Chlorination

A chlorination system doses a controlled quantity of chlorine or a chlorine-releasing compound into a water stream to disinfect it by inactivating bacteria, viruses and other pathogens, and to maintain a protective residual disinfectant concentration throughout the distribution or storage system. Chlorination is the most widely used water disinfection method globally, applied in drinking water treatment, wastewater effluent disinfection, cooling water biofouling control and a wide range of industrial and municipal applications.

IWTE designs and supplies chlorination systems for sodium hypochlorite solution (bulk delivered or on-site generated), calcium hypochlorite granules and tablets for small and remote applications, and chlorine gas systems for large municipal treatment works where the engineering and safety infrastructure is in place. The choice of chlorine form is determined by the application scale, dosing rate, site safety requirements, chemical availability and client preference. IWTE advises on the most appropriate form for each specific application during the design brief phase.

On-site sodium hypochlorite generation systems produce dilute hypochlorite solution by passing a direct current through a brine solution of salt and water. The electrolytic process generates sodium hypochlorite at a concentration of approximately 0.8 percent, which is dosed directly into the water stream. On-site generation eliminates the need for bulk chemical deliveries, reduces chemical storage volumes and removes the hazards associated with handling concentrated hypochlorite. It is particularly well suited to remote locations, sites with limited access for chemical deliveries and large municipal systems with high and continuous chlorine demand.

Free chlorine refers to dissolved chlorine species present as hypochlorous acid and hypochlorite ion, which are the active disinfecting forms. Total chlorine includes free chlorine plus combined chlorine, which is formed when free chlorine reacts with ammonia or organic nitrogen compounds in the water to form chloramines. Chloramines are less effective disinfectants than free chlorine but provide a more stable and longer-lasting residual in distribution systems. IWTE designs chlorination systems to achieve the specific free or total chlorine residual target required by the applicable drinking water standard or permit.

IWTE integrates online amperometric or colorimetric chlorine residual analysers at the dosing point outlet and at critical monitoring points in the treatment system. The measured residual is fed back to the PLC control system, which adjusts the dosing pump or gas chlorinator output to maintain the target residual as flow rate and chlorine demand vary. Flow pacing, where the dose rate is proportional to the instantaneous flow, provides a primary control loop with residual trim correction providing secondary closed-loop adjustment.

Safety requirements depend on the chlorine form used. Sodium hypochlorite systems require bunded chemical storage with secondary containment, overfill prevention, spill containment and appropriate personal protective equipment provisions. Chlorine gas systems require vacuum-operated chlorinator and injector design to prevent gas release on equipment failure, dedicated ventilated chlorine rooms with fixed gas detection, audible and visual alarms, automatic shutoff valves, emergency response procedures and operator training. IWTE designs all chlorination systems to comply with applicable chemical safety regulations and provides full safety documentation as part of the system package.

Yes. When chlorine reacts with natural organic matter present in the source water, it can form disinfection byproducts (DBPs) including trihalomethanes (THMs) and haloacetic acids (HAAs), which are regulated in drinking water standards due to their potential health effects at elevated concentrations. DBP formation is managed by reducing the organic precursor load in the water before chlorination through coagulation, sedimentation and filtration, optimising the chlorine dose to the minimum required for the target CT value, and considering alternative or supplementary disinfection technologies such as UV where DBP formation is a concern.

Yes. IWTE designs and supplies chlorination systems as standalone disinfection units and as integrated stages within complete water treatment plants, desalination systems and reuse schemes. The chlorination system is engineered to the plant flow rate, water quality and disinfection objectives, with unified PLC and SCADA control. IWTE provides commissioning, operator training, CT value calculation support and ongoing service contracts including chemical supply coordination and spare parts for all chlorination systems we supply.