Unblocking the rate-limiting step of the municipal sludge anaerobic digestion.

Anaerobic digestion stabilizes municipal sludge through total solids reduction and biogas production. It is generally accepted that hydrolysis accounts for the rate-limiting step of municipal sludge anaerobic digestion, impacting the overall rates of solids reduction and methane production. Technically, the sludge hydrolysis rate can be enhanced by the application of thermal hydrolysis pretreatment (THP) and is also affected by the total solids concentration, temperature, and solids retention time used in the anaerobic digestion. This study systematically analyzed and compared ways to take these four factors into the consideration of modern anaerobic digestion system for achieving the maximum solid reduction. Results showed that thermophilic anaerobic digestion was superior to mesophilic anaerobic digestion in terms of solids reduction but vice versa in terms of the methane production when integrated with THP. This difference has to do with the intermediate product accumulation and inhibition when hydrolysis outpaced methanogenesis in THP-enhanced thermophilic anaerobic digestion, which can be mitigated by adjusting the solids retention time. PRACTITIONER POINTS: THP followed by TAD offers the greatest solids reduction rate. THP followed by MAD offered the greatest methane production rate. FAN inhibition appears to be an ultimate limiting factor constraining the methane production rate. In situ ammonia removal technique should be developed to further unblock the rate-limiting step.

Pivotal role of municipal wastewater resource recovery facilities in urban agriculture: A review.

Urban agriculture provides a promising, comprehensive solution to water, energy, and food scarcity challenges resulting from the population growth, urbanization, and the accelerating effects of anthropogenic climate change. Their close access to consumers, profitable business models, and important roles in educational, social, and physical entertainment benefit both developing and developed nations. In this sense, Urban Water Resource Reclamation Facilities (WRRFs) can play a pivotal role in the sustainable implementation of urban agriculture. Reclaimed water as a recovered resource has less supply variability and in certain cases can be of higher quality than other water sources used in agriculture. Another recovered resource, namely, biosolids, as byproduct from wastewater treatment can be put to beneficial use as fertilizers, soil amendments, and construction material additives. The renewable electricity, heat, CO2 , and bioplastics produced from WRRFs can also serve as essential resources in support of urban agriculture operation with enhanced sustainability. In short, this review exhibits a holistic picture of the state-of-the-art of urban agriculture in which WRRFs can potentially play a pivotal role. PRACTITIONER POINTS: Reclaimed water can be of higher quality than other sources used in urban agriculture. Biosolids can be put to beneficial use as fertilizers, soil amendments, and construction material additives. The renewable electricity, heat, CO2 , and bioplastics produced can also serve as essential resources in support of urban agriculture.