Principles, Advances, and Perspectives of Anaerobic Digestion ofLipids

Several problems associated with the presence oflipids in wastewater treatment plants are usually overcome byremoving them ahead of the biological treatment. However,because of their high energy content, waste lipids are interestingyet challenging pollutants in anaerobic wastewater treatment andcodigestion processes. The maximal amount of waste lipids that canbe sustainably accommodated, and effectively converted tomethane in anaerobic reactors, is limited by several problemsincluding adsorption, sludgeflotation, washout, and inhibition.These difficulties can be circumvented by appropriate feeding,mixing, and solids separation strategies, provided by suitable reactortechnology and operation. In recent years, membrane bioreactorsandflotation-based bioreactors have been developed to treat lipid-rich wastewater. In parallel, the increasing knowledge on thediversity of complex microbial communities in anaerobic sludge, and on interspecies microbial interactions, contributed to extendthe knowledge and to understand more precisely the limits and constraints influencing the anaerobic biodegradation of lipids inanaerobic reactors. This critical review discusses the most important principles underpinning the degradation process and recent keydiscoveries and outlines the current knowledge coupling fundamental and applied aspects. A critical assessment of knowledge gaps inthefield is also presented by integrating sectorial perspectives of academic researchers and of prominent developers of anaerobictechnology.