Theses and dissertations (Engineering and Built Environment)
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Item Enhanced biohydrogen production from carbohydrate rich wastewater through anaerobic fermentation(2020-11-30) Mutsvene, Boldwin; Chetty, Maggie; Pillai, S. K. K.; Bux, FaizalIn recent times,“the world has faced serious problems emanating from the use of fossil fuels which are detrimental to the environment at large. On the other hand, due to the industrial boom, many industries produce wastewater that is harmful to the environment hence, carbohydrate-rich industrial wastewater can be advantageously used to reduce impact on the environment. If subjected to anaerobic fermentation, organic wastewater has the potential to produce renewable energy sources that have less impact on the environment, including biohydrogen, which has little or no carbon footprint. While reducing the impact of the problems caused by the disposal of wastewater to the environment, the biological methods also offer a solution to the detrimental effects of fossil fuels and their after use effects. The study was mainly based on environmental protection and clean, renewable alternative energy production by generating biohydrogen from organic industrial wastewater as a substrate. Anaerobic digestion has been extensively studied, but dark fermentation, which is an emerging technology within anaerobic digestion that involves the production of hydrogen from carbohydrate-rich substrates, has less information documented regarding this technology. This technology is crucial in the because it forecasts beyond fossil fuel usage and is accompanied with long-term economic expansion and energy security as there are many reservations about fossil fuel reserves and their high risk of exploitation.” Biohydrogen potential tests (BHP) were performed on five different wastewater streams (yeast, alcohols, brewery, sugar, and dairy industries) to determine the stream with the best hydrogen potential. Rigorous characterisation of various wastewater streams was conducted; the main parameters of interest were COD, BOD, VS, TS, pH, among others. The BHP tests were conducted in triplicates in 600 mL Schott bottles charged independently with various wastewater streams and inoculated by the seed sludge from a local wastewater treatment plant at the different substrate to biomass ratios. The highest hydrogen composition was recorded with the brewery wastewater, which had 40.1% H2 in the off-gas as analysed by the gas chromatograph; and the minimum was found in alcohol wastewater, 21.4%. The Kepner-Tregor decision-making tool was conducted to determine the most suitable stream for the scaled-up reactor. A conclusion to use the brewery wastewater in the scaled-up Anaerobic Baffled Reactor (ABR) was reached. Four 10 L Anaerobic Baffled Reactors were used as the scaled-up reactors to optimise operating conditions for the production of biohydrogen using the brewery wastewater. Design-Expert software, under response surface methodology, was used to produce the matrix of combinations of the experimental runs by varying temperature (32-38℃), batch time (4-16 h), and pH (3.5-7.5); in total 20 runs were formulated.” The highest hydrogen production rate of 18.16 mL/h and the hydrogen yield of 30.98 mmol/gCOD were observed at temperature, batch time, and pH of 35℃, 4-10 h, and 5, respectively. The optimum operating conditions were determined to be a temperature of 36℃, batch time of 10.2 h, and a pH of 5.6. A predictive model, quadratic polynomial in nature, was developed after an intensive analysis of variance, a regression coefficient between predicted and actual hydrogen production rates was found to be 0.92. A system was run on optimum conditions to validate the developed mathematical model. The maximum hydrogen potential rate (HPR) determined in this study was 6.11% higher than the predicted value. The validation runs were also performed as control experiments for comparison between a system with nanoparticles and a system without nanoparticles with regards to the HPR. 25.37% H2 and 21.85% H2 were determined for with magnetite nanoparticle system and a system without nanoparticles, respectively. The experiments with nanoparticles garnered 44% higher HPR (23.41 mL/h) than a system without nanoparticles.Item Development of a flat sheet woven fabric membrane fermenter for xylanase production by Thermomyces lanuginosus(2015) Thorulsley, Venessa; Rathilal, Sudesh; Pillay, Visvanathan Lingamurti; Ramsuroop, SureshFermentation processes are vital for the production of numerous bioproducts. Fermentation being the mass culture of micro – organisms for the production of some desired product, is an extensive field, with immense prospects for study and improvement. Enzyme production is of significance as these proteins are biological catalysts, finding niches in numerous industries, xylanase for example is utilized in the pulp and paper, animal feed, biofuel and food production processes. During enzyme production, a critical step is biomass separation, whereby the valuable product, the enzyme, is removed from the broth or micro – biological culture before it is denatured. This is typically achieved via centrifugation. The aim of this study was to develop and evaluate a submerged membrane fermenter system with the specific outcome of increasing the rate of production of xylanase, from the thermophilic fungal species Thermomyces lanuginous DSM 5826. Preliminary shake flask experiments were performed to determine the optimal production conditions, followed by partial characterization of the enzyme. A bioreactor was then fabricated to include a flat sheet membrane module, with outlets for permeate and broth withdrawal and inlets for feed and sterile air input. Experiments were conducted to determine the optimal dilution rate for maximum volumetric productivity. Results from the shake flask experiments indicated that the best conditions for xylanase production, yielding xylanase activity of 5118.60 ± 42.76 U.mL-1 was using nutrient medium containing beechwood xylan (1.5 % w/v), yeast extract (1.5 % w/v), potassium dihydrogen phosphate (0.5 % w/v), adjusted to a pH of 6.5 and inoculated with 1.0 mL of spore solution, rotating in a shaking incubator set to 150 rpm at 50 °C. Apart from analysis of the effect of the carbon source on xylanase activity, coarse corn cobs were used in the shake flask experiments as a cost saving initiative. The pH optima was determined to be 6.5 while the temperature optima of the enzyme was 70 °C. SDS PAGE analysis revealed that the molecular weight of the enzyme was between 25 and 35 kDa and qualitative analysis via a zymogram revealed clear zones of hydrolysis on a xylan infused agarose gel. During short run membrane fermenter experiments the percentage increase in enzyme activity between the batch operation (610.58 ± 34.54 U.mL-1) and semi – continuous operation (981.73 ± 55.54 U.mL-1) with beechwood xylan nutrient replenishment was 60.78 %. The maximum volumetric productivity achieved with beechwood supplementation after 192 hours in semi – continuous operation (5.32 ± 0.30 U.mL-1.hr-1) was 2.1 times greater than that of batch operation (2.54 ± 0.14 U.mL-1.hr-1) which equates to an increase of 110.28 % in productivity measured at its peak. The increase in total activity between batch (610 576.92 U) and beechwood xylan medium supplemented semi – continuous mode (1 184 937.50 U) resulted in a 94.07 % increase. During long run experimental periods, the increase in production of xylanase between the batch (873.26 ± 61.78 U.mL-1) and the xylan medium membrane system (1522.41 ± 107.65 U.mL-1) was determined to be 74.34 % while an overall average increase in productivity between the batch and xylan fed membrane system was 43.25%. The total enzyme activity with in membrane mode with beechwood xylan nutrient medium feed was 160 % greater than the batch process offering a 2.6 – fold increase. Experiments where de – ionized water was alternated with beechwood xylan nutrient medium had no significant impact on the productivity or enzyme activity. The optimal dilution rate for maximum volumetric productivity as determined to be 0.0033 hr-1. The results are indicative of the potential viability of such a design, yielding the desired outcome of a membrane integrated system to significantly increase the production of enzymes during fermentation.Item The purification of corn steep liquor as a fermentation feedstock by ultrafiltration(2010) Govender, Devan; Pillay, LingamTHE OBJECTIVE of this study was to devise a purification process, using ultrafiltration membranes as the core technology, for the preparation of corn steep liquor (CSL) as a fermentation feedstock. This process inherently required the development of a pretreatment system for the ultrafiltration membranes for the removal of suspended solids and high fouling material from corn steep liquor. The ultrafiltration membrane system was required for the separation and removal of colloidal solids from corn steep liquor, and to fractionate and separate out unwanted proteins, to render the feedstock suitable for sterilisation and subsequent fermentation. THE CONCEPT of membrane technology was investigated in order to find a more practical alternative for what was deemed to be a difficult process problem. In particular, various pretreatment technologies were investigated to form a compact and robust process package. THE CORN STEEP LIQUOR, a by-product of the corn wet milling process, was obtained from African Products, Germiston, in the form of a concentrated slurry directly from an evaporator system. A diagnostic of the feedstock was carried out and from this information, it was decided that three pretreatment options would be investigated. The first option was the pH treatment of the corn liquor, by the addition of ammonia which induced the precipitation of solids. This was followed by liquid-solid separation, and the clarified liquor was fed to the membrane system. The second option looked at the separation of suspended solids from the liquor by the use of broth conditioning additives and separation of the solids by a decanter centrifuge. The third option investigated was the use of a gyratory screening system for the removal of all solids greater than 100 μ in size. IN THE pH TREATMENT of CSL, the process is effected by the addition of base to pH 7. The technology involves neutralisation of CSL in a mixing system, under predetermined conditions of temperature, agitation and rate of addition, followed by subsequent liquid-solid separation. Trials were conducted on a pilot plant to test the process. Initial trials, conducted on a small scale pilot filter press, proved to be successful for this application. A suspended solids removal of up to 98% was achieved. The average suspended solids in the filtrate was found to range between 0.1 to 0.25 %. Tests were also conducted on a hired “state of art” filtration plant under various conditions. A diaphragm membrane press was found to provide the best performance. Protein recoveries of above 95 % at fluxes of 35 L/m2h at temperatures above 50 °C, and an incremental application of feed pressure was most suited for the process. The removal of the colloidal solids by the above-mentioned process was found to improve the quality of sterilisation. A reduction of more than 90 % in coagulated solids was achieved. v i IT WAS OBSERVED that the separation of suspended solids from CSL is enhanced by the use of coagulation and flocculation. Although not commonly used for this purpose, it was felt that a decanter centrifuge was well suited for the subsequent separation of the flocs from the clarified liquor. This work describes the results of the trials with such a device and the impact of broth conditioning on the efficiency of the separation. Trials have been conducted using an Alfa-Laval Model NX210 decanter, which was not specifically built for the work and therefore imposed several limitations on its performance. Despite these shortcomings, preliminary trials proved to be successful in achieving the separation objective. Tests were conducted using five different batches of CSL. With a maximum suspended solids loading of 4.3 % and a feed rate of 700 L/h, a solids recovery of 90 % was achieved. The clarified liquor contained residual solids between 0.5 and 0.8 %. The sludge had a solids concentration that ranged between 43 % and 65 %. COAGULATION AND FLOCCULATION dosages were kept within the limits of the laboratory evaluations. Flocculant dosages were controlled between 100 and 200 ppm, with the coagulant operating at higher dosages of between 400 and 2000 ppm. The only controllable parameter on the machine itself was the scroll differential speed. The best performance in terms of the cake dryness and centrate clarity was obtained at the lowest scroll differential speed of 4 rpm. THE USE OF GYRATORY SCREENS entailed passing the raw liquor through a set of two screens. The technology involves the use of a gyratory mechanism, which aids in the cleaning of the screens during continuous operation. Trials have been conducted on a pilot plant to test the system. Since the unit used was designed specifically for quick on-site screening exercises, it did not possess the added flexibility and robustness of a properly designed full scale unit. This imposed some limitations on its performance. However, despite these shortcomings, the trials conducted on the pilot plant proved to be successful in meeting the outlined objectives. A NUMBER OF TRIALS were performed on various batches of CSL. There was considerable batch to batch variation in the suspended solids content of the CSL and this was found to ultimately affect the throughput of the screening process. The feed suspended solids varied between 10 and 18 %. The highest throughput achieved was 400 L/h at a feed suspended solids loading of 14.5 %. It was found that temperature made a significant impact on the separation. The loss of heat in the feed stream caused excessive coagulation to occur thus increasing the suspended solids loading and lowering the throughput. The total solids in the sludge stream varied between 45 and 77 %. Protein loss in the sludge stream was around 1 %. Careful attention had to be given to the handling of the sludge stream. This stream displayed rheological characteristics typical of a non-Newtonian thixotropic fluid. The 100 μm screen operated best vi i when prior separation was done using a 180 to 200 μm screen. This reduced the solids loading on the tighter screen and increased the throughput by 10 to 15 %. The self cleaning mechanism also performed more efficiently under these conditions. THE SELECTED OPTION was then based on the influence the operation had on the ultrafiltration membranes, sterilisation of the product prior to fermentation and ultimately the fermentation performance. Subsequent testing of the pretreatment options were performed on an ultrafiltration membrane test cell. The product from the gyratory screens were found to produce the best overall results, where the highest fluxes and least amount of fouling occurred on the membranes tested. ONCE THE PRETREATMENT OPTION was decided, the development of the membane ultrafiltration system was then pursued. Trials were conducted on a laboratory scale, in a membrane test cell, to determine the preliminary screening of the membrane type, fouling effects and fluxes. It was found that polyvinylidene and polyacrylonitrile membranes produced the best overall fluxes of 11.25 and 10.96 L/m2h respectively. These membranes produced permeate protein concentrations of 121 and 115 g/L respectively. Sterilisation tests conducted on the permeate streams produced also showed that these two membranes had the lowest suspended solids concentrations. FERMENTABILITY tests conducted, showed that the ultrafiltered CSL, from these two membranes, produced increased cell counts and protein utilisation along with an increased product yield. Approximately 42 g/L of biomass was generated with lysine yields of 46 g/L. Further testwork revealed the non-Newtonian nature of CSL and its inherent viscosity effects. BENCH-SCALE testwork was conducted for various membrane configurations. With tubular membranes and hollow fibre membranes, average fluxes of 6.23 and 4.5 L/m2h were achieved respectively. Spiral wound membranes were found to be more consistent in their performance, with average fluxes of around 6.25 L/m2h. For the spiral wound membranes, it was found that the Desal-2 mesh spacer with a 80 mil thickness was most appropriate for the duty. PILOT PLANT testwork was conducted to scale-up the membrane system and to eliminate possible risks associated with the technology. The pilot plant studies showed up a number of principle design variables which needed careful attention. The flaws in the piloting system were subsequently rectified and this helped to improve the overall performance of the system.