Unblocking the rate‐limiting step of the municipal sludge anaerobic digestion

Abstract

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.

Valorization of food waste for biogas production; effect of co-ensiling with maize straw at different C/N ratios

“…As also shown in Figure 2, the maximum rate of daily methane production occured on day 1 in the silages but occured on day 3 in the unensiled FW. This can be explained by the fact that hydrolysis, which is the rate limiting step of biogas production [23], was enhanced by ensiling. The cummulative BMP of the substrates is shown in Figure 3.…”

Unraveling Anaerobic Digestion Instability: A Simple Index Based on the Kinetic Balance of Biochemical Reactions

“…The kinetics of biochemical reactions are highly susceptible to variations in substrate type and operational and environmental conditions. The hydrolysis of hardly degradable organic matter often requires physicochemical or biological pretreatment for anaerobic digestion [3][4][5][6]. However, the complexity of anaerobic digestion mainly arises from the distinct physiological characteristics of acidogenic bacteria and methanogenic archaea.…”