Effect of ultrasonic pretreatment subsequent anaerobic co-digestion on naphthalene and pyrene removal

The effect of ultrasonic pretreatment of waste activated sludge (WAS) before being fed to the anaerobic digestion and anaerobic co-digestion with wine distillery wastewater (WDW) under thermophilic conditions were investigated. Results showed that ultrasonically assisted disintegration significantly increased the amount of soluble chemical oxygen demand (SCOD), total soluble nitrogen (TSN), total soluble phosphorous (TSP), whereas viscosity of WAS decreased with increasing of specific energy input on WAS. During the ultrasonic pretreatment of WAS, total solids (TS), volatile solid (VS) and VS/TS were almost maintained constant based on mathematics statistic analysis. At the OLR of 1.384kgVS/m(3).d for anaerobic digestion on WAS alone, the daily biogas yield was 1.411, the removal rate of TS,VS,COD, naphthalene and pyrene are 19.1%, 29.6%, 35.3%, 27.3% and 15.4%, respectively. While at the OLR of 1.79 kgVS/m(3).d, anaerobic co-digestion on sonicated. WAS by adding 25% of WDW (in volume), the daily biogas yield was 5.21, and the removal rate of TS,VS,COD, naphthalene and pyrene were 40.3%, 55.8%, 57.5%, 39.5%, and 13.5%, respectively. The removal rates of naphthalene in co-digestion on WAS or sonicated WAS are more than that of digestion on WAS alone. But the removal rates of pyrene in co-digestion on WAS or sonicated WAS are less than that of digestion on WAS alone. Hence, it is benefit to enhance removal rate of naphthalene by ultrasound pretreatment or co-digestion but not to pyrene.