Study On Enhanced Coagulation Effect And Floc Performance Of Low Temperature And Low Turbidity Micro-polluted Water

The problem of low temperature and turbid water is difficult to deal with in winter in water plants in northern China.When the traditional coagulation process is used to treat low temperature and low turbidity water,the effluent effect is poor,and it is difficult to form a large and dense flocculant.As a result,a large number of bubbles float in the flocculation tank,and sludge is deposited on the upper inclined plate of the sedimentation tank,etc.,which increases the burden for the subsequent treatment structures.Therefore,it is more and more urgent to find a method to treat the low temperature and turbid water in north China.This study aimed at winter in shenyang,slightly polluted water low temperature and low turbidity water of dahuofang reservoir formation of the flocculation effect is poor and the present situation of the loose,on water quality as well as flocculation characteristics of the sludge produced by the two kinds of analysis indicators,the beaker coagulation experiment was carried out,at last,by fractal theory on the formation of coagulation flocculation effect of experiment research.In this paper,five coagulants of polyaluminum chloride(PAC),ferric chloride(FeCl3),aluminum sulfate {Al2(SO4)3},polyferric chloride,polyiron sulfate(SPFS)were screened.The results showed that PAC had the best effect on the treatment of low-temperature and low～turbidity micropolluted water,and the optimal dosage was 40mg/L.The removal effects of effluent turbidity,UV254 and ammonia nitrogen were the best under the test conditions,with removal rates of 88.2%,47%and 30%,respectively.Then,two kinds of activated silicic acid and polyacrylamide(PAM)coagulants were screened.The results showed that PAM was the optimal treatment effect,and the optimal dosage of PAM was 0.6mg/L.The removal rates of turbidity,UV254 and ammonia nitrogen in the water were 90.7%,55%and 14.2%,respectively.The optimal operating conditions of the water plant in the case of non-superstandard ammonia nitrogen in winter were determined by orthogonal test:the time point for adding coagulation aid PAM was 1min,the dosage of PAC was 45mg/L,the dosage of PAM was 0.6mg/L,and the pH value was 7.In the case of excessive ammonia nitrogen in winter,three pre-oxidants kMnO4,NaClO and H2O2 were screened.The results showed that the treatment effect was optimal when NaClO was used as the pre-oxidant,and the optimal dosage was 20mg/L.At this time,the turbidity,UV254 and ammonia nitrogen removal rates of the water after sedimentation were 82.6%,79.7%and 77.5%,respectively.In addition.orthogonal tests were conducted to determine the optimal operating conditions of the water plant in the case of excessive ammonia nitrogen in winter:the dosage of pre-oxidant NaClO was 20mg/L,the oxidation time of NaClO was 25min.the stirring speed was 100r/min,and the pH value was 7.Based on the characteristics of flocs formed by the treatment of low-temperature and low-turbidity micro-polluted water,the enhanced coagulation test was carried out.On the premise of ensuring the quality of effluent water,the flocculation test was conducted with polyaluminum chloride(PAC)and aluminum sulfate as flocculants.The results showed that the sludge formed with PAC as flocculant had better performance and the optimal dosage was 40mg/L.At this time,the lowest moisture content of sludge is 93%,and the specific resistance of sludge is 4.9 × 108s2/g.Then the coagulant aid was screened,and the results showed that the sludge formed by adding coagulant aid PAM had the best performance,and the optimal dosage was 0.6mg/L.At this time,the lowest moisture content of sludge is 84.3%,and the lowest sludge specific resistance is 6.3 × 108s2/g.By changing the time point of adding PAM,the results showed that when adding the coagulant PAM 2min after flocculation,the sludge formed had the best performance,the lowest moisture content was 83.9%,and the sludge specific resistance was 6.5 × 108s2/g.The results show that when pH=7.0,the sludge sedimentation performance is the best,the water content is 84.3%,the sludge specific resistance is 6.4 × 108s2/g.According to the results of the orthogonal test,the optimal operating conditions are as follows:the time point of addition of coagulation aid PAM is 1min,the dosage of PAC is 45mg/L,the dosage of PAM is 0.6mg/L,and the pH value is 7.Based on the fractal theory,the performance of floc was experimentally studied,and a 3d DLCA model was established on the MATLAB platform.The results show that the maximum fractal dimension of floc is 2.0315 when the PAC dosage is 40mg/L,and the floc is the most dense and the sedimentation performance is the best.With the increase of addition amount of coagulation aid PAM,the fractal dimension is increasing and the sedimentation performance is getting better and better.When the coagulant was added 2min after flocculation,the fractal dimension of floc was the largest(2.0998),the floc was relatively dense and the sedimentation effect was the best.With the change of pH,when pH=7.0,the fractal dimension of the floc formed was the largest,which was 2.1033.