Synergistic effect of electrooxidation and anaerobic digestion of waste-activated sludge for microbial inactivation

Electrochemical pretreatment and anaerobic digestion (AD), as well as a combination of both processes, were studied for the treatment of waste-activated sludge (WAS) to evaluate microbial inactivation, for faecal coliforms, Salmonella spp., bacteriophages, and helminth eggs. Electrooxidation (EO) of WAS was performed in a commercial cell with boron-doped diamond electrodes. 1 L of WAS (3% total solids) was fed to the electrochemical cell in recirculation mode. The conditions tested were 19.3 mA/cm², 30 min, and 3.8 L/min. For AD tests, raw and pretreated WAS were digested in an OxiTop^® OC 110 apparatus for 15 days. Inactivation of faecal coliforms, Salmonella spp., and bacteriophages reached more than 5 logs when EO was combined with AD. In contrast, EO alone did not inactivate these parameters, while AD achieved eliminations around 3 logs. Moreover, the combined process inactivated 91% of the initial viable helminth eggs, considerably higher than AD (29%) and EO (0%). The results suggest that EO separates extracellular polymeric substances and segregates particles, including microorganisms, that are exposed to environmental factors (e.g., volatile fatty acids or ammonia) during AD, showing a synergistic effect.