Effect And Mechanism Of Organic Compound Titanium Xerogel Coagulant In Enhancing Ultrafiltration On Algae-Related Pollution

In view of the algae bloom caused by eutrophication of water,ultrafiltration technology is currently used as a kind of treatment technology for algae-laden water.But during its operation,the membrane fouling caused by algae-related pollutants is often a big problem,which greatly limits the efficiency of ultrafiltration and increases the operating cost.Nowadays,in-line coagulation-ultrafiltration technology is more and more used in the treatment of algae-laden water.The main way is to use simple coagulation as pretreatment technology,and the flocculation flocs will enter the ultrafiltration unit directly with pollutants without precipitation.In this study,the complex membrane pollution behavior of algae containing water was analyzed systematically,and then the in-line coagulation-ultrafiltration process of novel TXC and organic flocculants were established to treat algae-laden water.Finally,the new composited coagulant was prepared by the combination of TXC and organic flocculant,which was put into application and explored its performance.At the same time,the relevant mechanism was also analyzed.The main conclusions are as follows:(1)The membrane pollution caused by five different types of algal pollutants followed an order of Intracellular organic matter(IOM)＞Algae/algae organic matter(AOM)＞AOM＞Algae＞extracellular organic matter(EOM).These pollutants reduced the efficiency of ultrafiltration in the process of circulating ultrafiltration,and the membrane pollution raised as filtration cycle increased.IOM was the most important organic pollutant.The mechanism of membrane pollution caused by algae cells and algal organic matter was quite different.The algae cells main caused the reversible pollution,while organic matter mainly led to irreversible pollution.And the combination of algae cells and organic matter would aggravate membrane pollution.(2)In case of poor performance of adding TXC alone,the treatment effect of coagulation-ultrafiltration on algae-laden water could be improved by combining with certain dosage of CPAM,and the membrane pollution could also be reduced effectively.In the range of p H 5.0-9.0,combined with 4-12 mg/L CPAM,the turbidity of algae-laden water with initial concentration of algae:～10~7 cell/m L and IOM:10 mg/Lcan be effectively reduced to about 1 NTU.However,APAM had no obvious effect on the removal effect in the system.The improvement of membrane pollution by CPAM in the process of coagulation-ultrafiltration was mainly achieved by enhancing the coagulation effect.Nevertheless,the addition of organic flocculant had some negative effects in in-line coagulation-ultrafiltration system.Over-dosed flocculant would cause serious flocs agglomeration,and became dense and viscous,which was not conducive to the formation of cake layer to protect the membrane.At the same time,the flocculants remained in the system would cause additional irreversible membrane pollution.(3)Due to some disadvantages of TXC in the application process,which was it greatly affected by p H and co-existing organic matter,it was difficult to play a good coagulation effect under alkaline condition and in the presence of high concentration of algal organic matter.A new composite organic-inorganic coagulant was fabricated by embedding PDADMAC into TXC structure and has been applied in In-line coagulation-ultrafiltration.The results showed that the P-T coagulant could effectively improve the treatment effect,and showed good resistance to p H and organic matter.In the range of p H 5.0-9.0,P-T pre-coagulation could effectively alleviate membrane pollution,while TXC had good effect only in acid condition.Acidic environment was conducive to the removal of algae and organic matter by pre-coagulation,which greatly improves the efficiency of ultrafiltration.The results also showed that the properties of floc cake layer affected the filtration behavior in the whole process.The looser the cake layer structure,the more suitable for filtration.Although the addition of PDADMAC would lead to floc aggregation,which could not protect the membrane and slightly reduce the recovery ability,the negative impact of composite coagulant on ultrafiltration was smaller than that of separate dosing.The correlation analysis showed that algae cells are closely related to the flux drop caused by reversible pollution,while organic matter mainly causes irreversible pollution and reduces flux recovery rate.Therefore,in order to alleviate membrane pollution and improve the efficiency of ultrafiltration process,removing organic matter effectively was still the main goal in the future.This paper systematically explored the effect and mechanism of TXC applied in coagulation-ultrafiltration treatment of algae laden water,and verified the application potential of TXC to effectively improve the performance of alleviating membrane pollution.Furthermore,it proved that the compound cationic flocculant could further enhance the application ability of TXC in this process,which would be a new way for the selection and development of chemicals in water treatment process.