Shock chlorination

Introduction

From swimming pools to wells, chlorine is a common chemical used to disinfect water sources.

Due to safety concerns, hypochlorite (bleach) is the most commonly used compound to conduct shock chlorination¹. Hypochlorite is used in one of three forms: commercial bleach (approx. 3.5-5% concentration), calcium hypochlorite (Ca(OCl)₂; 65-70% concentrated), or sodium hypochlorite (NaOCl; about 12% concentration)². These forms of hypochlorite are not as pure as chlorine gas, and will degrade in strength when in storage. However, like chlorine gas, they also react with water to form a disinfectant, hypochlorous acid (HOCl).

Microbial agents

Frequently, microbial factors infiltrate water sources through fecal matter. Many types of bacterial pathogens can initiate waterborne illnesses, including enteric bacteria, protozoa, or viruses³.

Helicobacter pylori

Electron micrograph of Helicobacter pylori, a microbe commonly found in public water sources. Courtesy: Timothy Hoover (Franklin College)

Helicobacter pylori is known to cause gastritis and peptic ulcers.
Studies done in Peru⁴ and Japan⁵ have shown the presence of the bacteria in public water sources, proving its possibility as a waterborne microbe.

Cryptosporidium

Immunofluorescence of Cryptosporidium, the microbe that caused an epidemic in Milwaukee in 1993. Over 104 deaths were credited to the waterborne microbe . Courtesy: H.D.A Lindquist (EPA)

Cryptosporidium parvum is a type of parasite capable of causing gastrointestinal illness. Unlike Helicobacter pylori, however, Cryptosporidium has been proven to be unresponsive to chlorination⁶.

Alternative methods

Scientists are not content with shock chlorination. As technology advances, methods to improve both testing and disinfection are created.

References

¹ Rutala W., Weber D. "Uses of Inorganic Hypochlorite (Bleach) in Health-Care Facilities". 1997. Clinical Microbiology Reviews 10(4). p. 597-610.

² "Chlorination Chemistry"

³ Leclerc H., Schwartzbrod L., Dei-Cas E. "Microbial agents associated with waterborne diseases". 2002. Crit Rev Microbiol 28(4). p. 371-409

⁴ Hulten K., Han S.W., Enroth H., Klein P.D., Opekun A.R., Gilman R.H., Evans D.G., Graham D.Y., El-Zaatari F.A. "Helicobacter pylori in the drinking water in Peru". Gastroenterology. April 1996. Volume 110(4). p. 1031-5.

⁵ Horiuchi T., Ohkusa T., Watanabe M., Kobayashi D., Miwa H., Eishi Y. "Helicobacter pylori DNA in dirnking water in Japan". Microbol Immunol. 2001. Volume 45(7). p. 515-9.

⁶ Bukhari Z., Marshall M.M., Korich D.G., Fricker C.R., Smith H.V., Rosen J., Clancy J.L. "Effects of ozone, chlorine dioxide, chlorine, and monochloramine on Cryptosporidium parvum oocyst viability". 1990. Appl Environ Microbiol 56(5). p. 1423-8.

Edited by Erika Jensen, student of Joan Slonczewski for BIOL 116 Information in Living Systems, 2013, Kenyon College.