Start-up phase optimization of two-phase anaerobic digestion of food waste: Effects of organic loading rate and hydraulic retention time.

The effects of organic loading rate (OLR) and hydraulic retention time (HRT) on the dynamics of acidogenic and methanogenic processes in two-phase anaerobic digestion (TPAD) of food waste (FW) were investigated to determine the start-up operational conditions. Seven arrangements of TPAD systems under mesophilic conditions were evaluated, each containing one acidogenic reactor and one methanogenic reactor. The work analyzed two HRTs (2 and 3 days) and four OLRs (2, 3, 4 and 5 kgVS.m.d). The 2D5KG system obtained VS and COD removal of 68% and 72%; SMP of 273 L.kg.VS. The 3D4KG system obtained VS and COD removal of 70 and 66%; SMP of 252 L.kg.VS. Valeric acid predominated in the acidogenic reactor in both HRT and OLR evaluated, followed by butyric acid. In the methanogenic reactor, the main methane production route was the butyric acid conversion into acetic acid and finally methane. Higher OLR benefits the methane production. The microbiological profile indicated the pathway of methanogenesis by acetoclastic methanogenesis. The canonical correlation analysis allowed to verify that the groups are independent and, therefore, the variables analyzed in the acidogenic reactor have an influence on the methanogenic reactor.