High solid temperature phased anaerobic digestion from agricultural wastes: Putting several reactors in sequence

•Temperature phased anaerobic digestion was tested with manure and silage as feedstock.•Stable operation was obtained at 19days HRT without recycling nor external inoculation.•Optimal temperatures were 65°C (hydrolytic stage) and 55°C (methanogenic stage).•HRT in the hydrolytic stage can be reduced to 2days. High solid anaerobic digestion of agricultural wastes (manure and grass silage) was tested on temperature phased anaerobic digester (TPAD) at lab-scale. A 4days hyperthermophilic hydrolysis was followed by a 15days methanogenesis. The TPAD was divided into 4 or 5 tanks in series without recycling: 2 sectors for hydrolysis (2days HRT each) and 2 or 3 sectors for methanogenesis (5+10 or 3×5days HRT). Two different combinations of temperatures (65°C–37°C, 65°C–55°C) were investigated to assess the process efficiency. For all tested conditions, the TPAD operated steadily with a methane productivity of 235+/−3 mLCH4STPgVS−1. Using four or five reactors in series enabled to identify that during the two first days of hydrolysis, the hydrolysis yield and acidification yield were much higher (22% and 13%, respectively) than during the next two days (2% and 2% respectively). Moreover, concerning methanogenesis it appeared that the retention time may be shortened by 5days with little loss in methane production (11%). In the methanogenic sectors, the uptake of volatile fatty acids and the methane production were higher at 55°C than 37°C. The results suggest that the hydrolytic sector could be limited at 2days HRT, while the methanogenic sector would support a 10days HRT with the feedstocks used.