Research On The Variation And The Removal Method Of Microcystins In Water Source & Waterworks

Eutrophication has become the main disease of water body in the world. Cyanobacterial blooms are the major environment disasters. Microcystins (MC) have also been examined in many lakes and reservoirs in China nowadays. Hongfeng Lake as the main drinking water source of Guiyang, it has appeared eutrophication since cyanobacterial blooms was found in 1996. With support of Sino-Japanese Cooperation Project, MC had been investigated primaryly in Hongfeng Lake in 2000. So far, no comprehensive investigation and study on MC in the depth lakes and reservoirs was done, neither did on the removal of MC on the conventional water treatment processes in waterworks which water supply from depth lakes and reservoirs. Based on the study of MC extraction, enrichment and analytical method, the variation and the removal method and it's strengthen removal technologies of microcystins in water source and waterworks were studied in this paper. The main conclusions achieved as follows:1. From June to December, 2008, the method of high performance liquid chromatography (HPLC) and enzyme-limited immunosorbent assay (Elisa) were used to examine MC in Hongfeng Lake. The results showed that the tendency of MC was the same as that of algaes growth in lake. It displayed higher in summer, then autumn and winter, but the peak content of MC was a little bit latter than the peak of algae biomass. The intracellular microcystins (IMC) was the main morphological characters in surface water and the extracellular microcystins (EMC) was the main in depth water. Water temperature was stratified in summer, which would prevent the convection in vertical. It was obvious that there were concentration gradient distribution of algae and MC in different depth. Water supply from deep lake could avoid the hazard of cyanobacterial blooms greatly.2. It was inefficient to removal MC by conventional water treatment processes. Only 30% of total microcystins (TMC), 7.9% of EMC and 89.6% of IMC could be removed. The experiment results showed that the EMC was effective removed by chlorination, and the IMC was higherly removed by coagulation sedimentation and filtration. So, when the EMC was the main morphological characters, it could be effectively removed by the main treatment process of oxidation. When the IMC was the main morphological characters, it could be effectively removed by the main treatment process of coagulation sedimentation.3. Comparison of the degradation of MC by potassium permanganate (KMnO₄) in different condition, it was found that the degradation process was with pseud-first-order reaction kinetics. The reaction half lives (t_1/2) for MC-RR and MC-LR were 7.15min and 12.16min, respectively. The removal velocity of MC was not influenced when COD_Mn was 2 or 4mg/L, but removal rata reduced about 7-11%. MC was removed with the cooperative effection of oxidation and adsorption of KMnO₄. Fresh manganese dioxide could remove the MC effectively.4. MC was adsorbed quickly by Powder activated carbon (PAC) within 30min. However, adsorption became slowly after 45min. About 40% of MC was removed when PAC was 100mg/L, and over 71% was removed while PAC was 300mg/L. The results showed that MC could not be removed effectively with low concentration of PAC.5. Results also showed that residual EMC were 0.06, 0.12, 0.25μg/L when EMC initial concentration were 2, 5, 10μg/L and KMnO₄ were 0.5, 0.8, 1.0mg/L, polyaluminium chloride was 10mg/L respectively. With chlorine disinfection in the processes of waterworks, it could ensure that the MC was less than 0.2μg/L in drinking water, this reduce the risk of promoting tumor under continuous exposure to low content MC. When the IMC was the main morphological characters, the combined processes of pre-oxidation of KMnO₄ + PAC adsorption + coagulation sedimentation could enhance the removal effection of algae, it could reduce the MC content in water effectively.