submersion method had custom moulds submerged in cementation solution that contained all the calcium and urea required for the MICP reaction for 7 days. For this reactor system, a low optimum bacteria activity (4.0 mmol/L·min) and CaCO3 precipitation rate constant was identified (0.11–0.18 day−1). However, the process required additives such as 0.3 M magnesium chloride to achieve bio-tiles that met international standards. The pumping method was only operated for 4 days. With this technique, cementation solution was pumped through custom sealed moulds at intervals. The highest tested effective urease activity of 40 mmol NH4-N/L·min of S. pasteurii was found to be most beneficial to the breaking strength of the bio-tiles. Pre-seeding of the geotextiles with CaCO3 was explored and the mass of seeds initially present on the geotextiles was found to offer significant improvement to the breaking strength of 21-82%, increasing with seed loading. These bio-tiles were able to far exceed the required strength standards. With the automated production technique, a binder jet 3D printing prototype, it was found that 3 wt.% freeze-dried bio-slurry, 8 days of operation and supplementary magnesium allowed the formation of bio-tiles that met internal strength standards. A supplement of 0.3 M magnesium chloride almost tripled the breaking strength of bio-tiles produced with the automated technique. While additional seeding with CaCO3 crystals had minimal effect on breaking strength, it was beneficial for enhancing the formation of bio-tiles at corners and edges. The process's scalability makes it suitable for commercial applications, where large volumes of bio-tiles could theoretically be produced with reduced operational costs. In summary, this research has shown for the first time that bio-tiles grown using MICP and multiple techniques can achieve a breaking strength and modulus of rupture that meets international standards, provided key conditions are met. This comprehensive investigation into MICP-based bio-tile production demonstrates the potential for innovative bio-materials to revolutionise the construction industry by offering sustainable, cost-effective, and high-performance alternatives to traditional materials. The findings provide a foundation for future research and development efforts aimed at optimising the production processes, enhancing the mechanical properties, and scaling up the manufacturing of bio-tiles for widespread commercial use. With the uptake of bio-tiles, there is potential to decarbonise an age-old industry and reduce dependence on fossil fuels, and other construction materials can now follow.
Open Access
Methods for removing pharmaceuticals from human urine
(2022) Mwale, Mwana; Randall, Dyllon; Edmonds-Smith, Cesarina
The concept of sustainability is changing the nature of everyday dialogue across many disciplines. The 2030 Sustainable Development Goals provide a practical way to ensure that the basis of sustainability is covered in all disciplines. One of the ways that sustainability can be achieved is through the reuse of various waste streams, such as wastewater. Conventional wastewater treatment plants aim to remove the nutrients in wastewater to prevent problems such as eutrophication. However, this removal process requires a substantial amount of energy. This increases the total cost for the operation of conventional wastewater treatment plants and contributes to greenhouse gas emissions, depending on the source of energy. Nonetheless, some wastewater streams (such as domestic wastewater) have valuable nutrients (nitrogen (N), phosphorus (P) and potassium (K)) which are essential for plant growth). Although urine accounts for 1% of the total volume of domestic wastewater, urine carries most of these key nutrients. For example, urine has 80% N, 70% P and 50% K. Consequently, the source separation and collection of urine provides an opportunity for the recycling of these nutrients for use as fertilizers. Among the many constituents of urine are micropollutants such as pharmaceuticals. Pharmaceuticals pose a challenge for the reuse of urine because fertilizers are required to be free of pharmaceuticals. Therefore, the aim of this work was to find a method for pharmaceutical removal from fresh human urine, while conserving urea. Methodology Four pharmaceutical removal methods were investigated namely: a high pH environment (>12), granular activated carbon, hydrogen peroxide and hydrodynamic cavitation. The pharmaceuticals investigated for this work were grouped into two categories: over the counter (OTC) common pharmaceuticals and the antiretrovirals (ARVs). The OTCs are used to treat a variety of common ailments such as pain, fever, allergies, inflammation, and heart problems in South Africa. The ARVs are used to treat and prevent the human immunodeficiency virus (HIV). Each pharmaceutical removal process had a specific methodology. The methodologies (including the experimental design parameters) were developed based on the literature review of the respective removal methods. Furthermore, the hypothesis for the four removal methods were informed by the results found in literature. The hypotheses were phrased in the following way: the pharmaceuticals can degrade in human urine because the stabilization of human urine using calcium hydroxide increases the pH (˃12), resulting in hydroxide ions that degrade the pharmaceutical molecules while conserving urea; granular activated carbon adsorbs the pharmaceuticals and urea in human urine; the addition of hydrogen peroxide to human urine with a high pH (˃12) forms hydroxyl radicals which degrade the pharmaceutical molecules, along with the excess hydroxide ions from the high pH, while conserving urea; and the hydrodynamic cavitation system generates high energy cavitation bubbles which result in the oxidation of the pharmaceutical molecules while conserving urea. In addition, the conservation of urea during the pharmaceutical removal process for each method was considered. It is known that fresh urine should be stabilized to prevent the enzymatic breakdown of urea into ammonia gas. The stabilization of urine can be achieved by acidification or alkalinization. In this work, urine was stabilized using calcium hydroxide (pH >12.5 at 25°C) and citric acid (pH 2 at 25°C) to keep the urea in solution and thus the investigated pharmaceutical removal methods had to ensure that the degradation of urea did not occur. Hence, the percentage urea degradation for each pharmaceutical removal method was also determined. Pharmaceutical analysis method development Three high performance liquid chromatography (HPLC) methods were used for this work. The first method was for the analysis of over the counter (OTC) common pharmaceuticals, the second for the analysis of antiretrovirals (ARVs) and the third method was for the analysis of a combination of specific OTCs and ARVs. Reverse phase HPLC was used for the three methods and the gradient elution technique was applied for the analysis of the pharmaceuticals. All three methods used acetonitrile as the organic solvent. However, the HPLC method to analyze OTCs and the HPLC method to analyze both the OTCs and the ARVs used a phosphate as an aqueous buffer, while the method to test for the ARVs used a phosphate buffer with the addition of hexanesulfonic acid as an ion pairing reagent. The calibration curves for each pharmaceutical were not developed since the degradation of the pharmaceuticals was expressed as a percentage loss. Nonetheless, the HPLC chromatograms for the individual pharmaceuticals and the mixture of the pharmaceuticals were generated as a reference for the analysis of the pharmaceutical degradation due to the pharmaceutical removal methods. Description and performance of the pharmaceutical removal methods The current work was a comparative study of the pharmaceutical removal methods. All pharmaceutical removal methods were tested in duplicate for the comparative study. Therefore, the standard deviation was not calculated, however, the performance of the pharmaceutical degradation shown in each sample was analyzed in comparison to the other samples. The use of calcium hydroxide as a urine-stabilizing agent was considered as the high pH pharmaceutical removal method. Fresh urine was spiked with pharmaceuticals and then stabilized with calcium hydroxide for at least 75 days. The calcium hydroxide dosage was kept at the recommended calcium hydroxide dosage of 10 g L-1 of fresh urine, to accommodate for urine with different compositions, since urine composition is influenced by factors such as diet. The range of degradation for the over the counter (OTC) common pharmaceuticals due to the high pH was 8 - 44%, with paracetamol and chlorphenamine maleate experiencing the lowest and highest degradation, respectively. Contrary, the range of degradation for the antiretrovirals (ARVs) due to the high pH was 0 - 100%. Abacavir sulfate and nevirapine experienced no degradation, while stavudine, lamivudine, zidovudine and tenofovir experienced complete degradation. The difference in the degradation of the pharmaceuticals was attributed to the difference in the functional groups of the pharmaceuticals. The complete degradation may be attributed to hydrolysis rather than oxidation, including tenofovir which undergoes hydrolysis in basic conditions due to a P – O moiety in its molecular structure. Furthermore, pharmaceuticals with similar functional groups (such as stavudine, lamivudine and zidovudine) showed a similar degradation pattern. In addition, the high pH only resulted in a 4% loss of urea. For the granular activated carbon (GAC) removal method, a GAC column was prepared, through which stabilized urine – spiked with pharmaceuticals – was passed. The adsorption from the GAC removed all the pharmaceuticals by more than 94.7%. However, the GAC also removed 83.4% of the urea present in the stabilized-spiked urine solution. The adsorption of both the pharmaceuticals and the urea was caused by microporous structure of the GAC which provides internal surface area on which the pharmaceutical and urea molecules can attach. Hydrogen peroxide was used as an oxidizing agent to degrade the spiked pharmaceuticals in stabilized urine. The range of degradation for the OTCs, resulting from the addition of hydrogen peroxide to urine with a high pH (˃12), was 0 - 64.7%. Diclofenac and chlorpheniramine maleate did not degrade, while salicylic acid experienced the most degradation (64.7%). On the other hand, the ARVs had a range of degradation of 17.2 - 73.4%. Stavudine experienced the least degradation (17.2%) while lamivudine experienced the most degradation (73.4%). The hydroxyl radicals from the addition of hydrogen peroxide and the excess hydroxide ions from the high pH degraded the pharmaceuticals at varying degrees due to the difference in the functional groups of the pharmaceuticals. Additionally, only 12.6% of the urea was degraded by this pharmaceutical removal method. The hydroxyl radicals generated from the hydrodynamic cavitation (HC) system were used to oxidize the pharmaceutical molecules in the spiked-synthetic urine solution at a low pH (pH 2) and a high pH (pH 12.4). Both the OTCs and the ARVs were analyzed together (due to the high- volume requirement of the experiments) unlike the other degradation methods. The HC system operated at a high pH achieved the highest degradation of 16.6% for chlorphenamine maleate, while paracetamol, zidovudine, lamivudine and stavudine experienced less than 5% degradation. The HC system operated at a low pH reached a degradation range of 10.4 - 49.2%, with paracetamol and zidovudine experiencing the lowest and highest degradation, respectively. The amount of urea which was lost due to the HC system was 6.8%. Thereafter, the HC system was optimized at pH 2, given that the HC system conserved more than 90% of the urea and that it could be readily optimized. The range of degradation improved between 54.5 and 87.6%, with paracetamol and zidovudine again experiencing the highest and lowest degradation, respectively. The difference in the degradation of the pharmaceuticals was attributed to the difference in the oxidation of the functional groups of the pharmaceuticals. Conclusion and applicability The optimized hydrodynamic cavitation (HC) system performed the best out of the four pharmaceutical degradation methods. The optimized HC system had an average pharmaceutical degradation of 74.5%, and resulted in a urea loss of only 5%. The approximate energy required to treat 1 m3 of treated urine using the optimized HC system under the optimized condition was calculated to be 1.84 kWh m-3 . The optimization of the HC system showed potential for the effective removal of pharmaceuticals in urine. Further optimization of the HC system will be beneficial for use as a designated pharmaceutical removal method for the overall urine treatment process.
Open Access
Refinement of a Fertiliser-producing Urinal
(2021) Mufunde, Tariromunashe; Randall, Dyllon
Wastewater recovery plays a crucial role in meeting sustainable and environmental challenges. Eco-friendly, nutrient recycling is a more sustainable and environmentally friendly method of waste recovery because it reclaims vital components from waste streams and utilises their potential as valuable resources. Effective wastewater treatment of human excreta retrieves nutrients that can make an essential contribution to fertiliser manufacturing, and thus to agriculture and food sustainability. Waste streams essentially become resources. This research investigated ways in which a novel fertiliser-producing urinal makes this possible. The most nutrient-rich portion of domestic wastewater is human urine. Urine contains the three nutrients that are essential for commercial fertilisers: nitrogen (N), phosphorus (P), and potassium (K). Commercially available P fertilisers contain rock phosphate, calcium orthophosphates, ammonium phosphates, ammonium polyphosphate and nitric phosphate but the production of these fertilisers is energy-intensive and not sustainable. In a sustainable eco-cycle, recovering valuable nutrients from urine allows for these nutrients to be recycled to the agriculture sector, thus reducing environmental pollution. Appropriately managed, wastewater recovery from design-specific urinals will also produce a financial reward because the recovered fertiliser can be sold. Although urine only makes up around 1% of the total domestic wastewater volume, when recovered, it offers significant value as a nutrient resource. Several technologies, such as urine diversion sanitation systems and waterless urinals, can be used to capture the nutrients identified above (N, P, and K) by separating concentrated urine at the point of collection. Waterless urinals are not as commonly used as they could be because urine salt precipitation can cause pipe clogging leading to maintenance problems. This research aimed to improve on one promising technology: a novel, waterless fertiliser-producing urinal that collects and treats nutrients on-site for subsequent recovery at resource recovery plants, either on-site or in larger decentralised plants. This urinal system is not connected to the sewer network and hence the pipe clogging concerns are avoided. The original, novel, fertiliser-producing urinal adapted for improvement in this research was made from plastic components: a 25 L container, urine collection funnel and a backsplash board to prevent urine from spraying back out of the funnel. The collection tank was pre-dosed with calcium hydroxide powder (10 g Ca(OH)2/L of urine). Once the pre-dosed calcium hydroxide came into contact with the urine, calcium phosphate precipitated. The resulting urinal contents were a mixed precipitate consisting of calcium hydroxide, calcium phosphate and magnesium hydroxide. Pre-dosing with calcium hydroxide maintained high pH values (above 11). These were required to inhibit enzymatic urea hydrolysis, thus preventing irreversible loss of nitrogen (as ammonia gas), an essential element of fertiliser production. The lack of mixing of the contents of this original urinal design would potentially result in a pH gradient, in which localised sections of the urinal would have pH levels below the enzymatic urea hydrolysis threshold (pH 11). Manual mixing was done once a day for 30 seconds by swirling the collection container. The design was adequate and completed the task of collecting urine using a single urinal in a university restroom but, as the volume of the urinal increased, manually mixing with the swirling method became laborious. Manual mixing (swirling) was therefore determined to be neither practical nor ideal when dealing with multiple fertiliser-producing urinals in a commercial building or any other public space. The research opportunity became clear – the urinal needed to include a mixing mechanism. The focus of this study was therefore to improve on the existing urinal by redesigning it to accommodate mixing within the system. Four urinal designs were considered: three with mechanical manual mixing and one with electrical mixing. These progressive designs improved on the original design. The primary refined urinal design used in this study included a 20 L collection tank with a funnel and a foot pedal with a link to the container, allowing the urinal contents to be mixed manually using a mechanical mechanism. The manual mixing urinals used circular discs, whereas the electric mixing urinal used an electric stirrer. In both design types, the urinal contents were mixed by stepping on the foot pedal while urinating. The mechanical manual system mixed for the duration of urination, while the electric mixing system mixed for 15 seconds. The pH recorded in the urinal system at a given time was used to determine mixing efficiency. Considering previous studies, a pH less than 11 indicated the possibility of enzymatic urea hydrolysis, while a pH greater than 11 indicated the possibility that enzymatic urea hydrolysis had not occurred. As a result, the pH of urinal contents was used as a proxy for the presence of enzymatic urea hydrolysis in this study. The third manual mixing design and the fourth electric mixing design successfully mixed and inhibited enzymatic urea hydrolysis. These two designs could both be implemented for the urinal system; however, the manual mixing design was determined to be more sustainable as it does not require any electrical power. The fertiliser produced from the collected urine could be recovered in two forms: solid (rich in calcium phosphate) and liquid (rich in urea and potassium). Because insufficient mixing in the system led to potentially localised pH gradient, a portion of this study focused on analysing the calcium phosphate (solid fertiliser) produced from the urinal contents at different pH values. Particles with needle-like shapes formed at a constant temperature of 21ºC and continuous stirring at 500 rpm. Phosphate compounds formed at low pH, hydroxyapatite formed across the pH range (7 to 12) and calcite formed at high pH values. Settling experiments were then carried out to determine how quickly the fertiliser sludge settled in three different mediums: water, stabilised real human urine and synthetic human urine. The settling velocity determines how long it takes for the urinal contents to settle in the urinal. As a result, the settling velocity would determine the frequency of mixing required in the urinal to inhibit enzymatic urea hydrolysis - a faster settling velocity would mean mixing frequency has to be high. The experimental results revealed that water had a settled sludge volume of 48% in the first two minutes, synthetic urine had a volume of 28% and stabilized urine had a volume of 22%. Stokes' Law was used to calculate the theoretical settling velocity, which was then compared to the experimental velocity. The Stokes' Law results showed a significantly high settling velocity of 1.22 cm/s on average. According to the urinal testing experiments, an hour without mixing was sufficient to keep the urinal contents above the enzymatic urea hydrolysis pH threshold of 11. Due to differences in densities, the actual fertiliser sludge would take longer to settle than the synthetic urine sludge. An economic analysis of the urinal operational system was also performed for a typical 1000-person commercial building (assuming urine was only collected from 500 men) to determine the feasibility of an external service provider (Urine Recovery company) installing and managing all associated operations of the urinal system investigated and refined in this study. This analysis considered capital costs, operating costs, indirect benefits, revenue, and profits. Net present value was also considered to measure viability of operating the system. The given scenario would see the Urine Recovery company collecting and treating the urine to recover fertiliser on-site (at the commercial building premises). The manual mechanical mixing urinal design was considered for urine collection. The treatment would follow the sequence of alkaline stabilisation (using Ca(OH)2), solid/liquid filtration and reverse osmosis (RO) for volume reduction. This scenario yielded revenue of ZAR1.25 million per year from fertiliser sales and an annual urinal system service fee of ZAR1 500/urinal charged to the commercial building based on 89.7 kL of urine/year collected from 20 urinals. A solid and liquid fertiliser would be produced, the fertiliser would be sold as three streams – solid (at ZAR18.50/kg), 41% of the niche liquid sold to nurseries (at ZAR153/L) and the remaining 59% sold as bulk liquid fertiliser (at ZAR 9.56/L). Indirect benefits of R32 000 per year are expected for the commercial building as a result of water savings, and an additional ZAR2 300 for the Urine Recovery company from recovered water permeate through the RO system. A net present value of ZAR1.8 million was calculated over a five-year investment period. The capital cost of ZAR77 900 was calculated which included the production of urinals and the RO unit (1.72 m3 /day). The urinal production (estimated at R5 590 per urinal) is expected to reduce over time considering economies of scale. In conclusion, this study demonstrated how the novel, fertiliser-producing urinal can aid in nutrient recovery by producing fertiliser through a mixing mechanism that inhibits enzymatic urea hydrolysis. The design was deemed adequate and completed the task of collecting urine in a restroom so that calcium phosphate (solid fertiliser) formed in the removable urinal collection container. The design only considered urine collected from men, but the fertiliser yields could increase substantially if unisex urinals or female-only urinals were also installed. The designed urinal system is characterised by its simplicity, easy installation, and maintenance. Literature has concentrated on using feet instead of hands to open taps both as a water-supply solution and as a method to combat infection. Hence, the use of foot pedals in sanitation process is not novel, but this is the first time it has been used to operate a urinal. Recovery of valuable resources from the urinal designed and refined in this study can contribute to a sustainable and circular sanitation economy.
Open Access
The development and operation of plant microbial fuel cells using municipal sludge
(2019) Gulamhussein, Mohamedjaffer; Randall, Dyllon
Wastewater treatment accounts for 3-5% of the total electricity demand in developed countries. However, wastewater is estimated to have 9.3 times more energy than which is required to treat it. A sediment microbial fuel cell (SMFC) can potentially be used to treat wastewater and produce electricity by utilising the organics found in the wastewater. The challenge associated with using SMFCs is efficiency and longevity. Literature has shown that the efficiency can be increased by growing plants in a SMFC. Plants release organics and oxygen into the rhizosphere which can increase microbial growth and increase oxygen at the cathode. This research undertook to design a batch plant microbial fuel cell (PMFC) and operate it on three different municipal sludge streams namely, thickened waste activated sludge (WAS), liquid WAS and primary sludge (PS). In addition, three indigenous South African plant species, namely, C. papyrus nanus, W. thyrsiflora and P. australis were tested based on their power output potential and organic removal potential. The highest PPD (1036 ± 59 mW/m3 ) was obtained from the system using thickened WAS as substrate and planted with W. thyrsiflora. This was followed by liquid WAS as substrate planted with W. thyrsiflora (290 ± 21 mW/m3 ) and the lowest in the unplanted system using PS (119 ± 31 mW/m3 ). It was also found that COD utilisation for power generation was most efficient when using WAS. Thickened WAS produced 1330 mW/m3 per gram of COD consumed followed by liquid WAS with 508 mW/(m3 ·gCOD) and the lowest conversion in PS i.e. 124 mW/(m3 ·gCOD). Based on these factors WAS was chosen as the most suitable feed for a PMFC. Furthermore, it was found that utilising the PS in an anaerobic digestion would have over 500 times more power output making its use in a PMFC not viable. The highest organic removal efficiencies were observed when systems were planted with C. papyrus. When using WAS, C. papyrus achieved 62.2 ± 12.8%, 62.8 ± 9.6%, 58.5 ± 14.0%, 75.4 ± 8.4%, 95.3 ± 2.8% and 94.4 ± 3.5% removal efficiencies of VSS, COD, TKN, TP, FSA and OP respectively. When using PS, C. papyrus achieved 59.4 ± 9.7% 45.7 ± 10.4%, 82.0 ± 3.3%, 65.6 ± 3.2%, 97.4 ± 2.4% and 78.5 ± 2.8% removal efficiencies of VSS, COD, TKN, TP FSA and OP respectively. Therefore, it was noticed that W. thyrsiflora produced the highest power densities, but the C. papyrus produced the highest organic removal. The decision between the two plants was made based on the plant species ability to grow in sludge. It was noticed that the W. thyrsiflora died in thickened WAS. When using liquid WAS and PS, the old roots died, and new roots grew on the surface for W. thyrsiflora. Given the uncertainty of the plants ability to survive in the long term, C. papyrus was chosen as the most suitable plant species as it was able to grow in all three sludge types. Using WAS and C. papyrus, three more optimisation experiments were conducted. In the first one, it was found that using a separator between the electrodes increased the power density by 35%. The power output increased from 141 ± 16 mW/m3 to 191 ± 16 mW/m3 when a separator was used. It was noticed that the separator system had more horizontal root growth along the top surface just under the cathode of the PMFC as the separator limited vertical root growth. This may be the reason for higher power densities since more roots meant more oxygen release that can be consumed by the cathode. The second optimisation experiment focused on the use of multiple electrodes. It was found that using multiple electrodes was more efficient than single electrodes. Furthermore, it was noticed that connecting the multiple electrodes in parallel within a set-up was more efficient than connecting them in series. The peak power densities followed the order of: parallel connection 443 mW/m3 , series connection 296 ± 46 mW/m3 and 156 ± 17 mW/m3 for the control. The third optimisation experiment was focused on varying electrode distance. It was noticed that the highest peak power density was achieved when the electrode distance was halved (664 ± 122 mW/m3 ) followed by the system with 1.5 times electrode spacing which produced 453 ± 74 mW/m3 and the lowest for the standard design (290 mW/m3 ). From the three optimisation experiments, it was noticed that some variables have a larger impact on the performance of the PMFC than others. Halving the electrode distance increased the PPD 2.3 times, while doubling the electrodes increased it 2.8 times. Adding a separator only increased it by 1.4 times. This indicates that more focus should be attributed to the electrode distance and number of electrodes. In summary, this research found that, of the three plant species investigated, using C. papyrus with WAS substrate was the most practical and best performing combination for a PMFC. Furthermore, having a separator between the electrodes, having multiple electrodes connected in parallel within a set-up and decreasing the electrode distance to half all increased the power production.
Metadata only
Treatment of textile wastewaters using Eutectic Freeze Crystallization
(IWA publishing, 2014) Randall, Dyllon; Zinn, C; Lewis, Alison Emslie
A water treatment process needs to recover both water and other useful products if the process is to be viewed as being financially and environmentally sustainable. Eutectic Freeze Crystallization (EFC) is one such sustainable water treatment process that is able to produce both pure ice (water) and pure salt(s) by operating at a specific temperature. The use of EFC for the treatment of water is particularly useful in the textile industry because ice crystallization excludes all impurities from the recovered water, including dyes. Also, EFC can produce various salts with the intention of reusing these salts in the process. This study investigated the feasibility of EFC as a treatment method for textile industry wastewaters. The results showed that EFC can be used to convert 95% of the wastewater stream to pure ice (98% purity) and sodium sulfate.
Open Access
Water resources management in Zambia: a case of cumulative impacts associated with copper mining in the Upper Kafue Catchment, Copperbelt Province, Zambia
(2021) Mwamba, Bright; Randall, Dyllon; Kunz, Nadja
Water resources management is high on the agenda both locally and globally because of its important role in social, economic and environmental development. For example, as part of the 2030 Agenda for Sustainable Development, all United Nations Member States adopted 17 Sustainable Development Goals (SDGs) in 2015 that covered thematic issues including water, energy, climate, oceans, urbanization, transport, science and technology. Sustainable Development Goal (SDG) no.6, which targets universal access to safe and affordable drinking water for all by 2030, is of particular interest in this study. The mining industry contributes to socio-economic development; however, it has also contributed to declining water quality in rivers and lakes in many regions globally. In this study, the status and governance of water resources within the Copperbelt province of Zambia over the period 2000 to 2020 was examined. The study investigated population and economic growth within the region and its correlation with changes in water quality and quantity. The research also focused on understanding the ways copper mining is affecting local water resources. The study also investigated challenges faced by regulators and institutions in the water sector, and considered how these challenges could be addressed. Secondary data was obtained from government institutions within Zambia such as National Water Supply and Sanitation Council (NWASCO), Water Resources Management Authority (WARMA) and Zambia Environmental Management Agency (ZEMA), which are the key institutions in the water sector and the environment. Semi-structured interviews were also conducted with the three key institutions in the water and pollution control sectors. The results showed that the total population in the Copperbelt province has increased by 20% since 2000 to a total of 1 972 317 in 2010. The population is projected to be 2 669 635 in 2020, representing about 27% increase from 2010. The rural population is projected to be 423 511 in 2020, representing about 11% increase from 2010 while the urban population will be 2 246 124 in 2020 representing about 29% increase from 2010. The majority of this growth has occurred in urban areas, which grew by about 30% from 2000 to a total of 1 595 456 in 2010. Rural population has increased by 8% since 2000 to a total of 376 861. The results also showed increased economic activities driven mainly by copper mining. Water abstraction has generally declined since 2000 mainly due to decrease in mining activities. In 2000, about 1 million m3 /day was abstracted in the Copperbelt province and about 600 000 m3 per day in 2005. The reduction in 2005 could be attributed to reduction in mining activities and institutional changes in the water sector. Water production and consumption from commercial utilities has generally been in decline from 2000 to 2017. This is also the case with water consumption per capita and water production per capita. For example, water consumption per capita per day in 2001 was 203 liters and reduced to 113 liters in 2017, representing a 44% reduction in consumption. The results showed that water consumption from 2004 to 2008 averaged 100 million m3 while the production averaged 160 million m3 per year. NWASCO attributed the general downward trend in water production and consumption in the province to maintenance and rehabilitation of water infrastructure, and investment in new infrastructure, thereby reducing the unaccounted-for water. The other reason could be that new housing developments prefer to use groundwater sources rather than utility water (supplied by water companies). The reduction could also be attributed to the cost of water and that consumers needed to adjust from the background where utility services such as water supply and sanitation were the sole responsibilities of the mines (ZCCM), prior to privatization. In terms of water supply and sanitation coverage, there has been an increased coverage since 2000. In 2001, the population that had access to water supply and sanitation was 81% and 46%, respectively. Therefore, roughly 50% of the population had no access to sanitation. However, in 2017 the population with access to water supply and sanitation was 91% and 75%, respectively. This represented only 25% of the population in serviced areas that had no access to sanitation. Between 2007 and 2008, the sanitation coverage had seen a reduction compared to the year 2006. This was due to institutional changes on the Copperbelt province, and the 2008 economic recession – the mine townships that were previously serviced by an asset holding after privatization of the mines were taken over by other utility companies. Consequently, the service delivery in the province initially dropped, but then started increasing again in 2009.

Browsing by Author "Randall, Dyllon"

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