Biogas from mono- and co-digestion of microalgal biomass grown on piggery wastewater

Biogas production has been suggested as a valid valorization solution for microalgal/bacteria biomass (MAB) grown on wastewater. The feasibility of utilizing MAB grown in an outdoor raceway fed on piggery wastewater for biogas production was assessed. Batch and continuous anaerobic tests were performed on the sole MAB and on a blend of MAB and carbonaceous substrates (deproteinated cheese whey and cellulose) to boost the carbon/nitrogen ratio. Results of batch biochemical CH4potential tests confirmed that the sole microalgal/bacteria biomass was poorly degradable (119 NmLmethane/gCOD) while blending it with deproteinated cheese whey or cellulose (80% of carbonaceous material and 20% of MAB, as chemical oxygen demand (COD)) had no synergistic effects on the CH4yield, although minimal improvements in the degradation kinetics were observed. Continuous anaerobic degradation tests at an organic loading rate of 1.5 gCOD/L-d, 35°C and 30 d of hydraulic retention time increased the overall CH4yield from 81 NmLmethane/gCOD(sole MAB) to 216 NmLmethane/gCOD(MAB and deproteinated cheese whey) and 122 NmLmethane/gCOD(MAB and cheese whey). However, data confirmed that no evident synergistic effects were observed.