Anaerobic co-digestion of food waste with sewage sludge from wastewater treatment plant of Sequele, Luanda-Angola

Abstract

This work aimed to evaluate the potential for methane production from anaerobic co-digestion of the organic fraction of urban solid wastes with sewage sludge. The tests were carried out using Bioprocess AMPTS II batch reactors operated at 37 °C in two different runs. In each run, a different food waste sample, inoculated with sludge, was tested varying the inoculum to substrate ratio (ISR) in each reactor. The experimental cumulative methane production by the mixture at the end of the tests was compared with the expected methane production in order to identify synergistic effects. The modified Gompertz model was fitted to experimental substrate cumulative methane yields. The results of this study suggest the suitability of this model to describe the degradation kinetics. ISR was found to be an important parameter for an efficient methane production, values ≥ 2 are recommended in order to prevent the pH drop in reactors. For one of the food waste samples, the highest substrate methane yield achieved was 91% of the theoretical value. For the other one, synergistic effects were observed in the mixtures of inoculum and substrate, that were attributed to an enhanced methane production by the sewage sludge when mixed with the food waste. The anaerobic co-digestion of food waste with sewage sludge from the Sequele WWTP is a sustainable treatment option for both organic wastes, which can be implemented in this WWTP where the sludge is simply discarded after dehydration.