Research On The Influencing Factors Of Ozone-coagulation Combined Treatment

Due to the increasing pollution situation of drinking water resource,traditional means of water treatment cannot meet the increasing standard of drinking water,therefore,people developed pretreatment and advanced treatment technologies as new means to improve the efficiency of drinking water treatment,and ozone-coagulation treatment was developed for this purpose.Therefore,to find how different factors affect the efficiency of ozone-coagulation dealing with dreading water,this paper studied the basic factors that affects the result of ozone-coagulation:ozone concentration,type of coagulant,and the effect of ozone on coagulation.What's more,I also verified whether this combined treatment could remove the precursors of disinfection by-product effectively.Results can provide the theoretical basis for the practical applications and a foundation for future research.During the process of drinking water disinfection(mainly using chlorine disinfectant),with the reaction between disinfectant and natural organic matters in the water(mainly humic acid and fulvic acid),a kind of"three to" by-products would be produced.In order to simulate natural water conditions,humic acid and kaolin was added into tap water to make water samples used in the experiments.This experiment focuses on the three indicators,which could reflect the efficiency of ozone-coagulation treatment with different conditions,they are turbidity,UV254 index and DOC concentrations.Four factors that might affect the efficiency of ozone-coagulation were chosen:types of coagulants,adding dosage of coagulant,ozone concentrations and the condition whether ozonation and coagulation function work at the same time(that is,whether ozone affects the coagulation process).Three most common types of coagulants were selected:ferrous sulfate,aluminum sulfate and poly aluminum chloride.After using three kinds of coagulants in separate coagulation respectively,the best coagulant dosage was known,and this dosage of coagulant was used during the following ozone-coagulation experiments.Experimental results showed that besides the physical and chemical properties of raw water,the main factors that affect the efficiency of ozone-coagulation were the concentration of ozone,the type and the dosage of coagulant.The involvement of ozone in coagulation process only affects certain types of coagulant(ferrous sulfate and aluminum sulfate).Pre-ozonation had a better result than the other group.For ferrous sulfate group,the removal rate of turbidity and UV254 index were slightly improved when using pre-ozonation,and DOC removal rate increased 10%;the result of aluminum sulfate group had a similarity trend.For aluminum sulfate,using pre-ozonation treatment could reduce the content of DBPs after chlorination disinfection(10?30%lower than the 'together' treatment group).Since ozone is able to change the performance of coagulant,the result of 'the ozonation and coagulation working together' group was not as good as pre-ozonation group.Therefore,to ensure the best result of combined treatment,it is needed to make sure that there is no or little ozone involved in coagulation process.The result comparisons of three coagulants showed that the turbidity removal of combined treatment was always better than separate treatment(5%higher).However,this maximum increase only showed up in low ozone concerntration.If higher ozone concentration was added into the system,this increase will be suppressed.The reason for this result could be that the increase of ozone concentration could led an increase of small molecular organic content,which increased the negative charge carried by particles,therefore reduced the removal effect on organic of coagulation.Another founding was that the coagulation was the main role of ozone-coagulation process,the role of ozone was to improve a small range of efficiency based on the result of single coagulation.Hence,choosing the suitable coagulant was the main determination factor of the ozone-coagulation efficiency.According to the results obtained,aluminum coagulant showed a better performance overall.Ferric coagulant could quickly from big alum and the turbidity removal rate was up to 96%.However,since the colored complexes ferric coagulant creates increase complexity of subsequent processes,aluminum coagulants therefore is still recommended in practical applications.For aluminum coagulant,no matter the ozonation and coagulation process work together or not,the performance of PAC is always the best and most stable,the maximum removal rate is up to 91.5%for turbidity,80%for UV254 and 52%for DOC.