Enhancing anaerobic digestion Efficiency: A comprehensive review on innovative intensification technologies

Anaerobic digestion (AD) is an established technology that plays a crucial role in breaking down the organic compounds and biomass during the sludge treatment processes. However, there are multiple challenges associated with the application of AD on different feedstocks and under various operational conditions. The AD process is highly sensitive to operational conditions (e.g., temperature and pH) with relatively slow reactions rates especially during the hydrolysis and methanogenesis stages. These limitations can significantly affect the performance of anaerobic digesters and the biogas production rate. Therefore, various intensification technologies were proposed and investigated in the literature to upgrade the biogas production and yield as well as enhancing the removal of organics and biomass during the sludge treatment processes. Although different review studies have examined some of these intensification technologies such as physical and chemical pretreatment techniques, limited studies have focused on reviewing the innovative intensification technologies, such as microbial electrolysis cells (MEC) and micro-aeration, in AD applications. Moreover, there are no systematic investigations that compared the performance, mechanisms, advantages, and challenges of these innovative technologies to draw strong conclusions about the applicability of each technology with different wastes, feedstocks, and operation conditions. In addition, the quantification of possible integration of these technologies with the current infrastructure and the technology readiness level were not well-investigated in literature. Therefore, in the current study, seven different innovative intensification technologies were reviewed including MEC-assisted AD, conductive functional materials, micro-aeration, anaerobic membrane bioreactors, hydrogen injection, IntensiCarb, and microbial hydrolysis process using Caldicellulosiruptor bescii. A detailed description of these technologies for increasing biogas yields was presented, with a special focus on the performance, reliability, efficiency gains, and applicability of each technology. The major insights of this review can serve as a reference for the potential intensification technologies that can be integrated with existing AD systems for enhanced biogas production and removal of organics and biomass.