Optimization of Biogas Production by Anaerobic co-Digestion

Abstract

The use of biomass as an energy source has escalated in recent times as a result of global initiatives in pursuit of alternative and renewable fuels. Biofuels comprise liquid, solid and gaseous fuels. Biogas is one of the common gaseous biofuels. It is a high methane fuel. The technology of producing biogas is relatively not sophisticated. Biogas has gained traction as an energy carrier with potential to contribute significantly to the global energy mix. Biogas is produced from degradable organic matter by anaerobic digestion. Anaerobic digestion is a technology that breaks down organic matter in the absence of oxygen, and the process produces biogas. Biogas typically consists of methane (50-75%), carbon-dioxide (25-50%), and trace quantities of contaminant gases. There is need to optimise anaerobic digestion in order to maximise biogas yields. Co-digestion is one option of optimising anaerobic digestion. Co-digestion refers to the synchronized digestion of a homogenous mixture of multiple substrates in a single digester. Co- digestion enhances the efficiency of anaerobic digestion and increases biogas yields for substrates that have low methane potential. Co-digestion increases methane yields from low-yielding or difficult to digest materials. Examples of co-substrates for co-digestion include food wastes, press-cakes, crop residues and animal manures. For the co-digestion process, selected feedstocks must be compatible to enhance methane yields. The co- substrates must complement each other in terms of carbon to nitrogen ratio, nutrients and other physical and chemical factors. This chapter presents an overview of the co- digestion process, focusing on the principles, selecting co-feedstocks, biomethane potential of feedstocks, merits and limits of co-digestion.