Boosting biogas production and process stability by pretreatment

With the increase in energy consumption and waste generation due to human activities, anaerobic digestion (AD), a technology that turns wastes into bio-energy, is receiving more attention. AD is a naturally occurring microbial process, encompassing the breakdown of organic materials, ensuring energy recovery with the reduction of greenhouse emissions, and facilitating sustainable development of energy supply from waste. AD is a complex microorganisms- driven, multi-phase biochemical process. It involves mainly four biochemical phases. In these phases, organic matter is metabolized by bacteria and archaea and is converted into methane and carbon dioxide. The state of biochemical reactions and activities in anaerobic digestion determines the process stability. Biochemical activities, such as syntrophic, metabolic, catalytic, and enzymatic activities, regulate the anaerobic efficiency for improved methane yield. However, AD has naturally inherent complications based on feedstock type and process parameters, such as slow mass transfer if total solid is high, volatile fatty acid accumulation, C/N ratio imbalance, the recalcitrance of lignocellulosic residues, ammonia inhibition, and micronutrient deficiency. These complications may sometimes lead to slower methanogenesis as well as low energy yield apart from hampering the microbial population of the AD process. In some cases, digester failure has been reported because of inhibitions. Different strategies have been adopted to mitigate these complications such as the addition of buffering agent in the reactor to maintain pH, co-digestion of substrates for a balanced C/N ratio, pretreatment to break the lignin barrier for enhanced methanogenesis, and supplementation of various materials as additives to the anaerobic reactors for better process stability. This work will present an overview of how to improve the stability and efficiency of anaerobic digestion, including pre-treatments for enhancing biochemical activities. This work will focus on the definition of pretreatment, the advantages, and disadvantages of pretreatment processes along with the different kinds of pretreatment applications to the different variates of wastes and biomass.