Two-stage versus single-stage anaerobic co-digestion on methane synthesis: Energy prospects and microbial community

Abstract

Cassava processing wastewater (CW), a byproduct generated during cassava processing activities, and glycerol (Gly), a byproduct of biodiesel production processes, have a high concentration of organic matter and digestibility, which provides them with great potential for hydrogen (H₂) and methane (CH₄) generation. This study evaluated the co-digestion of cassava wastewater and glycerol in a single-stage versus two-stage process using a fluidized bed reactor (AFBR), i.e., a mesophilic acidogenic reactor (MAR) + a sequential mesophilic reactor (SMR) and a mesophilic methanogenic reactor (MMR), operated at mesophilic temperature (30°C). Thus, the effect of increasing the organic matter concentration of 1–12.5 g [chemical oxygen demand] COD.L⁻¹ (50 %:50 % on a COD basis) on CH₄ production was verified. Co-digestion consistently yielded methane production in both single and two-stage processes. The two-stage process stood out as the single stage, providing a maximum CH₄ Yield (MY) of 341.10 mL CH₄. gCOD⁻¹_cons and CH₄ production rate (MPR) of 168.23 mL of CH₄.L⁻¹.h⁻¹, respectively. Regarding the microbial community, the methanogens Methanobacterium and Methanobrevibacter prevailed. Moreover, the two-stage and single-stage presented energy potentials of 161.23 kJ.d⁻¹ and 54.26 kJ.d⁻¹, in that order. Upon comparative analysis of the performance between two-stage and single-stage methanogenic reactors, it becomes apparent that the co-digestion of CW and Gly in a two-stage configuration exhibited enhancements over the single-stage.