Calculation of sodium hypochlorite for drinking water disinfection

Sodium hypochlorite is increasingly used for disinfecting drinking water. It is safe to use, and its transportation and storage do not require additional safety measures. Such a disinfection method is often practiced in the water distribution system of small businesses or households. Before using sodium hypochlorite, it is necessary to understand its characteristics and methods for calculating the required concentration.

Drinking Water Disinfection

Chlorine exists in 5 different acids – hypochlorous, chlorous, chloric, chlorous, and hydrochloric. Each has its own unique properties. Hypochlorous acid is considered the weakest in terms of action, but its excellent disinfecting properties are worth noting. Due to the instability of the compound, its salts are used instead, among which are potassium hypochlorite, sodium hypochlorite, and calcium hypochlorite.

Under normal conditions, these salts are solid crystals that decompose when heated, releasing free chlorine. They are widely used in the medical industry, industrial processes, and various household applications. Sodium hypochlorite is used for water treatment, allowing the removal of harmful substances and microorganisms.

Determining Solution Concentration

Before calculating the amount of sodium hypochlorite needed for disinfecting drinking water, it is necessary to determine the concentration in the dosing pump. To do this, you need to find out the solubility limit at a certain temperature using the Lurie handbook. This has become particularly important recently, as the precision of dosing in pump equipment has significantly increased. Using working solutions with high concentrations is due to the difficulties in finding suitable locations for installing large containers.

The concentration of the active substance also depends on the material of the flow part. Most often, this is polypropylene with ethylene-propylene seals. Dosing heads are made of polyvinyl chloride with seals made of polytetrafluoroethylene (PTFE or Teflon) or stainless steel, ensuring their long-term use.

Swimming pool water treatment with sodium hypochlorite

Regarding the durability of materials and seals, you can find information in the compatibility table. According to them, it can be determined that at temperatures up to 40 degrees Celsius, materials demonstrate good compatibility with a sodium hypochlorite solution with a concentration of no more than 2% active chlorine. Some manufacturers claim that their equipment can handle higher concentrations, but practice often disproves this.

Calculation of sodium hypochlorite

As an example, let’s calculate the amount of sodium hypochlorite needed to disinfect drinking water with a concentration of 2%, which is 2 mg/L. For calculations, let’s take the density of the working solution as 1130 g/L and a water flow rate of 10,000 L/h. Through simple calculations, it can be determined that 0.88 liters of the working solution will be required every hour. In a day, the pump should deliver 21.23 liters.

The commercial solution has a density of 1260 g/L, and its concentration is 15%. It is necessary to calculate how much commercial solution is needed to obtain the working mixture. First, calculate the mass, which will be 113,000 g. The amount of chlorine in it will be 2260 g (the mass needs to be multiplied by the concentration and divided by 100). The mass of the commercial solution is 15,066 g. To determine the volume of commercial solution needed to obtain the working solution, divide it by the density of the working solution. As a result, it turns out that 11.9 liters of commercial solution are needed.

Advantages of using sodium hypochlorite

Experts believe that water purification with sodium hypochlorite is safer than with chlorine.

Firstly, chlorine is a toxic substance, often causing serious accidents during transportation.

Secondly, laws regarding the handling of chlorinated compounds are constantly becoming stricter.

The use of sodium hypochlorite is not subject to oversight by the Federal Service for Environmental, Technological, and Nuclear Supervision. The effectiveness of this compound has been repeatedly tested in practice.