Experimental Study On Treatment Of Secondary Effluent By Hybrid Process Of PAC Four-stage Countercurrent Adsorption And Microfiltration

In previous studies of our group,PAC four-stage countercurrent adsorption-microfiltration hybrid process had been developed to remove the organic pollutants from a reverse osmosis concentration,this hybrid process was used for advanced treatment of the effluent from sewage treatment plant in this research.Decreasing concentration of organics in secondary effluent realized with less dosage of PAC.The dosage of PAC demanded by four-stage countercurrent adsorption was calculated through the jar test and the basic parameters and running conditions were determined.The membrane fouling problem was also be alleviated.The jar test was conducted for describing the adsorption behavior of powdered activated carbon?PAC?on organics in secondary effluent from a municipal wastewater treatment plant.The adsorption behavior characterized by DOC or UV₂₅₄ fitted well with Langmuir adsorption isotherm,with approximate 60 minutes for equilibrium.Based on Langmuir adsorption isotherm,calculation method of PAC four-stage countercurrent adsorption-microfiltration hybrid process for removing organics in secondary effluent was put forward,and it could be used to predict the dosage of PAC and the concentration of organics in treated effluent.The experiment of PAC four-stage countercurrent adsorption-microfiltration hybrid process for removing organics from secondary effluent was designed and it could validate the calculation method.The validation results indicated that when the removal rate of DOC was 50%,the relative error of measured values and calculated value of DOC and UV₂₅₄ in the effluent were 1.7% and 4.9%,respectively.Additionally the dosage of PAC could be saved for treatment of secondary effluent.When the removal rate of DOC was 50%,the dosage of PAC demanded by four-stage countercurrent adsorption was 89.4% and 68.3% of those used in second-stage countercurrent adsorption and single-stage adsorption,respectively.The lab-scale test existed serious membrane fouling phenomenon.When treating 691.2 L/m² of water,membrane specific flux?SF?fell by 79.59% sharply.Based on the analysis of membrane fouling,the main pollution of DOC and hardness was excluded,concentration polarization and filter cake layer resistance was 70.3% of the total membrane resistance.As a consequence,the filter cake layer formed by PAC and suspended solids in the influent was the cause of SF declining rapidly.In order to solve the membrane fouling problem,ferric chloride was used as flocculant.Taking advantage of ferric chloride can make PAC and suspended solids settle more quickly and completely,and the thickness of filter cake layer was reduced.The validation results indicated that when dosing 10 mg/L of ferric chloride and treating 1209.6 L/m² of water,SF fell by 49.90%;When dosing 20 mg/L of ferric chloride and treating 1504.8 L/m² of water,SF fell by 47.02%,SF continued to slow down,the reactor could operate steadily.In addition,it had positive effect to the removal efficiency of organics when dosing ferric chloride,concentration of DOC and UV₂₅₄ in the effluent reduced in different extent.