Anaerobic Co-Digestion of Wastes: Reviewing Current Status and Approaches for Enhancing Biogas Production

Abstract

Anaerobic digestion is one of the technologies that will play a key role in the decarbonization of the economy, due to its capacity to treat organic waste, recover nutrients and simultaneously produce biogas as a renewable biofuel. This feature also makes this technology a relevant partner for approaching a circular economic model. However, the low biogas yield of traditional substrates such as sewage sludge and livestock waste along with high installation costs limit its profitability. Further expansion of this technology encounters several barriers, making it necessary to seek improvements to attain a favorable financial balance. The use of co-substrates benefits the overall digestion performance thanks to the balancing of nutrients, the enhanced conversion of organic matter and stabilization, leading to an increase in biogas production and process economics. This article reviews the main co-substrates used in anaerobic digestion, highlighting their characteristics in terms of methane production, kinetic models commonly used and the synergistic effects described in the literature. The main process parameters and their influence on digestion performance are presented, as well as the current lines of research dedicated to improving biogas yields, focusing on the addition of hydrogen, bioaugmentation, supplementation with carbon compounds and nanoparticles, the introduction of bioelectrodes and adsorbents. These techniques allow a significant increase in waste degradation and reduce inhibitory conditions, thus favoring process outcomes. Future research should focus on global process efficiency, making particular emphasis on the extrapolation of laboratory achievements into large-scale applications, by analyzing logistical issues, global energy demand and economic feasibility.

Determinants of Return-on-Equity (ROE) of Biogas Plants Operating in Poland

“…A similar relationship can be observed for other biofuels obtained from agricultural raw materials [46]. In biogas production, one can strive to reduce the cost of the raw material and increase the efficiency of biogas from the raw material by using organic waste where available [47,48]. However, it is only profitable on the local scale, where there is no competition over the raw material and with low logistic costs [49,50].…”

Anaerobic co-digestion of sewage sludge with other organic wastes: A comprehensive review focusing on selection criteria, operational conditions, and microbiology

“…For instance, AD of readily biodegradable wastes with high carbohydrate content results in accumulation of volatile fatty acids (VFA) within the reactor, reduces the pH and consequently inhibits the process [28]. In this case, addition of a co-substrate with fewer biodegradable compounds is recommended to balance the process [29].…”

“…In addition, FW incineration contributes to 20% of the world's total greenhouse gas emissions [48]. By and large, AD is one of the promising options for FW management due to its high C/N ratio (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) [49] and high biodegradable organic content. On the other hand, the low C/N ratio (often between 6 to 9) and low level of the organic content of SS adversely affect the microbial community of the AD process, leading to decreased performance and even process inhibition [50].…”

Effect of chemical composition on the anaerobic co-digestion of source segregated organic fraction of municipal solid wastes

“…Addition of activated sludge (protein-rich) to fruit waste and cheese whey (carbohydrate-rich) increased the enzymatic activity by 22%, thereby increased methane yield by 31% [42]. Overall, mixing carbohydrate-rich and (or) lipid-rich substrates with protein-rich substrates increases the methane yield by providing proper chemical composition for microbial growth, there by increased microbial, and enzymatic activities [43]. This paper investigated the how chemical compositions of organic substrate (carbohydrates, protein, and lipids) effect on methane generation during AcoD of source segregated OFMSW.…”