This research focuses on anoxic ammonium oxidation (anammox). The anammox process for treating high ammonium and low organic carbon wastewater can reduce operational costs to a greater extent than the conventional autotrophic/heterotrophic treatment process can. The process has been widely researched because of its potential economic benefits. However, during long-term reactor operation, sudden reductions of nitrogen removal rates have been reported; maximum nitrogen removal rates in different reactor configurations could not approach values predicted based on mathematical modeling; and the crucial stability parameter, such as nitrite, did not have defined threshold concentration. It was hypothesised that free ammonia (FA) increase is the precursor of the instability of the anammox reactor. If it is true that nitrite up to about 200 mg N/L should stimulate nitrogen removal rate inside of the anammox reactor, when FA is kept below the inhibition threshold concentration. The research presented in the thesis argues that FA plays a larger role than has been previously considered in the instability of the anammox reactor. This study found FA inhibited nitrogen removal rates (NRR) at concentrations exceeding 2 mg N/L. In the pH range 7 to 8, the decrease in anammox activity was independent of pH and related only to the concentration of FA. Nitrite concentrations of up to 200 mg N/L did not negatively affect nitrogen removal rate. This study further found that low nitrite provided stable anammox reactor performance, but that high nitrite was not necessarily the cause for reactor destabilization. During the research high nitrogen removal rate was achieved when low FA was provided. During regular reactor operation at pH 6.5, the NRR at about 6.2 g N/Ld was archived. This value was never achieved before till this study was conducted. Conducted research showed controlling FA at low level is required to approach high rates in anammox reactors. Achieving high rates in anammox reactors allow significant reduction in reactor volume which saves resources. Further studies will be required to identify the FA effect on different microbial interactions, and that may provide more in-depth understanding of the nitrite and FA effect than observations based on NRR alone.

This research focuses on anoxic ammonium oxidation (anammox). The anammox process for treating high ammonium and low organic carbon wastewater can reduce operational costs to a greater extent than the conventional autotrophic/heterotrophic treatment process can. The process has been widely researched because of its potential economic benefits. However, during long-term reactor operation, sudden reductions of nitrogen removal rates have been reported; maximum nitrogen removal rates in different reactor configurations could not approach values predicted based on mathematical modeling; and the crucial stability parameter, such as nitrite, did not have defined threshold concentration. It was hypothesised that free ammonia (FA) increase is the precursor of the instability of the anammox reactor. If it is true that nitrite up to about 200 mg N/L should stimulate nitrogen removal rate inside of the anammox reactor, when FA is kept below the inhibition threshold concentration. The research presented in the thesis argues that FA plays a larger role than has been previously considered in the instability of the anammox reactor. This study found FA inhibited nitrogen removal rates (NRR) at concentrations exceeding 2 mg N/L. In the pH range 7 to 8, the decrease in anammox activity was independent of pH and related only to the concentration of FA. Nitrite concentrations of up to 200 mg N/L did not negatively affect nitrogen removal rate. This study further found that low nitrite provided stable anammox reactor performance, but that high nitrite was not necessarily the cause for reactor destabilization. During the research high nitrogen removal rate was achieved when low FA was provided. During regular reactor operation at pH 6.5, the NRR at about 6.2 g N/Ld was archived. This value was never achieved before till this study was conducted. Conducted research showed controlling FA at low level is required to approach high rates in anammox reactors. Achieving high rates in anammox reactors allow significant reduction in reactor volume which saves resources. Further studies will be required to identify the FA effect on different microbial interactions, and that may provide more in-depth understanding of the nitrite and FA effect than observations based on NRR alone.

A partial nitritation-anammox continuous flow reactor (CFR) was operated for eight months demonstrating that a mixture of large anammox-supported aerobic granules (ASAGs) and small conventional aerobic granules (CAGs) can be maintained stably for extended periods of time. The influent NH4+ was kept at 50 - 60 mg N L-1 to verify that the upper range of total ammonia nitrogen (TAN) for domestic wastewater can supply an inhibitory level of free ammonia (FA) for nitrite oxidizing bacteria (NOB) suppression in CFRs at pH around 7.8. The ammonia oxidizing bacteria (AOB):NOB activity ratio was determined for a series of granule sizes to understand the impact of mass diffusion limitation on the FA inhibition of NOB. When dissolved oxygen (DO) limitation is the only mechanism for NOB suppression, the AOB:NOB ratio was usually found in previous studies to increase with the granule size. However, the trend is reversed when FA has an inhibitory effect on NOB, as was observed in this study. The decrease in AOB:NOB ratio indicates that the resistance to the diffusion of FA along the granule radius limited its ability to inhibit NOB. This means smaller granules, e.g. diameter < 150 microns, are preferred for nitrite accumulation when high FA is present, e.g. in the partial nitritation-anammox process. The trend was further verified by observing the increase in the apparent inhibition coefficient, KI,FAapp, as granule size increased. This study for the first time quantified the effect of diffusion limitation on the KI,FAapp of NOB in granules and biofilms. A mathematical model was then utilized to interpret the observed suppression of NOB. The model predicted that NOB suppression was only complete at the granule surface. The NOB that did survive in larger granules was forced to dwell within the granule interior, where the FA concentration was lower than that in the bulk solution. This means FA inhibition can be taken advantage of as an effective means for NOB suppression in small granules and thin biofilms. Further, FA and DO were found to be both required for the stratification of AOB and NOB in partial nitritation-anammox CFRs. The structural stratification commonly observed in granules is then concluded to be a consequence but not a cause of the NOB suppression. / MS / A partial nitritation-anammox continuous flow reactor (CFR) was operated for eight months demonstrating that granular sludge can be maintained stably for extended periods of time. In this approach, NH3 is only partially converted to NO2 - (partial nitritation), and the conversion to NO3 - is prevented by the suppression of nitrite oxidizing bacteria (NOB). NH3 and NO2 - are then utilized by anammox bacteria to create N2 gas. The influent NH4 + fed to the reactor was kept at 50 to 60 mg N L-1 to verify that the upper range of total ammonia nitrogen (TAN) for domestic wastewater can supply a sufficiently high level of free ammonia (FA) to inhibit NOB growth in CFRs at a pH around 7.8. It is expected that the penetration of a substrate into granule sludge will experience diffusional resistance as it moves from water to denser solid material and is consumed by bacteria. The ammonia oxidizing bacteria (AOB):NOB activity ratio was determined for a series of granule sizes to understand the impact of mass diffusion limitation on the FA inhibition of NOB. When dissolved oxygen (DO) limitation is the only mechanism for NOB suppression, the AOB:NOB ratio was usually found in previous studies to increase with the granule size. However, the trend is reversed when FA has an inhibitory effect on NOB, as was observed in this study. The decrease in AOB:NOB ratio indicates that the resistance to the diffusion of FA, which increases with increasing granule size, along the granule radius limited its ability to inhibit NOB. This means smaller granules, e.g. diameter < 150 µm, are preferred for NO2 - accumulation when high FA is present. The trend was further verified by observing the increase in the apparent inhibition coefficient, KI,FAapp, as granule size increased. This coefficient quantifies the effectiveness of an inhibitor, with larger values indicating weaker inhibition. This study for the first time quantified the effect of diffusion limitation on the KI,FAapp of NOB in granules and biofilms. A mathematical model was then utilized to interpret the observed suppression of NOB. The model predicted that NOB suppression was only complete at the granule surface. The NOB that did survive in larger granules was forced to dwell within the granule interior, where the FA concentration was lower than that in the bulk solution. This means FA inhibition can be taken advantage of as an effective means for NOB suppression in small granules and thin biofilms. Further, FA and DO were found to be both required for the stratification of a layer of AOB at the surface over a layer of NOB in partial nitritation-anammox CFRs. The structural stratification commonly observed in granules is then concluded to be a consequence but not a cause of the NOB suppression.

The effect of ammonia on anaerobic digestion of the organic fraction of municipal solid wastes (OFMSW) was investigated in this study. This study involved two sets of experiments. First set involved the investigation of ammonia toxicity on AD of synthetic OFMSW only (SW), at three different phases and pH 7.5, 8.0 and 8.5. Phase 1 was the Batch Methane Potential (BMP) phase. BMP tests were conducted under ammonia concentration of 2500 mg/L, 5000 mg/L, 7500 mg/L and 10,000 mg/L and at pH 7.5, 8.0, and 8.5, using 500 mL Kimax® glass bottles. The total working volume of the mixture was 300 mL comprising 120 mL of mesophilic anaerobically digested inoculums, 30 g of OFMSW, various TAN concentrations ranging from 2,500, 5,000, 7,500 to 10,000 mg/L, and equal portions of buffer in form of NaHCO3 and KHCO3. The second phase of the experiment examined whether the tolerance of the bacteria to high ammonia concentration would improve by acclimating the microbes to high ammonia concentrations, through gradual TAN loading. TAN concentration was increased gradually at pH 7.5, 8.0 and 8.5 weekly. The third phase of the experiment was Semi-continuous batch phase. This phase examined the possibility of reducing the inhibitory effect of ammonia on AD, batch reactors at pH values of 8.0 and 8.5 containing initial TAN concentrations of 7500 mg/L and 10,000 mg/L. 3 g of the digestate containing high ammonia concentration(s) was replaced with fresh substrate at every 4 days, 7 days and 15 days. The second set of experiment involved study of the effects of ammonia on anaerobic digestion of OFMSW with real landfill leachate (SW+L). Phase 1 was BMP in which the effect of ammonia was examined at TAN concentrations of 7,500 and 10,000 mg/L. The phase 2 of the (SW+L) gradual TAN TAN loading. The possibility of adapting mesophilic bacteria to high ammonia concentration was examined. The results of the study confirmed that ammonia is toxic to AD, at high concentrations. Biogas production reduced with increase in TAN concentration. Reduction in Cumulative Biogas Production (CBP) compared with control reactors was as much as 43 %, 64 % and 77 % in reactors containing 7500 mg/L TAN at pH 7.5, pH 8.0 and pH 8.5. CBP reduced to 80-85 % in reactors containing 10,000 mg/L TAN across the pH examined. Also, replacing 3g of digestate containing high TAN concentrations of 7500 mg/L and 10,000 mg/L with 3 g fresh substrate improved the activity of the mesophilic bacteria as seen in the surges in biogas production when fresh substrate was injected into the reactors. Similar results were obtained on effect of ammonia on AD of OFMSW mixed with real landfill leachate to simulate an anaerobic bioreactor landfill. CBP reduced as the TAN concentration increased. Compared with control reactors, reactors containing 7500 mg/L TAN at pH 8.0 and pH 8.5 had 61 % and 80 % reduction in CBP. Likewise, reactors containing 10,000 mg/L TAN at pH 8.0 and pH 8.5 had 68 % and 85 % reduction in CBP, compared with control reactors. Study confirmed that pH influenced the toxicity and composition of Total Ammonia Nitrogen (TAN). At high pH (i.e. 8.5), FAN component of TAN was about 26 % and was inhibitory to the methanogens. Results also showed that mesophilic bacteria could be adapted to a TAN concentration of about 5000 mg/L at pH 7.5 through gradual TAN loading. Similar results were obtained on effect of ammonia on AD of OFMSW mixed with real landfill leachate to simulate an anaerobic bioreactor landfill. CBP reduced as the TAN concentration increased. Compared with control reactors, reactors containing 7500 mg/L TAN at pH 8.0 and pH 8.5 had 61 % and 80 % reduction in CBP. Likewise, reactors containing 10,000 mg/L TAN at pH 8.0 and pH 8.5 had 68 % and 85 % reduction in CBP, compared with control reactors. Study confirmed that pH influenced the toxicity and composition of Total Ammonia Nitrogen (TAN). At high pH (i.e. 8.5), FAN component of TAN was about 26 % and was inhibitory to the methanogens. Results also showed that mesophilic bacteria could be adapted to a TAN concentration of about 5000 mg/L at pH 7.5 through gradual TAN loading.

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