Pyrolysis of Municipal Sewage Sludge for Biofuel Production: A Review

Among the various problems the world is facing, two problems are addressed in this paper. On the one hand, biomass, the fourth largest and most important renewable energy option that can provide different forms of energy, is criticized because it competes, sometimes, with the food chain. On the other hand, the amount of municipal sewage sludge has continued to increase over the years, and its disposal remains a crucial point of discussion between urban planners, wastewater managers, and leaders of environmental protection. To address this problem, researchers are directing their focus toward alternatives to conventional biomass resources, such as organic wastes and residues. Thus, municipal sewage sludge is a likely candidate for energy and high-value added material production. Regarding this issue, one of the main methods proposed by researchers is the pyrolysis process. The aim of this paper is to review the research conducted on sewage sludge conversion through the pyrolysis process. After characterizing municipal sewage sludge, we present a summary of the sewage sludge pyrolysis process. Then, the effects of some of the most influential parameters are examined. The last main part of this work is dedicated to the nitrogen transformation pathway during this process.