| The characteristics of the high density sedimentation tank is that the PAC and the PAM are added simultaneously,and the sludge reflux is carried out.Therefore,the nature of return sludge is the key factor affecting the quality of effluent.When the organic matter or algae in the original water exceeds the standard,it will accumulate in the returned sludge and affect the properties of the sludge.Especially when the algae burst out seriously,the sludge will become green and stinky,which seriously affects the treatment effect.In this paper,the method of adding a certain proportion of attapulgite in the return sludge was used to study the effect of assisting coagulation and improving the properties of the return sludge,and to discuss the possibility of stopping the return of sludge under high algae raw water conditions.And the application prospect of attapulgite in high density sedimentation process was preliminarily studied.The specific results are as follows:(1)The coagulant effect of 13 different kinds of attapulgite was compared by experiments.The experimental results showed that the attapulgite with 160 mesh has better effect on removing turbidity.(2)The turbidity removal effect of PAC,PAC+PAM,and PAC+attapulgite were compared by experiments,and the results showed that the coagulation effect of attapulgite was lower than that of PAM.Orthogonal test was carried out on the three factors of PAC,PAM and attapulgite dosage.The experimental results showed that the order of the three factors affecting the turbidity of the effluent was:PAC dosage>PAM dosage>attapulgite dosage.Under the same conditions,the removal rate of turbidity could be increased by 3.3%by adding attapulgite,and the removal rate of Chl-a could be increased by 5.1%.(3)The coagulation effects of ten kinds of modified attapulgite were compared by experiments.The experimental results showed that the attapulgite modified by 400 ?,N2 and CS2 was better.Under the same conditions,when the same treatment effect was achieved,the modified attapulgite had a 33.3%reduction in the dosage of 160 mesh attapulgite produced from Gaojiawa.(4)The effects of turbidity of raw water,water temperature and addition point of attapulgite on the coagulation efficiency of attapulgite were experimentally analyzed.The results showed that the turbidity of raw water and water temperature would affect the coagulation effect of attapulgite.The addition of attapulgite before coagulation was more conducive to the formation of alum flower in the process of coagulation and sedimentation,and the removal effect of turbidity was better.(5)The sludge reflux ratio has a certain influence on the effluent turbidity.With the increase of sludge reflux ratio,the effluent turbidity would first decrease and then increase.In the pilot scale test?when the sludge reflux ratio was 4%?the turbidity of the effluent was the lowest and it was 0.86NTU.The sludge reflux ratio was too high,which could shorten the concentration time of the sludge and affect the water quality of the effluent.(6)Adding attapulgite in the refluxing sludge could improve the removal effect on the turbidity.With the increase of attapulgite dosage,the turbidity of effluent decreased first and then increased.When the amount of attapulgite added in reflux sludge was 1.20g/L,the turbidity of the effluent was the lowest and it was 0.57NTU.The removal rate of turbidity was 4.2%higher than that without adding attapulgite.When the return sludge was stopped,the concentration of attapulgite in the sludge storage tank was 1.6 g/L and the reflux ratio was 4%,the treatment effect was equivalent to that when the return sludge was used.Therefore,it is feasible to stop sludge reflux under the condition of high algae raw water. |
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