Low carbon disposal of urban green waste through biogas slurry recycling for preservation and pretreatment

[Display omitted] •Proposed a low carbon disposal and energy utilization process for green waste.•Adding sterilized biogas slurry during ensiling, the BMP increased by 14.65 %.•Using biogas slurry as the medium for HTP, the BMP increased by 62.4 %.•Analyzed the carbon reduction benefits and application prospects of this process. Green waste (GW) is the second-largest type of urban organic solid waste. The anaerobic digestion (AD) of GW to produce biogas is an effective low carbon method for waste treatment. However, current biogas projects using GW face challenges such as fluctuations in raw material supply, low fermentation efficiency, and difficulties in handling biogas slurry (BS). This study explores the effects of reusing BS in the preservation and pretreatment stages on GW composition and subsequent AD performance. Sustainable raw material supply is achieved by ensiling with BS added. Adding sterilized biogas slurry (SBS) to ensiling increased the biochemical methane potential (BMP) by 10.17 % and 14.65 % after 3 and 6 months, respectively, compared to fresh GW (FGW). Reusing BS during pretreatment improves hydrolysis and methanogenesis efficiency. Using BS instead of water as the hydrothermal pretreatment reaction medium boosts BMP by 62.40 % and 47.46 % for GW and ensiling green waste (EGW), respectively. This study also briefly analyzes the carbon reduction benefits of BS recycling, and the application prospects of using this process to treat GW in Guangzhou. After sufficient collection and allocation, Guangzhou can stably produce 2.30 × 107 m3 biogas per month, reducing 3.33 × 107t of carbon dioxide emissions. These findings provide enlightening value for addressing urban GW disposal challenges to reduce carbon emissions.