The effects of substrate pre-treatment on anaerobic digestion systems: A review

Focus is placed on substrate pre-treatment in anaerobic digestion (AD) as a means of increasing biogas yields using today’s diversified substrate sources. Current pre-treatment methods to improve AD are being examined with regard to their effects on different substrate types, highlighting approaches and associated challenges in evaluating substrate pre-treatment in AD systems and its influence on the overall system of evaluation. WWTP residues represent the substrate type that is most frequently assessed in pre-treatment studies, followed by energy crops/harvesting residues, organic fraction of municipal solid waste, organic waste from food industry and manure. The pre-treatment effects are complex and generally linked to substrate characteristics and pre-treatment mechanisms. Overall, substrates containing lignin or bacterial cells appear to be the most amendable to pre-treatment for enhancing AD. Approaches used to evaluate AD enhancement in different systems is further reviewed and challenges and opportunities for improved evaluations are identified.

► Pre-treatments may potentially enhance the biodegradability of most substrates.
► Matching pre-treatment techniques to substrate characteristics remains a challenge.
► Full-scale experience of pre-treatment is limited.
► Systematic studies of technical, energy and economic effects are necessary.
► Further development of descriptive and predictive variables is required.