Research On The Treatment Of Micro-polluted Algae-laden Water Using Ferrate (Ⅵ) Pre-oxidation

The frequent occurrence of algal blooms in DaQing drinking water reservoirscauses problems to water supply. In this paper,we investigated the effect of pHvalues,settling time,pre-oxidation time,the growth phase of algal, algogenic organicmatter （AOM）,humic acid on the removal of algae by pre-oxidation with potassiumferrate（VI）. A comparison of the treatment efficiency from raw water was studie bypre-oxidation with K2FeO4and KMnO4, and with the following coagulation by usingPolymeric Aluminum Chloride（PAC）,Polysilicate Aluminum Ferric Flocculant（PFAS）,Polymerization Aluminium Ferric Chloride（PACL） respectively.The algae removal performance of K2FeO4pre-oxidation shows that the lower pHvalue, the better algaecide rate，and pH>8.5,the removal efficiency of algae declinedsharply; Increase the settling time can significantly improve the algaecide rate ofpre-oxidation with K2FeO4, sedimentation time extended from30min to60min, chl-aremoval efficiency can be increased by more than10%;A prolong pre-oxidation time，algae removal efficiency of pre-oxidation with K2FeO4increased slightly, but more than10mins，the removal rate of algae declined; In the declining phase of Microcystisaeruginosa contains more organic matters which can reduction the algaecide rate ofCoagulation， so, relative to exponential growth phase of Microcystis aeruginosa，thedeclining phase more difficult to handle. To achieve the same harvesting efficiency, thedeclining phase need to be adding more coagulant, K2FeO4pre-oxidation cansignificantly improve the effect of coagulation on the removal of algae both of thedeclining and the exponential phase.Lower concentration of Extracellular organic matter（EOM）of algae can promotethe removal of algae，but higher concentration of EOM inhibit algae removal. Resultsshow that humic acid in the water caused the reduction of algae removal efficiencycoagulated with PAC alone，Pre-oxidation with K2FeO4could reduce significantly theinfluence of humic acid on algae removal by coagulation. as the K2FeO4oxidation-reduction product，the positively charged [Fe （OH）₃]，is a potential coagulantwhich adsorbed to the algal cell surface or organic matter surfaces，reducing thenegative charge of algae-laden water therefor the Zeta potential of algae-laden water hasbeen reduced.Under the conditions of the same Chlorophyll a，K₂FeO₄pre-oxidation on severaldifferent kinds of algae removal efficiency results show that removed EOM Microcystisaeruginosa is most likely to be harvested， Followed by Spirulina, Microcystis aeruginosa of not removed EOM, and finally the chlorella. K₂FeO₄pre-oxidation canobviously enhanced harvesting efficiency of Microcystis aeruginosa and Chlorella，while almost no role in promoting the removal of spirulina,contrary，the UV₂₅₄valueincreased.The pre-oxidation of DaQing drinking water reservoirs with K₂FeO₄and KMnO₄was conducted with respect to its impact on the following coagulation。The resultsshowed that, when the K₂FeO₄pre-oxidation associated with PAC，the raw water needto be acidified in order to obtain a good harvesting efficiency, while K2FeO4combinedwith PFAS and PACL，acidification is not required because of PFAS and PACL areable to reduce the pH of the water body. KMnO4pre-oxidation get a better harvestingefficiency under acidic conditions than alkaline conditions,but associated with that threecoagulants KMnO4pre-oxidation can still achieve a good coagulant effect although theraw water is not acidified.Just dosing1mg/L KMnO₄can achieve the same turbidity andCODMnremoval rate with dosing4mg/L K₂FeO₄. K₂FeO₄pre-oxidation can effectivelypromote the removal of ammonia nitrogen and orthophosphate， while KMnO₄pre-oxidation is almost no role in promote the removal of ammonia nitrogen andorthophosphate.Both KMnO₄and K₂FeO₄pre-oxidation can enhance the removal ofalgal cells，but to achieve the same algaecide, KMnO4dosing less than K2FeO4.