Expert Interview with Bill Stimeling
In 2009, the city of San Benito, TX completed the construction of a new six-million-gallon-per-day (MGD) microfiltration plant, which replaced a plant that had been in operation since 1928. The new facility is considered one of the most modern and innovative water treatment plants in the region and has been recognized for its use of microfiltration and solar power. Its chlorination system, while more traditional than these technologies, was selected for its cost-efficiency, reliability and flexibility.
The safe handling of chlorine gas and a secure chlorination system includes a proper facilities design, an operation and maintenance program, the appropriate safety equipment and an emergency action plan. The following, while not all-encompassing, will cover the chemical and physical characteristics of chlorine, as well as the many safety steps and procedures that must be followed to keep your facility safe.
Chlorine is commonly available in three different forms: gaseous chlorine, calcium hypochlorite, and sodium hypochlorite, which are all used in chlorination.
Gas chlorine is typically packaged in 150 lb cylinders and 1-ton containers. This is 100% elemental chlorine stored as a liquified gas under pressure. The chlorine is fed to the process using a pressure feed system which applies the chlorine gas directly to the process or a vacuum operated - solution feed system which uses a water operated ejector to create a chlorine solution which is applied to the process.
Calcium hypochlorite is typically packaged as a solid tablet containing 60% active chlorine. The chlorine is fed to the process using a simple tablet feeder that passes the process water through a tube of tablets, causing the tablets to dissolve into the water. More sophisticated tablet systems dissolve the tablets in water making a solution of controlled chlorine concentration, which is then fed to the process using a chemical dosing pump.
Sodium hypochlorite is a liquid containing 12-15% active chlorine when fresh. Sodium hypochlorite is typically delivered to plant storage tanks by truck and applied to the process using chemical dosing pumps. With this form of chlorine, the concentration decays over time.
In today’s credit-crunched, bottom-line-oriented economic environment, utilities in the water and wastewater sectors are scrapping plans to replace old equipment with new technologies and are looking for ways to improve existing equipment performance with system upgrades.
What is chloramination?
Chloramination is a secondary disinfection process by which chlorine (Cl2) and ammonia (NH3) are combined to produce chloramines, a persistent disinfectant used to maintain a residual in a long distribution system . The residual chloramine aids in preventing post microbial growth in the distribution system.
Since chlorine technology was first used in the US to disinfect drinking water in Jersey City, NJ, in 1908, most waterborne diseases have been eliminated in the U.S. Chlorine is still the most common disinfectant for drinking water and wastewater. Chlorine is also used for disinfection and as a biocide in numerous industries.