On-site generators (OSGs) produce chlorine when a solution of sodium chloride is passed through an electrolytic cell and electricity is added. In essence, OSGs take a solution of sodium chloride (salt) and water and apply electricity, which produces chlorine and other oxidant species.

Water coming into the OSG goes through a softener, and then splits into two lines. One line is used to feed a salt filled tank, creating a saturated brine. The other line enters the OSG, acting as a dilution stream prior to the electrochemical process. Saturated brine is then precision mixed with the softened water stream prior to entering the electrolytic cell. Application of an electrical current to the cell results in the production of an oxidant solution from the diluted brine.

After leaving the electrolytic cell, the oxidant solution is temporarily stored in the oxidant tank. Then it is metered or injected into the water moving through the treatment process, typically with similar equipment as an existing chlorine system.  Injection options include a venturi or other eductor -, centrifugal feed pumps, or chemical metering pumps. Sites with multiple injection points may use a combination of these options.

Hydrogen gas is also produced inside the electrolytic cell and is removed from the cell and the oxidant storage tank through vents and/or dilution air blowers.

Process Flow Diagram

The OSG operates via a signal from the level switch/transmitter located in the downstream oxidant tank. When the tank is empty, the transmitter/switch sends a signal to the Programmable Logic Controller (PLC) to put the OSG online. As soon as the tank is full of oxidant, the transmitter/switch sends a signal to the PLC to put the OSG in standby mode. This means very minimal operator attention is required during normal operation.

Many communities are turning to OSGs for their water distribution systems because of the benefits, including better safety, high-quality disinfection, greener operations, and substantial economic savings. Because of the benefits that OSGs provide, many companies prefer OSG systems as opposed to more traditional chlorine delivery systems such as chlorine gas, concentrated sodium hypochlorite, and bulk calcium hypochlorite.

Click here for a tech brief on the science behind OSGs.