Co-treatment of potassium ferrate and ultrasonication enhances degradability and dewaterability of waste activated sludge

Abstract

The enhancement of the degradability and dewaterability of waste activated sludge (WAS) is important scientific and engineering topics because sludge treatment has strict environmental regulations due to increased urbanization. The impact of three co-treatments (alkali combined with ultrasonication, potassium ferrate (K2FeO4) combined with ultrasonication, and potassium ferrate combined with alkali) on the degradability and dewaterability of sewage sludge and the nutrient release during the co-treatment was investigated. The soluble chemical oxygen demand (SCOD) and disintegration degree (DDSCOD) increased sharply after the co-treatment and the increase in the DDSCOD was almost 40% for the potassium ferrate combined with an ultrasonication treatment after 90 min. The decreased dewaterability observed for the alkaline and potassium ferrate pretreatments was further lowered when combined with ultrasonication based on the increase in the capillary suction time (CST) from 26.4 ± 1.8 s to 1614.1 ± 131 s. The ultrasonication treatment produced a high proportion of colloidal solids (d (0.9) = 6.492) and eluted soluble extracellular polymeric substances (EPS), which are detrimental to the filterability of the WAS. Fe (III) was highly flocculated in the solution and re-coagulated the small particles formed during the ultrasonic crushing process. The evidences regarding the soluble EPS, total organic carbon, total nitrogen, total phosphorus, and volatile suspended solids indicated that the co-treatment of potassium ferrate and ultrasonication was effective for disintegrating WAS, and provided a new way for WAS pretreatment.