- VIRUSES
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 which 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 which states that 99.99% reduction or inactivation for viruses. Major enteric viruses and their diseases are shown below.
Virus |
Disease |
|
Enteroviruses |
Polio, Aseptic meningitis, and Encephalitis |
|
Reoviruses |
Upper respiratory and gastrointestinal illness |
|
Rotaviruses |
Gastroenteritis |
|
Adenoviruses |
Upper respiratory and gastrointestinal illness |
|
Hepatitis A |
Infectious hepatitis |
|
Norwalk-type |
Gastroenteritis |
Treatment
- Ultraviolet Light Technology 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, bromine or iodine may also be utilized as oxidizing agents.
