Enhancement of biogas production from industrial solid pineapple wastes by two-stage anaerobic digestion systems

The use of agricultural waste to produce biofuel is challenging for waste management. This study investigated the biogas including methane production, and chemical oxygen demand (COD) removal efficiency by anaerobic digestion (AD) from mixed pineapple pulp and peel (MPP). Two-stage of anaerobic digestion system was configured as a continuously stirred tank reactor (CSTR) installed with an anaerobic hybrid reactor (AHR). Total solids (TS) of MPP loading at 4% (w/v) was used with four different hydraulic retention times (HRT) to investigate the subsequent effects, such as pH, alkalinity, biogas and methane production, and COD removal efficiency. The overall pH in CSTR was more acidic than the AHR system and exhibited less stability of the AD process by highly volatile acids. The highest biogas production (0.39 v/v-d) was obtained at HRT 7 with the biogas yield of 0.43 m3/kg COD removed and COD removal efficiency of 67.05% in the AHR system. The separated acidogenic and methanogenic stages in the two-stage system improved the digestion performance. The methane yields in the AHR system remained stable except for the lowest HRT condition (HRT5). Biogas production from pineapple wastes by two-stage anaerobic digestion systems was elucidated and could be applied for a larger digestion scale.