The state of technologies and research for energy recovery from municipal wastewater sludge and biosolids

Wastewater resource recovery facilities produce wastewater solids that offer potential for energy recovery. This opinion article provides a perspective on state-of-the-art technologies to recover energy from sludge (unstabilized wastewater residual solids) and biosolids (stabilized wastewater solids meeting criteria for application on land). The production of biodiesel fuel is an emerging technology for energy recovery from sludge, whereas advancements in pretreatment technologies have improved energy recovery from anaerobic digestion of sludge. Incineration is an established technology to recover energy from sludge or biosolids. Gasification, and to a greater extent, pyrolysis are emerging technologies well-suited for energy recovery from biosolids. While gasification produces high-energy gases, pyrolysis has the benefit of producing biochar in addition to pyrolysis gas. Research on the use of pyrolysis liquids, however, must proceed to advance pyrolysis implementation efforts. Future research on improvements to dewatering and drying of sewage sludge and biosolids will help advance all technologies reviewed.