Experimental Research On Compound Enhanced Coagulation For Treatment Of Micro-polluted Raw Water

In this study, the micro-sand, enhanced coagulation process is used in the treatment of the micro-polluted reservoir water. This paper is studied on the effect of the factors to the coagulation, which includes the coagulant type, coagulant dosage, temperature and pH optimizes the combination of micro-sand, coagulant and coagulant aid.The best coagulant is presented by the beaker test. The PAFC is better than the FeCl3 and Al2(SO4)3. The best dosage of FeCl3 and Al2 (SO4)3 are 80mg/L, while the optimal dosage of PAFC is 50mg/L.When FeCl3 is added, the removal rate of the CODMn and UV254 are respectively 63% and 37%, to the Al2(SO4)3, the removal rate of the CODMn and UV254 are respectively 52.6% and 25.8%, and to the PAFC, the removal rate of the CODMn and UV254 are respectively 62% and 33%. The removal rate on organic of PAFC and FeCl3 are higher than Al2(SO4)3. PAFC is more efficient and more economical coagulant.The pH has a great influence on coagulation effect. When the pH range from 2.0 to 6.5, with the increase of pH, the removal rate of turbidity, CODMn, and UV254 gradually increases, while the pH to a certain extent, the removal rate is essentially the same, this time to increase pH, the removal rate has gradually been decreased. The best pH value of PAFC is 6.5～8.0.The temperature has a major impact on coagulation effect. In between 0℃and 20℃, with the temperature gradually increased,the coagulation effect is better and better. Does not change the raw water pH, add 50mg/L PAFC, and adjust the water temperature to 4℃, the removal rate of turbidity and CODMn are 33%; when the water temperature is 20℃, the removal rate of turbidity and CODMn are respectively 91% and 62%.Compared with 4℃, the removal rate of turbidity and CODMn have been respectively increased by 58% and 29%.PAM+PAFC experimental results show that:Room temperature (20℃), compared a single dosage of PAFC, adding PAM can make the coagulation effect significantly improved. When 50mg/LPAFC+0.6 mg/L PAM are added, the removal rate of CODMn and UV254 are respectively 70% and 45%, when compared with single dosing PAFC, the removal rate have been respectively increased by 8% and 12%. Adding PAM does not improve the turbidity removal rate, but the floc's formation speed and settling time are significantly reduced. When adjust the water temperature to 4℃and adding 50mg/L+0.8 mg/L PAM, the removal rate of CODMn and UV254 are 39% and 20%, compared to 20℃, the removal rate have been decreased by 31% and 25%. The effluent turbidity degree is 5.5NTU, compared to 20℃, the water turbidity has been increased by 4.8NTU.Micro-sand+PAM+PAFC test results show that:When the water temperature is about 4℃, adding micro-sand is better than conventional coagulation (PAFC+PAM).Adding micro-sand has greatly improved the coagulation effect, especially in the turbidity removal. When 50mg/L PAFC+0.6mg/L PAM+0.8 g/L micro-sand whose sizes are 40～60um are added, the removal rate of CODMn and UV254 are 50% and 32%, compared to single adding PAFC+PAM, the removal rate have been increased by 11% and 12%. The effluent turbidity is 1.6NTU which has reduced by 3.9NTU.To PAFC dosage, PAM dosage, micro-sand dosage, size of micro-sand as factors, do orthogonal tests whose results show that:the factors which affect the coagulation whose order of importance is size of micro-sand, PAFC dosage, micro-sand dosage, PAM dosage, and the best combination of coagulation which are 50mg/L PAFC,0.6mg/L PAM, 1.0g/L micro-sand, size of 40～60μm.Micro-sand continuity coagulation tests results show that:adding micro-sand make the effect of coagulation greatly improved, especially in the removal of turbidity. For low temperature and turbidity micro-polluted reservoir water, when 40mg/L PAFC+0.4 mg/L PAM+0.8 g/L micro-sand are added, the removal rate of CODMn and UV254 are respectively 51% and 30%, compared with without adding the micro-sand, the removal rate have been respectively increased by 13% and 10%. The turbidity of effluent is1.0NTU, compared to adding PAFC+PAM only, turbidity has been reduced by3.8NTU. Compared with the beaker experiment, the effect of coagulation is worse, and the best dosage of PAFC, PAM and micro-sand are not all equal.Flow Control tests results show that:when the flow is during the 1 m3/h～3 m3/h,with the flow increased, the removal rate of turbidity and organic increase slowly at first, when the flow to a certain value, increasing the flow again can make the removal rate slightly decreased, but the overall change little. When the flow is 2.5 m3/h, the effect of coagulation reach the best.Micro-sand Enhanced Coagulation can largely remove the organic pollutants of the water which especially can greatly reduce the turbidity at low temperature. It is a high efficiency, economy process that is easy to operate. The technology provides a reference for the treatment of low temperature and micro-polluted raw water.