Steam explosion and thermal pretreatments are widely investigated for improving biogas production from different dedicated materials such as forest residuals [65] and wastes of e.g. activated sludge [66,67], cattle manure [68] or municipal solidwastes. However, there are several investigations on combining “thermal” pretreatment with addition of bases such as NaOH, which usually give a better result than individual thermal or
chemical pretreatment [69,70].