Biochemical Methane Potential of Potato-Chips Processing Wastes, Process Mechanisms and Microbial Community Shifts

Anaerobic digestion (AD) is an environmentally friendly promising solution for recycling of agro-industrial wastes. However, overloading of an anaerobic digester with the substrate might cause inhibition of the AD process. Present study investigates effects of substrate to inoculum (S/I) ratio on the AD of Potato-chips processing (PCP) wastes from Potato-Chips Processing Industry (PCPI). The PCP wastes include expired potato-chips (EPC), recovered potato starch (RPS) and potato peels (PP). Mesophilic AD was carried out in batch-wise static reactors at 35±1 oC using 4 different S/I ratios (0.5, 1.0, 1.5 and 2.0 g VS/g VS) for each waste. Different optimum S/I ratios were obtained for the different wastes; however, pH ranges were comparable (7.0 to 7.5) for all batches. The optimum S/I for EPC, RPS and PP were 1.0, 1.5 and 2.0 respectively. Cumulative biogas yields for EPC, RPS and PP were 367.5±6.3, 310.0±5.5 and 202.5±4.9 ml/g VS added, respectively. Methane content of biogas yields ranged between 60% and 70%. There was a variable remarkable shift in the microbial population at the optimum S/I ratio of each waste. Firmicutes increased in case of EPC and RPS while decreased in case of PP. Conversely, Proteobacteria increased by using PP as substrate and decreased in case of EPC. Herein the results of AD of PCP wastes confirm its potential for onsite production of renewable bioenergy and reduction of energy bill in the PCPI. Also it provides guidance for optimizing the AD of PCP wastes for large scale application.