| In northwest China,surface water sources are characterized by low temperature and low turbidity in winter and spring,and some surface water sources have algae blooms in summer.Therefore,in order to efficiently remove the organic matter in low temperature and low turbidity water and solve the problem of algae outbreak,the pre-oxidation/pre-pressure combined coagulation and sedimentation technology were studied.The experimental water was raw water from a deep water stratified reservoir in Xi’an.On this basis,the Hanjiang River water and Heihe River water,which are in flood season at the same time in the"Hanjiang to Weihe River Project",are mixed in different proportions to explore the change of water quality and the effect of pre-oxidation on the removal of organic matter.The main research results and conclusions are as follows:（1）The best process and the effect of pre-oxidation strengthening on the removal of organic matter in low temperature and low turbidity water were studied by two pilot lines（Grid flocculation-inclined tube sedimentation and mechanical flocculation-air floatation,which were established in a water plant in northwest China.）.The results showed that the grid flocculation-inclined tube sedimentation process has better removal effect on turbidity,CODMn,UV254and DOC,and lower total operating cost.Potassium ferrate,potassium permanganate and chlorine dioxide were selected for pre-oxidation enhanced grid flocculation-inclined tube precipitation process.The optimal removal effect of organics was obtained when the dosage of potassium permanganate was 0.6mg/L.Ultraviolet analysis showed that the absorbance of organic matter removed by different pre-oxidation agents was mainly between 250 nm and 450 nm.EEMs parallel factor analysis showed that different preoxidation agents had different emphasis on the removal of organic matter of different components.（2）The Heihe River water and Hanjiang River water were mixed in different proportions in flood season.The results showed:When the proportion of Heihe River water was less,and the proportion of Hanjiang River water was more,the turbidity and CODMncontent of the mixed water are higher,while the UV254and DOC content are lower.When the water quality was changed,the optimal dosage of PAC and PAM in the same group was able to adapt to the water quality fluctuation within a certain range.The more dissolved organic matter,the more pre-oxidizing drug dose is needed.In this experiment,potassium permanganate was chosen as the best pre-oxidation agent.（3）The effects of different pressure,different pressure time and PAC addition sequence on algae removal were investigated by pre-pressure experiments on natural algal water.The results showed that the removal rates of turbidity,algal density,Chl-a concentration and CODMnin the firstly pressurized experimental group were better than those in the simultaneous pressurization plus PAC experimenta group.The removal rates of turbidity,algae density,Chl-a concentration and CODMnwere 84.5%,53.0%,51.8%and 23.0%,respectively,when the pre-pressure was 0.7 MPa and the pressure time was 60 s.Relative to the pressure time,the pre-pressure is the main factor that causes the difference of the effluent.The removal of green algae by pre-pressure technique also has some effect.（4）Four different pre-treatment methods were carried out on three pure algae Spirulina,Chlorella and Microcystis aeruginosa to explore the removal effect and mechanism of different pre-treatment methods on different algae species.The results showed that the removal effects of four different pre-treatment methods on the algal density and organic matter of Spirulina and Chlorella were as follows:Pre-oxidation of potassium ferrate>Pre-oxidation of sodium hypochlorite>Pre-pressure>No pressure.The removal effects of Microcystis aeruginosa on algal density and organic matter were as follows:Pre-pressure>Pre-oxidation of potassium ferrate>Pre-oxidation of sodium hypochlorite>No pressure.It was proved again that pre-pressure was also beneficial to the removal of Chlorella. |
