Effects of Thermal Pretreatment and Trace Metal Supplementation on High-Rate Thermophilic Anaerobic Digestion of Municipal Sludge

Abstract

This study involves high-rate thermophilic anaerobic digestion of sewage sludge at 1 days hydraulic retention time by using thermal pretreatment (17°C and 1 h) of the waste-activated sludge portion in influent sludge and trace metal supplementation (.49 mg Ni and .54 mg Co per liter of influent). The thermal pretreatment not only increased destruction of volatile solids (VS) and volatile suspended solids (VSS) by 6 and 9%, respectively, but also much improved dewaterability of the digested sludge. The trace metal supplementation showed limited effect on the overall performance, except for reduced volatile fatty acid concentrations in the digested sludge. The diffusive gradients in thin-films (DGT) technique was applied to estimate bioavailability of the trace metals in digested sludge filtrates. The DGT analysis suggests that 7–88% (96–113 μg/L) of soluble Ni and only 5–1% (.9–2.1 μg/L) of soluble Co were present in a bioavailable form.