Study On Electric Flocculation Strengthening Immersed Ultrafiltrationcellar Water

In the rural regions of China, especially in some underdeveloped areas, surface drinkingwater sources are contaminated; With the constraints of economic，technical and managementlevel in rural areas, there is a big security risk in the water supply, especially the decentralizedwater supply and the water quality is difficult to achieve the targets of existing drinking waterstandards. In this topic, the combined process of ultrafiltration and electro-coagulation wasused to treat the collecting rain water which was the research object.Experiments of this paper includes three parts:①separate ultrafiltration experiments.Thefiltration of pure water determines the initial membrane flux; Every cycle the turbidity，NH3-N,CODMn, TP, UV254of the mixing filtered water were measured and the average of theremoval rate was obtained. The length of10min backwash was operated after one cycle(100min) and then the changes of membrane flux in multiple cycles were investigated.②Thecombination process of two-dimensional electro-coagulation with ultrafiltration was used totreat the collecting rain water, then the removal and its influencing factors of the turbidity,NH3-N, CODMn, TP, UV254were studied; The of the combined process of two-dimensionalelectro-coagulation with ultrafiltration and the separate ultrafiltration process were compared,and the influence of electro-coagulation to the transmembrane pressure was studied.③Thecombination process of multi-dimensional electro-coagulation with ultrafiltration was used totreat the collecting rain water and the activated carbon was used to act as the workingelectrodes after adsorption saturation and drying. The influence of the amount of workingelectrodes to the water treatment was investigated and the energy consumption of thetwo-dimensional multi-dimensional electrode reaction were compared in the same watertreatment effect.The experimental results showed that:①In the separate ultrafiltration process, due tothe good solid-liquid separation effect of ultrafiltration,water turbidity reached existingdrinking water standards and the removal rate was up to94.71%.But the removing effect ofNH3-N, CODMn, TP, UV254was so bad that water quality could not reach the standards;Inthe pure water filtration process, the transmembrane pressure stabilized at0.017MPa, theoriginal flux of9.422L/(h㎡); In the raw water filtration process, due to the continuousblockage of membrane pore, transmembrane pressure increased gradually. After one cycle(100min), the transmembrane pressure,which increased20.6%, increased from the original0.017Mpa to0.0205Mpa.After four cycles, due to the irreversible contamination which wasonly backwashed could not be restored, transmembrane pressure returned to0.018Mpa with10min backwash which was slightly higher than the initial transmembrane pressure.②Theremoval of turbidity, CODMnand UV254by the combination of two-dimensionalelectro-coagulation with ultrafiltration depended on the high adsorption activity flocculant (such as hydroxide and aluminum coagulant complex ions) which was generated from theelectro-coagulation process.Then the floc was removed by the interception of ultrafiltrationmembrane; The removal of NH3-N by the combination of two-dimensionalelectro-coagulation with ultrafiltration based mainly on electric adsorption and the role of Cl-indirect electro-oxidation. The removal of TP depended mainly on Al3+and PO43-which wasgenerated from the electrolysis reacted to form insoluble AlPO4produced by electrolysis. Inthe combination process of two-dimensional electro-coagulation with ultrafiltration, whenthe plate distance was10mm and the current density was18.51A/m2and electrocoagulationtime was15min, the removal rates of turbidity,NH3-N, CODMn,TP, UV254were95.91%,47.00%,54.14%,90.1%,33.5%. In addition to turbidity, the removal rates of NH3-N、CODMn, TP, UV254were increased by34.73%,46.42,80.38%,14.65%thanultrafiltration.Two-dimensional electrode flocculation had obvious effect on ultrafiltrationso that water quality meet the drinking water standards. When the flux was stable at9.422L/(h m2) and the water temperature was stable at21~25℃, the transmembrane pressureupward trend of the former was relatively slow, the transmembrane pressure restored to itsoriginal value after the backwash. Electro-coagulation delayed the clogging of ultrafiltrationmembrane and extended its working time.③The removal principle of the combinationprocess of multi-dimensional electro-coagulation with ultrafiltration was as same as Thecombination process of two-dimensional electro-coagulation with ultrafiltration. The dosageof activated carbon, which act as the working electrode, affected the efficiency of themulti-dimensional electrode flocculation directly. Within limits, the more dosage ofactivated carbon were additioned, the better water quality would have. When theexperimental conditions of multi-dimensional electro-coagulation was as below: currentdensity was12.34A/m2, hydraulic retention time was15min,the plate distance was10mm,the dosage of activated carbon was50mg/L, the removal rates of turbidity, NH3-N, CODMn,TP, UV254were95.70%,48.20%,56.75%,89.90%,34.46%. Under the same experimentalconditions, the removal effect of turbidity, ammonia, CODMn, TP, UV254by the combinationprocess of multi-dimensional electro-coagulation with ultrafiltration with the current densityof12.34A/m2was equivalent to the combination process of two-dimensionalelectro-coagulation with ultrafiltration with the current density of18.51A/m2. Due to thecomparation of calculated parameters in the energy equation, the multi-dimensionalelectro-coagulation saved more energy than the two-dimensional electro-coagulation.