Single-Stage and Two-Stage Anaerobic Digestion of Food Waste: Effect of the Organic Loading Rate on the Methane Production and Volatile Fatty Acids

Abstract

The high organic content of food waste (FW), which represents the largest proportion of municipal solid waste (MSW) (in Latinamerican countries 50–75%), makes its treatment increasingly common trough technologies such as anaerobic digestion (AD), to obtain value-added by-products, such as renewable energy in the form of methane, digestates and other by-products of biotechnological applications such as long-chain fatty acids. In this study, the influence of semi-continuous reactors in single-stage (R1) and two-stage (R2: acidogenic and R3: methanogenic reactors) configurations on the AD-FW was evaluated (including parameters related to process monitoring, organic matter conversion and process reactions) with the following organic loading rate (OLR: kgVS m-3 d-1) values: i. R1: 0.7, 1.5, 3.0 and 6.0; ii. R2: 3.0, 4.0, 9.0 and 15.0; and R3: 1.0, 2.0, 4.0 and 7.0. The two-stage configuration showed a better performance in terms of: i. the OLRs: 35% higher than that in the single-stage configuration, with chemical oxygen demand (CODtotal) and volatile solid (VS) removal efficiencies > 80%; ii. the best performance in terms of methane production, with statistically significant differences (p<0.05) in the quantity and quality of biogas and iii. obtaining other by-products with high added value, such as behenic and caproic acid, which are useful in biotechnological applications. Additionally, it was found that total reducing sugars (TRS) are an important parameter in the monitoring and conversion of matter organic, mainly in two-stage configuration.