Evaluation of anaerobic codigestion of microalgal biomass and swine manure via response surface methodology

In an attempt to propose an integrated system to treat swine manure, the codigestion of this residue and microalgal biomass was evaluated. Response surface methodology showed that chemical oxygen demand/volatile solids (COD/VS) and COD algae supplement presented a significant effect on methane yield. Second-order polynomial model fitted quite well with the experimental results. Nevertheless, methane yield values achieved were not expected. Highest methane yield was exhibited by swine manure as a sole substrate, while algal biomass digestion reported the lowest. A closer examination to methane production rates showed that methane production was taking place in a higher extent on samples with higher proportion of algae. In agreement with that, nitrogen organic mineralization was low for those trials; hence the recalcitrant nature of the algal cell wall was evidenced. Even though methane production, hence breakage of the cells, was steadily occurring, the need of an algal biomass pretreatment seems to be imperative for the feasibility of this integrated system.