Performance and microbial community dynamics in a two-phase anaerobic co-digestion system using cassava dregs and pig manure

• The two-phase anaerobic co-digestion of CD with PM was evaluated using 4 SBRs and a CSTR.
• Co-acidification of PM and CD promoted the production and accumulation of VFAs, SCOD and NH4–N.
• Methanogenic fermentation of the acidification products was efficient and steady.
• Co-digestion of PM and CD supported higher quantity and diversity of methanogens.

The two-phase anaerobic co-digestion of cassava dregs (CD) with pig manure (PM) was evaluated using four sequencing batch reactors (SBRs) and a continuously stirred tank reactor (CSTR). The effect of seven different PM to CD volatile solid ratios (10:0, 8:2, 6:4, 5:5, 4:6, 2:8 and 0:10) on the acidification phase was investigated. Results indicated the concentrations of soluble chemical oxygen demand, NH4–N and volatile fatty acids increased substantially at seven ratios. Co-acidification of PM and CD performed well. Methanogenic fermentation of the acidification products at seven ratios was steady in CSTR. The highest methane yield and VS removal of 0.352 m3/kg VSadded and 68.5% were achieved at PM:CD (4:6). The microbial population in CSTR was analyzed using molecular methods. Findings revealed that bacteria such as Firmicutes and Bacteroidetes, archaea such as Methanobacteriales and Methanomicrobiales were advantageous populations. Co-digestion of PM and CD supported higher quantity and diversity of methanogens.