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. This research is aimed at assessing the feasibility to use MAB grown in an out-door raceway fed on piggery wastewater for biogas production. Batch and continuous anaerobic tests were conducted on the sole MAB and on a blend of MAB and carbonaceous substrates (deproteinated cheese whey and cellulose) to improve the C/N ratio. Results of batch biochemical methane potential tests confirmed that the sole microalgal/bacteria biomass was poorly degradable (119 NmL CH4 ·g COD −1 ), while blending it with deproteinated cheese whey or cellulose (80% of carbonaceous material and 20% of MAB, as COD) had no synergistic effects on the methane yield, although slight improvements in the degradation kinetics were observed. Continuous anaerobic degradation tests (at an organic loading rate of 1.5 g COD ·L −1 ·d −1 , 35 °C and 30 days of hydraulic retention time) increased the overall methane yield from 81 mL CH4 ·g COD −1 (sole MAB) to 216 NmL CH4 ·g COD −1 (MAB and deproteinated cheese whey) and 122 NmL CH4 ·g COD −1 (MAB and cheese whey). However, data confirm that no evident synergistic effects were obtained.