Hypochlorination / Dechlorination

After final settling, the supernatant from the secondary settling tanks flows into the chlorine contact tanks for disinfection. Disinfection by sodium hypochlorite solution is intended to kill or inactivate the pathogenic bacteria, viruses and protozoan cysts commonly found in wastewater. Disinfection is the critical step necessary to insure that waterborne diseases are not spread through the discharge of treated sewage. The BCUA’s NJPDES Permit contains fecal coliform limits of 200/100 ml 30-day average and 400/100 ml during a seven day average.

Chlorination by chlorine or sodium hypochlorite is one of the most commonly used methods for the destruction of pathogenic organisms in wastewater. However, residual chlorine compounds in wastewater can also be toxic to aquatic life forms. Therefore the BCUA utilizes sodium bisulfite to reduce the level of chlorine produced oxidants (CPOs) in the effluent to a maximum of 0.1 mg/l.

Sodium hypochlorite and sodium bisulfite solution is delivered in bulk in tank trucks and stored in four fiber glass reinforced 8,000 gallon capacity tanks. The solutions are fed by positive displacement metering pumps that are controlled by a chlorine residual signal.

Just prior to discharge and measured by parshall flume, the flow is sampled at each of the BCUA’s four outfall channels.

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