Theses and dissertations (Engineering and Built Environment)
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Item Sulphur-driven anammox systems for nitrogen removal from wastewater(2023-09) Hassan, Magray Owaes; Seyam, Mohammed; Gani, Khalid Muzamil; Pillai, Sheena Kumari Kuttan; Bux, FaizalThis thesis explored sulphur-driven Anammox systems as a potential solution for removing nitrogen from wastewater. It focused on using sulphur compounds as electron donors to drive the Anammox process, aiming to reduce energy requirements and costs compared to conventional methods. The thesis provided an overview of existing nitrogen removal techniques in wastewater treatment plants, highlighting the limitations of conventional methods and the potential of Anammox as an alternative. The theoretical framework of sulphur-driven Anammox systems was discussed, emphasizing their advantages in terms of energy efficiency, carbon footprint reduction, and cost-effectiveness. The study examined the principles and significance of the Anammox process in wastewater treatment, where anaerobic microorganisms convert ammonium and nitrite into nitrogen gas, thereby eliminating nitrogen pollution. By harnessing the power of sulphur-driven Anammox processes, this study aimed to address these environmental challenges and develop innovative and sustainable wastewater treatment technologies. The research investigated the potential of sulphur compounds, such as sulphide (S2-), sulphate (SO4 2-) and elemental sulphur (S0), as electron donors in Anammox systems. These compounds serve as alternative sources of reducing equivalents, enabling the Anammox bacteria to carry out the conversion process efficiently. The performance and microbial dynamics of sulphur-driven Anammox systems were extensively analyzed. Various parameters, such as nitrogen removal efficiency, sulphur compound dosage, pH and temperature, are evaluated to optimize system performance. The study also investigated the microbial community composition and metabolic pathways involved in sulphur-driven Anammox, shedding light on the key micro-organisms and their functional roles. The combination of partial nitrification (PN) and anaerobic ammonium oxidation was investigated as a promising technology for nitrogen removal from wastewater. Strategies such as intermittent aeration, pH shocks and sulfide addition were studied for PN start-up and suppression of nitrite-oxidizing bacteria (NOB). Intermittent aeration with low dissolved oxygen (<5 mg/L) suppressed NOB activity, resulting in a 93% nitrite accumulation rate (NAR). Low pH (5) reduced both ammonia oxidising bacteria (AOB) and NOB activity while raising it to pH 7.5 increased AOB activity (84% NAR) but kept NOB suppressed. Adding sulfide (up to 25mg/L) without pH control raised NAR from 63% to 85%. These factors affect nitrite accumulation in our system. The study provided insights into establishing PN in a sequential batch system and highlighted the sensitivity of nitrite oxidation to sulfide. The incorporation of sulphur into carbon and nitrogen removal processes in a wastewater treatment plant was explored in this study. A dosage of 15 mgS/L of sodium salt of sulphide combined with 2-3 mg/L dissolved oxygen, established PN effectively in synthetic and real wastewater. PN was established when pH naturally rose due to sulfide hydrolysis, suppressing NOB activity. Long-term operation achieved a nitrite accumulation ratio of 70 ± 19%, with ammonia and nitrite concentrations of 19 ± 4 mgN/L and 18 ± 4 mgN/L, respectively. NOB communities diminished during stable PN but returned when sulfide dosing stopped, indicating the need for continuous sulfide dosing.The study emphasized the continuous adoption of this strategy for sustained PN and its potential application in nitrogen removal from domestic wastewater. This study explores the intriguing sensitivity of Anammox bacteria to sulfide, revealing captivating insights into their unique response to this compound. The short-term negative effect of sulfide on Anammox performance was observed but quickly recovered under low sulfide stress. Reducing or removing sulfide in the influent is suggested to accelerate the recovery of Anammox performance. The stoichiometric ratio was identified as an indicator of Anammox performance and consortium development. The study highlighted the importance of environmental conditions and sulfide concentration control in optimizing Anammox processes and nitrogen removal in wastewater treatment systems. The study extensively examines the performance of the sulfide-driven Anammox (SPDA) process, specifically focusing on the impact of various hydraulic retention times (HRTs) and external sulfide dosing. The objective was to understand how variations in HRTs and the addition of external sulfide influence the efficiency and effectiveness of the SPDA process in removing nitrogen from wastewater. To gain a deeper understanding of the microbial communities involved in the SPDA process, next-generation high-throughput sequencing techniques were employed. These advanced sequencing methods allow for a comprehensive analysis of the structural and functional dynamics of the microbial communities present in the SPDA system. By analyzing the genetic material of these micro-organisms, it becomes possible to identify and quantify their abundance, diversity and potential functional roles in the nitrogen removal process. The findings from this study are expected to provide valuable insights into optimizing the performance of the SPDA process. By examining the effects of different HRTs and external sulfide dosing, researchers can determine the most favorable conditions for achieving efficient nitrogen removal. Additionally, by evaluating the microbial communities' dynamics, the study aimed to uncover the relationships between specific microorganisms and their contributions to the SPDA process. Ultimately, the results obtained from this investigation can contribute to the development of improved strategies for nitrogen removal from wastewater using the SPDA process. This knowledge can inform the design and operation of wastewater treatment systems, leading to enhanced performance, reduced energy consumption and increased cost-effectiveness in the treatment of nitrogen-rich wastewater.Item Wastewater treatment and photo-reduction of CO2 using an integrated magnetized TiO2 anaerobic- photocatalytic system(2022-09-29) Tetteh, Kweinor Emmanuel; Rathilal, SudeshConventionally, the treatment of municipal wastewater involves a sequence of treatment units aimed at reducing pollutants to acceptable discharge levels. Herein wastewater treatment plants in South Africa’s municipalities are being challenged recently due to emerging contaminants (nanomaterials, pesticides, antibiotics, COVID-19 RNA, etc.) that impede their efficiency. This calls for robust technological water solution systems targeted at promoting sustainable water supply and mitigating anthropogenic gas (CO2) emission via biogas production. Against this background, the novel of this study is aimed to develop an integrated AD-AOP (anaerobic digestion – advanced oxidation process) magnetized system to improve wastewater for reuse with biogas production and nanoparticles recoverability benefits. To obtain an optimal balance between robustness and cost-effectiveness of the integrated system, a series of feasibility and engineering works were explored. The first phase involved the synthesis via a co-precipitation technique, characterization, and applicability of the magnetized-photocatalysts (MPCs) for wastewater treatment. Analytically, the scanning electron microscopy and energy dispersive X-ray (SEM/EDX), Fourier transforms infrared spectra, X-ray diffraction (XRD), and Brunauer- Emmett-Teller (BET) techniques showed the tailored MPCs were successfully magnetized. Among the MPCs studied, Fe-TiO2 (with a BET surface area of 62.73 m2 /g) was found as the best with greater potential for above 75% decontamination of the wastewater and methane yield. In the technological design and evaluation, Fe-TiO2 was examined using biochemical methane potential (BMP), biophotocatalytic (BP), biomagnetic (BM), and biophotomagnetic (BPM) systems. Due to the external magnetic field influence on the BPMs, it was found very promising for future adventures. Above all, the novel integrated AD-AOP magnetized system proof of concept showed great potential for recoverability of the MPCs for reuse, reducing the toxicological effects of trace metals (27 elements considered), and improving water and biogas quality. The bioenergy economy of the integrated AD-AOP magnetized system demonstrated net energy being able to subsidize the energy required by the UV-lamp of the AOP system. Conclusively, this finding provides an insight into synthesizing novel MPCs and their applicability for wastewater remediation and biogas production. Also kinetics modeling and response surface methodology (RSM) optimization coupled with artificial neural network (ANN) predictability showed the potential to develop an optimized integrated AD-AOP magnetised system towards the treatment of industrial wastewater, biogas production , and CO2 emission reduction. The prospects necessitate a techno-scientific revolution to upscale the current integrated system into a pilot scale with smart-online monitoring towards improving the wastewater circular economy.Item Effect of operating conditions on the hydrothermal valorisation of sewage sludge(2021-02) Madikizela, Mbaliyezwe PreciousThe accelerated population growth, in conjunction with the rapid urbanisation rate, are the principal driving forces behind the augmented volumes of municipal sewage sludge generated worldwide. The traditional approaches of sewage sludge treatment, which include landfilling and agricultural application, are no longer within the realms of possibility due to rigorous regulations, deficiency in the capacity of land available and the environmental and health adversities associated with detrimental constituents of sewage sludge. The population and urbanisation advancements do not only influence the emergent volumes of sewage sludge, but they also instigate fundamental provocations to the global energy demand. The reliance on fossil fuels poses a significant threat, not only to sustainable development, however they are also hugely responsible for the cumulative carbon dioxide and other greenhouse gas (GHG) emissions that deteriorate the environment, trigger global warming and deleteriously impact the livelihood of all life on earth. In line with the quest for sustainable and renewable alternative energy sources, the thermochemical treatment of municipal sewage sludge has a triple advantage of valorising the abundant volumes of the sludge, addressing the injurious nature of conventional fuels to the environment and seeking to bridge the gap as their supply diminishes. This study followed a quantitative approach, with the purpose to convert municipal sewage to valuable bio-oils. The sewage sludge was subjected to hydrothermal liquefaction in 60 ml stainless steel batch reactors, where the effect of temperature, solvent composition, and solvent content were investigated, and all the other process parameters were maintained at a constant. The six temperatures that were explored were 220oC, 250oC, 280oC, 310oC, 340oC, 370oC. The two solvents investigated were de-ionised water (H2O) and ethanol (E) which were applied in the following compositions: 1:0, 1:1 and 0:1 (H2O:E). The five solvent contents investigated were 75%, 80%, 85%, 90% and 95%. The process yielded bio-oils, solid phase and gaseous products and an aqueous phase. Dichloromethane was used as an extraction medium. The obtained results revealed that the temperature, solvent type and solvent content had a significant influence on the yield of bio-oil produced while temperature was the most influential out of the three parameters. When temperatures approached supercritical conditions of water, a notable decline in the bio-oil yields was observed. For each temperature, the bio-oil yields initially increased until about 85% solvent content, and then slightly decreased thereafter. The highest bio-oil yields were achieved at 310oC and the best yields were obtained when the ratio of H2O and E were 1:1. This study found that the optimum operating conditions were obtained at 310oC, 85% solvent content and a 1:1 composition of H2O and ethanol; the bio-oil yields at those conditions was determined to be 40,6 wt%. The bio-oils were contained in the following order of prevalence, fatty acids, aliphatic hydrocarbons, N-containing compounds, O-containing compounds, aromatics and acid esters. Aliphatic hydrocarbons and fatty acids were the dominant functional groups. The following were the most abundant compounds in the 90 runs: heptadecane, pentadecane, eicosane, hexadecane 2,6,10,14-tetramethyl hexadecane and 9-octadecanoic acid.Item Comparative study of anammox-mediated nitrogen removal in three reactor configurations(2021-05-27) Kosgey, Kiprotich Eric; Pillai, Sheena Kumari Kuttan; Kiambi, Sammy Lewis; Bux, Faizal; Chandran, KartikAnaerobic ammonium oxidation (ANAMMOX) is an efficient and cost-effective process developed for biological nitrogen removal from wastewater. However, widespread application of the ANAMMOX process for wastewater treatment remains constrained due to the slow growth of ANAMMOX bacteria, propensity for out-competition by fast growing microbes, and its sensitivity to environmental and operational conditions. Consequently, understanding the influence of mixing conditions in different reactor configurations on this process is paramount in its improvement. This study focused on the comparative analysis of ANAMMOX-mediated nitrogen removal in a hybrid up-flow anaerobic sludge blanket reactor (H-UASB), moving bed biofilm reactor (MBBR) and a gas-lift reactor (GLR). The study involved experimental study of nitrogen removal, bacterial population dynamics and physical properties of the bacterial biomass within the reactors, as well as the description of process performance and the growth of nitrifying and ANAMMOX bacteria in the reactors using a calibrated mechanistic model. All the reactors were operated for 535 days using the same synthetic feed under anaerobic conditions. K1-type carrier materials were added to each reactor for biofilm development. The concentrations of ammonium (NH4 + ), nitrite (NO2 - ) and nitrate (NO3 - ) in the effluent from the reactors were determined colorimetrically. Among the three reactors, MBBR displayed the highest nitrogen removal efficiency (NRE) during the study (66±36%), and contained the lowest concentration of free ammonia (FA) (19±22 mg-N/L) and free nitrous acid (FNA) (0.001±0.001 mg-N/L). In comparison, the NRE and the concentrations of FA and FNA in H-UASB during the study were 63±28%, 91±41 mg-N/L and 0.006±0.004 mgN/L, respectively, while in the GLR, they were 54±39%, 28±29 mg-N/L and 0.002±0.002 mg-N/L, respectively. Based on the ratios of NO2 - consumed to NH4 + consumed, and the ratios of NO3 - produced to NH4 + consumed, the start-up of ANAMMOX process was faster in the MBBR (144 days) compared to H-UASB (193 days) and GLR (272 days). MBBR also displayed less fluctuations in the NREs and nitrogen removal rates (NRRs) during the study compared to H-UASB and GLR. The microbial communities in the suspended biomass in the reactors were characterised using high-throughput sequencing on an Illumina MiSeq platform on days 125, 192, 260, 309 and 535, while the microbial communities in the biofilms were only characterised on day 535 (last day) due to slow biofilm development. Gradual increases in the relative abundance of ANAMMOX bacteria were observed in the suspended biomass in all the reactors between days 125 and 309, which corroborated the observed increases in the NREs. The relative abundance of ANAMMOX bacteria remained consistently higher in H-UASB during the study than in MBBR and GLR. On the contrary, the highest relative abundance of ammonia oxidising bacteria (AOB) was observed in the suspended biomass in the MBBR on day 125 at approximately 38%, while the highest relative abundance of nitrite oxidising bacteria (NOB) and complete ammonia oxidising (COMAMMOX) bacteria was recorded in the suspended biomass in the MBBR at approximately 30% and 5%, respectively. In all the reactors, the relative abundance of AOB in the biofilms and the suspended biomass was comparable on day 535. In addition, on day 535, higher relative abundance of NOB was observed in the biofilms in both GLR and H-UASB at approximately 7% compared to the suspended biomass, while their abundance in the suspended biomass in the MBBR was comparable to that recorded in the biofilms. Furthermore, in both H-UASB and MBBR, higher relative abundance of ANAMMOX bacteria was observed in the suspended biomass compared to the biofilms on day 535, while comparable abundance was observed in the GLR. The highest total microbial diversity (Shannon and Simpson indices) and evenness (Pielou’s Evenness) was observed in the suspended biomass in the MBBR. Granulation of the suspended biomass was observed in both GLR and H-UASB, while the suspended biomass in the MBBR was flocculent. In the MBBR, the colour of the biomass had turned brown on day 125, while the biomass in H-UASB and GLR on this day was tawny and dark-tawny, respectively. However, on day 309, the biomass in all the reactors had turned red, corroborating the highest relative abundance of ANAMMOX bacteria observed during the study. Faster attachment of biomass on the carrier materials in MBBR was observed in the course of study compared to H-UASB and GLR. On the last day, the concentrations of the biomass on the carrier materials in the MBBR was also higher (12 mg/carrier) in the MBBR than in the H-UASB (8 mg/carrier) and GLR (10 mg/carrier). Activated sludge model 1 (ASM 1), which was modified by separating the activities of Nitrospira spp. from those of Nitrobacter spp. as well as by adding both ANAMMOX and COMAMMOX bacterial activities, was used to describe process performance in the reactors. The modified ASM 1 was able to predict the trends in the effluent concentrations of NH4 + , NO2 - and NO3 - in all the reactors. In addition, the correlation of the actual relative abundance of nitrifying and ANAMMOX bacteria, with the model-predicted relative abundance, was positive. The model also indicated higher heterotrophic activities in both GLR and MBBR compared to H-UASB, an indication that continuous mixing in MBBR and alternation of plug-flow conditions with internal gas circulation in GLR favoured heterotrophic bacterial growth. However, the model was limited in predicting the fluctuations in bacterial abundance and the fluctuations in the effluent concentrations of NH4 + , NO2 - and NO3 - in the reactors. The obtained results indicate that better-mixed conditions in the MBBR led to comparable relative abundance of nitrifying bacteria between the biofilms and the suspended biomass, while plug-flow conditions in the H-UASB favoured ANAMMOX bacterial growth in the suspended biomass and the nitrifying bacterial growth in the biofilms. The alternation of internal gas circulation with plug-flow conditions in the GLR also favoured the growth of nitrifying bacteria in the biofilms. Overall, nitrogen removal in H-UASB was likely dominated by ANAMMOX process, while nitrogen removal in MBBR and GLR was as a result of combined ANAMMOX and sequential nitrification-denitrification processes. The novelty of this study stem from the impact of mixing conditions on process performance and microbial ecology of ANAMMOX-mediated systems.Item Anaerobic co-digestion of agricultural biomass with industrial wastewater for biogas production(2021-03-26) Armah, Edward Kwaku; Chetty, Maggie; Deenadayalu, NirmalaWith the increasing demand for clean and affordable energy which is environmentally friendly, the use of renewable energy sources is a way for future energy generation. South Africa, like most countries in the world are over-dependent on the use of fossil fuels, prompting most current researchers to seek an affordable and reliable source of energy which is also,a focal point of the United Nations Sustainable Development Goal 7. In past decades, the process of anaerobic digestion (AD) also referred to as monodigestion, has proven to be efficient with positive environmental benefits for biogas production for the purpose of generating electricity, combined heat and power. However, due to regional shortages, process instability and lower biogas yield, the concept of anaerobic co-digestion (AcoD) emerged to account for these drawbacks. Given the considerable impact that industrial wastewater (WW) could provide nutrients in anaerobic biodigesters, the results of this study could apprise decisionmakers and the government to further implement biogas installations as an alternative energy source. The study aims at optimising the biogas production through AcoD of the agricultural biomasses: sugarcane bagasse (SCB) and corn silage (CS) with industrial WW sourced from Durban, KwaZulu-Natal, South Africa. The study commenced with the characterisation of the biomasses under this study with proximate and ultimate analysis using the Fourier transform infrared spectroscopy (FTIR), the thermo gravimetric analysis (TGA), the scanning electron microscopy (SEM) and the differential scanning calorimetry (DSC). The untreated biomass was subjected to biochemical methane potential (BMP) tests to optimise and predict the biogas potential for the selected biomass. A preliminary run was carried out with the agricultural biomass to determine which of the WW streams would yield the most biogas. Among the four WW streams sourced at this stage, two WW streams; sugar WW (SWW) and dairy WW (DWW) produced the highest volume of biogas in the increasing order; SWW ˃ DWW ˃ brewery WW > municipal WW. Therefore, both SWW and DWW were selected for further process optimisation with each biomass. Using the response surface methodology (RSM), the factors considered were temperature (25-55 °C) and organic loading rate (0.5-1.5 gVS/100mL); and the response was the biogas yield (m3 /kgVS). Maximum biogas yield and methane (CH4) content were found to be 5.0 m3 /kgVS and 79%, respectively, for the AcoD of CS with SWW. This established the association that existed among the set temperatures of the digestion process and the corresponding organic loading rate (OLR) of the AcoD process operating in batch mode. Both CS and SCB have been classified as lignocellulosic and thus, ionic liquid (IL) pretreatment was adapted in this study to ascertain their potential on the biogas yield. Results showed that the maximum biogas yield and CH4 content were found to be 3.9 m3 /kgVS and 87%, respectively, after IL pretreatment using 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) for CS with DWW at 55°C and 1.0 gVS/100mL. The IL pretreatment yielded lower biogas but of higher purity of CH4 than the untreated biomass. Data obtained from the BMP tests for the untreated and pretreated biomasses were tested with the existing kinetic models; first order, dual pooled first order, Chen and Hashimoto and the modified Gompertz. The results showed that for both untreated and pretreated biomass, the modified Gompertz had the best fit amongst the four models tested with coefficient of correlation, R 2 values of 0.997 and 0.979, respectively. Comparatively, the modified Gompertz model could be the preferred model for the study of industrial WW when used as co-substrate during AcoD for biogas production. The study showed that higher biogas production and CH4 contents were observed when CS was employed as a reliable feedstock with maximum volume of the untreated and pretreated feedstock reported at 31 L and 20 L respectively.Item Anaerobic co-digestion with industrial wastewater for biomethane production(2020-10-20) Adedeji, Jeremiah; Chetty, MaggieThe increasing demand for energy has led to the utilization of fossil fuels more abundantly as a quick alternative for generation of energy. The use of these sources of energy however as led to the generation of greenhouse gases which tend to cause climate change, thus affecting the ecosystem at large. Thus, there have been the search for alternative sources which cannot be depleted but do generate minimal greenhouse gases. One of such alternate sources is industrial wastewater which have shown to have high concentration of nutrients in the form of organic contents which can be converted by micro-organisms into energy, usually known as biogas, comprising majorly of CH4, CO2 and H2. Another important factor is that industrial wastewaters are a renewable energy source which are continuously generated due to increasing urbanisation and population growth. In this study, the characteristics of three agro-industrial based wastewaters used shows their potential for application in anaerobic co-digestion”. Anaerobic co-digestion method was utilized to harness the synergetic effect of both sewage sludge and agro-industrial wastewater as co-substrate for the generation of biomethane. The result of the effect of varying mix-ratio of the substrates on biomethane production of sugar wastewater and dairy wastewater indicated that mix-ratio of 1:1 for sewage sludge to sugar wastewater operated at 35oC was suitable for optimum generation of biomethane of 1400.99 mL CH4/g COD added and COD reduction of 54%. The model generated using design expert was found to navigate the design space and could perfectly predict the yield of biomethane effectively for the sugar wastewater mix. The biomethane potential tests (BMP) experiment using varying inoculum-substrate ratio (ISR) showed that operating at mesophilic temperature of 25oC with ISR of 1:2 and 2:1 for sugar wastewater and dairy wastewater respectively does increase the methane production within the first three (3) weeks. The kinetic models that best fit the anaerobic co-digestion for sugar wastewater was the first order model while the simplified Gompertz model favoured the dairy wastewater perfectly. The biomethane potential tests indicate significant increase the biomethane production and as well reduction in the volatile solid and chemical oxygen demand (COD) content. In conclusion, both sugar and dairy wastewater can be recommended as co-substrates for anaerobic digestion of sewage sludge for increased and improved biomethane production while simultaneously reducing their COD content at the same time.