ObjectiveThe production tailwater from water treatment plants (WTPs) primarily includes sludge discharge water from sedimentation tanks and backwash water from filters, accounting from 6% to 10% of the water production capacity of the WTP. By analyzing the water quality characteristics of production tailwater and investigating its direct reuse technologies, this study can provide technical references for the recycling of WTP tailwater, which holds significant practical importance for advancing the construction of a water-saving society.MethodsIn the paper, a pilot-scale plant for the reuse of supernatant from a concentration tank was used to systematically study the water quality characteristics of the supernatant from the concentration tank and the impact of direct reuse of supernatant from the concentration tank (reuse ratio of 3∶1) on the water quality of raw water, sand filter outflow, sedimentation tank sludge discharge, and filter backwash water.ResultsThe turbidity of the supernatant in the concentration tank was less than 6 NTU, significantly lower than the turbidity of the raw water. The ammonia content was from 0.04 mg/L to 0.12 mg/L, almost equivalent to the ammonia content in the raw water. The permanganate index was equivalent to the raw water, and it was lower than 4 mg/L. The total bacterial count fluctuated between 500 CFU/mL and 1 000 CFU/mL, significantly higher than the raw water. The aluminum content was about 10 times higher than that in raw water, and the overall fluctuation was from 0.04 mg/L to 0.12 mg/L. The formation potential of chloroform, dichloroacetic acid and dichloroacetonitrile were slightly lower than that of raw water. After direct reuse of supernatant from the concentration tank to raw water, the turbidity of the raw water and the formation potential of chloroform, dichloroacetic acid and dichloroacetonitrile slightly decreased, the ammonia content did not change significantly, the permanganate index slightly increased, and the aluminum and total bacterial count significantly increased, suggesting that aluminum and total bacterial count were water quality indicators that urgently need to be focused on for the reuse of supernatant from concentration tanks. Based on the continuous operation study of the pilot scale plant, it was found that the direct reuse of the supernatant from the concentration tank had no significant effect on the effluent quality of the carbon sand filter, and the direct reuse of the supernatant from the concentration tank would not lead to the enrichment of aluminum in the sludge water of the sedimentation tank and the backwash water of the carbon sand filter.ConclusionThis paper indicats that the supernatant from the concentration tank can be directly reused in the process of drinking water treatment.