Browsing by Author "Randall, Dyllon G"

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    Open Access
    Desktop study on Novel Treatment techniques to treat industrial fertilizer effluent
    (2018) Fortuin, Jordache; Randall, Dyllon G; Ikumi, David
    Fertilizer 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.
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    Open Access
    Development of a brine treatment protocol using Eutectic Freeze Crystallization
    (2010) Randall, Dyllon G; Lewis, Alison Emslie
    Hypersaline inorganic brines are generated from many global mining operations and the volume of these brines is increasing at an exponential rate. The environment and water resources in the vicinity of these mining operations are at a risk of being polluted as a result of this increase in brine volume. These are the key reasons why these brines need treatment...This thesis ultimately showed that EFC could be used to treat multi-component streams and that pure salts could be sequentially produced along with potable water.
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    Heat and mass transfer effects of ice growth mechanisms in water and aqueous solutions
    (2013) Kapembwa, Michael; Randall, Dyllon G; Rodriguez-Pascual , Marcos; Lewis, Alison Emslie
    Research into ice crystallization processes is an important area of study. The desire to improve product quality and efficiency of processes involving ice crystallization in industries such as desalination by freezing, freeze drying, freeze concentration and freeze crystallization for food processing, requires insight into the ice growth mechanisms. More so, a novel technology called Eutectic Freeze Crystallization, where water is recovered in the form of ice, requires that ice crystals are of high purity as this directly determines the quality of the water obtained. During ice crystallization, ice growth mechanisms play an important role in determining the structure, size and morphology of ice which have an effect on separation processes and product purity. Heat and mass transfer play a fundamental role in ice growth processes as they affect the thermodynamics and kinetics of the crystallization process. Ice growth experiments were carried out in pure water, in 8.4 wt% and 16.8 wt% magnesium sulphate and in 8.4 wt% sodium nitrate using a 10x5x31 mm test cell made of Plexi-glass®. The Colour Schlieren optical technique was used to conduct the experiments. This is because of its capability to map refractive index gradients related to either temperature or/and concentration gradients of the solution during crystal growth.
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    An investigation of improvements to electrochemical precipitation of struvite from source separated urine
    (2016) Malanda, Nicole Mulenga; Von Blottnitz, Harro; Randall, Dyllon G
    Access to decent sanitation remains a problem in developing countries. At the same time, sanitation technology is constantly evolving specifically regarding resource recovery solutions. Some chemical elements found in human excreta derived from non-renewable resources, and the recycling of phosphorous from sewage in particular is a possible solution to the growing issue of resource scarcity. A potential way to recover phosphorous from urine or water-borne sewage is through struvite precipitation. Struvite (MgNH₄PO₄. 6H₂O) is a mineral that can be used as a slowrelease magnesium, ammonium and phosphate based fertilizer and can be produced from urine by adding magnesium to the ammonium and phosphate rich urine. Usually, magnesium is dosed chemically using salts such as MgCl₂, MgO, MgSO₄ or bittern, together with pH regulating agents but these reactants produce unfavourable chemical by-products and the process tends to be expensive. Previous studies have proven that electrochemical dosing of magnesium is a feasible and reliable method of struvite precipitation. It not only produces high grade struvite that is valuable and marketable, but it also eliminates the need for alkalinity dosing in order to create a suitable pH environment for struvite precipitation. Further to that, electrochemical precipitation does not produce any harmful chemical by-products. Previous work shows that one main challenge that is associated with this method is the formation of a mineral layer on the magnesium anode called nesquehonite (MgCO₃ · 3H₂O). This leads to increased electrode potentials and hence high energy consumptions and may also lead to system failures of the reactor. Further to that, struvite generally precipitates as small crystals that are difficult to separate from the solution, leading to low mass recoveries of the product. These small crystals are formed as a result of the high supersaturation, which generally occurs for most processes that are employed to make struvite. In view of these problems, this dissertation presents an investigation of the potential improvements to the electrochemical precipitation of struvite from source-separated urine. The main aim is to minimise or eliminate the formation of mineral precipitates on the anode surface. It also looks into ways of increasing the crystal sizes of the struvite being precipitated in the electrochemical system. The methodology for this investigation involved modelling and experimental work. The specific objectives for this study were to: a) Investigate how thermodynamic modelling of struvite precipitation compares to the experimental results from an electrochemical precipitation reactor, b) Employ the aspect of seeding in an electrochemical reactor for struvite production and determine the technical feasibility of the proposed process, c) Establish how to minimise the formation of nesquehonite so that the quality of struvite produced in the electrochemical reactor is not compromised, d) Investigate how the crystal sizes of the struvite particles produced in the seeded electrochemical precipitation batch reactor setup compare to those produced in the continuously stirred reactor setup with a recycle that gives the particles a longer residence time, e) Investigate the economics and energy requirements of the SEP (Seeded electrochemical precipitation reactor).