Anaerobic treatment of source-diverted blackwater-maximizing biomethane recovery

• Author / Creator

  Gao, Mengjiao

• 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.

• Subjects / Keywords

  • Microbial community
  • Decentralized sanitation
  • Food waste co-digestion
  • Biomethane recovery
  • Anaerobic digestion
  • Blackwater
  • UASB

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-acq2-vg63

• License

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