Long-term acclimatization of sludge microbiome for treatment of high-strength organic solid waste in anaerobic membrane bioreactor

Abstract In this study, anaerobic membrane bioreactor (AnMBR) was applied for the treatment of a model slurry of high-strength organic solid waste. Continuous monitoring of reactor performances by chemical analyses and fine-scale tracing of the AnMBR sludge microbiome by high-throughput 16S rRNA gene sequencing were conducted during the long-term operation with increased organic loading rates (OLRs) up to 5.26 kgCOD m−3 day−1. Stable treatment was achieved at the highest OLR for over 170 days. The chemical oxygen demand removal rate of around 99%, membrane flux of 3.31 ± 0.40 L m−2 h−1, and biogas production rate of 31.1 ± 4.8 L day−1 were observed. The latter two parameters were improved after the sludge retention time (SRT) control, showing 4.76 ± 0.25 L m−2 h−1 and 34.5 ± 6.9 L day−1, respectively. The principal coordinate and taxonomic analyses of the sequence data showed that the sludge microbiome was changed drastically in response to both the OLR increase and SRT control. The species-level characterization showed that the relative abundances of aceticlastic methanogens, e.g., Methanosaeta concili, decreased at high OLRs, whereas those of hydrogenotrophic methanogens, such as Methanolinea mesophila, as well as a syntrophic bacterium Smithella propionica, increased under the high OLRs and SRT control conditions. These results strongly suggest that the effective treatment of the high-strength organic solid waste slurry was mediated via the syntrophic methanogenesis pathway in the AnMBR.