700 Filtration of ng Pumpin Storage tanks station Flocculant w water reservoir Mixing tank Flocculation tank Particulate filter Consumer Raw water held 2A Water is mixed 2B As aggregates @ Water Water is stored in reservoir to with flocculant of floc settle out undergoes before use by allow particulates they carry colloidal filtration consumers to settle particles out of Water is disinfected suspension by chlorination. ozone treatment or exposure to igure 27.15 The steps involved in water treatment in a typical municipal water purifi- cation plant. Municipal drinking water is usually filtered and disinfected phia, 1890-1935. (Source: E Steel, Water Supply and Sewerage,二、水体中的微生物 (一)江河水 1)数量和种类与接触的土壤有密切关系； 2)分布上更多的是吸附在悬浮在水中的有机物 上及水底； 3)多能运动,有些具有异常的形态(例如柄细菌); 4)靠近城市或城市下游水中的微生物多,且有很 多对健康不利的细菌,因此不宜作为饮用水源； 5)水体自身存在自我净化作用： a)致病菌一般对营养要求苛刻,因此在一般的 水中只能存活2-3天； b)水表微生物会受辐射等作用而被杀灭； c)原生动物等的吞噬作用； d)由固形物吸附再沉积到水底； 水中的病原微生物会对水质产生重要影响 饮用水的微生物指标： 总菌数： < 100个/ml 大肠杆菌：< 3 个/L