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Theses and dissertations (Applied Sciences)

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    Impact of chemical oxygen demand to nitrogen ratio on anammox bacterial growth in an up-flow anaerobic sludge blanket reactor
    (2023) Msimango, Sandile Simiso; Kumari, Sheena; Nasr, Mahmoud; Bux, Faizal
    The anaerobic oxidation of ammonium (ANAMMOX) process has been suggested as an economical and innovative means of removing nitrogen from wastewater. Nevertheless, very few studies have evaluated the effect of the chemical oxygen demand (COD) to nitrogen (N) ratio on bacterial communities in an ANAMMOX-mediated system. Heterotrophic bacteria can readily outcompete the slow-growing ANAMMOX bacteria in the presence of organic carbon. This study examined the effect of the organic carbon to nitrogen (C/N) ratio on the performance of ANAMMOX in an upflow sludge blanket reactor using synthetic wastewater as the feedstock. Two UASB reactors (UASB-A and UASB-B) were seeded with biomass from a labscale ANAMMOX reactor and operated for a period of 593 days. Both reactors were operated using similar operational conditions during the enrichment phase (0-400 days). Thereafter, the addition of organic carbon in the medium altered the C/N ratio of one of the reactors (UASBB). During this period, UASB-A served as a control reactor. A CN ratio of 1.0, 1.5, and 2.0 was achieved in the UASB B reactor by increasing the organic carbon concentration every 60 days. The reactors were analyzed at three-day intervals per week for nitrogen and COD removal efficiency. The quantitative PCR method was used to detect the dominant N-removing organisms within both reactors at different phases. In addition, cDNA quantification or reverse transcriptase qPCR (RT-qPCR) was also conducted to determine the dominant and active nitrifying communities. The results indicated that when the C/N ratio is 1.0, almost complete removal of NH4 + -N is observed (92%), and nitrogen removal efficiency (NRE) is approximately 82%. The ratios of ΔNO2 - /ΔNH4 + and ΔNO3 - /ΔNH4 + ratios during this phase (C/N=1) fluctuated from >1.25 to <1.6 and from >0.35 to <0.45 <0.11 to >1.6, respectively, which was within the range of the expected ANAMMOX stoichiometric ratio. In addition, when the C/N ratio was increased from 1 to 1.5, NRE rose from 82 to 88%. However, a decrease of NRE to 83% was observed when the C/N ratio was further increased to 2. The quantitative PCR results showed an increase in total bacteria from 1.4 × 106 copies/µL to 2.3× 106 copies/µL, and 2.4× 106 copies/µL as the ratio of C/N increased from 1.0 to 1.5 and thereafter to 2, respectively. ANAMMOX bacteria showed an increase from 16 × 103 copies/µL to 6.5× 10 4 copies/µL, and 2.06 × 105 copies/µL when the C/N ratio was increased from 1 to 1.5, and 2, respectively. The cDNA analysis further showed an increase of ANAMMOX bacteria transcript abundance from 4.6 × 104 copies/µL to 2.52× 106 copies/µL with an increase in C/N ratio to 1.5. Subsequently, a decrease in ANAMMOX bacteria transcript abundance to 1.09 × 106 copies/µL was observed when the C/N ratio was further increased to 2. The expression of the hzo gene encoding for hydrazine dehydrogenase (HDH), which catalyses the oxidization of the unique ANAMMOX intermediate hydrazine to N2 was 169 folds of expression, which was very high at C/N=1, but showed a decrease to 39 folds expression at C/N=1.5. Almost complete inhibition of hzo gene was observed when the C/N ratio was further increased to 2. Based on chemical analysis, it was further confirmed that the decrease of both ANAMMOX and AOB abundance at a higher C/N ratio caused an increase in effluent NH4 + -N concentrations. In conclusion, the study has shown that a higher C/N ratio could significantly affect the overall nitrogen removal rate and the activity of the diverse microbial populations, more specifically the ANAMMOX bacterial activity.
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    Characterisation of the microbial communities present in an anaerobic baffled reactor utilising molecular techniques
    (2005) Lalbahadur, Tharnija; Bux, Faizal
    The provision of safe and sanitary water is a constitutional right and above all, a necessity of life. As a result of the rapid urbanisation and the past policies of apartheid, a large population of South Africa dwell in informal settlements, where there is very little hope of development, as the government does not possess the resources that are necessary for a full-scale sanitation programme. Therefore, on-site treatments have been considered to provide sanitation in these dense peri-urban areas. The anaerobic baffled reactor (ABR) is one such sanitation system. This reactor utilises the phenomenon of anaerobic digestion to degrade substrates. One of the major disadvantages of any anaerobic treatment processes is the extreme sensitivity of the bacterial communities, thus inducing slow recovery rates following toxic shocks. Therefore, an understanding of these microbial consortia is essential to effectively control, operate and optimise the anaerobic reactor. Fluorescence in situ hybridization, 4’,6-diamidino-2-phenylindole (DAPI) staining and DNA sequencing techniques were applied to determine the microbial consortium, as well as their reactions to daily operating conditions. With an understanding of these populations and their responses to perturbations within the system, it is possible to construct an anaerobic system that is successful in its treatment of domestic wastewater. In situ hybridizations were conducted for three operating periods, each characterised by specific flow rates. Results showed Eubacterial population dominance over the Archaeal population throughout both of the operating periods investigated. However, these cells cumulatively consisted of 50% of the total biomass fraction, as determined by DAPI staining. Group-probes utilised revealed a high concentration of fermentative acidogenic bacteria, which lead to a decrease in the pH values. It was noted that the ABR did not separate the acidogenic and methanogenic phases, as expected. Therefore, the decrease in pH further inhibited the proliferation of Archaeal acetoclastic methanogens, which were not present in the second operating period. DNA sequencing results revealed the occurrence of the hydrogenotrophic Methanobacterium and Methanococcus genera and confirmed the presence of Methanosarcina. Sequencing of the bacterial DNA confirmed the presence of the low G+ C Gram Positives (Streptococcus), the high G+C Gram Positives (Propionibacterium) and the sulfate reducing bacteria (Desulfovibrio vulgaris). However, justifications were highly subjective due to a lack of supportive analytical data, such as acetate, volatile fatty acids and methane concentrations. Despite this, findings served to add valuable information, providing details on the specific microbial groups associated with ABR treatment processes.