Inoculum mixture optimization as strategy for to improve the anaerobic digestion of food waste for the methane production

Abstract

Food waste (FW) represents the highest proportion of municipal solid waste (MSW), which due to its high biodegradability can be treated and recycled via anaerobic digestion (AD). Although in Latin America there is a high availability of flocculent sludges, they present deficiencies that limit their use as potential inoculum. In this study, the influence of incorporating a granular inoculum on the production of methane by the AD of FW, in combination with a flocculent inoculum from a sludge digester of a municipal wastewater treatment plant (inoculum A) was evaluated by biochemical methane potential (BMP) tests. The granular sludge was obtained from a methanogenic reactor that treats cattle slaughterhouse wastewater (inoculum B). The evaluated A:B mixtures (100:00, 75:25, 60:40, 50:50, 40:60, 25:75 and 00:100), showed that the incorporation of inoculum B (granular) improved the hydrolytic activity of the mixtures (values from 0.16–0.91 gCODGlucose) and provided adequate equilibrium between the specific acidogenic activity (SAA: 3.6–0.88 g CODGlucose gVS−1 d−1) and the specific methanogenic activity (SMA: 0.047–0.19 gCODCH4 gVS−1 d−1). The 75:25 and 50:50 inoculum mixtures produced superior BMP and physicochemical characteristics and microbiological activities. The expected Kh behavior was not observed due to the extended lag-phase that occurred in the experiment (8–12 days) and the presence of particulate organic matter, which is common for this type of substrate. With respect to the stability determination factor (If), the inoculum mixtures with higher proportions of granular sludge demonstrated greater stability during the AD process.