Microbial Dynamics During the Anaerobic Digestion of Raw Sewage and Electro-Flocculated Wastewater for Biohydrogen and Biomethane Production using Synthetically Designed Microbial Consortia.

Electrocoagulation is used for wastewater (WW) management; however, the disposal of organic carbon- and metal ion-enriched electro-flocculated WW (EF) remains a significant challenge. We investigated the anaerobic digestion (AD) of raw sewage WW (RW) and EF for biohydrogen and biomethane production using a microbial consortia designed from complementary natural wastes selected for their distinct microbial complexity and buffering capacity. The consortia design included sequential mixing, heat-pretreatment, organic load shock, and anaerobic acclimatization for selective enrichment of fermentative, hydrogen-producing, and methanogenic communities. Three different heat-pretreatment consortia and their untreated counterparts were tested in two AD batch experiments (B1 and B3). Biogas production, gas compositions, and microbial dynamics were explored using gas chromatography and 16S rRNA gene sequencing. B3 reactors produced more biogas than B1 and controls, highlighting enhanced microbial activity after acclimatization. For RW, the heat-pretreated inoculum (R.C2Tx) yielded highest cumulative gas (81 mL) with 37% biomethane, attributed to enrichment of fermentative and hydrogenotrophic taxa. In contrast, the untreated consortia (E.C2UTx) performed better for EF (76.7 mL total biogas, 12.7% biomethane, and 5.8% biohydrogen), highlighting the enrichment of microbes with ability for degradation of Fe-rich, complex substrates. Enrichment of Proteobacteria, Pseudomonas, and Methanobacterium in most B3 samples correlated with higher gas yield.