Background on chlorination

by Kim N. Irvine, Gary W. Pettibone, Salmatou Bako, Jim Caruso, Roseanne Frandina, Gary Aures, Jane Ork, and Dan Bentivogli

Chlorination is a common method of disinfecting effluent from municipal wastewater treatment plants. The French and English used chlorine as a general disinfectant beginning in the early 1800s, and the first recorded chlorination of sewage on a large scale was conducted in 1854 when the Royal Sewage Commission added chloride of lime to sewers in London. Chlorination at a wastewater treatment plant (WWTP) scale was first done in Hamburg, Germany in 1893. This was soon followed at a plant in Brewster, New York in 1894.

The Buffalo Sewer Authority treats wastewater for the city of Buffalo at the Bird Island WWTP. This plant was constructed in response to complaints from downstream communities that Niagara River and Lake Ontario waters were being contaminated by the city's untreated sewage discharges. These complaints were first recorded in 1892, and by 1935 the New York State Health Department, under the direction of State Health Commissioner Thomas Parran, required the city to treat its sewage discharge. When the Bird Island primary WWTP began operation in 1938, it had the largest chlorination system in the world. A year after the plant went on-line, bacteria levels in the Niagara River were reduced by 97%.

While the ability of chlorine to kill pathogenic micro-organisms is not disputed, the mechanisms that explain the disinfecting action are not fully understood. The strong oxidation capability of chlorine may be one factor important in disinfection. Industry also uses this characteristic whereby hydrocarbons react with chlorine to produce stable persistent low-energy chlorinated organic compounds that include polyvinyl chloride (PVC), PCBs, CFCs, and certain pesticides.

Some chlorinated organic compounds raise environmental concerns:.

PCBs, dioxins, furans, hexachlorobenzene, and mirex, for example, are of concern because of their persistence, bioaccumulative tendency, and the potential for toxicity, mutagenicity, and effect on the endocrine systems in biota.
Many of these compounds have been detected in Great Lakes water, precipitation, sediment, and biota.
Potentially carcinogenic chlorinated hydrocarbons, such as chloroform and carbon tetrachloride, are formed as the result of wastewater chlorination.

Against this background, there has been a demand from some environmental groups that the use of chlorine and chlorine-containing compounds be stopped. These demands have been given weight by the International Joint Commission (IJC) in the Sixth and Seventh Biennial Reports on Great Lakes Water Quality which recommended that U.S. and Canadian Governments:

 . . . consult with industry and other interests to develop timetables to sunset the use of chlorine and chlorine-containing compounds as industrial feedstocks, and examine the means of reducing and eliminating other uses, recognizing that socio-economic considerations must be taken into account in developing the strategies and timetables.