The Research About Coagulation+Sand Filter/Activated Carbon Process For Depth Treatment Of Wastewater Treatment Plant Tailwater

Water pollution and the shortage of water resources make it urgent to study tailracefurther treatment and reuse. After biological sewage treatment, tiny floating particles areusually small and in low concentrations, and mostly are insoluble biodegradable organicpollutants. To cope with the problems of low filtering with large space in the currenttailrace further treatment, the paper suggests a combined technique by sand filter/activatedcarbon and investigates the effect.The following aspects were studied in this paper:(1) Study on the conditions of coagulation:The effects of the optimal dosage, the best raw water pH, the hydraulic condition andstanding time on coagulation effect using PAC as a coagulant were studied. The resultsshowed that suitable conditions were: the dosage was50mg/L, initial pH was6~7. Thethree hydraulic conditions were300r/mins、1mins，170r/mins、3mins，70r/mins、5minswith50mins depositing time.(2) Experiment on sand filter/activated carbon technique: indicators (turbidity,COD, nitrogen, total phosphorus, dissolved organic matter DOM, UV254, UV410, TOC) andthree-dimensional fluorescence spectra were analyzed. The results showed that thecombined process of turbidity, COD, DOM (to SMP for example), TP, UV254, UV410andTOC removal rates were98.58%,82.34%,68.73%,85.76%,88.68%,90.13%,81.25%respectively,35.73%for ammonia and32.78%for TN.Coagulation sedimentation was good and stable to remove colloidal particles due toits hydrolysis Polymerization aluminum chloride (PAC) between the colloidal particles andthe electric double layer compression adsorption charge neutralization, adsorption bridgingand four volumes sweep coagulation. In addition, chemical phosphorus removal ofphosphorus in water may occur with PAC related reactions, resulting in high phosphorusremoval after coagulation and sedimentation. Besides mechanical filtration, sand filtrationalso had sticking effect on floating particles and filtration material, mainly removingcolloid particles, with little effect on the removal of soluble pollutants. Granular activatedcarbon had absorbing effect which could remove more dissolved organic matter, UV254,TDP and ammonia in water.This paper provides valuable experimental and theoretical basis for further pollutant treatment in tailrace by sand filter/activated carbon technique.