Investigation On Coagulation Behavior And Mechanism Of Algal Surface Water Treated With Titanium Salt Coagulant

Based on the wide application prospect of titanium coagulant in the process of water treatment,compared with traditional coagulant,this paper systematically studied the coagulation efficiency and coagulation behavior of titanium salt coagulant in treating surface water containing algae.Meanwhile,this work also investigated the influence of algae organic matter(AOM)on surface water treatment by Ti(SO4)2 coagulation followed by LPUF technology.By the analysis the composition of algae organic matter,the effect of organic matter removal,flocs characteristics,membrane flux and the membrane resistance analysis were investigated.The main research contents and conclusions are as follows:(1)This study investigated coagulation performance of titanium tetrachloride(TiCl4)for algae removal by comparison with conventional coagulants,aluminum sulfate(AS),polyaluminum chloride(PACl)and ferric chloride(FeCl3)for Microcystis aeruginosa synthetic water treatment.Results show complete algal cells removal by TiCl4 coagulation without damage to cell membrane integrity even under harsh conditions.This avoids the possible of algal cells breakage in the coagulation process and reduces the burden of coagulation water treatment.Compared with aluminum salt and ferric salt coagulant,TiCl4 not only has a higher removal efficiency of UV254(over 50%);but also has a better removal efficiency of fluorescent substances in water sample.(2)By exploring the influence of coagulant type,dosage and initial pH on the flocs characteristics,the advantages of titanium coagulation were found.Results showed that,compared with the conventional coagulants,TiCl4 coagulant required more compact coagulation and sedimentation tanks due to its significantly improved floc growth and sedimentation speed.The recovery factor of TiCl4 flocs is higher than that of other coagulants under different pH,but the flocs strength is relatively low.The study on the characteristics of TiCl4 floc provides a new theoretical basis for setting up the sedimentation tank in actual water treatment process.(3)Cyanobacterial bloom causes the release of algal organic matter(AOM),which inevitably affects the treatment processes of natural organic matter(NOM).This study works on treating micro-polluted surface water(SW)by emerging coagulant,namely titanium sulfate(Ti(SO4)2),followed by Low Pressure Ultrafiltration(LPUF)technology.In particular,we explored the respective influence of extracellular organic matter(EOM)and intracellular organic matter(IOM)on the removal efficiency of synergetic SW-EOM/SW-IOM,functional mechanisms and subsequent filtration performance.Results show that the IOM inclusion in surface water body facilitated synergic IOM-NOM composite pollutants removal by Ti(SO4)2,wherein loosely-aggregated floes were produced,resulting in floc cake layer with rich porosity and permeability during LPUF.On the contrary,the surface water invaded by EOM pollutants increased Ti(SO4)2 coagulation burden,with substantially deteriorated both UV254-represented and dissolved organic matter(DOC)removal.Corresponded with the weak Ti(SO4)2 coagulation for EOM-NOM removal was the resultant serious membrane fouling during LPUF procedure,wherein dense cake layer was formed due to the compact structure of flocs.Although the IOM enhanced NOM removal with reduced Ti(SO4)2 dose and yielded mitigated membrane fouling,larger percentage of irreversible fouling was seen than NOM and EOM-NOM cases,which was most likely due to the substances with small molecular weight,such as microcystin,adhering in membrane pores.This research would provide theoretical basis for dose selection and process design during AOM-NOM water treatment.