1、河海大学环境学院给排水工程毕业设计 第 1 页共 109 页 2英语论文翻译 Elimination of microcystins by water treatment processes examples from Sulejow Reservoir, Poland 4. Discussion The conventional water treatment process using preoxidation,coagulation, sand filtration, ozonation andchlorination in the Sulejow-Lodz waterworks sys
2、tem,and coagulation, sedimentation, sand filtration, ozonationand chlorination in the Tomaszow-Lodz waterworkssystem were effective in the elimination ofextracellular and cell-bound microcystins. These twowaterworks had similar, rather simple treatmentprocesses. The health hazard caused by microcyst
3、insin the water used for drinking water productionwas higher in the Sulejow-Lodz waterworks systemdue to the localization of water intake in the narrowbay of Sulejow Reservoir where mass occurrencesof cyanobacteria were found. The water intake of theTomaszow-Lodz waterworks system, localized inPilic
4、a River, was less prone for cyanobacterial problems.The results showed an efficient removal of microcystinsin water during treatment processes in the Sulejow-Lodzand in the Tomaszow-Lodz waterworks. Similarefficiencies have been observed in two Australiandrinking water treatment plants reported by H
5、oegeret al. (2004). Cyanobacterial toxins can enter a water treatment plantin two forms, either as intracellular toxins (bound withinthe cyanobacterial cells) or as extracellular (dissolved)toxins. An elevated level of extracellular toxins wasobserved in Sulejow Reservoir in 2002 (Table 3ae.g.13 Aug
6、ust 2002). The high concentration of free toxin inraw water could be explained by a collapsing cyanobacterialbloom and a lysis of cyanobacterial cells. Althoughthe studied water utilities could eliminate extracellularmicrocystins in an efficient manner, high extracellulartoxin may jeopardize the eff
7、iciency of some simplertreatment plants in the elimination of microcystins. 河海大学环境学院给排水工程毕业设计 第 2 页共 109 页 In this study, the most effective step of the treatmentprocess in the removal of microcystins was the filtrationprocess, which reduced microcystins by 75.4% comparedto the concentration at the
8、end of the precedingstep (Fig. 4). Rapid filtration, a method usuallyemployed after coagulation to remove the flocculants,does not effectively remove cyanobacterial cells (Lepistoet al., 1994； Steffensen and Nicholson, 1994). Theefficiency of sand filtration, reported by Hoeger et al.(2004) in the r
9、emoval of M. aeruginosa, was 84.8%. Intheir studies an efficiency of 99.9% for flocculationcombined with sand filtration was demonstrated in theelimination of cyanobacterial cells. The concentration of microcystins can be effectivelyreduced also by activated carbon filtration. From watertreatment st
10、udies conducted at the laboratory and pilotplant scale it was concluded that granular activatedcarbon (GAC) filtration is effective in removingcyanobacterial toxins from drinking water (Hoffman,1976； Falconer et al., 1983； Keijola et al., 1988； Falconeret al., 1989； Himberg et al., 1989； Mereish and
11、 Solow,1989； Donati et al., 1994； Lambert et al., 1996).Powdered activated carbon (PAC) was shown to removetoxins but at doses higher than generally used at watertreatment facilities (Wheeler et al., 1942； Hoffman, 1976；Falconer et al., 1983； Keijola et al., 1988； Himberg et al.,1989). The use of ch
12、lorine dioxide in this study for a preoxidationprocess (1.62.8 mg l_1 for a contact time of30 min) caused a reduction of total microcystin concentrationby 40.4% (78.2% reduction for cell-boundmicrocystins and 17.2% increase for dissolved forms) (Fig. 4). These findings are in accordance with results
13、presented by Nicholson et al. (1994). Tsuji et al. (1997)showed that a chlorine dose of 2.8 mg l_1 for a contacttime of 30 min was sufficient for a 99% destruction ofMC-LR. Pre-oxidation by ozone, chlorine and permanganatefollowed by coagulation process has been widelyused, especially in the removal
14、 of some algae andcyanobacteria. Effective removal of algal cells wasachieved especially with chlorine and permanganate.However, pre-oxidation leads to cell lysis and toxinrelease into water which should be avoided (Bonne lyeet al., 1995； Hrudey et al., 1999； Pietsch et al., 2002).This situation was
15、 also observed in the present study(Table 3a). 河海大学环境学院给排水工程毕业设计 第 3 页共 109 页 Therefore, it is not recommended to carryout preoxidation if toxin removal is a priority. Onlywhen the total toxin concentration (both intra- andextracellular) is so low that lysing is irrelevant,preoxidation can be consid
16、ered acceptable (Houseet al. (2004). Coagulation and flocculation are defined as a processin which suspended particles are aggregated through theaddition of a chemical coagulant. Coagulants used forthis purpose (especially aluminium sulphate dosed at100160mg l_1 in 2002 and also polyaluminium chlori
17、de used in 2003 dosed at 120150 mg l_1) caused areduction of microcystins, mainly cell-bound microcystins,by 37.9% in 2002 compared to the preceding step.This process is ineffective in the removal of extracellularcyanotoxins (Keijola et al., 1988； Himberg et al., 1989；Lambert et al., 1996； Chow et a
18、l., 1998). However, it canbe effective in removing intracellular cyanotoxinsthrough the removal of intact cyanobacterial cells.Coagulation is considered an efficient method forelimination of cyanobacterial cells from water, whereassoluble cyanotoxins are not very efficiently removed bythis method (J
19、ames and Fawell, 1991； Rositano andNicholson, 1994). The efficiency of the cyanobacterialcell removal is dependent on the optimisation of thedosing of chemicals and adjusting the coagulation pH(Mouchet and Bonne lye, 1998). However, coagulation may cause additional problems such as lysis ofcyanobact
20、erial cells leading to a release of toxins (Jamesand Fawell, 1991). In the studies presented here chlorine and ozone wereonly used as disinfectants and for colour and/or odourremoval in the last steps of the water treatmentprocesses. The efficiency of chlorination seems todepend largely on the chlor
21、ine compounds and theconcentration used. Aqueous chlorine and calciumhypochlorite with contact time of over 30 min at aconcentration of 1mg l_1 removed more than 95% ofmicrocystins (Himberg et al., 1989； Nicholson et al.,1993； Nicholson et al., 1994； Rositano and Nicholson,1994； Carlile, 1994). Ozonation can be effective for the destruction ofmicrocystins since it is one of the most powerfuloxidants. Several studies have shown that the toxinremoval is
