Enhanced Production of Methane from Waste Activated Sludge by Pretreatment Using a Gas Diffusion Cathode

Anaerobic digestion is an alternative technology for the pretreatment of waste activated sludge (WAS) before final disposal. Hydrolysis is the rate-limiting step in this process; therefore, pretreatment of WAS to allow for high-efficiency anaerobic digestion is beneficial. In the present work, an electrochemical system characterized by a gas diffusion cathode (GDC) was established to facilitate WAS pretreatment. This GDC was composed of a carbon black diffusion layer and a Ni/NiOx catalytic layer. H2O2, an essential component of the pretreatment, was evolved on the electrode surface at a rate of 27.3 mg cm(-2) day(-1). Upon varying the potential of the GDC from 0 to -1.0 V (versus Ag/AgCl), the soluble chemical oxygen demand (SCOD) and the protein and carbohydrate concentrations increased from 134 +/- 6, 38 +/- 6, and 20 +/- 3 mg/L to 3617 +/- 65, 1436 +/- 121, and 470 +/- 64 mg/L, respectively, over 8 h. The ratio of SCOD to the total chemical oxygen demand (TCOD) was 48 1.3%. The total methane output of the GDC pretreated sludge at the end of 10 days was close to 234 mL/g TCOD, which was 33.8% greater than that of the control sludge. The Ni/NiOx-modified GDC also exhibited excellent stability performance. The results of this work demonstrate the pivotal role of the combination of H2O2 and alkali generated by the GDC in the enhanced pretreatment of WAS.