Effect of feedstock composition and organic loading rate during the mesophilic co-digestion of olive mill wastewater and swine manure

In the present study, the optimisation of the mesophilic anaerobic co-digestion process of olive mill wastewaters (OMW) together with swine manure (SM) was investigated. Batch and continuous mode experiments were performed in order to define the most efficient mixing ratio and to determine the performance of the reactors under different organic loading rates (OLR). In batch experiment, the most efficient mixing ratio consisted of 40% OMW and 60% SM, since it presented the highest methane production equal to 277 mL CH4/g COD, which corresponded to 79% of the theoretical yield. It was found that the effectiveness of this mixing ratio was not affected in the continuous operation of the reactors. The stepwise increase of the OLR did not affect negatively biomethanation, although the concentration of the inhibitory compounds of the OMW was higher. Under OLR of 4.4 g volatile solids/(L-feed·day) the methane yield of the reactors fed with 40% OMW reached 373 mL CH4/gVS (78% of the theoretical yield). The findings of the present study proved that the co-digestion of OMW together with SM is a sustainable solution, capable to efficiently treat simultaneously these residual residues. •Biomethanation from different ratios of olive mill wastewater and swine manure was compared.•Codigestion of the tested substrates is a plausible method to treat these wastes.•Addition of olive mill wastewater up to 40% enhanced biomethanation.•Stepwise increase of organic loading rate did not affect negatively biomethanation.