Anaerobic Digestion and Dewatering of Biological Trickling Filter Sludge

Abstract

This study investigated digestibility of biological trickling filter (BTF) sludge (in terms of the mass and volume reduction of the sludge) and the effect of anaerobic digestion on sludge dewatering. Nine 20-L anaerobic digesters fed with BTF sludge were set up in a dark constant-temperature room at 20°C and operated for 6 months. The anaerobic digesters removed ∼33% of volatile solids (VS) after 3 months of operation, and a further ∼19% after 6 months of operation (total VS removal = 52%). The average methane production of the digesters was 0.17 m3/kg VSadded, which is within the range of literature values for mesophilic (or thermophilic) sludge digestion (0.15–0.25 m3/kg VSadded). Anaerobic digestion substantially improved dewaterability of the BTF sludge, with ∼3–5 times lower specific resistance to drainage (SRD, a parameter describing sludge dewaterability) than fresh or 1-day anaerobically stored BTF sludges. Moreover, the improved SRDs achieved by anaerobic digestion resulted in a decrease in drainage time from ∼4 and 7 h required for fresh and anaerobically stored BTF sludges, respectively, to less than 3 h. These results suggest that the anaerobic digestion could greatly reduce the size of subsequent sludge dewatering and disposal systems such as centrifugation or sludge treatment reed beds.