Development of an Efficient Anaerobic Co-digestion Process for Biogas from Food Waste and Paper

Abstract

This world is dependent on fossil fuel and there are various environmental problems caused by human activities such as global warming and pollution from municipal, industrial and agricultural waste. It is necessary for sustainable development to treat wastes adequately and to develop renewable energy. Utilization of biomass wastes has attracted a lot of interest because it is a way of waste management and also a source of renewable energy. Anaerobic digestion is one of them and has high potential to produce energy (Noike et al., 2009; Ghosh et al., 1975). Processing methods of anaerobic digestion are classified by solid content of feedstock and fermentation temperature (IEA BIOENERGY, 2001). The dry thermophilic anaerobic digestion is expected to be suitable in Japan because it occurs a small amount of digestate. Anaerobic digestion is also sorted out by the used feedstock. Anaerobic co-digestion, that is the process using the feedstock made from several kinds of substrates, has some advantages to anaerobic digestion from single substrate due to be able to adjust component of feedstock. Nakajima showed that anaerobic co-digestion from food waste with rich nitrogen and paper with rich carbon improves biogas generation because the C/N ratio of the feedstock is optimized (Nakajima et al., 2016). Food waste and paper constitute the second and third largest unused biomass waste in Japan (Excerpts from “Biomass Nippon Strategy”, Cabinet Decision, March 31, 2006). The efficient recycling method of these waste has been required to achieve sustainable development and the dry thermophilic anaerobic co-digestion is one of the important options. Although anaerobic digestion has many advantages such as the simultaneous treatment of waste, the utilization of digestate as a fertilizer and the robustness to the environment, it is not popular in Japan. There is the problem that reaction intermediates of anaerobic digestion including volatile fatty acid (VFA) and ammonia cause inhibition of methanogenesis easily. Overloading of organic matter leads to the accumulation of reaction intermediates and results in failure of the process. In spite of the biological vulnerability, anaerobic digestion has the robustness to the environment because the process proceeds in the closed reactor. Anaerobic digestion could play the role of supply and demand adjustment in the energy mix with environmental dependent renewable energies like wind and solar power. The numerical optimization of organic loading rate (OLR) has been studied for various purposes. MendezAcosta regulated the VFA concentration and total alkalinity (TA) to improve the stability of anaerobic digestion process with the dynamical model (Mendez-Acosta et al., 2016). Mauky developed the feeding management to compensate the divergence between supply and demand energy with ADM1 (Mauky et al., 2016; Batstone et al., 2002). The used models in these studies were proper for each control strategies (e.g. Mendez-Acosta set up a state variable about TA and Mauky used substantially simplified ADM1 to predict daily biogas production). This study aims to make the anaerobic digestion process stable and produce