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−3.d−1). The 2D5KG system obtained VS and COD removal of 68% and 72%; SMP of 273 Lmethane.kg.VS−1. The 3D4KG system obtained VS and COD removal of 70 and 66%; SMP of 252 Lmethane.kg.VS−1. 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. [Display omitted] •Proposed technique enabled selection of apposite start-up operational conditions.•Valeric acid predominance in all OLR evaluated in the acidogenic reactor.•Higher OLR improved methane production.•Butyric acid to acetic acid was the main methane production route.•CCA shows the interdependence between the variables apply in the TPAD reactors.