On-site chlorine generation cuts delivery risks, stabilizes disinfectant quality, and turns a brine stream into chlorine exactly when you need it. In this guide I explain how on-site chlorine generation works in plain English, when it beats delivered bleach, and how a modular chlor-alkali approach lets you scale from simple disinfection to full chemical independence.
What “on-site chlorine generation” really means
On-site generation systems use salt and water, apply electricity in an electrolytic cell, and produce a low-strength oxidant solution for disinfection. Utilities shift to OSGs to improve operator safety, reduce logistics, and lower total cost compared to gas chlorine or delivered bleach. These systems typically produce a fresh oxidant with less than 0.8 percent free available chlorine, which reduces hazards while providing effective disinfection.
How it works: from salt and water to free chlorine
Inside the cell, chloride ions are oxidized at the anode to chlorine gas that dissolves to form hypochlorous acid. At the cathode, water is reduced to hydrogen gas and hydroxide. The hydroxide then shifts the equilibrium to hypochlorite, which is the active disinfectant in solution. The overall reaction is salt plus water to sodium hypochlorite and hydrogen. The resulting oxidant typically has a pH close to nine, which is expected for low-strength hypochlorite from OSGs.
OSG skids usually include a softener, a brine tank, metering pumps, an oxidant storage tank, a heater or chiller when needed, and dedicated hydrogen vents for safe off-gassing.
ON SITE CHLORINE GENERATION WITH WELYSIS
REQUEST ASSESSMENTOSGs vs delivered bleach: who wins and why
If you operate in a place with volatile prices, long supply routes or strict storage rules, on-site generation often wins. You remove recurring purchases of concentrated chemicals and cut transport and insurance exposure. For many plants the payback on OSG equipment is commonly reported in the range of two to three years, driven by avoided chemical purchases and lower handling costs.
Freshness also matters. Stored hypochlorite degrades over time, especially with heat and sunlight, which reduces free chlorine and increases chlorate or perchlorate byproducts. Producing only a two to three day supply on site keeps oxidant potency high and byproducts lower.
OSGs vs modular chlor-alkali plants: which model fits your scale
At small to medium flows, a low-strength OSG is often the simplest way to make disinfectant on tap. When your strategy includes chemical independence and value creation beyond disinfection, a modular chlor-alkali plant becomes compelling.
In Welysis projects, we start upstream by preparing high-purity brine and feed it to membrane electrolyzers. The same core electrochemistry produces three saleable products at once: high-purity chlorine gas, sodium hydroxide, and hydrogen.
With this configuration you can feed chlorine to a dedicated hypochlorite loop for 12 to 15 percent product, use caustic at 32 percent as is or concentrate to about 50 percent, and valorize hydrogen as process fuel or for downstream uses. The decision comes down to capacity, product portfolio, and the value of independence in your market.
Safety by design: the three essentials
Safety in on-site chlorine generation systems is not optional—it is a fundamental requirement built into the design from day one. A well-planned installation minimizes operational risks, protects personnel, and ensures process continuity. These three technical pillars are essential for any successful implementation:
- Hydrogen management. Electrolysis generates hydrogen that must be vented safely from the cell and oxidant tanks. Proper ventilation and adherence to hydrogen safety standards are non negotiable for indoor installations.
- Softened water and temperature control. Hardness forms scale on electrodes and can damage cells. Maintain softened feed and keep cell inlet water in the 40 to 80 degrees Fahrenheit range. Where raw water falls outside this band, include a heater or chiller.
- Salt quality. Use high-purity, food-grade salt and keep bromide low. Bromide may oxidize to bromate, which has a 0.01 mg per liter maximum contaminant level in drinking water.
Real-world costs: what drives CAPEX and OPEX
Capital costs are dominated by the electrolytic cell, ancillary tanks, softening, ventilation, and controls. Operating costs are driven by electricity, salt, periodic cell cleaning, and routine maintenance.
The big economic lever is the avoided purchase and delivery of high-strength chemicals. Many plants report a two to three year payback once chemical purchases and insurance exposures are removed.
Where OSGs shine
Municipal drinking water, desalination intakes, cooling towers and industrial circuits benefit from fresh oxidant and simplified logistics. OSGs reduce truck deliveries. For example a single salt delivery can replace multiple bleach deliveries to yield the same chlorine capacity, which lowers the site’s carbon footprint.
Implementation checklist
How Welysis executes the chlor-alkali route for on-site chlorine
Welysis plants follow a brine-to-chemicals flow designed for reliability, circularity, and digital control.
Brine preparation and polishing
We start from local solid salt, solar salt or brine reuse from desalination reject. The target concentration is around 300 to 320 grams per liter of NaCl. After coarse filtration, we dose sodium carbonate and sodium hydroxide to precipitate calcium and magnesium, then remove precipitates with fine filtration and polishing.
We adjust to less than 0.1 milligrams per liter of calcium and less than 0.05 milligrams per liter of magnesium with a pH between 10 and 11, and maintain high conductivity with no suspended solids.
Membrane electrolysis
We feed the purified brine to membrane electrolyzers where the global reaction produces chlorine gas, hydrogen gas, and sodium hydroxide at about 32 percent. The anode releases wet chlorine while the cathode produces hydrogen and hydroxide.
This is the heart of the process and the basis for both on-site hypochlorite and broader chemical production.
Chlorine handling and hypochlorite loop
We separate liquid carryover, dry chlorine and route it either to liquefaction and storage on large units or to a hypochlorite reactor. There chlorine reacts with sodium hydroxide to form sodium hypochlorite. This loop produces 12 to 15 percent active chlorine for water treatment and sanitation.
Caustic handling
We use the 32 percent caustic as a process reagent or concentrate it through multiple-effect evaporation to about 48 to 50 percent, depending on site demand. Caustic can also support pH control and cleaning in place.
Hydrogen valorization
We collect and dry low-pressure hydrogen and apply it as clean combustion fuel, as a process gas, or for chemical valorization paths such as AdBlue when projects justify it.
Closed brine circuit and zero liquid discharge
We neutralize purges and recirculate to the dissolver for a closed-loop brine circuit. Our objective is no liquid discharge so the plant operates under a zero liquid discharge strategy wherever feasible.
Digital layer and remote O&M
All plants integrate the Welysis International Network for SCADA, remote supervision, predictive maintenance and fleet optimization. We standardize sensors, communications and analytics across installations so operating practices improve continuously.
ON SITE CHLORINE GENERATION WITH WELYSIS
REQUEST ASSESSMENTWho benefits most from the chlor-alkali approach
Frequently asked questions
- What chlorine strength do OSGs typically produce
A. They generally produce low-strength oxidant with less than 0.8 percent free available chlorine. - Is hydrogen a concern in OSG rooms
A. Yes. Hydrogen is generated by electrolysis and must be vented from cells and tanks with proper ventilation and safety design. - What feed water quality do OSGs need
A. Use softened water and keep the cell inlet temperature near 40 to 80 degrees Fahrenheit to prevent scaling and cell damage. - What salt specification is recommended
A. Food-grade salt with low hardness contaminants and low bromide, since bromide can oxidize to bromate regulated at 0.01 milligrams per liter. - How fast do OSG investments pay back
A. Many plants report two to three years due to avoided chemical purchases, lower logistics and reduced safety overhead.
