HIGH-SOLID THERMOPHILIC ANAEROBIC DIGESTION OF SEWAGE SLUDGE AND NITROGEN AND PHOSPHORUS RECOVERY

Abstract

 This study evaluated a laboratory-scale system of high-solid thermophilic sludge anaerobic digestion with nitrogen and phosphorus recovery. Influent sewage sludge was adjusted to 9-10% total solids (TS) by centrifugation. The anaerobic digester used was a completely-mixed reactor of 2.0 L, and was operated at 55℃ and 20 days hydraulic retention time. Ammonia stripping of digested sludge and its return to the digester reduced total ammonia to 1,760 mgN/L in the digester, achieving VS destruction of 57.8% and methane production of 0.321 NL/gVS. Ammonia stripping was performed at 70℃, initial pH of about 9 for 2 hours, and recovered 20.7% of influent nitrogen as ammonia. Adsorption by porous iron hydroxide at pH 4-5 for 24 hours was employed for phosphate adsorption from digested sludge, and recovered 54.6% of influent phosphorus as phosphate. The acidic pH enabled centrifugal dewatering of digested sludge with only a polymer coagulant, showing capillary suction time of 84 sec and water content of 82.0% at the polymer addition of 1.92%TS. Therefore, this study demonstrated the possibility of high-solid thermophilic sludge anaerobic digestion and concomitant nitrogen/phosphorus recovery.