ClorTec Sodium Hypochlorite Generators

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History & Capabilities

De Nora Water Technologies, Inc. is an international provider of solutions to municipal, industrial water and wastewater treatment operations. ClorTecon-site sodium hypochlorite generating systems have been designed, manufactured, installed, operated and serviced since 1988. Over that time, De Nora Water Technologies, Inc has sold and installed over 2000 ClorTec systems. The experience gained from these endeavours is unparalleled in the water treatment industry as their relentless drive for product improvement continues.

The Process

NaCl + H2O + 2e NaOCl + H2

(Salt + Water + Energy = Sodium Hypochlorite + H)

Generating sodium hypochlorite on-site is a simple and straight forward process. STS systems operate by feeding softened water into a brine dissolver. The salt dissolves to form a 30% brine solution, which is further diluted twelve parts water to one part brine (12:1). This ratio achieves the desired 2.6% salt solution, which is passed through the electrolytic cell(s). The cells apply a low voltage DC current to the brine and 0.8% sodium hypochlorite is produced on-site. The sodium hypochlorite is safely stored in a day tank designed to accommodate one or more day’s system output. When the sodium hypochlorite reaches the low-level set point, the ClorTec system will automatically restart to replenish its supply. A metering pump injects the hypochlorite as needed.

Benefits of the Process

On-site sodium hypochlorite generation has many advantages over conventional chlorine systems. The advantages include safety, reduced operational costs, consistent solution strength, and production on demand. On-site generation also eliminates OSHA process safety management training, risk management planning purchasing and transportation of Haz Mat Chemicals while reducing disinfection by-products. The most important benefit is improved water quality.

On-site Generation

On-site generation has proven itself to be cost effective, reliable and a safe alternative to stringent regulations and the rising costs of chlorine gas and bulk sodium hypochlorite. On-site generation is the best solution to a major regulatory challenge facing all water and wastewater utilities. With the development of the patent-pending CT Split Flow Cell from Severn Trent Services, there is a guaranteed 20% reduction in consumable operating cost over competitive on-site generation systems.


ClorTec systems are component based, which allows tremendous flexibility in adapting the equipment to new or existing facilities. Any model may be custom configured for unique applications.

Electrolytic Cell

The heart of any on-site chlorine generation system is the electrolytic cell. This is where the brine solution and DC current are reacted to form dilute hypochlorite (0.8%). The CT series cell houses an array of one piece vertical solid plate electrodes that allow the electrolyte to flow rapidly across the surface. Because the electrolytic process liberates hydrogen, it is important to accommodate dual phase flow through the cell. It is also desirable to achieve rapid hydrogen separation to produce maximum gas lift at the electrode surface and minimize calcification of the electrodes. These elements of cell design directly affect overall system efficiency by minimizing electrolyte heat gain, calcium deposition, and electrical consumption. The pre-assembled matrix provides uniform electrode spacing and easy disassembly.

More electrode surface means lower current density (maximum 1.2 amps/sq. in.) and results in longer electrode life and lower cell temperature.


Each CT Series cell houses an array of electrodes within a clear seamless acrylic cylindrical structure sealed with bolted end flanges. Each electrode bank contains an equal number of anodes (+) and cathodes (-) made of titanium. Both the anodes and cathodes have a proprietary coating of mixed metal oxides. These coatings are specifically formulated for maximum electrical efficiency and longevity. Severn Trent Services’ recent work specifically with cathode coatings has resulted in large gains in cell efficiency.

The clear cylindrical cell allows full visibility and easy access to the electrode array. Cells can be removed as a single unit, eliminating the time and labour spent to disassemble sandwich-type cell structures and handle electrodes individually.

The CT cell design operates using the new, patent-pending, split flow chiller design. The benefit of this is that the internal cell operating temperature is maintained within the optimum range of 65–80°F.

This is achieved by injecting 100% of the brine and 1/3 of the softened water at the front of the cell. The balance or 2/3 of the softened water is then directed to an optional water chiller where it is cooled and injected into the last 2/3 of the cell. The chiller requirement is based on the site-specific raw water temperature.

Maintaining the cell within the optimum temperature range reduces salt and power consumption while minimizing by-product formation and optimizing efficiency.


ClorTec’s unique electrolytic cell is comprised of concentric cylindrical anode and cathode assemblies, one inside the other. This T.E. design eliminates deficiencies experienced with expanded metal electrodes. Electrolyte flow is forced vertically in the annular space between the concentric cylinder.


Hydrogen is the only by-product. The electrolytic cell(s) and the hypochlorite storage tank are designed to safely contain and vent the hydrogen from the cell directly into the atmosphere. Dilution and dispersal is managed via ClorTec’s proprietary hydrogen dilution system, which incorporates a blower providing ventilation of both the sodium hypochlorite storage tank and the cell assembly vent stack.

The system has software monitored safety interlocks that sense current draw on the blower motor, flow in the ventilation pipework and positive pressure on the ventilation stack outlet. In addition, the ventilation system is designed to allow passive venting of the plant to atmosphere in the event of total equipment failure, therefore preventing the build up of hydrogen.


A programmable logic controller (PLC) monitors each aspect of ClorTec’s operation, which can also be upgraded to an HMI package. This technology greatly improves disinfection management processing and reporting operating parameters, system status and alarm conditions. ClorTec controls are telemetry/SCADA ready and are pre-configured for most communication protocols. Control systems are commonly customized for specialized applications. Severn Trent Services has many systems in service and offers off-the-shelf, as well as customized programming packages with full data logging and communications capabilities. 

Process Advantages

• Safe
• Cost effective and efficient
• Consistent solution strength and reduction of disinfection by-products
• Process safety management exempt
• Risk management planning exempt
• Improved water quality

Product Advantages

• Modular design
• Configuration versatility to meet a wide range of output requirements
• Expandability – ClorTec’s modular configuration supports upgrading outputs to meet expanding needs
• The ClorTec’s system design improves the ability to service and allows quick repair or replacement of components.

Multiple Cell Design

• Easy access for maintenance is one of the key elements of this advanced system. The cells can be disassembled and reassembled in less than 30 minutes.
• Clear cylindrical cell body allows for viewing of the process, and electrode condition.
• Electrode Matrix – ClorTec’s unique vertical flat-plate electrodes are assembled in a single uniformly spaced array for maximum operating efficiency and ease of service.

Modern PLC Controls

Each ClorTec system features PLC based controls.
• Easy SCADA & Telemetry integration.
• Uninterrupted power supply backup on “CT” series.
• Customized computer and command option available with full communication and data logging capabilities.