Mineral packings enhance performance of two-phase anaerobic digestion in leach bed reactors coupled to anaerobic filters: Methane production, Feammox and metabolic pathways.

In this study, zeolite and volcanic rock were used as packings of anaerobic filter (AF) to set up leach bed reactor (LBR)-AF two-phase anaerobic system for treating high-solid food waste residue. Results indicated that NH4+-N in the AF with mixed packings was reduced by 86 %, significantly alleviating ammonia inhibition. Methane production of mixed packings group reached 336.39 mL/g VSadd. Mixed packings had a significant impact on microbial community, promoting the dominance of Proteobacteria among hydrolytic and acidogenic bacteria. Simultaneously, mixed packings promoted hydrogenotrophic methanogens (Methanobrevibacter), enhancing methane content in the biogas. Moreover, iron-reducing bacteria were found and the absolute abundances in the zeolite and mixed group were up to 1277 and 1149, respectively, which indicated the presence of iron-ammonia oxidation (Feammox) in the zeolite and mixed groups. These findings provide valuable insights for achieving stable and efficient treatment of high-solid organic waste in anaerobic digestion systems.