Anaerobic digestion of organic fraction from municipal solid waste with methano production as objective: acidification phase control with no chemicals

Urban solid waste (USW) contains a significant proportion of organic matter, represented by the Organic Fraction of Municipal Solid Waste (OFMSW), quantified as Volatile Solids/Total Solids (VS/TS). This organic fraction can be leveraged for energy production. This study proposes an innovative approach to controlling the FOS/TAC ratio (FOS: Volatile Organic Acids (VOAs, C2-C6); TAC: Total Alkaline Carbonate) in anaerobic digestion using a Continuously Stirred Tank Reactor (CSTR). Instead of adding external alkalizing agents, the method relies on feed interruptions to promote self-recovery of buffering compounds. The process was analyzed by correlating the FOS/TAC ratio, volatile organic acids (VOA) levels, and biogas and methane production. Experiments utilized organic loading rates (OLR) of 0.5, 1.0, and 1.5 g VS L^-1 d^-1, with the latter yielding a VS removal efficiency of 68-91%, methane content of 50-75%, and acid accumulation. The FOS/TAC ratio ranged from 0.5 to 2.0, with acetic and propionic acid concentrations reaching 7,422 mg L^-1 and 4,596 mg L^-1, respectively. The process was halted when biogas production stabilized at 0.06 L biogas L^-1 reactor d^-1, with methane content at 50%. The results demonstrate that anaerobic digestion of OFMSW is a viable treatment strategy at OLRs up to 1.5 g VS L^-1 d^-1, achieving efficient biogas production without the need for chemical additives.<b>HIGHLIGHTS</b>The alkalinity increased, represented by FOS/TAC ratio, was positivity influenced by methane gas concentration.Programmed stops were the key-tool used to get a no acidification reator during the experimental time.The OLR of 1.5 g SV Kg^-1 d^-1 was the limited the charge where the reator was capable to recovery of acidification started, only with the programmed stop.It was possible to remain in stable condition for the reactor for 52 days, with the FOS/TAC ratio in 0.6 and OLR in 1.5 g SV Kg^-1 d^-1.