Improved methane production from waste activated sludge by combining free ammonia with heat pretreatment: Performance, mechanisms and applications.

Graphical abstract Highlights • CFHP was applied to improve methane production from WAS for the first time. • Hydrolysis rate of WAS are improved through CFHP. • Biochemical methane potential of WAS are improved through CFHP. • CFHP is an attractive technology for the application in real-world situations. Abstract Anaerobic digestion of waste activated sludge (WAS) is often limited by low hydrolysis efficiencies and poor methane potentials. This work presents a novel pretreatment technology for WAS anaerobic digestion, i.e., combining free ammonia with heat pretreatment (CFHP). Experimental results showed that compared with control, solo free ammonia (135.4 mg NH 3 -N/L) and solo heat (70 °C) pretreatment, the combined free ammonia and heat (135.4 mg NH 3 -N/L with 70 °C) obtained 52.2%, 25.5% and 30.2% faster in hydrolysis rate and 25.2%, 17.9% and 16.5% higher in biochemical methane potential, respectively. Mechanism investigations showed that the combined pretreatment not only largely facilitated the disintegration of WAS but also increased the proportion of biodegradable organic matters, thereby providing better contract between biodegradable organics and the anaerobic microbes for methane production. Considering its effectiveness and renewability, the combined pretreatment is an attractive technology for the application in real-world situations. [ABSTRACT FROM AUTHOR]