| Microcystins (MC) are hepatotoxins containing cyclic heptapeptides. Microcystin-LR (MC-LR) is a strongly liver tumour promotor. MC are chemically stable in water and can't be effectively removed by conventional water treatment processes. The water treatment processes for removing MC from drinking water must be studied urgently. The enzyme-linked immunosorbent assay (ELISA) and high performance liquid chro-matography (HPLC) analysis for detection of MC were optimized. The removal rates of MC by conventional water treatment processes were investigated through the laboratory study and the detection of MC in every process in Meiyuan Drinking Water Treatment Plant. Results showed that the prechlorination of eutrophic water led to the release of intracellular toxins to water phase. The extracellular MC had no change in coagulation sedimentation process. 17.2%~40.4% of extracellular MC and 19.0%-36.6% of total MC were removed by filtration. 30%~45.3% of extracellular MC and 30%~51.7% of total MC were removed by chlorination.Cascade biological contact oxidation reactor was more effective and stable for the treatment of eutrophic water than one-step reactor. The removal rates of NH3-N, NO2- -N and CODmn in the cascade biofilm reactor were higher than those in conventional water treatment processes. When HRT was 2 hours, more than 90% of NH3-N, NO2--N , turbidity value and algaes were removed , more than 20% of CODmn was removed. Meanwhile, the removal rates of extracellular MC, MC-RR and MC-LR reached over 85%, 81.7% and 86.7%, respectively, and the removal rates of total MC, MC-RR and MC-LR reached over 84%, 80.5% and 71.5%, respectively. When the ratios of gas to water of three steps were 2:1, 0.5-1:1 and 0-0.5:1, respectively, pollutants were removed effectively from water. In the biological pretreatment procedure for eutrophic water, MC were degraded by special bacteria and assimilated by heterotrophic microorganisms.When drinking water containing MC was advanced treated by the ultraviolet/micro-ozone (UV/microO3) process, 61.9% of MC-RR, 81.9% of MC-YR and 91.7% of MC-LR were removed within 1.5 hours. The photochemical degradation was characterized by pseudo-first order reaction kinetics. The reaction half lives (t1/2) for MC-RR, MC-YR and MC-LR were 74.5 min, 32.2 min and 24.2min, respectively. When the laboratory-scale photochemical reactor ran continuously, the average degradation rates for MC-RR, MC-YR and MC-LR were 39.8%, 62. 7% and 74.0%, respectively. Ultraviolet radiation and ozone in high doses accelerated the degradationof MC.The biological activated carbon (BAC) process was used for the advanced treatment for drinking water containing MC. 60.6% of MC-RR, 63.3% of MC-YR and 68.8% of MC-LR were removed within 1.5 hours. In this process MC were removed by two paths, one was MC degraded directly by microorganisms and the other was MC degraded by microorganisms after adsorbed by active carbon.In cascade biological contact oxidation with flocculation, sand filtration and chlorina-tion procedures, the removal rates of CODmn, UV254, NH3-N and total MC were 70.2%, 27.9%, 84.5% and 88.0%, respectively. The kind and quantity of organic substances were reduced by 29.8% and 90.7%, respectively, determined by GC/MS analysis. In flocculation with sand filtration, BAC and chlorination procedures, the removal rates of CODMn, UV254, NH3-N and total MC were 78.9%, 43.6%, 79.2% and 84.9%, respectively. The kind and quantity of organic substances were reduced by 65.9% and 97.4%, respectively. In flocculation with sand filtration, chlorination and UV/microO3 procedures, the removal rates of CODmn, UV254, NH3-N and total MC were 74.1%, 50.0%, 58.3% and 76.9%, respectively. The kind and quantity of organic substances were reduced by 64.9% and 97.3%, respectively.MC reduced obviously in cascade biological contact oxidation, UV/microO3 and BAC processes. The three combination water treatment processes referred in above paragraph could be used for the treatment of safe drinking water from eutrophic water.
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