Effect of inoculum on the anaerobic digestion of food waste accounting for the concentration of trace elements

Abstract

The production of renewable energy in the form of methane from the anaerobic digestion (AD) of food waste (FW) varies depending on factors such as the quantity and quality of the inoculum. This research evaluated the influence of trace elements (Ca, K, Fe, Zn, Al, Mg, Co, Ni, and Mo) present in inoculum from different sources (wastewater treatment plants (WWTPs): 2 agro-industrial WWTPs and 1 municipal WWTP) on the AD of FW. This study found that the source of the inoculum determines the content of macronutrients and trace elements, which can alter the requirements of the AD process and therefore affect methane production. The inoculum obtained from municipal WWTPs contain potentially inhibitory concentrations of Zn and Al that negatively affect methane production (<70 mL CH4·gVS−1), the hydrolysis constant (<0.19 d−1), and the lag-phase (>7 days). It was also found that high concentrations of trace elements such as Ni (35.2 mg kg−1) and Mo (15.4 mg kg−1) in the inoculum increase methane production (140.7 mL CH4·gVS−1) and hydrolysis constant (>0.18d−1) in addition to presenting short lag-phase (<1 day) in the AD of food waste.