An on-site sodium hypochlorite generator makes a dilute disinfectant solution from salt, water and electricity, so you avoid storing toxic chlorine gas or buying and storing concentrated bleach that degrades over time. It suits drinking water, sewage, pools and aquaculture where chemical supply is unreliable or safety rules are strict, and its main running costs are salt, power and periodic cell descaling.
Why choose an on-site sodium hypochlorite generator?
An on-site sodium hypochlorite generator (also called an electrochlorinator) produces a dilute disinfectant solution from salt, water and electricity, exactly where it is used. It removes the need to transport and store chlorine gas or concentrated bleach, which improves safety, avoids supply interruptions and gives a stable product. The trade-off is higher upfront equipment cost and the need for routine maintenance, mainly cell descaling.
This guide compares on-site generation with delivered bleach and chlorine gas, explains what drives salt and power consumption, and outlines typical applications and maintenance. Browse our disinfection equipment for available capacities.
How does electrolytic hypochlorite generation work?
A brine solution, made by dissolving salt (sodium chloride) in softened water, flows through an electrolytic cell containing coated titanium anodes and cathodes. When direct current is applied:
- At the anode, chloride ions are oxidized to chlorine.
- At the cathode, water is reduced to hydrogen gas and hydroxide ions.
- In an undivided cell, the chlorine and hydroxide react immediately to form sodium hypochlorite (NaClO).
The overall reaction is NaCl + H₂O + electrical energy → NaClO + H₂. The product is stored in a tank and dosed with metering pumps, while the hydrogen is diluted with air from a fan and vented outdoors.
How does on-site generation compare with bleach and chlorine gas?
| Factor | On-site NaClO generator | Delivered sodium hypochlorite (bleach) | Chlorine gas |
|---|---|---|---|
| Product strength | Dilute, typically under 1% | Typically 5–15% | 100% chlorine |
| Hazard class of stored chemical | Low (dilute solution, salt is non-hazardous) | Corrosive liquid | Toxic, compressed gas |
| Main safety risks | Hydrogen venting, electrical | Spills, splashes, mixing with acids | Toxic gas leaks |
| Supply chain | Salt only; easy to store and transport | Regular deliveries of liquid | Cylinder or tonner deliveries, strict regulation |
| Product stability | Generated as needed; little storage loss | Degrades over time, faster when warm; forms chlorate | Stable in cylinder |
| Byproduct concerns | Low chlorate when made fresh | Chlorate and bromate can build up in storage | Minimal |
| Capital cost | Highest | Lowest | Moderate (plus safety systems) |
| Operating cost drivers | Salt, power, cell replacement | Chemical price and freight | Chemical price, safety compliance |
| Regulatory burden | Low | Moderate | High (leak detection, scrubbers, permits in many regions) |
| Best fit | Remote sites, strict safety rules, steady demand | Small or intermittent demand, reliable supply | Large plants with trained staff and full safety systems |
Why does delivered bleach lose strength?
Concentrated sodium hypochlorite decomposes during storage, and the rate rises with higher concentration, higher temperature, exposure to sunlight and the presence of metal impurities. As it decomposes, available chlorine falls and chlorate accumulates. Diluting bleach on delivery and keeping it cool slows the loss, but cannot stop it. On-site generation avoids this because the solution is dilute and used within a short time.
Why are many operators moving away from chlorine gas?
Chlorine gas is cost-effective at large scale, but a leak can create a serious toxic hazard for staff and neighbors. Safe use requires leak detectors, emergency scrubbers or containment, trained staff, and compliance with transport and storage regulations. For small and medium facilities, those requirements often outweigh the chemical savings.
What affects salt and power consumption?
Running cost is dominated by salt and electricity per kilogram of available chlorine produced. The main factors are:
- Cell design and electrode coating. Electrode materials and spacing determine how efficiently current converts chloride to hypochlorite.
- Brine concentration. Too weak a brine raises power use; too strong wastes salt. Systems are designed for a specific brine strength.
- Product concentration. Driving for a stronger product generally reduces current efficiency because more hypochlorite is reduced back at the cathode.
- Water temperature. Very cold water raises cell voltage, while very warm water increases side reactions such as chlorate formation. Many systems specify an inlet temperature range.
- Water hardness and salt purity. Calcium and magnesium form scale on the cathode, which increases voltage and power use. Softened feed water and high-purity, low-impurity salt are strongly recommended.
- Cell condition. Scaled or worn electrodes raise voltage and power demand; regular cleaning keeps consumption close to design.
For low-concentration brine electrolysis systems, typical published figures are roughly 3–4 kg of salt and around 4–6 kWh of electricity per kilogram of available chlorine. Treat these as screening values and compare suppliers on the same basis, including rectifier losses and auxiliaries.
Where are on-site hypochlorite generators used?
Drinking water
Water treatment plants and rural water supply schemes use on-site generation for primary disinfection and to maintain a residual in the distribution network. It is especially useful where chemical deliveries are irregular.
Sewage and wastewater
Municipal and package sewage treatment plants use hypochlorite to disinfect effluent before discharge or reuse. Hospital wastewater plants rely on it to meet pathogen limits. Good upstream solids removal improves disinfection, because suspended solids shield microorganisms and consume chlorine.
Swimming pools and water parks
Pools need a continuous free chlorine residual. On-site generation avoids storing large volumes of chemical near the public and gives steady dosing.
Aquaculture
Hatcheries and fish farms use hypochlorite to disinfect intake water, tanks and equipment. Chlorine is highly toxic to fish, so treated water must be dechlorinated (for example with sodium thiosulfate) before contact with stock, and dosing must be carefully controlled.
Other uses
Food processing sanitation, cooling water biofouling control and livestock water disinfection are also common applications.
What safety features should a generator include?
Although on-site generation is far safer than handling chlorine gas, a well-designed system still needs engineered protections. Look for these features when you compare equipment:
- Hydrogen dilution and venting: a dedicated fan that dilutes hydrogen with air, with an airflow switch interlocked to the rectifier so electrolysis stops if ventilation fails.
- Flow and level interlocks: electrolysis should stop on low brine or water flow, and on high level in the product tank.
- Temperature protection: cell outlet temperature monitoring to prevent overheating.
- Electrical protection: properly rated rectifier, earth-fault protection and a control panel suitable for a humid, corrosive environment.
- Corrosion-resistant materials: PVC, CPVC, PP or similar plastics for pipework and tanks in contact with brine and hypochlorite, rather than ordinary metals.
- Spill containment: bunding around product storage tanks.
The equipment room should be well ventilated, and acid used for cell cleaning should be stored separately from hypochlorite.
How do you size an on-site generator?
- Determine the flow to be treated (average and peak, m³/h).
- Set the chlorine dose (mg/L), based on chlorine demand testing and required residual.
- Calculate daily chlorine demand: flow (m³/day) × dose (mg/L) ÷ 1,000 = kg/day of available chlorine.
- Add a margin for peak demand and future growth.
- Size product storage to cover peak periods and short outages; storage time should be kept reasonable to limit degradation.
- Confirm utilities: power supply, softened water, salt storage and hydrogen vent route.
For example, 1,000 m³/day dosed at 5 mg/L needs 5 kg/day of available chlorine before margins.
What maintenance does an electrolytic cell need?
Cell descaling
Scale (mostly calcium and magnesium compounds) builds up on the cathode. Signs include rising cell voltage, falling output and higher power use. Cells are cleaned by circulating dilute hydrochloric acid at the concentration recommended by the manufacturer, then flushing thoroughly with water. Never mix acid with hypochlorite: this releases chlorine gas, so drain and rinse the system before cleaning.
Routine checks
- Check and regenerate the water softener so feed hardness stays low.
- Keep salt quality consistent and the brine tank clean.
- Verify the hydrogen dilution fan and vent are working; interlocks should stop electrolysis if airflow fails.
- Monitor rectifier output, cell voltage and product concentration.
- Inspect pipework, valves and dosing pumps for leaks.
Electrode replacement
Electrode coatings wear over time. Life depends on operating current density, cleaning practice and water quality, so budget for eventual electrode replacement.
Request a hypochlorite generator proposal
Send your flow rate, required chlorine dose or residual, water hardness, power supply and application to [email protected], or use our contact page. We will size an on-site sodium hypochlorite generator with brine, storage and dosing equipment. You can also explore our full product range.
FAQ
What concentration does an on-site sodium hypochlorite generator produce?
Most on-site generators using brine electrolysis produce a dilute solution, typically below 1% available chlorine (commonly around 0.6–0.8%). This is well below the concentration of delivered commercial bleach, which reduces hazard and slows degradation.
How much salt does an electrolytic hypochlorite generator use?
Salt consumption depends on cell design, brine strength and water temperature. Low-concentration systems typically use roughly 3–4 kg of salt per kilogram of available chlorine produced; always confirm with the specific equipment data.
Why must a hypochlorite generator vent hydrogen?
Electrolysis produces hydrogen gas at the cathode alongside the hypochlorite. Hydrogen is flammable, so it must be separated and diluted with air to well below its lower explosive limit and vented safely outdoors.
How often does the electrolytic cell need cleaning?
Descaling frequency depends mainly on water hardness and salt purity. With softened water and good-quality salt, cells often need acid cleaning only every few weeks to months; hard water can require much more frequent cleaning.
