Study On The Removal Of Algae In Raw Water By Biological Contact Oxidation Process

There is the risk of sudden algae pollution in Dong-Shen Water Supply Project. This study is to develop the new function of algae removal on the basis of raw water biological pretreatment of Dong-Shen Water Supply Project. And the purpose is to avoid event of the eutrophication and guarantee the safety of water quality. Combining with the actual situation of Dong-Shen Water Supply Project, YDT elastic filler biological contact oxidation process is used to test the removal efficiency of algae. In this paper, the removal rules of different gas-water ratio, hydraulic retention time, raw water algae concentration, ammonia nitrogen concentration and alkalinity have been especially investigated. Besides, in order to maximize its potency, effective algae removal treatment process has been established through optimizing the technical parameters of contact oxidation aeration time and intensity. Here, the removal mechanism and pathway of algae and various pollutants have been discussed based on experiment results and algae removal pathway. The conclusion shows thatIt is found that raw water show mild eutrophication status and planktonic algae mainly composed of diatoms, green algae and cyanobacteria. Numbers of algae cells in the raw water are orders of magnitude more than in 107. Concentration of chlorophyll a have been possessed a high values relatively and blooms threshold was as same as lakes and reservoir of the country. Moreover, algae growth of raw water is most affected by nitrogen and phosphor pollution, temperature and pH value.It take about 32 days to succeed in biological contact oxidation process using of the method of artificial inoculation with activated sludge. The recator had formed membrane successfully during the removal rate of NH4+-N and CODMn were steady at 60%,15% above, and the removal ratio of NH4+-N, CODMn gets to 72.20% and 52.41%.The best HRT and gas water ratio was 1.0h and 1.2:1 when treating raw water with algae (chlorophyll a=34.54 mg·m-3)by biological contact oxidation reactor. By using the best technological conditions of dealing with the raw water with high density algae (chlorophyll a=71.12 mg·m-3), chlorophyll a, CODMn and NH4+-N removal rate reached 65.48%,47.81% and 70.54%, respectively. The outlet concentration of CODMn and NH4+-N can reach the goals for Dong-Shen Water Supply Project. The emergency treatment scheme is feasible.Chlorophyll a removal rate decreases with the increase of the concentration of NH4+-N, the removal rate of chlorophyll a from 72.34% to 32.43%. NH4+-N removal rate decreases with the increase of the concentration of NH4+-N, a rise in NH4+-N concentration of 1 mg/L would reduce removal rate between 4 and 6 percent. NH4+-N removal amount increases with the increase of the concentration of NH4+-N, a rise in NH4+-N concentration of lmg/L would increase removal amount 0.42 mg/L.CODMn removal rate increases with the increase of alkalinity. Under the condition of three kinds of alkalinity, the reactor can remove large concentrations of NH4+-N, removal rate increases with the increase of the water alkalinity; When alkalinity in 4 times,6 times and 8 times, chlorophyll a removal rate was 48.51%,65.23% and 72.54% respectively, chlorophyll a removal rate increases with the increase of the alkalinity.High-molecular polymer in biofilm has strong flocculation sedimentation performance, algae discharged in biological sludge by fall off of biofilm, this is one of the ways algae can be removed. The decomposition of biofilm to algae is exist, because the algae shell in biofilm and sediment. The cavities in biofilm indicate that the protozoan predation function is one of the ways to remove the algae.