Engineered methanotrophic syntrophy in photogranule communities removes dissolved methane

Area of Science:

• Environmental microbiology
• Wastewater treatment technologies
• Greenhouse gas mitigation

Background:

• Anaerobic wastewater treatment releases dissolved methane, a potent greenhouse gas.
• Methane emissions can negate the environmental benefits of energy recovery from anaerobic digestion.
• Low-temperature operations exacerbate methane loss in wastewater effluent.

Purpose of the Study:

• To demonstrate the removal of dissolved methane from wastewater using an engineered microbial community.
• To investigate the efficacy of methanotrophic communities within oxygenic photogranules for methane elimination.
• To assess the potential of this technology for post-treatment of anaerobic effluent.

Main Methods:

• Construction and maintenance of a syntrophic community of methanotrophs and cyanobacteria in photogranules over two months.
• Continuous operation of a reactor system to treat wastewater effluent.
• Analysis of methane removal efficiency, removal rate, biomass yield, and COD balance.
• Microbial community analysis using MiSeq amplicon sequencing of 16S and 23S rRNA genes.

Main Results:

• Achieved an average dissolved methane removal of 84.8±7.4%, with an effluent concentration of 4.9±3.7 mg CH4∙l−1.
• Observed an average methane removal rate of 26 mg CH4∙l−1∙d−1 and a combined biomass yield of 2.4 g VSS∙g CH4−1.
• Identified a potential syntrophic chain and noted that smaller photogranules exhibited higher methane removal efficiency.

Conclusions:

• Engineered methanotrophic photogranules offer a viable solution for dissolved methane removal from anaerobic wastewater effluent.
• The syntrophic community effectively mitigates greenhouse gas emissions, enhancing the overall environmental benefit of anaerobic treatment.
• Photogranule size and microbial community composition influence methane removal efficiency, suggesting potential for further optimization.