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Research on the Treatment of Micro-polluted Algae-laden Water Using Ferrate (¢ö) Pre-oxidation

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Tutor: DuMaoAn
School: Harbin Institute of Technology
Course: Municipal Engineering
Keywords: potassium ferrate,pre-oxidation,coagulation,Microcystis aeruginosa,potassium per
CLC: TU991.2
Type: Master's thesis
Year:  2012
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Abstract:
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.
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