WWTP Tour - Chlorine Disinfection

Although the number of microorganisms is greatly reduced by treatment processes and natural purification, the term disinfection is used in practice to describe treatment processes that have as their major objective the destruction of pathogenic organisms. Strictly defined, disinfection is the destruction or removal of all pathogenic organisms, while sterilization refers to the destruction or removal of all microorganisms. No attempt is made to sterilize wastewater, which is both unnecessary and impractical. Chlorine is a non-selective killer. It affects organisms on the basis of sensitivity, growth rate, concentration and exposure time.

Because chlorine and some of its compounds disinfect so well, and because they are available at reasonable cost, they have been used almost to the exclusion of other disinfecting agents. The main use of chlorine in wastewater treatment is disinfection.

Wastewater contains organisms from both healthy and sick people discharging their wastes into the collection system. Pathogenic (disease-producing) organisms are potentially present in all wastewaters, and these organisms must be removed or destroyed before treated wastewater can be discharged to the receiving waters. Typical waterborne bacterial diseases are typhoid, cholera, paratyphoid, and bacillary dysentery. Many wastewater effluents are discharged to receiving waters which are used as a source of public water supply, shellfish growing areas, for recreational purposes, or for the propagation of fish and wildlife. Therefore removal of pathogenic organisms is required to minimize the health hazards caused by treated and untreated waste discharges to these receiving waters. The clear effluent from the secondary clarifiers is chlorinated as it flows by gravity to the Effluent Pumping Station.