Temperature-phased enhanced the single-stage anaerobic co-digestion of sewage sludge, wine vinasse and poultry manure: Perspetives for the circular economy

The effect of hydraulic retention time (HRT) on single-stage (mesophilic and thermophilic range) and temperature-phase anaerobic co-digestion processes (TPAD) of sewage sludge, wine vinasse, poultry manure was studied. The HRTs studied were 20, 15, 13 and 10 days for the single-stage and TPAD process. For the TPAD with an HRT of 20 days, 65 % of total chemical oxygen demand (TCOD) were removed, which was higher than the single-stage process (26 % and 17 % TCOD removal, respectively for the thermophilic and mesophilic phases). Regarding the volatile solids (VS) removal, TPAD process presented a higher efficiency (90 %) when compared with the thermophilic (41 %) and mesophilic (43 %) single-stage digesters. At an HRT of 13 days 155 mLCH4/ gVSadded (thermophilic), 260 mLCH4/gVSadded (mesophilic), and 202 mLCH4/gVSadded (TPAD) were obtained. The maximum methane yield was achieved for the TPAD process operated at an HRT of 20 days (320 mLCH4/ gVSadded) with the additional benefit of obtaining hydrogen in the first stage (40.41 mLH2/gVSadded). The digestate obtained from the TPAD process were classified as class A biosolids, and could be used for agriculture fertilizer. In conclusion, TPAD waste management process presented better operational performance and methane yield when compared to a single-stage conventional system, direcly contributing for the framework of a circular economy transition of the agri-food industry.