Anaerobic digestion of Chinese cabbage waste silage with swine manure for biogas production: batch and continuous study

The aim of this study was to investigate the potential for anaerobic co-digestion of Chinese cabbage waste silage (CCWS) with swine manure (SM). Batch and continuous experiments were carried out under mesophilic anaerobic conditions (36-38 degrees C). The batch test evaluated the effect of CCWS co-digestion with SM (SM: CCWS = 100: 0; 25: 75; 33: 67; 0: 100, % volatile solids (VS) basis). The continuous test evaluated the performance of a single stage completely stirred tank reactor with SM alone and with a mixture of SM and CCWS. Batch test results showed no significant difference in biogas yield up to 25-33% of CCWS; however, biogas yield was significantly decreased when CCWS contents in feed increased to 67% and 100%. When testing continuous digestion, the biogas yield at organic loading rate (OLR) of 2.0 g VSL-1 d(-1) increased by 17% with a mixture of SM and CCWS (SM: CCWS = 75: 25) (423 mL g(-1) VS) than with SM alone (361 mL g(-1) VS). The continuous anaerobic digestion process (biogas production, pH, total volatile fatty acids (TVFA) and TVFA/total alkalinity ratios) was stable when co-digesting SM and CCWS (75: 25) at OLR of 2.0 g VSL-1 d(-1) and hydraulic retention time of 20 days under mesophilic conditions.