Study On Removal Of Organic Matter From Recirculating Cooling Drainage From Thermal Power Plant

In this paper,the recirculating cooling drainage of a thermal power plant in Tianjin was taken as the research object,and the removal of organic matter was studied by the various processes.Finally powdered activated carbon(PAC)four-stage countercurrent adsorption-microfiltration process was studied extensively,and the problems appeared during the experiments were explained.Chemical oxygen demand(COD)in three sources of wastewater discharged from the plant was high,and had to be treated before discharge.Among them,the COD of the recirculating cooling drainage was highest,which was the main source of organic pollution,and it was determined that the recirculating cooling drainage was used as the object of removal of organic matter in the thermal power plant.Through the preliminary studies,COD inhibitors and Fenton reagent oxidation process were not suitable for the removal of organic matter from recirculating cooling drainage,otherwise in the previous study,the PAC four-stage countercurrent adsorption-microfiltration process was stable and the removal efficience was high.Therefore,the PAC four-stage countercurrent adsorption-microfiltration process was determined to be used in the removal of organic matter.In the jar test,the adsorption of organic matter in recirculating cooling drainage was characterized by NPOC.The adsorption process was in accordance with the pseudo-second order kinetic model and the adsorption thermodynamics was in accordance with the Freundlich adsorption isotherm,and the adsorption equilibrium time was within 60 minutes.According to the adsorption isothermal and the cumulative adsorption principle,the calculation method in the four-stage countercurrent adsorption-microfiltration process was set up.In the lab-scale test,when the calculated removal rate of NPOC was set at about 50%,the experimental removal rate was about 44%,and the relative error with the calculated value was 12%.The calculation method with a larger error was found in the relationship between organic matter concentration and PAC dosage.There were some differences between the calculated and measured values in the study,and a lab-scale test of a large dosage of PAC was designed to explain the reason.When the dosage of PAC was 0.90g/L,the experimental removal rate and calculated one were respectively 50.6% and 80.8%,and the relative error was 37.4%.The reason was that the adsorption isotherm constants were different and could not satisfy the hypothesis in the adsorption isothermal constants.Secondly,the adsorption of organic matter in the wastewater existed a limit.With the increase of the dosage of PAC,the increase of removal rate was not obvious,resulting in the greater relative error.At the same time,membrane fouling phenomenon was more in the experiment.The reason to lead to membrane fouling may be PAC dosed and suspended solids in the wastewater.Taking the way of reducing the membrane flux and increasing the ratio of gas to water,the membrane specific flux(SF)decreased from 74.9% to 59.2% when the same amount of water was treated,and the membrane fouling was slowed down to a certain extent.Also these measures made the membrane specific flux more stable.