Assessment of Batch and Semi-continuous Anaerobic Digestion of Food Waste at Psychrophilic Range at Different Food Waste to Inoculum Ratios and Organic Loading Rates

Abstract

At present, most studies have been focused on anaerobic digestion (AD) of food waste (FW) at temperatures above 35 °C. While AD of FW at psychrophilic temperature has been rarely reported, this may be a more economical procedure for municipal solid waste (MSW) management by reducing the organic fraction content and the corresponding environmental impact from its disposal. FW and inoculum have been characterized and AD of FW assays have been run for 12 weeks in accordance with VDI 4630. The effect of FW to inoculum ratio (FWIR) has been assessed in batch assays and the organic load rate (OLR) has been tested in semi-continuous operation mode. In addition, soluble chemical oxygen demand (SCOD) evolution has been periodically measured during all tests. Results showed an important reduction of specific methane yield (SMY) (up to 65%) when FWIR is increased (from 0.5 to 1.5) in batch tests while SCOD removal remains quite constant (approx. 90%). On the other hand, during semi-continuous operation SMY and SCOD removal have been highly reduced (up to approx. 70 and 73%) when OLR is increased (from 1 to 3 g_VS L−1 d−1). Despite the low SMY, the AD of FW at psychrophilic temperature is a feasible solution, especially at low organic loads. Therefore, it may be used in decentralized strategies for improving the MSW management. This operation mode reduces installation costs and reactor operation complexity at the same time decreases the SCOD of municipal waste stream.