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Abstract: The anaerobic treatment of wastewater is considered a promising technology for simultaneous organic matter removal and energy recovery. Compared to aerobic digestion, anaerobic digestion conserves energy and is cost-effective in handling high-strength wastewater and wastes. However, the high sensitivity of anaerobic systems to operational conditions such as temperature, pH, mixing conditions and feeding regimes has limited their application. In particular, feeding patterns have been shown to significantly impact the reactor operations, while a flexible feeding regime is commonly needed when treating the unequalized feedstock. To date, our understanding of the impact of bioreactor feeding strategies on anaerobic bioreactor performance is still limited. The overall objective of this thesis is to evaluate the impact of various feeding strategies on the development of robust microbial communities in bioreactors and the anaerobic bioreactor treatment performance. Three feeding strategies, including continuous, semi-continuous (with starvation-feast cycle), and alternate feeding (with high loading-low loading cycle), were compared in this study to assess anaerobic digestion of synthetic wastewater and methane yields using three continuously operating laboratory-scale up-flow anaerobic sludge blanket (UASB) reactors. Observation of this study revealed that both long and short starvation-feast cycles provided by semi-continuous feeding did not sustain stable anaerobic digestion, whereas alternate feeding with high and low loading cycles promoted microbial community development. With dominant methanogens shifted from Methanosaeta in the continuous reactor to Methanosarcina in semi-continuous feeding reactors, significantly higher methanogenic activities were observed once reactors were recovered. Interestingly, the reactor undergoing the alternate feeding mode successfully maintained a stable operation and thus the alternate feeding pattern is preferred over semi-continuous feeding when reactor feeding is not continuously and consistently available.

Abstract: New sanitation is developed based on wastewater source-diversion and on-site treatment to maximize resource recovery from domestic wastewater. Blackwater stream collected from toilets is rich in organics and nutrients, and the rest greywater stream contains major water content. The primary objective of this thesis was to obtain high biomethane recovery from blackwater using anaerobic digestion (AD) technology. Bioreactor operational performances accompanied the microbial community developments in various treatment conditions were demonstrated. The limitations in blackwater AD processes were systematically revealed and resolved to help establish a high-rate blackwater treatment process.The research chain started from characterizing blackwater collected from different types of toilet flushing systems to gain insights in the limiting factors in biomethane generation. Vacuum toilet blackwater (1 L water/flush) generated 29% lower biomethane production potential (BMP) than conventional and dual flush toilet blackwater (9 L and 6 L water/flush) when treated at 35°C. The high free ammonia concentration of 393 mg/L in vacuum toilet blackwater was identified as the inhibition factor, and the methanogenesis process was found to be directly inhibited by free ammonia while the substrate hydrolysis and fermentation processes were not significantly affected. Continuous upflow anaerobic sludge blanket (UASB) reactors were operated at 35°C to treat different types of blackwater from water-conserving (vacuum) and water-wasting (conventional) toilets. Sulfate inhibition was observed in conventional toilet blackwater UASB treatment, which resulted in a low methane production rate of 58.0 mL/L reactor /d. A high organic loading rate (OLR) of 4.1 kg COD/m3/d was obtained in vacuum toilet blackwater UASB operation through stepwise acclimatizing the system to increasing OLRs. Methane production rate of 0.68 m3 CH4/ m3 reactor/d and chemical oxygen demand (COD) removal efficiency of 84% were obtained, representing the highest blackwater treatment efficiency up to date. When the OLR was further increased to 4.9 kg COD/m3/d, a 40% reduction in solid substrate hydrolysis was observed due to sludge loss. Food waste and vacuum toilet blackwater co-digestion was then performed to resolve the substrate hydrolysis limitation. The maximum OLR of 10 kg COD/m3/d and methane production rate of 2.42 m3 CH4/ m3 reactor/d were obtained for blackwater and food waste co-digestion process using a UASB reactor, which was attributed to the enhanced bioreaction conditions with more favorable carbon/nitrogen (C/N) ratio and readily biodegradable substrates. The treatment performances for blackwater and food waste co-digestion in the current research represented the maximum bioenergy recovery efficacy from household biowaste up to date. The 16S rRNA gene sequencing results revealed that different groups of bacteria and archaea were enriched with different blackwater sources (conventional toilet blackwater or vacuum toilet blackwater with and without food waste addition) and changed OLRs in UASB operations. The combined syntrophic acetate oxidation (SAO) and hydrogenotrophic methanogenic (HM) pathway was established in blackwater treatment processes. Hydrogenotrophic methanogens dominated the archaeal communities in all blackwater UASB operations. Methanogens from genus Methanospirillum and Methanolinea dominated in conventional toilet blackwater UASB reactor, and their abundances shifted with different feed sulfate concentrations. Methanogens from genus Methanogenium were predominant in vacuum toilet blackwater mono-digestion system using the UASB reactor, and the dominant communities shifted to genus Methanoculleus and uncultured genus from family Methanospirillaceae in food waste co-digestion condition. SAO bacteria groups, e.g. from order Clostridiales were enriched in all blackwater treatment systems. The establishment of the SAO-HM methanogenic pathway in the vacuum toilet blackwater treatment system was associated with the environmental factors of high ammonium concentration and/or high OLRs.

This thesis includes both experimental and conceptual analysis of anaerobic treatment of municipal wastewater at sub-optimal temperature (optimal = 35°C). The purpose of this research was to evaluate the application of anaerobic biotechnology for full-scale treatment of mainstream liquid municipal wastewater under moderate climate conditions. Whereas anaerobic digestion of waste biosolids has been widely integrated into the waste management industry, there have been minimal advances in applying full-scale anaerobic reactors for treatment of municipal wastewater. Previous research suggests that anaerobically treating municipal wastewater is not yet gainful because the quality of treatment is not comparable to that of conventional wastewater treatment methods. In order to determine performance capabilities, the first phase used two laboratory-scale anaerobic reactors, the upflow anaerobic sludge blanket (UASB) and anaerobic baffled reactor (ABR), to treat synthetic wastewater with 306 mg/L COD for approximately one year. The primary findings of reactor operation were: · The UASB and ABR were able to achieve and maintain SCOD removal efficiencies of 94% and 89%, respectively, at a temperature of 20°C and hydraulic retention time of 12 hours. · Effluent SCOD was consistently at or below U.S. secondary discharge BOD limits, with the majority of residual SCOD believed to be the result of soluble microbial products. · At 20°C, 57% - 68% of produced methane was lost to reactor effluent as dissolved methane. The UASB and ABR both exhibited supersaturation at more than 2 times the expected saturation limit of methane, respectively. The results indicate that percent COD removal and methane gas production could affect methane solubility in anaerobic reactors. · It was determined that at temperatures equal to or above 14°C, aceticlastic methanogenesis is not the limiting factor of the overall anaerobic process. The second phase of this research investigated the energy and greenhouse gas (GHG) implications of applying anaerobic biotechnology for full-scale treatment of municipal wastewater. In order to successfully apply a full-scale anaerobic treatment system, it was believed that pairing anaerobic biotechnology with an aerobic post-treatment process offered the best alternative. Several conceptual comparisons were performed between conventional aerobic treatment systems and hybrid anaerobic-aerobic systems, with respect to energy requirements and GHG emissions. Although previous studies have been performed in a similar nature, none of them have analyzed the energy requirements and GHG emissions of treatment systems capable of removing BOD, nitrogen, and dissolved methane from municipal wastewater. Principal findings from the conceptual comparisons include: · Due to the anaerobic reactor, dissolved oxygen requirements were significantly reduced in the hybrid systems, subsequently reducing energy consumption and GHG emissions. · Applying anaerobic treatment as the primary biological process enabled the majority of influent BOD to be converted to methane, thereby relegating aerobic processes to a "supportive role" in effluent polishing. This resulted in significant reductions in excess biosolids with related decreases in energy demand and GHG emissions without compromising effluent quality. · Removing and oxidizing dissolved methane from anaerobic effluent imposes minimal energy demands in comparison to those for nitrogen removal. It was concluded that at 20°C, a full-scale treatment system employing an anaerobic reactor followed by aerobic post-treatment could exhibit both net-energy neutrality and net-zero GHG emissions.