Browsing by Author "Ikumi, David"
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- ItemOpen AccessA Comparison of Wastewater Process Modelling Tools: Case Study of Potsdam WWTW(2022) Govender, Neeren; Ikumi, DavidA wastewater process model can either be based on a steady-state or dynamic mathematical modelling approach. The characterisation of the influent wastewater and specific wastewater parameters are critical input parameters to the mathematical model, whether for design, optimisation or to measure the expected performance of a wastewater treatment works (WWTW). A wastewater treatment process is inherently dynamic because of the changes in wastewater characteristics and flow rates, impacting the plant's process capacity and performance. Mathematical models have the capability to model such changes with ease and predict the expected performance of the plant. This dissertation involves a theoretical modelling approach to compare steady-state and dynamic-state modelling tools on an existing full-scale WWTW, namely the Potsdam WWTW located in Cape Town (South Africa). The models adopted for this research included: i) A plant-wide steady-state model developed by the Author as part of this dissertation (Author's PWM); ii) Plant-Wide Steady-State Design (PWSSD) developed by Wu (2014); iii) BioWin 5.0 (developed by Envirosim Associates Ltd; Barker and Dold, 1997; Envirosim 2007); and iv) UCTPHO dynamic model (Wentzel et al., 1992). The goal was to compare the output and results of the various models adopted for this research under steady-state and dynamic-state conditions where the models have been calibrated on historical field data and to examine the impact that specific wastewater characteristics have on the process capacity and the overall performance of the WWTW. To accomplish this goal, the following objectives were achieved: 1. The characterisation of the influent wastewater is critical in modelling. For a new plant (green field site), the wastewater characterisation will be based on typical norms as published in the relevant research literature. For an existing plant, the wastewater characterisation is typically based on historical sampling data. There can be challenges with historical sampling data, as data is often not measured, missing or not credible. In this case, designers are required to make assumptions to fill the gaps in the wastewater characterisation, adopting typical norms as published in the research literature and using sound process engineering judgement which was the scenario for the case study WWTW. 2. The documented design capacity of the Potsdam WWTW is 47 Mℓ/day (47,000 kgCOD/day) whereas the total theoretical process capacity estimated as part of this dissertation is 60.75 Mℓ/day (64,660 kgCOD/day), 37.5% higher than the documented process capacity. 3. The various models correlated well in terms of output results for both steady-state and dynamic-state conditions when compared across all process units for both the liquid and sludge streams, using the same input process parameters (flow rates, load patterns, wastewater characterisation, fractions and design assumptions). The steady-state models (Author's PWM and PWSSD) were almost identical in output results except for the aerobic digester. The output results of the dynamic-state models (BioWin and UCTPHO) were similar to the steady-state models but did differ for a few variables, attributed to the fact that the dynamic models use dynamic kinetic equations under constant or dynamic flow and load conditions, and this will produce different results than the less complex steady-state models which are based on constant flow and load conditions. 4. An evaluation of the impact of selected influent characteristic parameters on the system performance variables for biological nutrient (nitrogen and phosphorus) removal was performed for each of the steady-state and dynamicstate models. The parameters selected included the influent TKN (TKN/COD ratio), the maximum specific growth rate of nitrifiers (µMax) and readily biodegradable COD (RBCOD), and during the analysis, all other input parameters to the models were kept constant. The influent TKN and RBCOD are specific wastewater characteristics that can vary during the lifetime of a WWTW having a strong impact on its N and P removal performance. µMax is also a critical wastewater parameter and at sludge ages close to the minimum sludge age for nitrification, this parameter impacts severely on the performance of biological nitrogen removal systems. It was concluded that substantial changes in the influent TKN, µMax and RBCOD will significantly impact a WWTW, specifically concerning N and P removal, therefore, impacting effluent and sludge quality. The various models followed similar trends; however, the following discrepancies were noted: ▪ When the TKN was increased, only the BioWin model considered the impact that the pH outside the range of 7.2 – 8.0 would have on the µMax and nitrification capacity of the bioreactor. This is a shortfall in the other models ▪ When the µMax was varied, the different models followed the same trend, but nitrification problems occurred at different µMax values. The BioWin model showed partial nitrification at a higher µMax threshold value than the other models, which occurred under minimum temperature conditions only ▪ When the RBCOD was varied, the only difference in the models is the RBCOD fraction at which complete biological phosphate removal took place. The steady-state models had the same RBCOD fraction, and the dynamic-state model (i.e., BioWin) had a higher RBCOD fraction at which complete biological phosphorous removal took place due to the fact that BioWin adopts two different maximum specific growth rates for the poly accumulating organisms (PAOs), namely a higher growth rate constant under phosphorous rich conditions which results in a higher uptake of phosphorous, and a lower growth rate constant under phosphorous limited conditions, where phosphorous uptake is limited. With a lower PAO growth in the BioWin model resulting in a lower PAO population, there is less potential for aerobic polyphosphate uptake, resulting in higher effluent Ortho-P concentrations. A WWTW is complex with many interactions of different processes (biological, chemical and physical) and products taking the form of various phases (aqueous, gas and solid), complicated further by variations in influent characteristics, concentrations and flows. To manage these complexities, wastewater process models have been developed over the last three decades from stand-alone models for individual process units to plant-wide computational steady-state and dynamic models, which cater for a broad spectrum of wastewater engineering objectives. Steady-state models are powerful as they comprise simple and explicit algebraic equations that easily allow the estimation of design requirements and operation requirements for a WWTW with much less input information than dynamic models. They are often pre-processers to the dynamic models. In contrast, dynamic models require detailed input formation and sophisticated mathematical solvers but are more accurate in predicting effluent quality, system responses to dynamic conditions and the inhibitory effects of pH, temperature and metabolic products. The decision of selecting a steady-state or dynamic-state model is influenced by several factors, such as available information and influent data, user competency and modelling experience, size and complexity of the plant, as well as the detail and accuracy required by the designer. Wastewater process models therefore serve as a valuable tool for design, optimisation and operational and control strategies.
- ItemOpen AccessA prototype dynamic model for the co-treatment of a high strength simple-organic industrial effluent and coal-mine drainage(2020) Harding, Theodor; Ekama, George A; Ikumi, DavidThis research study's the use of biological sulfate reduction technologies for the treatment of Sasol Secunda's coal-mine drainage (CMD) using Fischer-Tropsch Reaction Water (FTRW) as a cost-efficient carbon source. The research aims to develop a prototype dynamic model that describes this co-treatment of FTRW and CMD in both a continuously stirred tank reactor (CSTR) biological sulfate reduction (BSR) system and a BSR gas-lift (BSR-GL) integrated system. The BSR-GL system recovers elemental sulfur (S0 ) from the H2S produced and stripped from the BSR unit. Furthermore, this study aims to use the prototype model for a quantitative comparison of the CSTR-BSR and BSR-GL systems. Two bench-scale 5-litre CSTR-BSR and a 20-litre BSR-GL system were operated, under varying feed COD concentrations and hydraulic retention times (HRTs), to generate datasets for use in verification and a rudimentary validation of the prototype model. The BSR-GL integrated system includes 1) a 1-litre H2S gas reactive absorption (ABS) unit utilising an aqueous ferric solution for the recovery of elemental sulfur (S0 ) from sulfide and 2) ferrous biological oxidation reactor to regenerate ferric from the ferrous for re-supply to the ABS unit. The datasets generated in the experimental study allowed for the identification, mathematical modelling and reaction verification of 32 components that interact as reactants and products in 23 reactions observed in the two BSR systems. The prototype model is presented in a mass and charge balanced Gujer matrix that includes, i) 5 SRB mediated processes, ii) 2 liquid-gas mass transfer processes, iii) 3 processes describing the ABS and Fe2+ bio-oxidation units, iv) 4 processes describing sulfide and elemental sulfur oxidation and v) the S0 and poly-sulfide aqueous equilibrium and vi) 9 processes describing death regeneration and BPO hydrolysis. This prototype model was implemented in the DHI WEST® software for initial stage simulation trials. The experimental datasets allowed for the first-stage estimation of the best-fit reaction rate equations and the calibration of the kinetic parameters related to the 23 reactions, using MATLAB® curve fitting toolbox. A pre-processor that describe the pH and equilibrium chemistry of the components of the artificially prepared FTRW+CMD feed mixture batches under varying total concentrations have also been developed in this research. This was done to generated influent file to the DHI WEST® simulations that incorporated the dynamics related to the FTRW+CMD feed mixtures. The sulfate utilisation rate (gSO4 -2 .l-1 .d-1 ) of the GL-BSR and CSTR-BSR systems were compared to determine which system had the best sulfate removal. The results were found to be as follows; a. On comparison it was found that the sulfate substrate utilisation rate for the CSTR_BSR system is 39.28% of that of the BSR-GL_N2 system, where both systems were fed at feed mixture of COD of 2500mgCOD/l, where the COD:SO4 2- was 0.7, b. For the same systems fed a feed mixture of COD at 5000mgCOD/l (COD:SO4 2- = 0.7), the sulfate substrate utilisation rate for the CSTR_BSR system was found to be 17.86% less than that of the BSR_GLN2 system. c. Finally, it was also found that the substrate utilisation rate for the CSTR_BSR system was 30.06% less than that of the BSR_GLN2 system at Se of 4gCOD/l, for both systems fed substrate at 5000mgCOD/l. Thus, it can be concluded that the sulfate substrate utilisation rate for the BSR-GL system is higher than that of the CSTR_BSR system, for systems fed COD feed mixtures at 2.5 or 5gCOD/l where both systems have the same effluent substrate concentrations. However, the difference in the comparative substrate utilisation rate is less at higher feed substrate concentrations. This is the influence of substrate inhibition on the active SRB biomass, which increases with higher effluent substrate concentrations. Finally, this research found that the use of gas-lift reactor technologies is superior to CSTR technologies in the treatment of coal-mine drainage utilising biological sulfate reduction (BSR). The CSTR-BSR system, fed sulfate between 1.6 to 14gSO4 2- /l, produced effluent with high dissolved H2S concentrations, on average 285mgS/l and maximum at >600mgS/l. Releasing this effluent to the environment would be hazardous to aquatic and human health and corrosive to infrastructure. As such, the effluent from the CSTR-BSR system requires further treatment to stabilise the water for any use. The BSR-GL technology allows for the conversion of the H2S produced during BSR reactions to form elemental sulfur, which is a resource recovered from this process, thus complying to the circular economy aim of this study.
- ItemOpen AccessAlternative water sources for urban consumers – A novel technology for the City of Cape Town urban resident(2019) Yiannou, Angelos; Ikumi, David; Ekama, GeorgeSouth Africa is classified as being the 30th driest country in the world and is regarded as a water scarce country. However, for the urban residents of the City of Cape Town, the ability to reduce their municipal water consumption through initiatives, other than simply using less water, is limited. Hence, there is a need for affordable, simple and compact technical solutions which allow urban populations residing in high density developments to make use of alternative sources of water, specifically greywater, to reduce their municipal water demand. Existing commercial technologies were considered, together with the socio-economic and technical constraints of an illustrative middle-income urban household in the City of Cape Town (CoCT). It was found that each commercial technology considered satisfied some, but not all, constraints characteristic of the household. For instance, the treatment device may produce treated water of a high quality. However, it may not be financially feasible for the consumer. Of the commercial technologies considered, there is no single commercial technology which can offer a complete solution within the socio-economic and technical constraints of the household. For this reason, the opportunity exists to produce an innovative technical solution. The proposed greywater treatment device consists of four cylindrical chambers in a vertical arrangement. Raw greywater enters the top chamber and treated greywater is extracted from the bottom chamber forming the base. The treatment processes undergone as the greywater flows through the treatment device include, in the following order, pre-filtration, biological treatment (Activated Sludge), clarification, filtration and disinfection. The process is driven by a combination of gravity and electrical energy. The proposed design is constructed using readily available materials and components. It is modular in its construction, allowing for easy maintenance, assembly and an increase in design flexibility. Evaluating the design against the same evaluation criteria stipulated for the existing commercial technologies showed that the proposed design may be an appropriate solution for the illustrative middle-income household within the City of Cape Town and is a novel technical solution.
- ItemOpen AccessCase study of the implementation of a membrane bioreactor (MBR) package wastewater plant for treatment of domestic effluent in a remote location(2022) Kritzinger, Johan Andries; Ikumi, DavidThe global population is more than it has ever been before; as it continues to grow, pressure on water resources increases due to the demand for the inalienable human right of access to basic services. Additionally, the detrimental impact of human activity on the environment has been realized and active measures to mitigate the threats posed by pollution (amongst other forms of environmental impact) are receiving high priority by numerous stakeholders and throughout the various parts of industry. These challenges all come into play in a unique manner when focusing on sanitation provision and wastewater treatment in rural areas. Rural communities are often disenfranchised by the lack of opportunities and services available to them and this is certainly compounded by the unique and challenging conditions for service provision and infrastructure implementation and management in these areas. Decentralized wastewater treatment is an emerging approach that is well suited to meeting the needs of people in rural areas and as a result has attracted the interest of researchers and started to gain traction in industry. Principles of conventional technologies such as the Activated Sludge (AS) system are incorporated with newer technologies such as the membrane bioreactor (MBR) to come up with innovative solutions that have promising potential but must be designed and implemented to be fit for purpose. The stringent emission control that is now common in many countries and being applied in South Africa under the National Water Act (NWA) means that sewage and effluent need to be handled according to the highest quality requirements which will not be met in areas with insufficient infrastructure (such as many rural areas). As with all things, the cost of implementing and maintaining a solution could determine the feasibility thereof and thus understanding through quantifying and optimizing the cost would be prudent. Some researchers have found that MBR plants tend to cost more than conventional treatment systems, but that they do carry their own strategic advantages of which not least is the high-quality effluent that it produces. This study provides a case study of a design and implementation of an MBR wastewater treatment plant (WWTP) on an agricultural farm in a rural area in the Western Cape of South Africa. The objectives were to (a) design the plant fit for purpose, using a scientifically accepted wastewater treatment process model, (b) evaluate the plant's performance in terms of effluent/emissions produced and (c) perform the operation cost evaluation of the designed WWTP. The AS model with biological nutrient removal (BNR) was developed in a Modified-Ludzack Ettinger (MLE) system adapted for MBR while using experimental raw water data as input. The outputs acquired from the model were used to size and design the practical implementation of the WWTP. The raw and treated effluent water and sludge quality data was obtained by experimental samples taken on site at the operational WWTP and tested by an analytical laboratory. The data was evaluated based on its trends, using statistical methods, using the effluent quality index for pollution and emissions, and using mass balances for verification. The operational costing was performed and evaluated according to the operational cost index. The wastewater treatment plant was designed for 49.2 kl/day of wastewater in a bioreactor with MLSS of 12 000 mg/l and a sludge age of 25 days which yielded a reactor volume of 22 kilolitres. The minimum anoxic mass fraction was determined as 0.14 and then chosen as 0.24, but since it is an MBR plant the volume fraction of the anoxic was 0.27. The optimal a-recycle was determined as 3.5 and then chosen at 5. The total oxygen demand was found to be 28.6 kgO/day of which the membrane air scouring blower supplied 4.7 kgO/day and reduced the air supply required from the aeration blower to 23.8 kgO/day. To be conservative, two hundred membrane sheets were used which would operate at a flux of 15.4 LMH. The reactor volume was also enlarged by a safety factor of 25% to 28 kilolitres. The small footprint of the WWTP comes at the cost of high energy usage. The model compared fairly well with the implemented WWTP particularly in terms of effluent ammonia and nitrate concentration. The effluent water quality was good with all measured parameters on average being compliant with general limits for wastewater discharge. Particularly the removal of TSS (99%) and of COD (93.5%) was highly effective and there were less than 5 outlierresults in total, which were for ammonia and nitrate. Out of the total number of parameters tested across all samples, 93% were compliant. The EQI for water was calculated as 12.1 with all contributions being positive while the EQI for sludge was 431.8 with one negative contribution from faecal coliforms amongst only positive contributions from the other parameters. The operational cost was determined as R123 316 ex VAT per year of which more than 80% is attributed to energy usage. The aeration energy alone is 58% of the operational cost. The cost per kilolitre of treated effluent is R6.73 ex VAT, which for comparison is less nearly half the cost of what the local municipal rates for sanitation would be for the application and it is also less than the cost of irrigation water from the municipality which makes it an attractive prospect for reuse. The conclusion from the study is that the WWTP design and implementation was accomplished by its cogent performance and reasonable operational cost. The objectives were achieved so that the design was developed and implemented with success, the effluent water quality was compliant, and the operational cost was understood and found to be feasible. The implications of the study are that decentralized sanitation service is being provided to a community that did not previously have access to this and that the wastewater produced by this community is now being adequately treated according to regulations, which ensures protection of the environment and advances public health.
- ItemOpen AccessComparing the Metcalf and Eddy and UCT steady state guidelines for sizing of biological nutrient removal activated sludge wastewater treatment plants(2020) Murphy, Katelyn; Ekama, George A; Ikumi, DavidThis dissertation aims to provide both a qualitative and quantitative comparison of two steady state activated sludge (AS) design guidelines - the University of Cape Town (UCT) guideline used in South Africa and the Metcalf and Eddy (M&E) guideline used in North America and other parts of the world. It looks at the key similarities and differences between the two steady state AS design guidelines and how, under dynamic conditions, a system that is sized using a particular guideline (i) compares to its steady state results and (ii) performs under these dynamic conditions. In order to achieve the aims and objectives of this dissertation, an AS steady state model was created in a Microsoft Excel spreadsheet for the UCT guideline and M&E guideline respectively, and the models were analysed in terms of the key similarities and differences in the design guidelines in terms of inputs, equations, approaches and assumptions used. The results produced from each model were also analysed by setting the influent wastewater characteristics the same for each guideline and then analysing the results. The systems that were sized using the steady state AS models were then input into an AS system dynamic simulation software program, UCTOLD (which predicts virtually identical results as ASM1), together with a full set of diurnal influent data, to predict the behaviour of the system under steady state and dynamic conditions and compare the steady state predictions to those calculated in the steady state models and assess how the steady state model sized systems perform under dynamic loading conditions. The results of the analyses found that the two guidelines are similar in terms of organic material removal, nitrification and the sizing of the secondary settling tank, but differ significantly in the sizing of the anoxic reactor to achieve a certain nitrate removal. The key findings are: (1) Both UCT and M&E guidelines close the COD and N flux balances within 1%. (2) For organics removal only, at the same SRT, sludge production and oxygen demand are about 5% higher and lower respectively for the M&E guideline than the UCT guideline. When a UCT and M&E sized fully aerobic system is simulated with ASM1, this difference is repeated. The UCT guideline results are closely correlated with the ASM1 results but the M&E results deviate from those of ASM1. These differences arise because the M&E guideline assigns different values to the kinetic, stoichiometric and temperature sensitivity constants. If these constants in the M&E guideline are assigned the same values as the UCT guideline, virtually identical results are obtained. (3) For nitrification under fully aerobic conditions, the M&E guideline calculates a slightly shorter minimum aerobic SRT for nitrification than the UCT guideline. Again, the M&E guideline assigns different values to the nitrification kinetic (μAm20, bA20), stoichiometric (YA, Kn20) and temperature sensitivity constants (θμAm, θbA, θKn) than the UCT guideline. The M&E guideline calculates the minimum sludge age for nitrification, Rsm, using a fixed maximum specific growth rate of nitrifiers at 20oC (μAm20) at 0.90 g/(g.d), and after correcting for temperature, DO concentration in the aerobic reactor and assigning a safety factor (Sf = 1.5), the minimum sludge age for nitrification is slightly shorter than for the UCT guideline for a selected maximum specific growth rate of nitrifiers at 20oC (μAm20) of 0.45 g/(g.d) and assigning Sf = 1.25. In the M&E guideline the mass of nitrifiers is added to the reactor MLSS concentration which increases the MLSS mass in the reactor by about 1-3%. This is not done in the UCT guideline to maintain the COD balance for organics removal. At the same SRT in a fully aerobic system (i.e. aerobic SRT = system SRT), the oxygen demand for nitrification is closely similar in the two guidelines. This is because the calculated concentrations of nitrate produced by nitrification (called nitrification capacity Nc in the UCT guideline) are closely similar – the difference in the sludge production of the two guideline make little difference to the N taken up for sludge production. (4) If fully aerobic nitrifying reactors sized with the M&E and UCT guidelines are simulated with ASM1 at the same SRT, the same differences as with organic removal are observed. Hence the main difference in the sizing for nitrification in fully aerobic reactors in the two guidelines is the shorter aerobic SRT for nitrification in the M&E guideline (as a result of the different nitrification kinetics and safety factors) than in the UCT guideline. (5) Significant differences between the two guidelines emerge when adding an anoxic reactor for denitrification, such as for the anoxic aerobic nitrification - denitrification (ND) Modified Ludzack-Ettinger (MLE) system. This is because (5.1) the nitrifiers are assumed to behave differently under anoxic conditions in the two guidelines and (5.2) the effective specific denitrification rates of the OHO biomass in the anoxic reactor are much higher in the M&E guideline than in the UCT guideline. (6) With regard to difference (5.1), in the UCT guideline, the nitrifiers are assumed to grow only in the aerobic reactor but die in both the anoxic and aerobic reactors. In the M&E guideline, the nitrifiers are assumed to die (and grow) only in the aerobic reactor, i.e. they neither grow nor die in the anoxic reactor. Hence in the M&E guideline, the MLE system is sized based on an aerobic SRT, which excludes the mass of sludge in the anoxic reactor as in (3) above, but in the UCT guideline the MLE system is sized based on a system SRT, which includes the mass of sludge in the anoxic reactor. (7) With regard to difference (5.2), the faster specific denitrification rate determined with the M&E guideline yield much smaller anoxic reactors by at least 50% to achieve the same nitrate removal. (8) The consequence of these two differences is that the system SRT of the MLE system determined with the UCT guideline is considerably longer than that determined with the M&E guideline leading to larger anoxic, aerobic and system reactor volumes. This difference widens as the influent TKN/COD concentration ratio increases, i.e. as the concentration of nitrate to be denitrified increases. (9) When simulating the UCT sized MLE systems (under steady state conditions) with ASM1, very similar reactor MLVSS and MLSS concentration, effluent ammonia and nitrate concentrations and total oxygen demands are obtained with ASM1 and the UCT guideline. This indicates that the denitrification kinetics of the UCT guideline are well aligned with ASM1. This is not the case when simulating with ASM1 M&E guideline sized MLE systems under steady state conditions – while the effluent ammonia concentration compares well, the effluent nitrate concentration is far higher (increases from 6 mgNO3-N/l to above 20 mgNO3-N/l). This indicates that even though the denitrification kinetics of the M&E guideline were derived in part from ASM1 simulations, the denitrification kinetics of the M&E guideline are very poorly aligned with ASM1. (10) When the fmanx,M&E of the denitrification MLE system in (9) is increased to fmanx,UCT of 0.318 (but keeping the SRT = SRTsys,M&E) and simulated with ASM1, the effluent nitrate concentrations reduce from around 20 mgNO3-N/ℓ to around 6 mgNO3-N/ℓ, which is aligned with the UCT guideline ASM1 results. (11) The enhanced biological phosphorus removal (EBPR) parts of the UCT and M&E guidelines were not compared. While the EBPR part of the UCT guideline is complete and accounts for the phosphorus accumulating organisms (PAO) and their polyphosphorus content in the VSS and TSS calculations, as well as the differences in the denitrification kinetics in NDEBPR system compared with ND systems, which aligns the UCT NDEBPR guideline with ASM2, this is not the case in the M&E guideline. Because there is insufficient information in the M&E guideline to execute a complete NDEBPR system design calculation, the EBPR parts of the guidelines could not be compared. (12) The M&E overflow rates can be aligned with the UCT 1DFT to determine very similar SST surface areas. The lower resultant reactor MLSS of the M&E sized systems when simulated with ASM1 means that the SSTs will operate at a lower than designed for MLSS and thus under peak conditions (fq is 2.5 or greater) the SST will operate at a higher than permissible overflow rate. This is because the M&E SST sizing procedure does not include a 1DFT flux rating of 0.80 (as the UCT guideline does), which has the effect of increasing the SST surface area estimated by the 1DFT by 25%.
- ItemOpen AccessDesktop study on Novel Treatment techniques to treat industrial fertilizer effluent(2018) Fortuin, Jordache; Randall, Dyllon G; Ikumi, DavidFertilizer production is a massive global industry with the global consumption of the three main fertilizer nutrients, nitrogen, phosphate and potassium estimated at 187 million tonnes in 2016 with an anticipated annual growth of approximately 2% for the foreseeable future. In 2016 the global fertilizer market was estimated to have an overall market value of 141 billion US dollars. Fertilizer production produces significant liquid waste as process water used for the various separations, cleaning, emulsifying and dilution processes absorbs various nutrients and contaminants from these production processes. This liquid waste has characteristically high concentrations of nutrients derived from the base fertilizer, such as various dissolved phosphate compounds for phosphate-based fertilizer production or dissolved nitrogenous compounds for nitrogen based fertilizer production. These contaminants are inherently nutrients that could be recovered for beneficial re-use. The phosphate and potassium minerals used in fertilizer production are obtained from ores mined from the earth, thus the re-use of these mineral present particular significance when taking into accounting the declining global supply of these ores. Furthermore, if these liquid wastes are not disposed of correctly they can lead to detrimental environmental impacts such as eutrophication and ecological degradation in water courses. This study addresses this problem by presenting three novel treatment techniques to treat the liquid waste produced from a fertilizer production plant. A liquid waste sample obtained from a particular fertilizer production plant producing primarily nitrogen-based fertilizer is used as a design basis to evaluate the three presented treatment techniques. The techniques are evaluated based on their economic feasibility, technical feasibility and resource recovery ability. The three treatment techniques studied were the Sharon-Anammox bioreaction process, electrodialysis with struvite recovery process and combined forward-reverse osmosis process. The technical feasibility of the processes was primarily evaluated based on the effluent water quality from the treatment systems. The effluent quality index (EQI) was used as a comparative measure of the effluent quality of the processes. All three processes were found to perform inadequately from a technical feasibility perspective as demonstrated by the negative EQI values obtained for the processes. The Sharon-Anammox bioreaction process was found to perform poorly because its application is limited to treatment of waste streams containing high ammonia concentrations such as in conventional domestic waste. Therefore, the Sharon-Anammox process was not suited to the fertilizer effluent which also contained high nitrates, phosphates and total dissolved solids. The electrodialysis process performed poorly as it was unable to effectively remove the ammonium cations from the process water. The combined forward-reverse osmosis process performed poorly because a resource recovery step was not included to treat the concentrated waste stream discharged from the forward osmosis step of the process. It was identified that a similar struvite recovery step should be added to the combined forward-reverse osmosis process to improve the technical feasibility of the process and to provide the process with resource recovery capabilities. From an economic feasibility perspective, it was found that the addition of the struvite recovery setup to the electrodialysis process increased the capital costs of the process to between 300% and 500% of the other two options. However, with the omission of the struvite recovery setup the capital costs of all three processes were in a similar range.
- ItemOpen AccessThe Development of a Calibration Methodology for a Realistic Primary Settling Tank (PST) Model(2020) Matesun, Joshua; Ikumi, DavidThe comprehensive characterisation of influent waste to water and resource recovery facilities (WRRFs) is key to tracking the material elements through the entire WRRF system to ensure accurate prediction of system behaviour/performance or avoidance of system failure. Current models for activated sludge (AS) and anaerobic digestion (AD) unit processes of WRRF are well verified. However, previous models that replicated primary sedimentation units assumed that all the total settleable solids (TSS) components settled at the same velocities, which resulted in poor predictions of primary sludge characteristics and subsequently poor AD model predictions (with the PST underflow linked to AD in plant-wide settings). In this investigation, the raw wastewater entering the WRRF via the primary settling tank (PST) is comprehensively characterised by categorising the TSS according to inorganic settleable solids (ISS), biodegradable particulate organics (BPO) and unbiodegradable particulate organics (UPO), each with five settling velocity distributions profiles. The BPO is further defined in terms of its elemental composition and hydrolysis rate kinetic constants to allow for accurate prediction of the AD system performance, when linked to the virtual PST. With the composition of raw wastewater and primary sludge (PS) known the settled wastewater that leads to the activated sludge (AS) system can be determined using the principles of material mass balance over the PST unit process. This project introduces (i) the modification of the University of Cape Town Primary Sedimentation Unit (UCTPSU) physical process model of Polorigni (2020), by the inclusion of hydrolysis and acid fermentation bio-processes and (ii) calibration of the UCTPSU model through (a) the performance of a sensitivity analysis on the modified UCTPSU model and (b) utilisation of information generated from settleometer tests and augmented bio-methane potential (ABMP) tests to accurately predict the characteristics of PS to AD and settled wastewater to AS systems, hence allow for accurate tracking of elements along the entire WRRF, when using the model for design and optimised operation of WRRF systems. The settleometer, AD and ABMP tests showed that primary sewage sludge (or the total settleable solids) fractionated according to the particle size and density, and their corresponding wastewater characteristics were determined. The findings also showed that the unbiodegradable particulate organics formed the largest total settleable solid components removed from the PST underflow.
- ItemOpen AccessDevelopment of a Design Tool for Rapid Gravity Media Filtration in Water Treatment(2022) Ingle, Laura; Ikumi, DavidFiltration is the most commonly used water treatment process (Gray, 2010) and can be found at every water treatment plant in South Africa (Van Duuren, F. A., South Africa Water Research Commission., 1997). Therefore, the design, evaluation and improvement of filtration systems is (and should be) ongoing. Currently there is seemingly a lack of consolidated information to enable filter designers to quickly and easily design and evaluate various filtration systems, as it is not always possible to conduct thorough pilot-testing at design stage. This study addresses the development of a detailed filter design tool that enhances the plant-wide water treatment design tool that incorporates a high-level filter design spreadsheet previously developed by Morrison (2019). This study presents guidelines to filter designers for the whole filtration process based on a literature review that consolidates key aspects and design parameters such as media selection and characterisation, filtration rate selection, operation and control, backwash rates, head losses, filter components, configuration and geometry. These parameters are documented in this dissertation and incorporated into the design tool, thus ensuring that the designer obtains relevant insights to the various parameters and their effects. This study focuses on rapid filtration as it is the most common granular filtration technology (Crittenden et al., 2012). The design tool is developed in Microsoft Excel and is intended for exclusive use by the author's employer at the time of submission. The tool itself provides a mechanism for the designer to easily review the effects of various interlinked parameters in developing and refining a filter solution. The outputs of such a tool can be utilised further in plant-wide treatment models.
- ItemOpen AccessDevelopment of a Dynamic Simulation Model for Equalization Tanks(2021) Simo, Eugene Fotso; Ikumi, David; Ekama, GeorgeThe influent to a water and resource recovery facility (WRRF) generally exhibits significant diurnal variations in flow rate and load concentration. This makes determining the operating parameters and subsequently the overall operation of plants difficult, especially in developing countries due to the lack of highly skilled operators. Hence, there is an incentive for the control and operation of WRRFs in developing countries to be improved. Flow equalization tanks were identified as a potential method to attenuate the diurnal variations in flow rate and load concentration into plants. The main aim of this research was to develop a viable dynamic simulation model for the operation of flow equalization tanks, within a plant-wide framework (to allow for the evaluation of design and control strategies). The next aim was to determine the benefits of equalization tanks towards design and optimised operation of future WRRFs via scenario analyses. Finally, the effects of the equalization tank on the performance of various unit processes in a WRRF were to be investigated. The model was developed in three steps; i) the development of the required equations to model equalization tanks, ii) mass balance throughout the model for internal consistency and iii) scenario analyses to determine if the model generated reasonable and scientifically sound outputs. The model was developed using Microsoft Excel Visual Basic (VBA) and WEST®. Two scenarios were considered to assess the equalization tank modelled. Scenario One involved the comparison of the capital cost, unit process sizes and total footprint of a balanced sludge age Modified Ludzack-Ettinger (MLE) system with and without an equalization tank. Scenario Two compared the plant performance of the MLE system designed in Scenario One with and without a flow equalization tank. A dynamic simulation model replicating equalization tanks was successfully developed. From scenario analyses, it was determined that using an MLE system and only considering equalization of flow, there was a reduction in the size of several unit processes by 8-9% (primary settling tank, biological reactors, secondary settling tank, flotation unit, anoxic-aerobic digester), due to the less conservative design values that could be used as the variations of the influent were decreased. Despite this, a 13% overall increase in the footprint of the WRRF was observed due to the addition of the equalization tank. The attenuation of diurnal flow variations also resulted in reduction of various plant parameters by up to 50% (flow, OUR, VSS flux). Finally, there was a 10% improvement in the performance of various unit processes due to the presence of the equalization tank. In conclusion, the inclusion of equalization tanks in WRRFs has significant positive effects. These results were obtained with equalization of flow only. Some other limitations were experienced during the project resulting in the following recommendations: further research will be needed to validate and calibrate the model, As the model was not successfully incorporated in a plant-wide framework, further developments in that direction are required, as well as including the equalization of load in the model.
- ItemOpen AccessDevelopment of a Dynamic Simulation Model for Equalization Tanks(2021) Fotso, Simo Eugene; Ikumi, David; Ekama, GeorgeThe influent to a water and resource recovery facility (WRRF) generally exhibits significant diurnal variations in flow rate and load concentration. This makes determining the operating parameters and subsequently the overall operation of plants difficult, especially in developing countries due to the lack of highly skilled operators. Hence, there is an incentive for the control and operation of WRRFs in developing countries to be improved. Flow equalization tanks were identified as a potential method to attenuate the diurnal variations in flow rate and load concentration into plants. The main aim of this research was to develop a viable dynamic simulation model for the operation of flow equalization tanks, within a plant-wide framework (to allow for the evaluation of design and control strategies). The next aim was to determine the benefits of equalization tanks towards design and optimised operation of future WRRFs via scenario analyses. Finally, the effects of the equalization tank on the performance of various unit processes in a WRRF were to be investigated. The model was developed in three steps; i) the development of the required equations to model equalization tanks, ii) mass balance throughout the model for internal consistency and iii) scenario analyses to determine if the model generated reasonable and scientifically sound outputs. The model was developed using Microsoft Excel Visual Basic (VBA) and WEST®. Two scenarios were considered to assess the equalization tank modelled. Scenario One involved the comparison of the capital cost, unit process sizes and total footprint of a balanced sludge age Modified Ludzack-Ettinger (MLE) system with and without an equalization tank. Scenario Two compared the plant performance of the MLE system designed in Scenario One with and without a flow equalization tank. A dynamic simulation model replicating equalization tanks was successfully developed. From scenario analyses, it was determined that using an MLE system and only considering equalization of flow, there was a reduction in the size of several unit processes by 8-9% (primary settling tank, biological reactors, secondary settling tank, flotation unit, anoxic-aerobic digester), due to the less conservative design values that could be used as the variations of the influent were decreased. Despite this, a 13% overall increase in the footprint of the WRRF was observed due to the addition of the equalization tank. The attenuation of diurnal flow variations also resulted in reduction of various plant parameters by up to 50% (flow, OUR, VSS flux). Finally, there was a 10% improvement in the performance of various unit processes due to the presence of the equalization tank. In conclusion, the inclusion of equalization tanks in WRRFs has significant positive effects. These results were obtained with equalization of flow only. Some other limitations were experienced during the project resulting in the following recommendations: further research will be needed to validate and calibrate the model, As the model was not successfully incorporated in a plant-wide framework, further developments in that direction are required, as well as including the equalization of load in the model.
- ItemOpen AccessDevelopment of an evaluative framework promoting a paradigm shift towards resource recovery in wastewater treatment(2022) Coothen, Yuva; Ikumi, DavidResource recovery from wastewater is a rapidly emerging research area promoting the development of several technologies that have the potential to increase the sustainability of process operations in wastewater treatment. With the implementation of appropriate treatment technologies, nutrients such as phosphorus and nitrogen can be recovered from nutrient rich sludge dewatering liquor in various forms to be used as agricultural fertilisers; portion of power demands at WWTPs can be offset by extracting energy from wastewater; the undesirable impact of wastewater treatment processes on air quality from emission of greenhouse gases, on land from sludge disposal and on downstream water bodies via effluent discharge can be mitigated. The performance of WWTP design and control strategies can be evaluated, based on their impact on downstream water bodies and the associated net operational costs of each unit operation, by using the performance indices developed by the IWA BSM task group. With the impact of products generated from WRRFs on air quality and land, the value of resources recovered, and other operational costs being overlooked in the current evaluation system, it is unclear whether the fate of products generated from WRRFs would influence the design and operation of WWTPs. This dissertation addresses the hypothesis that a WWTP model evaluative framework that considers the fate of WWTP products and value of resources that can potentially be recovered from WRRFs will generate a useful tool for design and operation of WWTPs in South Africa and aid in their transition to future WRRFs. To fill the gaps in the current evaluation system, it was important to extend the term “effluent” to be now inclusive of greenhouse gases that evolve from WWTPs and sludge disposed. As such, two new evaluative equations were formulated accordingly (EQIgas and EQIsludge) in addition to the existing effluent quality index now known as EQIwater. The latter has been modified such that the weighting assigned to each pollutant is a function of the regionspecific or WWTP-specific pollutant concentration limits. This flexibility allows the EQIwater evaluation to be tailored towards the effluent quality goals specific to each plant or region. The EQIgas is function of the greenhouse gasses that evolve from WWTPs with weighting factors set equal to their respective global warming potentials. The EQIsludge was formulated based on the South African sludge disposal guidelines taking into consideration the stability, pollutant and microbiological classes. Additionally, the existing operational cost index was modified to include fines for violation of pollutant limits in the effluent, the monetary benefits of nutrient recovery and dosing of additives such as lime or magnesium. The PWM_SA by Ikumi et al. (2015a) was used to replicate Module 4 of Waterval WCW for the simulation of two scenarios: (1) without side-stream treatment and (2) with side-stream treatment including recycle of side-stream effluent to head of works. Due to model limitations, the effluent quality evaluation was limited to the EQIwater. On the other hand, fines for noncompliance to effluent regulations and cost recovered from the sale of struvite were not considered in the OCI evaluation since the determination of an appropriate future unit cost for each component in a South African context was outside of the scope of this project. From the simulated results, it was noted that Module 4 of Waterval WCW has sufficient capacity to treat the influent wastewater as well as the recycled sludge dewatering liquors generated from that module to acceptable quality with respect to the standards of the Waterval Water Use License (08/C22C/fg/646). Thus, the implementation of side-stream struvite precipitation in this case significantly increases the net operational costs for marginal benefits in terms of effluent quality. The extended performance indices framework is currently being implemented, as an evaluative protocol, in the simulation of all considered strategic scenarios in order to determine the most impactful in future decision making for the given WRRF systems. However, in order for this evaluative framework to be more effective, the models will require modifications, such that the predictions made regarding system performance include the variables of significance, related to prioritised criteria for the products generated by the system.
- ItemOpen AccessDevelopment of an Integrated thermal hydrolysis process - Anaerobic Digestion (THPAD) Model(2022) Olando, Alexander; Ikumi, David; Gaszynski, ChrisHistorically, anaerobic digestion is one of the most common processes used to treat sludge generated from wastewater treatment plant (WWTP) processes. However, with the exponential increase in populations, which implies an increase in WWTP loads, the amount of waste generated poses an imminent problem to the handling capacity of current anaerobic digesters. Subsequently, there has been a lot of research into various physical and chemical processes that would allow for a more efficient sludge handling mechanism. Studies have reported various advantages associated with digesting sludge at higher temperatures known as thermophilic temperatures. These advantages include increased sludge handling capacity, a higher degree of sludge biodegradability and subsequently increased methane production and better sludge dewatering characteristics implying cheaper sludge transportation costs just to mention a few. However, despite the advantages associated with thermal treatment, this technology has not yet been proven in a South African context. This project involved the development of an integrated thermal hydrolysis process (THP) and anaerobic digestion (AD) model capable of simulating these processes at elevated temperatures. A comparative desktop case study of the existing AD facility at the Cape Flats wastewater treatment works (CFWWTW) in Western Cape, South Africa was investigated following the City of Cape Town's (CCT) initiative to retrofit a THP unit to the anaerobic digesters to help deal with the increase in sludge handling capacity. A comparison was therefore carried out, investigating the base case scenario of maintaining the existing conventional mesophilic anaerobic digesters (MAD) and retrofitting a THP unit to the conventional anaerobic digesters (THPAD). A steady-state THP and AD model was developed and used in conjunction with an integrated dynamic THP and modified AD (termed as the Extended-UCTSDM3P) model for simulating both the conventional MAD and THPAD processes. This allowed for a comparison of results not only between the two processes, but also the two types of models. These models were then used to simulate the treatment of a mixture of primary sludge (PS) and waste activated sludge (WAS) at a ratio of 60:40 with the WAS obtained from a Nitrification Denitrification Biological Excess Phosphorus Removal (NDBEPR) activated sludge treatment. The AD models, therefore, accounted for the increased phosphorus concentration as a result of iv polyphosphates (PP) breakdown and consequently the possible precipitation of struvite (MgNH4PO4) from the AD liquor. The results showed that the THPAD configuration allowed the digesters to process 2.3 times more sludge than with the conventional mesophilic anaerobic digesters. Furthermore, the methane production in the THPAD was conservatively calculated to be 2.5 times higher than the MAD. This implied an increased potential for use of the methane gas as an alternative source of energy in the wastewater treatment plants. Given that no laboratory experiments were carried out, the results were based on theoretical scenarios and knowledge collected from an extensive literature review. However, given the capacity, flexibility and detail the model has been developed to, different scenarios in the anaerobic digestion process can be investigated and valuable practical insight extracted. Furthermore, through calibration with accurate meaningful data from a pilot or full-scale plant, the developed model is a tool that could be used in predicting digester performance.
- ItemOpen AccessEvaluation of a data-driven primary sedimentation tank model using settleometer data(2023) Mazivila, Christina; Ikumi, DavidData-driven primary sedimentation (or settling) tank (DDPST) model was recently developed to improve the existing primary sedimentation (or settling) tank (PST) models which are largely total suspended solids (TSS) based. The purpose of the DDPST model is to realistically simulate the full-scale PST (FS-PST) underflow and overflow outputs in terms of biodegradable particulate organics (BPO), unbiodegradable particulate organics (UPO), and inorganic suspended solids (ISS) compositions. This characterization is fundamental to the planning of the downstream resource recovery systems such as anaerobic digestion (AD) and activated sludge (AS) systems through accurate process predictions. The DDPST model was previously subjected to rigorous mass balance verifications and has undergone a general sensitivity analysis (GSA) to identify the most important parameters required to allow the accurate predictions. The settling velocities and settling proportions of the five particle settling velocity groups (SVGs) were identified as significant. These five SVGs are characterized by different proportions of settleable BPO (BPOset), settleable UPO (UPOset) and settleable ISS (ISetS). Due to variability in wastewater (WW) characteristics from plant to plant, the DDPST model requires settleability data that is specific to a plant to make correct predictions. A five-column settleometer (5C-settleometer) has been proposed as a tool that can provide this necessary data. Essentially, the 5C-settleometer is regarded a labscale PST that allows detailed study of the FS-PST critical parameters through segregation of settleable TSS into five different SVGs. Along with the Augment Biomethane Potential (AugBMP) test procedure and parameter estimation tools, the particles from the SVGs can be fractionated into BPOset, UPOset, and ISetS. To this date, however, the accurateness of the 5C-settleometer to provide accurate FS-PST settleability characteristics has not been confirmed. This implies that the 5C-settleometer, as a suggested tool to provide the necessary data, cannot be used with confidence, and so is the DDPST model. The purpose of this study was to evaluate the DDPST model through comprehensive characterization of the primary sewage sludge (PSS). To achieve this, the ability of the 5Csettleometer to accurately characterize the PSS in terms of settling velocities and settling proportions was verified. This was done by collecting the FS-PST influent, underflow, and overflow diurnal data in parallel with the 5C-settleometer test runs at the Bellville Wastewater Treatment Works (WWTWs). Using the FS-PST diurnal data, the related percentage removals for settleable solids (in terms of BPOset, UPOset, and ISetS) were determined. Using the 5Csettleometer characterized PSS outputs, the parameters required to run the DDPST model (i.e., five settling velocity groups and their corresponding BPOset, UPOset, and ISetS settling proportions) were determined to allow the PST underflow and overflow model predictions. Following this, the PST percentage removals (underflow) and overflow characteristics from (i) the DDPST model, and (ii) the FS-PST, were compared to confirm whether the model predictions fully replicate the FS-PST. Important to note is that both the FS-PST and the 5Csettleometer received the same influent characteristics to ensure that the settleometer overflow and underflow are reasonably compared with the FS-PST to check the representativeness. While the 5C-settleometer has proven (i) the ability to segregate the particles into distinguishable particle sizes, and (ii) the ability to somewhat account for the overall removal proportions that are comparable to the FS-PST at a flow rate fluctuating between 0.6 and 0.8 l/min, its relationship with the DDPST model needs to be reassessed. The settleometer upflow velocities appeared to be too high to allow accurate model predictions. Unfortunately, it is impossible to achieve very low velocities to fulfil the DDPST model requirements with the current settleometer design. This shortfall on the model to represent the 5C-settleometer makes it impossible to yield reasonable predictions. This gap requires to be addressed to ensure that the 5C-settleometer, as a lab-scale version of the FS-PST, is correctly translated into the DDPST model, not only in terms of the upflow velocities which govern the particle settling, but also, the accompanying settleometer features which affects the particle or flow movements, i.e., (i) the occurrence of sharp bends or curvatures in a 5C-settleometer, or (ii) the increased probability of inter-particle forces especially when operating the settleometer at low flow rates. While it may be a challenge to model these interfering instances, it is essential that they are accounted for in the model to ensure accurate DDPST model predictions. It is further recommended to explore ways to improve the operation of the current settleometer. For instance, investing in a higher capacity pump and a settleometer flow meter will, with no doubt, add a benefit to the quality of the settleometer output data. In addition, the use of multiple settleometer runs with a combination of high and low flow rates can be explored, to achieve exceptionally representative FS-PST data. In terms of the elemental compositions (EMs), the five SVGs showed a marginally varied BPOset and UPOset compositions. This could be the result of particulate material differences between the SVGs. Nonetheless, the average BPO and UPO compositions recorded in terms of CXHYOZNAPB are C1H5.99O1.13N0.05P0.00 and C1H1.79O0.45N0.22P0.02, respectively. The subscript “Y” (i.e., 5.99) of the BPO composition marginally differs from what has already been reported on literature. This difference could be linked to (i) the discrepancies related to the carbon measurements experimentally (carbon is calculated from biogas measurement and alkalinity), and (ii) the source of Bellville WW, i.e., Bellville WWTWs receives both domestic and industrial WW. Overall, the ISetS (76.7%) and UPOset (78.1%) were found to be removed in greater proportions than BPOset (37.7%) in the FS-PST.
- ItemOpen AccessIdentification of Wastewater Primary Sludge Composition using Augmented Batch Tests and Mathematical Models(2021) Gaszynski, Christopher; Ekama, George; Ikumi, DavidOver the past 40 years, there has been a continuous progression in generating concrete solutions in the design and operation of wastewater treatment systems. This progression has included the development of various integrated and logical-mathematical glass box models geared towards the recovery of resources. However, the accuracy of these models relies on characterising the influent waste stream accurately, which includes identifying the molecular composition of the biodegradable organics. Municipal wastewater contains an array of organics, and it is crucial to accurately identify the composition of these organics before they are fed into the virtually replicated (i.e. modelled) system. This identification of influent organics ensures that the performance of the system can be predicted, and system upset, or failure can be avoided. The overarching aim of this project was to characterise the composition of the organics present in municipal wastewater using experimental analysis and mathematical bioprocess modelling. The project extended and improved current analytical methods by developing: 1. The Augmented Biochemical Methane Potential (AugBMP) Test: A test run identically to the BMP test but extended to include the methane and carbon dioxide production, the aqueous phase volatile fatty acids (VFAs), H2CO3 and total alkalinity, ammonia and orthophosphate concentrations and the reactor pH. 2. The Augmented Biochemical Sulphide Potential (AugBSP) Test: A test aimed to improve the accuracy of the AugBMP test, as methanogenesis was replaced by Biological Sulphate Reduction (BSR), minimising the gas measurement error commonly experienced during the BMP test. The proposed AugBMP and AugBSP tests coupled with mathematical bioprocess modelling, provides a powerful tool for determining the composition of the biodegradable organics present in wastewater substrates. The project incorporated a holistic approach which included fabricating the proposed testing vessels, performing multiple experiments and as accurately as possible, simulating the observed outcome using mathematical models. The outcome of this project allowed for the composition of unknown substrates, such as the organics present in primary sewage sludge to be identified confidently. This thesis unpacks and describes this new methodology developed to characterise substrates with unknown composition.
- ItemOpen AccessInvestigation into the start-up and operation of upflow anaerobic sludge bed reactors(2022) Stott, Rory; Harrison, Sue; Ikumi, DavidHigh-rate anaerobic biological wastewater treatment using the upflow anaerobic sludge bed (UASB) reactor technology offers the potential to reform wastewater treatment. However, the lack of clarity regarding the mechanisms responsible for self-immobilisation of the microbial consortia involved, known as granulation, presents an obstacle to the wide-spread use of this technology. In this study, two laboratory-scale UASB reactors were commissioned for the purpose of generating datasets for model development. A sucrose-based feed was used for the experiments, which were conducted at 37°C. Deterioration of the sludge granules used as inoculum into undesirable bulking-type sludge resulted in refocusing the study to investigate the granulation process. After consulting the literature on granulation, an experimental investigation into the effect of providing additional hydraulic mixing by recycling reactor effluent on granulation was conducted. It was hypothesised that the additional hydraulic mixing would result in the formation of more settleable granules. However, it was found that inclusion of the additional hydraulic mixing resulted in a less dense sludge bed which contained more visual signs (presence of both more loosely-bound exogenous polymeric substance and long filaments presumed to be Methanosaeta Spp.) of bulking-type sludge. In hindsight it was found that application of too low a sludge loading rate in the experimental investigations was the cause of the granulation issues, but that this was exacerbated by the additional hydraulic mixing. Apart from granulation issues, a low effluent pH of 6.5 was obtained from the reactors during the experimental investigations in spite of a high feed pH of 8.0. It was hypothesised that the production of VFA and consumption of NH3 were the primary causes of the acidity generation. A fixed-conversion model of the digester pH was developed to investigate the conversions of the relevant weak acid and base species present and the effects of these conversions on the digester pH. It was found that the dissolution of CO2 to satisfy the vapour-liquid equilibrium between the headspace CO2 partial pressure and dissolved carbonic acid concentration was predominantly responsible for the decrease in pH across the reactors. It is on the basis of these findings that both hypotheses were refuted.
- ItemOpen Access]Performance of Waste Stabilisation Ponds in the Eastern Cape Province(2023) Tolobisa, Gcina; Ikumi, DavidWater is a scarce natural resource, which requires to be treated with much care and importance. It is a finite resource and should be used sparingly. The process of treating domestic wastewater varies from ponds to the more advanced system, namely the activated sludge system. The main purpose of wastewater treatment is the reduction of pathogenic contamination, coliform bacteria, suspended solids, oxygen demand, and nutrient enrichment. The application or use of stabilisation ponds, as a part of the wastewater treatment process, depends on, among other factors, the influent loading and climate conditions. Waste Stabilisation Ponds (WSPs) are used to biologically treat domestic wastewater or industrial wastewater. The present study focuses on the treatment of domestic wastewater by using the WSPs in the absence of mechanical and electrical equipments. Different countries use different methods of pond design or WSP sizing and different parameters to ensure that the effluent discharge guidelines of the Department of Water and Sanitation (DWS) and World Health Organisation (WHO) are met. There are insufficient literature studies focusing on the design models and water quality data that can be used for sizing the WSPs in South Africa. There is a requirement for a study that can compare the existing WSP design models in different countries and check their suitability for South Africa, particularly their applicability to provinces with respect to climate and domestic wastewater quality. The comparison between the WSP design models will assist the process designers in the early stages of projects, particularly in the feasibility study stages (Scenario 1). The objective of the present study is to perform a comprehensive review of the use of WSPs in domestic wastewater treatment, their design and operating requirements for optimal performance, and the existing mathematical models used to virtually replicate the WSP treatment processes. Also considered is the development of a simplified model to demonstrate its application as a tool for the effective design of WSPs, including a case study of a WSP in the Eastern Cape (EC).
- ItemOpen AccessPoultry Slaughterhouse Wastewater Treatment Using an Integrated Biological and Electrocoagulation Treatment System: Process Optimisation Using Response Surface Methodology(Multidisciplinary Digital Publishing Institute, 2022-08-03) Ngobeni, Philadelphia Vutivi; Gutu, Larryngeai; Basitere, Moses; Harding, Theo; Ikumi, DavidThe feasibility of a biological (EcoflushTM) and/or electrocoagulation (EC) treatment system in removing chemical oxygen demand (COD) and fats, oils, and grease (FOG) from poultry slaughterhouse wastewater (PSW) were studied. The response surface methodology (RSM) was used to identify the optimum operating condition for EC and its integration with EcoflushTM as a pre-treatment for the removal of lipids. The optimum operating conditions were obtained at a pH of 3.05, a current density of 66.9 A/m2, 74-min of treatment time, and without Ecoflush™. These conditions produced a high-quality clarified effluent after 92.4% COD reduction and 99% FOG reduction. The treatment with EcoflushTM only resulted in 85–99% FOG reduction, 20–50% COD reduction, and odourless effluent. However, the combination of both processes (EcoflushTM and EC) did not yield a significant difference (F test, p > 0.05) when compared to the performance of EC alone. Despite the low removal percentages of nitrogen and phosphorus, the present study proved that EC is an effective method for the removal of COD and FOG, rendering an effluent that meets the permissible discharge standards for the City of Cape Town. The novel Ecoflush™ also proved to be very efficient in the removal of FOG from PSW.
- ItemOpen AccessSimplification of Complex WWTP Models into Simple Design and Evaluative WRRF ToolNsengiyumva, Olivier; Ikumi, David; Ekama, GeorgeWastewater treatment plant (WWTP) steady-state models have been used, historically, by consulting engineers and researchers for design, process optimisation, and to study and evaluate various operating scenarios. These models have, however, been generally developed for single unit process which limits their use. In addition, there have been three recent shifts in the past two decades from conventional design and modelling of WWTPs. Firstly, the shift from single unit to plant-wide modelling. Secondly, WWTPs are considered as water and resource recovery facilities (WRRFs). Lastly, there has been a growing interest to use the developed plant-wide steady-state models by stakeholders i.e., plant operators, designers and decision-makers who have limited technical expertise in WWTP modelling. These stakeholders use these models for design, evaluation and optimisation of scenarios. The later shift has raised the debate of complexity versus simplicity of the developed steady-state models. In addition to the aforementioned shifts, there has been limited research on the impact of sludge return liquors on the overall plant performance especially in the context of South African WWTPs. Wastewater treatment plants treat influent wastewater to a specified effluent quality, through several processes, before discharging it into the receiving water bodies. One of the by-products of these treatment processes is a nitrogen (N) and phosphorus (P) rich dewatering liquor (DWL). Generally, South African WWTPs recycle the DWL to the mainstream treatment process without first undergoing any side-stream treatment process (SSTP). The recycling of such N and P rich DWLs to the mainstream process, without first going through any SSTP and/or addition of organics to the mainstream process (organics have a role to play in nutrient removal, through the provision of substrate for biomass growth and provision of electron donors in the process of denitrification) poses a problem to the treatment process. Consequently, the reactor is overloaded with nutrients without sufficient organics to remove them; hence, the plant produces poor effluent quality i.e., high N and P concentrations at high operational cost. A simplified full-scale steady-state WWTP simulation tool, namely, plant performance evaluation tool (PPET), with a user-friendly interface was developed, based on principles of sound mass balance and kinetic and stoichiometric relations over the full-scale plant, to bridge the gap between the complexity of WWTP models and the lack of technical expertise of the stakeholders. This simulation tool analyses the impact of recycling sludge dewatering liquors on the overall plant performance. Furthermore, it gives the user a platform to analyse different scenarios and provides uncompromised results that enable the user to make better design and operation decisions. The bio-augmentation batch enhanced (BABE) and struvite precipitation SSTPs, and plant performance indices i.e., effluent quality and operational cost indices, EQI and OCI, respectively, were incorporated into PPET to analyse case studies on South African plants. It was found that there are added benefits of using a SSTPs to mitigate the detrimental impacts of recycled DWL when the capacity of the plant has been exceeded. However, both BABE and struvite precipitation processes achieve different results based on the composition of the DWL that is being treated i.e., for DWL from an anaerobic digester treating waste activated sludge that is not P rich (with low EBPR), then the recommended SSTP operation would be BABE process rather than struvite precipitation. Due to the different treatment systems (i.e., with variations in influent loads, system configurations and priority end products required - energy, water, phosphorus, etc.), further investigations are required on strategies for implementation of the various SSTPs.
- ItemOpen AccessThe Comparative Study between the Adsorptive Capacity of Activated Carbon Obtained from the Enhanced Hydrothermal Polymerization Process with Conventional Activated Carbons in the Removal of Micropollutants of Concern(2023) Kasonde, Vimbai; Ikumi, DavidAdsorption is one of the most widely used techniques employed for the tertiary treatment of wastewater to remove micropollutants. One of the most popular adsorbents used towards adsorption is activated carbon. However, due to the high cost of the conventional commercial activated carbon (produced from coal, which is a finite resource), it is important to find alternative precursors that are readily available, low cost, and can potentially produce activated carbon which is effective in the adsorption process. Sludge from wastewater treatment plants is one alternative which has been investigated and found desirable due to its high organic content. It is an unavoidable by-product of water treatment facilities that is becoming difficult to manage due to stricter disposal laws. The use of sludge as a precursor for activated carbon production serves to address the issue of an alternative, relatively low-cost adsorbent and the sludge disposal dilemma. Hence the sludge, which is an otherwise waste product is converted into a useful resource to aid in the reduction of the pollution of water which is a scarce commodity. In this study, hydrochar derived from primary sludge combined with waste activated sludge was used to produce activated carbon through pyrolysis. The hydrochar derived activated carbon (HC-AC) was characterized along with a commercial granular activated carbon (GAC) and a green alien wood activated carbon (AW-AC). The three carbons were later used in batch adsorption tests to determine the optimum conditions needed for each carbon to achieve maximum removal of methylene blue dye and lead (II) ions in aqueous solution by varying parameters such as pH, adsorbent dosage, initial concentration of the adsorbate, and contact time. Results from these tests were compared at the optimum conditions for each adsorbent and it was found that for methylene blue dye adsorption the percentage removal was in the order HCAC (99.28%) > GAC (99.13%) > AW-AC (98.73%). The percentage removal of lead (II) ions was in the order HC-AC (99.33%) > GAC (97.25%) > AW-AC (96.92%), showing that at optimum conditions, HC-AC performed slightly better than the other adsorbents in the removal of the pollutants
- ItemOpen AccessThe Economic and Technical Feasibility of the Application of Partial Nitritation Anammox Technology Over Conventional Nitrification Denitrification for the Treatment of Sidestream Liquor at Cape Flats WWTP(2021) Jelliman, Shanen; Ikumi, David; Gaszynski, ChrisThe objective of this study was to provide a comparative analysis for treating sidestream liquor from a future regional anaerobic digestion (AD) facility (Thermal Hydrolysis Process (THP)+AD) at Cape Flats WWTP in South Africa. The study focused on comparing a conventional nitrification denitrification (Modified Ludzack-Ettinger (MLE) configuration) with a novel partial nitritation/ anammox (PN/A) process. The sidestream liquor was characterised by mass balance over the AD process. Steady-state models were used to predict equipment sizes and determine the process efficiency for each treatment technology. The models were evaluated using an effluent quality index (EQI) and operational cost index (OCI). The capital cost of each treatment solution was calculated and used to perform an economic lifecycle cost analysis (LCCA). The study concluded that the sidestream liquor (untreated) would recycle 3 415 kg TKN/d back to the mainstream process which represented 29% of the design capacity of the plant. The MLE process required a 53% smaller reactor volume but consumed 93% more energy and produced 64% more sludge which resulted in the MLE OCI being 10.2 times higher than the PN/A process. The total capital cost of the PN/A and MLE processes were calculated to be R139 537 000 and R117 420 000 respectively. Although the MLE process costs 16% less to implement initially, the LCCA over a 20-year operational period indicated that the net present value of the MLE process is 2.8 times higher than the PN/A process.