Effect of mixture ratio on co-digestion of vegetable and fruit waste with macro-algae, chicken manure and tofu dregs

Abstract

Fruit and vegetable wastes (FVW) are generated in many traditional markets in Indonesia and mostly disposed directly to landfill. Various studies highlighted that FVW could be further valorised either as bioenergy resources or other high-value products. In this study, the biochemical methane potential (BMP) and its electrical energy potential from co-digestion of FVW with macro-algae (MA), chicken manure (CM) and tofu dregs (TD) were investigated. The research design used was a Completely Randomised Design (CRD). All treatments were prepared in triplicate at a ratio of 100:0; 70:30 and 50:50, respectively. All individual anaerobic co-digestion tests of FVW with CM and TD were carried out at the organic loading rate (OLR) of 3 kg VS/m3/day. The effects of different feedstock ratio on stability and performance indicators were further evaluated. The biomass characterisation analyses showed that FVW, MA, CM and TD samples have a high amount of carbohydrates, proteins, and fats, indicating their suitability as feedstock for biogas production. All tested samples have pH value within the ideal range of 6.8-8.0, indicating that there was no pH inhibition during the digestion process. Increasing co-digestion feed ratio of FVW: CM (70:30) or FVW: TD (70:30) was found to reduce biogas or methane potential. The theoretical estimation of electrical potential from co-digestion of FVW indicated that changing the feed to a ratio of 50:50, produced higher energy generation. This finding confirmed that co-digestion could be an option to enhance biogas and methane yield due to additional nutrient supply from the co-substrates.