Comparison of microwave thermohydrolysis and liquid hot water pretreatment of energy crop Sida hermaphrodita for enhanced methane production

Highlights: • Microwave and liquid hot water pretreatment methods were evaluated in this study. • Considerable increasing in biogas production with both methods was noted. • Microwave pretreatment reduced the pretreatment temperature and time. • The net energy output was unfavorable for most conditions tested. • Only for microwaves (150 °C, 15–30 min) a positive energy balance was obtained. -- Abstract: The study was aimed to compare the methane potential from the silage of Sida hermaphrodita mixed with cattle manure pretreated by microwave (MW) thermohydrolysis with liquid hot water (LHW) pretreatment. It was illustrated that both pretreatment methods significantly improved degradation of the lignocellulosic structure and improved the methane production. The maximum methane production of MW pretreated biomass was 590 NL/kg VS at 150 °C and 15 min with an improvement of 39.1% to an untreated sample. In turn, LHW treatment provided the maximum methane production of 575 NL/kg VS with the same pretreatment conditions. The net energy output significantly higher than calculated for the control sample was achieved only for MW pretreatment at 150 °C and 15–30 min. In other variants, pretreatment step needed higher energy input than the net energy gain from methane production.