Continuous Anaerobic Degradation of Liquid Condensate from Steam-Derived Hydrothermal Carbonization of Sewage Sludge

Hydrothermal carbonization (HTC) at an industrial level most likely will use steam as heating media. Excess steam will yield a condensate rich in water-steam volatile organic compounds. This experimental study investigated the use of HTC condensate as the sole substrate for anaerobic digestion (AD). Process performance at 37 degrees C (mesophilic) and 55 degrees C (thermophilic) was determined with two identical anaerobic filters (26 L each). Both reactors were continuously fed for five weeks at a constant organic loading rate of 0.8 g(COD) L-1 d(-1) After a start-up of 15 days, both reactors yielded up to 0.22 L-CH4,L-STP g(COD)(-1). Increased temperature had slightly negative impacts on phenol removal and COD degradation. Macro- and micronutrients were not found in sufficient concentrations in the HTC condensate and could cause deficiencies during long-term operation. Presumably, co-digestion of the HTC condensate together with its corresponding process liquor could alleviate these problems and therefore seems to be an easy and beneficial solution.