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根据以往的检验结果说明,用标准的滤膜法检测经氯处理污水中的总大肠菌群数或粪大肠菌群数,一般都低于用多管法(即最近似值法,MPN)检测的结果,有时相差可达10倍。因而在1975年美国环境保护局建议在检测经氯处理的污水中的粪大肠菌群时,应采用多管法。所以存在这种差别,可能由于培养的环境不同,即多管法所用的液体培养基环境有利于经氯处理而受损害的粪大肠菌群细胞的修复,特别是将此种细菌立即培养于44.5℃的高温情况下更易复苏。为解决此种检测结果的差别,Rose等(1975年)提出用双层培养基,即底层为一般滤膜法用的标准培养基,上层为乳糖琼脂培养基。将已采样的滤膜置于此
According to the previous test results, the total amount of coliform bacteria or fecal coliform bacteria in the chlorine-treated sewage by the standard membrane filtration method is generally lower than that detected by the multi-tube method (ie, MPN) The result, sometimes up to 10 times difference. Therefore, the United States Environmental Protection Agency recommended in 1975 when detecting fecal coliform bacteria in chlorine-treated sewage should be used multi-tube method. Therefore, this difference may be due to the culture environment is different, that is, the liquid medium environment used in the multi-tube method is conducive to repair of fecal coliform cells damaged by chlorine treatment, in particular, the bacteria immediately cultured at 44.5 ℃ under the conditions of more easily recovered. In order to solve the difference between these test results, Rose et al. (1975) proposed a double-layer medium, that is, a standard medium with a common membrane method at the bottom and a lactose agar medium at the upper layer. Place the sampled filter on it