Technical feasibility and modeling of enzymatic pre-treatments of organic fraction of municipal solid waste to improve anaerobic digestion

Abstract

The study explored the combined effects of enzymatic pre-treatment and anaerobic digestion (AD) on the organic fraction of municipal solid wastes (OFMSW) through experimental and multicriteria decision-making approaches. Five enzymes (UPP2, MPCS, USC4, USE2, and A. niger) and their dosages were studied. AD parameters included two inoculum origins (waste active sludge - WAS - and cow-agricultural sludge - CAS), the substrate: inoculum (SI) ratio, and inoculum incubation time (INOC). Desirability functions were used to optimize the multiple experimental responses simultaneously by converting each of them into values from 0 (unacceptable) to 1 (completely acceptable) and then combining these into a global desirability (D). D highlighted that higher enzyme dosages, INOC, and SI, improved AD performances, with optimal DOSE (at the highest level adopted for each enzyme) and INOC (5–10 d). AD tests with the five enzymes increased CH4 production by 10–13%v/v compared to untreated OFMSW. For UPP2 and MPCS, increasing DOSE boosted the biogas production, while increasing INOC enhanced the CH4 content. MPCS reached the highest efficiency (478. 43 NL CH4/kg VS with CAS, SI = 2:1, INOC = 10 d), followed by UPP2. Furthermore, higher INOC reduced A. niger doses, increasing CH4 production by 9%v/v compared to literature, with 5–10 d INOC (452.86 NL s/kg VS with WAS, SI = 2:1).