Study On Enhanced Removal Efficiency Of Typical POPs Organochlorine Pesticides In Drinking Source Water

Since the 20th century,humans have used a large number of Persistent Organic Pollutants(POPs).Because of high toxicity,“three causes”(carcinogenic,teratogenic,and mutagenic)effect,hard-to-degrade,long-distance transmission,and accumulation and amplification in animals and humans through the food chain,discharge of POPs leads to serious pollution problems in the global environment.Its pollution has spread to various water bodies around the world,unfortunately,and surface water,which is a source of domestic water,is also polluted.Pollution of drinking water sources will inevitably affect the quality of tap water.In view of the major technical challenges of our country's implementation of the Stockholm Convention and the implementation of mandatory national drinking water standards,it is imperative to carry out research on POPs control technology in drinking water production.Based on the coagulation and filtration processes in the conventional drinking water production process,without changing the existing production process,this thesis studies the enhanced efficiency of enhanced coagulation,deep-bed filtration and micro-flocculation direct filtration processes,and uses the principle to study the theory and technology of POPs pollution control in drinking water sources,which are "composition classification,selection of typical models,discussion of the structure-effect relationship,gradual promotion",gradually forms the technical theory of POPs pollution control in drinking water source water.This is undoubtedly of great significance for ensuring the safety of drinking water for the broad masses of people and responding to POPs pollution emergencies.Intensified coagulation treatment method,using Poly Aluminum Chloride(PAC),Poly Ferric Sulfate(PFS),Poly Dimethyl Diallyl Propyl Ammonium Chloride(PDMDAAC)as flocculants to process the typical POPs in water-Organic Chlorine Pesticides(OCPs).Response Surface Methodology(RSM)was employed to optimize the various factors affecting the removal of OCPs in enhanced coagulation process,such as pH value,turbidity,coagulant dosage and the initial concentration of OCPs.The optimization results show that the interactions of the factors were significant.The best combination of coagulation conditions with PAC and PFS as flocculants for the combined effects of various factors are pH of 5.0,raw water turbidity of 150 NTU,dosage of 12 mg/L,and initial concentration of200 ng/L.The best combination of coagulation conditions using PDMDAAC as the flocculant is: pH of 7.5,raw water turbidity of 300 NTU,dosage of 0.1 mg/L,and initial concentration of300 ng/L.Under the best conditions obtained by model verification experiments,the removal rate of OCPs by PAC can reach 49.5%?80.4%,the removal rate of OCPs by PFS can reach66.72%?82.32%,and the removal rate of OCPs by PDMDAAC can reach 68.8%?82.7%,the measured value is closed to the predicted value of the model,which indicates that the prediction of the model is accurate and effective.The experimental comparison investigated the use of PAC and PDMDAAC,PFS and PDMDAAC as two composite flocculants prepared from raw materials are used to study the removal effect of OCPs and turbidity in high turbidity water.The elimination of turbidity and OCPs in high-turbidity water by enhanced coagulation were studied.The effect of dosage of the composite coagulant,PAC-PDMDAAC ? PFS-PDMDAAC composite ratio,initial turbidity,the time for slow stirring and pH on the elimination efficiencies of turbidity and OCPs were tested and characterized by fractal dimension of flocs and Zeta potentials to verify the result.The results show that PAC-PDMDAAC?PFS-PDMDAAC composite ratio has great influence on the removal effect of OCPs and turbidity.The removal rates of turbidity and OCPs reach the highest values when two composite ratios are 5:1,the dosage of PAC-PDMDAAC?PFS-PDMDAAC are 1mL/L,and the time for slow stirring are 15 min.With the increase of initial turbidity,the removal rate of OCPs in the water also increases.It shows that the two composite flocculants are suitable for the removal of OCPs and turbidity in water.Compared with other coagulants,The PAC-PDMDAAC ? PFS-PDMDAAC composite coagulants have wide pH range suitable for use.Polysilicate aluminium sulphate(PASS)flocculant was prepared by sodiumsilicate and aluminum sulphate.The elimination of OCPs by coagulation with PASS was studied.The effects of the dosage of coagulant,pH values,initial turbidity as well as modified attapulgite coagulant aid on the elimination efficiency of OCPs were determined.The result showed that under the dosage of 5 mg/L PASS,the removal rates of OCPs and turbidity reached 57% ? 87% and 99.1%,respectively,much higher compared with PAC.The best range of pH values was 6 ? 7 for OCPs elimination.The removal rates of OCPs were relevant to the turbidity,and increased with the increasing in initial turbidity.Modified attapulgite and powder activated carbon used as assistant coagulants significantly enhanced the coagulation,with the removal rates of OCPs of78% ? 100% by powder activated carbon and 72% ? 95% by modified attapulgite,respectively.As attapulgite is abundant,cheap and easy to acquire,it is more suitable to be used as the assistant coagulant compared to powder activated carbon.The comparative test of deep bed filtration found that the depth of the filter bed has different effects on the removal of OCPs and turbidity of the four filter media.The order of HCH and DDT removal efficiency of the four filter media is: anthracite > zeolite >manganese sand > quartz sand,which is consistent with the order of surface wettability,but is opposite to the change of the polar component of the surface free energy.The removal rate of turbidity and OCPs of the four filter media increases firstly and then decreases with the increase of filtration rate.The best filtration rate is 10 m/h;zeolite has little influence on OCPs removal rate due to its surface properties,and the change is not obvious;the removal rate of OCPs by anthracite generally decreases slowly with the increase of filtration rate,and the residual turbidity gradually increases.When the same filter material has different particle sizes,the removal rate of OCPs is not much different,and there is no obvious rule between the OCPs removal rate and the particle size of the filter media.The fine particle filter bed mainly plays a role of retention to remove suspended colloidal particles,and the coarse particle filter bed mainly plays a role of adsorption to remove suspended colloidal particles.The removal of suspended colloidal particles and OCPs is not only affected by the adsorption and retention of the filter material,but also has an important relationship with the surface properties of the filter material and the properties of OCPs.Select PAC,PDMDAAC,PAC-PDMDAAC as flocculants,and use quartz sand fine and coarse particle size filters to conduct parallel experiments to optimize and determine the flocculant dosage,raw water turbidity,effluent turbidity filtration rate,bed depth and other influencing parameters,discuss the removal efficiency of OCPs in water by micro-flocculation direct filtration process under optimal conditions.The results show that when the inorganic coagulant PAC is used as the flocculant,it is advisable to use the fine particle size quartz sand filter bed to filter at low speed,and the turbidity and OCPs removal effect is the best at this time.When PDMDAAC is used as a flocculant,the best choice for direct filtration is to perform low-speed filtration on a coarse particle size quartz sand filter bed,which not only ensures the quality of the effluent,but also prolongs the filtration cycle and maximizes the efficiency of the filter bed.Under the conditions of plateau water turbidity and high filtration rate,it is not suitable to add PAC-PDMDAAC.This paper has completed the research on the removal efficiency and mechanism of various enhanced processes on OCPs in drinking water source water.The optimal treatment parameters and conditions of different enhanced processes have been determined through experiments,the research results can provide reference and support for the operation of urban drinking water plants.