Sonication and electrooxidation for municipal wastewater primary sewage sludge stabilization

During wastewater treatment (WT), sewage sludge (SS) is produced containing organic matter and pathogenic microorganisms that represent health risks so it must be stabilised. Several authors have reported secondary SS (sludge from the bioreactor for WT) stabilisation for its use in soil as fertiliser, but to date primary SS (sludge from primary settler or chemical precipitation tank in WT) is not exploited. In this study, we applied sonication and electrooxidation on primary SS in order to reduce the concentrations of total coliforms, fecal coliforms (FC), and chemical oxygen demand (COD). Here, we show that sonication, compared with electrooxidation, decreases twice as much FC in wastewater SS, and the process is influenced by the interaction of time and applied pH. Also, the interaction of pH and the current intensity influence the decrease of FC and COD in the treated primary SS by electrooxidation. Our results demonstrate that the application of sonication with pH 5 for 10 minutes decreases the concentration of FC by 31% in the primary sludge, compared to untreated sludge. It is necessary to apply complementary treatments in order to further reduce the concentrations of pathogenic microorganisms.