- False. Disinfection of water is the selective destruction of pathogenic or disease causing organisms. Sterilization is the complete destruction of all organisms. Sterilization is not necessary in drinking water treatment.
- False. Most bacteria are harmless, but a few types cause serious illness and even death in humans.
- a and c. Typhoid fever can be transmitted in water by the bacterium Bacillus typhosus and cholera by Vibrio cholerae. Infectious hepatitis is a waterborne virus and Giardia lamblia (giardiasis) is a protozoan. The AIDS virus does not live in water.
- More. Most viruses are more resistant to chlorine than are bacteria. Therefore, higher chlorine concentrations and longer contact times are necessary to kill virus agents. The protozoa are the most resistant to chlorine.
- More. Protozoan cysts such as giardia and cryptosporidium normally are not killed by the concentrations of chlorine typically used in water treatment. UV treatment has been found to be very effective.
- False. The National Primary Drinking Water Regulations specify microbiological compliance based on presence/absence of total coliform bacteria in sample results. The maximum contaminant level (MCL) for public water systems analyzing at least 40 samples per month is no more than five percent of the monthly samples may be total coliform positive. The MCL for systems analyzing less than 40 samples per month is no more than one sample per month may be total coliform-positive. There is no drinking water standard or limit for the numerous non-health-related heterotrophic plate count bacteria that also exist in water supplies.
- False. Disinfection is necessary for complete destruction of all pathogenic organisms in water, but it is not effective unless it is preceded by water clarification. Filtering water through granular or equivalent filters is an effective means of removing pathogenic and other organisms from water. The removal rates vary from 20 to 99 percent depending on the coarseness of the filter media and the type and effectiveness of pretreatment such as coagulation, flocculation and/or settling. Well-designed fine membrane and ultrafilters can remove even higher percentages of microorganisms.
- Ultraviolet. Ultraviolet rays with wavelengths that peak at about 253.7 nanometers and lie between 200 and 300 nanometers disrupt various organic components of the cell causing a biological change that inactivates the microorganism.
- Ultrasonic. Ultrasonic waves can destroy microorganisms by vibration.
- Heat. Heat has been used universally in emergency situations to disinfect water. Boiling water for about five minutes will destroy essentially all microorganisms.
