Treatment Of Secondary Effluent Organic Matter From Sewage Treatment Plants Using The Combination Of Coagulation And Ozonation

Due to the increasing shortage of water resources,urban sewage reuse has gradually gained attention,the demand for reclaimed water is increasing,and the requirements for the quality of reclaimed water are also improving.The conventional coagulation and filtration process can not meet the ecological security requirements of reclaimed water,so an oxidation process can be used to reduce the problems caused by micropollutants in water.Coagulation is often used as a pretreatment process due to its low cost and capacity on organic matter removal.In the present study,the combination of coagulation and ozonation process was applied to treat the effluent of oxidation ditch（OD）and membrane bioreactor（MBR）,and the organic matter removal and reaction mechanism were studied.The effects of the types and dose of coagulants,hydraulic conditions,pH,temperature and polyacrylamide（PAM）on the organic matter removal in water were investigated.The best removal efficiency on organic matter was obtained at initial pH 5for ferric chloride coagulant.When the dose was 0.1 mM,the TOC removal efficiency of secondary effluent from OD was 51.7%,which was higher than that from MBR（43.7%）.After coagulation,the Ultaviolet-Vis（UV）absorbance of the two secondary effluents decreased slightly in the range of 185-400 nm.The results of fluorescence excitation-emission matrix spectra（EEM）revealed that the organic components in the two secondary effluents were mainly aromatic proteins,soluble microbial products（SMP）and fulvic acid-like,and a small amount of humic acid-like.The content of SMP in OD secondary effluent was higher than that of MBR secondary effluent.Since coagulation may change the properties of the effluent and affect the process of ozonation,ozonation directly and ozonation after coagulation were applied to treat the secondary effluent from sewage plant separately.The effects of ozone dose,pH and temperature on the oxidation process and the organic matter removal in secondary effluent from sewage treatment plant were studied by ozonation process.At pH=7,scavenging capacities of water matrix in OD and MBR secondary effluent were 1.35×10⁵ and1.23×10⁵ s^-1,respectively.Under the same ozone dose,the O₃ exposure in OD effluent was lower than MBR effluent.O₃ exposure,^·OH exposure and^·OH yields in both effluent increased with the increase of ozone dose.The increase of pH will lead to the decrease of O₃ exposure,while the^·OH exposure will increase first and then decrease,and the removal efficiency of UV₂₅₄ is consistent with the^·OH exposure.The higher the temperature,the lower the ozone exposure,the higher the^·OH exposure,and the higher the removal efficiency of organic matter.The results of UV spectra revealed that with the increase of ozone,the absorbance at all wavelengths decreased,and the absorption peaks was blue-shifted.The reaction between ozone and fulvic acid-like or humic acid-like is faster than that of aromatic protein or soluble microbial products,so these two types of organics could be remoced effectively.The effects of ozone dose,pH and temperature on the oxidation process and the removal of organic matter in the secondary effluent from sewage plant were investigated by coagulate and ozonation process.Scavenging capacities of water matrix in the effluent after coagulation were lower than that in the secondary effluent water.Under the same ozone dose,the ozone exposure and^·OH exposure in the effluent after coagulation was much lower than the exposure in the secondary effluent water which was ozonation directly.The effect of pH and temperature on the oxidation process is as same as that of ozonation directly.In addition,the soluble microbial products in the coagulated MBR effluent are removed by ozone faster than the coagulated OD effluent.