Anaerobic co-digestion of cocoa husk with digested swine manure: evaluation of biodegradation efficiency in methane productivity

The purpose of this study was to investigate the potential of methane production from anaerobic co-digestion of coco husk with digested swine manure. The experiment was set up in the batch system. Inoculum utilized in this experiment was derived from semi-continuous reactor run at steady state condition, with 25 days of hydraulic retention time and mesophilic condition. The temperature applied in this experiment was maintained under mesophilic condition, which was 35oC. The highest methane productivity generated from anaerobic co-digestion of cocoa husks (CH) with digested swine manure was 345.8 ± 7.82 mL/day, which was higher compared with the anaerobic digestion of digested swine manure alone (286.97 ± 16.8 mL/day). CH reactors had less methane yield (60.3 ± 1.6 mL CH4/g VS added) compared with control reactors (104.1 ± 4.4 mL CH4/g VS added). However, chemical oxygen demand (COD) removal and volatile solids (VS) reduction of CH reactors were 45.1 ± 4.3%, 19.9 ± 0.5%, respectively, which were higher compared with control reactors (20.3 ± 5.0%, 14.7 ± 1.0%, respectively). Based on the results, it can be known that a lower biodegradation efficiency of anaerobic co-digestion of cocoa husks with digested swine manure was affected by the high cell wall content of cocoa husks that may hinder the anaerobic microbes to convert cocoa husk into methane