Single-Phase and Two-Phase Anaerobic Co-Digestion of Residues from the Treatment Process of Waste Vegetable Oil and Pig Manure

The co-digestion of residues from the pre-treatment process of waste vegetable oil (OW) and pig manure (PM) was performed under different OW/PM feed ratios (1:0, 1:1 and 1:3 v/v) and at organic loading rates ranging from 0.25 to 3.1 kg VS m^?3 day^?1 in lab-scale single-phase (SP) and two-phase (TP) systems. From the experiments, it was observed that digestion of OW alone was inhibitory for the anaerobic degradation. Mixing OW with PM neutralized the negative effects of lipids accumulation and high VS removal efficiencies were realized in both systems (63 and 71 % in SP system and 69 and 72 % in TP system, at 1:1 and 1:3 OW/PM mixtures, respectively). Under the same operational conditions, the methane yield was 0.30 and 0.22 m³ CH₄ kg^?1 VS removed for the SP anaerobic digester and 0.30 and 0.27 m³ CH₄ kg^?1 VS removed for the TP configuration. Additionally, TP digestion presented more stable operation and higher treatment capacity.