Study On The Elimination Of OCPs In Micro-polluted Water By Integration Process Of Optimized Enhanced Coagulation-filtration

Organochlorine pesticides(OCPs) are typical persistent organic pollutants with long-term residual, bioaccumulation, high ecological toxicity. Its pollution throughout the global atmosphere, soil, water and organisms was detected. The great river system of our country suffers from the serious pollution, and there exist potential hazards in the drinking water for residents. At present, our country has entered the high incidence of environmental emergency, and the form of sudden accident is very serious to prevent the OCPs pollution emergencies effectively. Therefore, it is very necessary to control and management of OCPs pollution in drinking water, at the same time, it is significance to Provide a plan for dealing with the OCPs emergency and protect the safety of drinking water masses. Now, physical adsorption, chemical oxidation and reduction, biological treatment and radiation degradation are considered the main approaches of the OCPs treatment, but these processing is only suitable for small scale and few amounts of organic pollutants. OCPs is hydrophobic compounds, more easily transferred to the sediments or attached to the surface of the organic and inorganic solid material, which could be considered to remove in micro-polluted water by the method of coagulation and filtration. Under different conditions, the effect and mechanism about the elimination of OCPs in micro-polluted water by enhanced coagulation with polydimethyldiallalammonium chloride(HCA) and anionic polyacrylamide(HPAM) and the helps of modified attapulgite and powder activated carbon was investigated, and the influence of filter material, bed depth and filtration velocity to remove OCPs was analyzed. To achieve maximum removal of OCPs in the raw water, conduct preliminary study on the reinforcing and complementary function of the OCPs removal by the integration process of optimized enhanced coagulation-filtration. The main contents and results of this study mainly include:(1)To examine the mechanism of the turbidity and OCPs removal by coagulation with HCA, an enhanced coagulation test was designed with dosage, the turbidity of raw water, pH, as well as slow stirring time. The results showed that the best dosage of HCA was 0.1mg/L, when other conditions were constant. The removal effect of DDTs was better than HCHs by HCA coagulation. The higher the turbidity of raw water did, the greater the removal rate of OCPs would get, therefore the adsorption precipitation should be the main mechanism of its removal. The neutral water environment was conducive to the removal of turbidity and OCPs, which were 7.5 about the pH value. Too long or too short to slowly stir time was not conducive to the removal of the residual turbidity and OCPs, and the best slowly stir time was 20 min. The optimum flocculation condition to remove OCPs was the maximum probability of colloidal particles collision at the stage of flocculation by the strong "Bridging adsorption action" of HCA.(2)By designing an enhanced HCA coagulation test, the effects of coagulant dosage, pH values, initial turbidity, as well as the slowly stir time on the elimination efficiency of OCPs were determined respectively. The results showed that the removal rates of different OCPs isomers reached 57.00~74.56% with the coagulant dosage of 0.05~0.1 mg/L. The removal rates of turbidity and OCPs were significantly correlated, and the correlation coefficients of DDTs were greater than HCHs. The best pH values for the OCPs elimination was in the range of 5~6. The higher turbidity of raw water was helpful to the removal of OCPs. The best slowly stir time was 20 min. Adsorption precipitation was the main mechanism to remove OCPs by HPAM coagulation.(3)Based on previous research achievements, the effects of flocculant types as well as the addition of powder activated carbon and modified attapulgite on the elimination efficiency of OCPs by enhanced coagulation with HCA and HPAM were analyzed briefly. The modified attapulgite used as assistant coagulants improved the removal of OCPs efficiently, while the improvement was not obvious and spent more money when powder activated carbon was used as the assistant coagulant, therefore the modified attapulgite is more suitable to be used as the assistant coagulant in the enhanced coagulation to remove OCPs compared to the powder activated carbon. Under the optimal dosage, the effect of OCPs removal by HCA coagulation was equivalent to PASS, as well as the effect of HPAM and PFS was second, and PAC effect was the worst.(4)The effect of filter material type, bed depth and velocity affected the filtration on the elimination of OCPs were detected. From those aspects, the mechanism which homogeneous material filtration removed OCPs in micro-polluted water was preliminarily explored. The experimental results showed that the mechanisms with removal of OCPs and turbidity influenced by bed depth on five kinds of filter materials were different. The best bed depth was 80 cm. The increase of filter speed was adverse to the removal of OCPs and turbidity. The removal effects of OCPs on five kinds of filter materials followed the order of Anthracite > Ceramsite >(Zeolite) > Manganese sand > Silica sand, which was correlated well with the order of surface embellish wash sex and matched with reverse order of surface free energy of polarity. The removal of OCPs was influenced collectively by filtration mechanism and the adsorption performance of filter material itself, and the removal efficiency of ∑DDT was better than ∑HCH.(5)Based on the optimization of enhanced coagulation and filtration, the two processing units under the optimum operating conditions were optimization integrated technology and theory. Then the removal efficiency of OCPs by integrated technique was investigated. The experimental results showed that enhanced coagulation and filtration have good effect on removal of OCPs and its heterogeneous homologue. The removal efficiency of ∑HCH and ∑DDT were 76.76 ~98.02% and 94.96~98.02%, respectively and turbidity removal efficiency was 90.25 ~ 99.72%. Anthracite and ceramsite can well remove p,p’-DDE. Compared with strengthening coagulation or filtration separately, strengthening coagulation—filtration optimization and integration can improve the removal rate of OCPs nearly 3~25%, 10 ~ 15%, respectively. Besides, it played significant role on enhancing and complementing and can remove OCPs in micro-polluted water to a large extent. What’s more, the series process can save infrastructure investment cost of water plant and avoid complex and expensive equipment modification.