Effect of pre-treatments on biological methane potential of dewatered sewage sludge under dry anaerobic digestion

[Display omitted] •Pre-treatment methods were investigated and evaluated in terms of BMP and biodegradation.•Ultrasonic pre-treatment had the best result among the single technologies and physical technology reflects better results than chemical technologies.•Ultrasonication-ozone pre-treatment showed better effect than single methods.•Ultrasonication-ozone pre-treatment has the potential for economic and energy conservation. The aim of the study is to enhance hydrolysis of dewatered sewage sludge to tackle the problem of low biological methane potential (BMP) and low efficiency of dry anaerobic digestion. Different pre-treatment i.e. physical (ultrasonication), chemical (acid, ozone) and combined (ultrasonication-ozone) methods were investigated and evaluated in terms of BMP and biodegradation. Ultrasonic pre-treatment had the best result among the single technologies, the BMP increased by 104.7%, while total solid (TS), volatile solid (VS) and chemical oxygen demand (COD) reduction were improved by 30.1%, 36.9% and 33.9%, respectively, over control. Combined pre-treatment (ultrasonication-ozone) showed more significant enhancement than single methods as evidenced by 138.2% higher BMP and 53.7%, 63.7% and 57.3% more reduction in TS, VS, COD, respectively, over control. The BMP increment positively correlated either with energy input, concentration or dose of pre-treatment applied. Among the tested methods, the physical pre-treatments out-compete chemical ones. Ultrasonic combined with ozone pre-treatment technology has good energy and economic feasibility.