Experimental and modelling optimisation of sustainable techniques for the pre-treatment of the organic fraction municipal solid waste to improve anaerobic digestion

The study investigated and compared the anaerobic digestion (AD) of real organic fraction municipal solid waste (OFMSW) prior pre-treated with four types of pre-treatments: mechanical, thermal, hydrodynamic-cavitation (HC), and ultrasound (US). The tested pre-treatments and AD configurations were selected through Design of Experiments and then regression models were built to find the most promising configurations in terms of biogas production and energetic sustainability of the whole process. The novelty of the research is the simultaneously study of the working conditions of the pre-treatments; and AD parameters like the two origins of the inoculum, its incubation time, and the substrate: inoculum ratio (SI). The results demonstrated that the best configurations of pre-treatments and AD were the ones performed with thermal pre-treatment at 120 degrees C for 45 min (with inoculum incubation of 10 d at substrate: inoculum (SI) ratio of 2:1) and HC at 55 degrees C (with inoculum incubation of 10 d at SI of 3:1). The thermal, and to some extent the mechanical pre-treatment, evidenced as significant the interaction between the pre-treatment time and the inoculum incubation time. AD of US-OFMSW achieved the lowest performances since inhibition occurred, probably due to the lignocellulosic inhibitors release after ultrasound pre-treatment