Treatment of ultra-high-strength compost leachate using an anaerobic biomass biofilm reactor

Leachate produced during the composting of the organic fraction of municipal solid waste (OFMSW) is highly concentrated and acidic (chemical oxygen demand (COD) -125 g/L, pH 3-5). Its recalcitrant nature necessitates long hydraulic retention times for effective digestion, which, in turn, leads to high organic loads and, consequently, large reactor footprints. This study evaluated the treatment performance, bioenergy potential, and microbial ecology of the Anaerobic Biomass Biofilm Reactor (ABBR) for ultra-high strength leachate treatment. The reactor employed lignocellulosic wastes such as coir, ridge gourd, and dried acacia leaves as natural biofilm supports. Operated over 180 days with a gradually increasing organic loading rate from 1.1 to 11.2 kg COD/m³/d, the reactor achieved 92.9% COD removal and a methane yield of 0.357 NL/g COD removed at the maximum loading rate. Moreover, the reactor also exhibited exceptionally high space utilization efficiency (3.5-4 L CH₄/L/d), highlighting its enhanced volumetric productivity and effectiveness in treating high-strength leachate. Metagenomic analysis revealed a diverse microbial community, with Methanospirillum (3%) and Methanosaeta (2.6%) identified as dominant archaea contributing to methanogenesis. The high moisture content of OFMSW, coupled with tropical climatic conditions, leads to rapid fermentation and the generation of large volumes of leachate. Therefore, the ABBR represents a sustainable and high-rate alternative to conventional anaerobic systems, enabling efficient leachate treatment and enhanced bioenergy recovery in windrow composting facilities.