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Viruses are infectious organisms that range in size from 10 to 25 nanometers [1 nanometer one billionth (10-9) of a meter]. They are particles composed of an acidic nucleus surrounded by a protein shell. Viruses depend totally on living cells and lack an independent metabolism. There are over 100 types of enteric viruses. Enteric viruses are the viruses that infect humans. Enteric viruses, which are of particular interest in drinking water, are hepatitis A, Norwalk-type viruses, rotaviruses, adenoviruses, enteroviruses, and reoviruses. The test for coliform bacterial is widely accepted as an indication whether or not the water is safe to drink; therefore tests for viruses are not usually conducted. The US EPA has established an MCL(最大污染物水平) that states that 99.99% reduction or inactivation for viruses. Major enteric viruses and their diseases are shown below.
Virus (Disease)
Enteroviruses肠道病毒 (Polio脊髓灰质炎, Aseptic meningitis无菌性脑膜炎, and Encephalitis脑炎)
Reoviruses 呼吸道肠道病毒(Upper respiratory and gastrointestinal illness上呼吸道和胃肠道疾病)
Rotaviruses 轮状病毒(Gastroenteritis肠胃炎)
Adenoviruses 腺病毒(Upper respiratory and gastrointestinal illness上呼吸道和胃肠道疾病)
Hepatitis肝炎 A (Infectious传染性)
Norwalk-type (Gastroenteritis) 诺沃克因子(肠型流感的致病因子)
Treatment
Chemical oxidation / disinfection is the preferred treatment. Chlorine feed with 30 minute contact time for retention, followed by activated carbon filtration is the most widely used treatment. Ozone or iodine may also be utilized as oxidizing agents. Ultraviolet sterilization or distillation may also be used for the treatment of viruses.
