Anaerobic cometabolism of fruit and vegetable wastes using mammalian fecal inoculums: Fast assessment of biomethane production

Abstract

Anaerobic digestion (AD) is a biological process which produces biomethane as energy source, using waste as substrate. Cometabolism is a novel way to enhance liquid AD, via augmenting the biodiversity of inoculums, especially in the hitherto little-studied 96-h initiation period critical to AD startup. Dog, horse and sheep feces were used as sources of inoculum and mixed with fruit and vegetable waste (FVW) and water. Thermophilic (55 C), mesophilic (39 ) and psychrophilic (25 C) AD conditions were tested. As inoculum and water quantities alter the abundance and diversity of the anaerobic communities, 1:1 and 1:4 ratios of FVW feedstock to inoculum solutions were compared. Live Saccharomyces cerevisiae was supplemented as probiotic in the anaerobic reactors. Biogas, CO2 and CH4 were measured as well as digestion of FVW. Results showed consistently more CH4 production under cometabolism, higher inoculum density and thermophilic conditions; higher CH4, pH and digestion simultaneously occurred in the mixed-inoculum reactors. A strong relationship between biogas and its CO2 and CH4 main components was found. Horse inoculum in the mixed reactors enhanced CH4 production; sheep inoculums improved digestibility; and the dog inoculum seemed to neutralize pH. S. cerevisiae may have improved cellulolytic activity in FVW digestion at 25 and 39 C, and provided an energy and nutrient source at 55 C.