Feasibility Study on Combined Recirculation of Production Wastewater at Water Treatment Plants

This study investigates the feasibility of reusing production wastewater from drinking water treatment plants through combined recirculation of sedimentation sludge water (SSW) and filter backwash water (FBW). Jar tests and response surface methodology (RSM) were employed to optimize the recirculation point, coagulant dosage, and recirculation ratio. Single-factor experiments revealed that direct recirculation of SSW and FBW at 4%-6% achieved optimal turbidity removal, while recirculation of their supernatants (SSS and FBS) at 4% was more effective for UV₂₅₄ removal. RSM optimization indicated that the recirculation ratio was the dominant factor influencing pollutant removal. Under optimal conditions (predosage recirculation, PACl dosage of 16.84 mg/L, recirculation ratio of 5.38%), turbidity and UV₂₅₄ removal rates reached 94.69% and 63.87%, respectively. Notably, combined recirculation of SSS and FBS further enhanced UV₂₅₄ removal to 70.05%. The combined recirculation process also reduced coagulant consumption by 15%-20% while maintaining effluent quality. Under laboratory conditions, this study demonstrates the technical feasibility and potential energy-saving benefits of the proposed strategy for wastewater reuse, pending pilot-scale validation.