Advanced Biosolids Treatment Using H2O2-Oxidation

Abstract

Municipal and industrial wastewater treatment plants produce large amounts of sludge, mostly mechanically dewatered to approx. 25% DS and containing organic and mineral components. This sludge needs to be evacuated. Possible reductions of the amount of sludge produced are, hence, important. This paper describes the experimental results of peroxidation of thickened sludge (6% DS content). It can be concluded that peroxidation is efficient in reducing the residual sludge amounts. The optimum conditions correspond with adding 0.037 g H₂O₂/100 mL sludge at pH = 3 and in the presence of Fe²⁺ ions (1 mg Fe²⁺/100 mL sludge). Under these conditions, the rate of mechanical dewatering is significantly improved, and the amount of DS to be dewatered is reduced to approx. 80% of the initial untreated amount. Peroxidation preferentially releases ODS into the water phase. The slightly increased BOD/COD ratio converts this water phase into a more biodegradable and accessible carbon source for nitrification/denitrification. Heavy metals are also released in the water phase, and can be subsequently precipitated, thus reducing the residual heavy metal concentration in the residual DS.