Anaerobic degradation of digestate based hydrothermal carbonization products in a continuous hybrid fixed bed anaerobic filter

This study investigates the suitability of continuous hybrid fixed bed anaerobic filter reactor for treating sewage and agro-industrial digestate hydrothermal carbonization (HTC) products; hydrochar and HTC liquor (HTCL). The reactor was operated for 300 days under mesophilic conditions at different organic loading rates (OLR); maximum OLRs of 7.4 and 10 gCOD/L/d were reached while treating HTC liquor and slurry, respectively. 15 g/L hydrochar were added to the reactor as a supplement while treating HTCL solely thus increasing the biogas production up to 153%. The reactor was fed with HTCL and hydrochar with an increasing mixing ratio, and the co-digestion impact was dependent on hydrochar concentrations. The results of the study indicate that the hybrid fixed bed anaerobic filter reactor is a promising anaerobic digestion configuration for treating HTCL and overcoming the HTC upscaling challenges, and the suitability of digestate hydrochar utilization as supplement material for anaerobic digestion.