Determining proper chlorine levels
Editor’s note: The following request was received in Spanish and translated for “Ask the Expert” by Agua Latinoamérica editor Ingvi Kallen.
Question: Allow me to congratulate you for publishing Agua Latinoamérica, which is a very useful source of information.
Some time ago I had the opportunity of reading your magazine in a friend’s business, and took advantage of the free subscription offer, and later paid for a long-term subscription. I would like to know where I can find information about the limitations of drinking water disinfection with chlorine and its by-products (hypochlorites) specifically, if there is a table available that shows the effects of chlorine on virus, bacteria, parasites (protozoa), algae and fungi spores.
This information is extremely important to me since, in these Latin American countries, chlorine is used with the belief that it eliminates any type of microbiological contamination. It would be very interesting to know the levels of residual chlorine that present a germicidal effect on each one of the microorganism groups previously mentioned.
Answer: The following website (for the Wilkes University Center for Environmental Quality in Pennsylvania) has some information related to the data you’re seeking: http://wilkes.edu/~eqc/chlorinecontact.htm
A table can also be found at a webpage for a “Water Sanitation” course at Kansas State University: www.oznet.kus.edu/grsc_subi/Teaching/GRSC651_Courses_ Material/lecture_slides/GRSC651_lect_ 32_Water_ Sanitation.ppt
Additional information can be found directly at the U.S. Environmental Protection Agency website. See:
- Microbial and Disinfection By-Product Rules: Simultaneous Compliance Guidance Manual, August 1999: http://www.epa.gov/safewater/mdbp/simult.pdf is a 150-page document that provides a full explanation of chlorine contact time values for effective disinfection using chlorine and its derivatives.
- “Chapter 2: Disinfectant Use in Water Treatment,” EPA Guidance Manual: Alternative Disinfectants and Oxidants, April 1999: www.epa.gov/safewater/mdbp/pdf/alter/chapt_2.pdf includes a table for CT values regarding Giardia and information regarding sodium and calcium hypochlorite—frequently used in well water disinfection. The larger 346-page Guidance Manual this chapter comes from can be found at: www.epa.gov/safewater/mdbp/alternative_disinfec-tants_ guidance.pdf
Unfortunately, all of these web-pages listed above are in English. But you might be able to request the information in Spanish, particularly from the USEPA as the agency increasingly has provided such data in both English and Spanish.