Characteristics and recycling effect of solubilized organics derived from drinking water treatment sludge using ultrasound

Ballast flocculation by recycling drinking water treatment sludge (DWTS) is an alternative to traditional coagulation and pretreatment of the membrane-based process. However, the enhancement of organics removal is limited due to the release of organics derived from sludge. This study mainly focused on the characteristics of solubilized organics derived from DWTS exposed to different ultrasound conditions (ultrasound dose of 2.53, 5.10, 7.73, 10.42, and 15.79Wh/L, frequency of 25/40kHz). The effect of solubilized matter in the coagulation process of recycling pre-sonicated DWTS on organics removal was also assessed. The results indicated that protein-like substances (Peaks T-1 and T-2) and humic-like substance (Peak A) occurred in raw DWTS samples. The kinetic model of soluble chemical oxygen demand (SCOD) solubilization was pseudo-linear, and the rate of SCOD released at 40kHz was higher than that at 25kHz, which could be confirmed by the increase in fluorescence intensities of Peaks A, T-1, and T-2 in the supernatant of sonicated DWTS. Additionally, the release velocity of protein-like substances at 40kHz was more rapid than that at 25kHz. The results of recycling trials indicated that solubilized organics could deteriorate the settled water quality, independent of the ultrasound conditions used.