Sodium hypochlorite is generally recognized to be an efficient and cost-effective disinfectant. It is used in swimming pools to disinfect water and to oxidize water pollutants. As each swimmer deposits tens of millions of micro-organisms in the water, it is important that the swimming pool is disinfected.
To maintain the quality of the water, it is passed through a water treatment system. A standard water treatment system consists of a buffer tank, which keeps water levels consistent, a sand filter, which in combination with a flocculant removes suspended solids, and dosage points for sodium hypochlorite and acid (usually hydrochloric acid or sulphuric acid).
Swimmers deposit a variety of undesirable materials in the water, including urine, sweat, hair, skin, blood and cosmetics. Further additional impurities are introduced via the added feed water. These ‘pollutants’ are oxidized using sodium hypochlorite, creating harmless compounds and preventing the accumulation of pollutants that could trigger microbiological problems or algae growth. Effective disinfection of public swimming pools, which welcome large volumes of swimmers, is essential to prevent ear infections, stomach problems, diarrhea, or, even worse, viral infections such as meningitis.
To keep unwanted by-products to a minimum, sodium hypochlorite should be dosed after dilution and active chlorine levels must be actively monitored. At Nouryon, we have considerable knowledge of these processes and are able to offer advice that takes into consideration your particular circumstances.
Considerable research has been conducted into the use of sodium hypochlorite in combination with other technologies such as UV treatment. These studies have shown that the quality of the pool water can be optimized if sodium hypochlorite is used in combination with other disinfection techniques.
Cooling water is often (pre-) treated to prevent various types of bio-fouling. Pipes, heat exchangers and cooling towers are particularly susceptible to bio-fouling. Airborne bacteria such as legionella pneumophila also present a health risk, and require the cooling water used in ‘open’ cooling towers to be disinfected.
Seawater and inland water contain mussels, which can cause serious damage if they are pumped into a cooling installation. Once inside, they attach themselves to metal surfaces, enabling them to grow further. In turn, this causes the heat exchangers or intake pipes to become blocked.
This also results in an enormous loss of energy and causes corrosive problems. The resulting financial damage can be considerable. Using the right amount of sodium hypochlorite prevents mussels from attaching themselves to metal surfaces.
Of all disinfectants, the chemistry of sodium hypochlorite has been studied to the greatest extent. Given its proven track record, widespread industrial use and low cost, sodium hypochlorite is the most commonly used antifouling solution to date.
Drinking and process water
Both drinking and process water are derived from either groundwater or surface water. However, as surface water (in particular) contains many microorganisms, some of which are pathogenic, the water must be disinfected before it can be used.
As far as process water is concerned, this is done to prevent micro-organisms, algae and similar microbiological compounds from growing (the process temperature conditions are conducive to this growth process). When treating drinking water, disinfectants are used to prevent the water distribution system being infected by pathogenic microorganisms.
Many European countries use sodium hypochlorite to disinfect their drinking water. Although the Dutch have opted for the non-chemical removal of micro-organisms, for instance through filtration by sand filter, reverse osmosis or by means of ozone/UV treatment, most water treatment plants in the Netherlands have a sodium hypochlorite stand-by facility. It should be noted that the majority of nutrients for microorganisms are removed as the drinking water is produced.
Given its proven track record, widespread industrial use and low cost, sodium hypochlorite remains the most commonly used water disinfectant to date.
Disinfection and odor removal in municipal wastewater
The use of sodium hypochlorite is not as common in wastewater treatment as in drinking water production because wastewater is much polluted and would consume a lot of sodium hypochlorite.
It would result in high concentrations of chlorinated byproducts in the effluent. Sodium hypochlorite is mainly used for polishing: treating wastewater just before discharge and after most impurities have been removed by other technical means, such as bio filtration.
Traditionally chlorine or sodium hypochlorite was used for treating domestic wastewater after biological treatment. The objective was to minimize the concentration of micro-organisms and ammonia being discharged into receiving streams.