Effect of Continuous Direct Recycling of Combined Residual Streams on Water Quality at the Pilot Scale in Different Seasons.

The overall objective of this study is to conduct pilot-scale experiments to examine the effects of the direct continuous recycling of combined residual streams (CRS) of clarifier sludge (CS) and filter backwash water (FBWW) on effluent quality in summer and winter. Specifically, the parameters of sedimentation and filtration effluent quality such as turbidity, color, organic matter [e.g., dissolved organic carbon (DOC) and total organic carbon (TOC)], ultraviolet absorbance at 254 nm (UV254), Trihalomethane formation potentials (THMFPs), and metallic elements (e.g., Fe, Al, and Mn) were measured. The experimental results indicate that the continuous direct recycling of the CRS is a feasible method for not only reducing the required coagulant dosage but also improving the contaminant removal efficiency. The coagulant usage was reduced by up to 33.33% at 20°C and 25.00% at 4°C compared to control trials. Over the entire operation period, there was no significant accumulation of contaminants. The temperature exerted a significant impact on the required coagulant dosage and treatment efficiency. Additionally, this study proposes that the continuous operation periods are at the range of 10 to 12 days. [ABSTRACT FROM AUTHOR]

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