How to calculate the dosage of water treatment scale inhibitors, bactericides, reducing agents, and pH adjusters

Due to differences in water conditions and water production processes, the following descriptions of water treatment scale inhibitors, bactericides, and reducing agents are for reference only. The calculation method for pH chemical dosage is for reference only. The actual dosage should be based on the stability of the treated water quality.

I. Dosage of Scale Inhibitors

        The recovery rate of the first-stage reverse osmosis system in the desalination water treatment system is calculated as 75% calculated under 20-50℃ conditions. This water quality has a strong scaling tendency, indicating that an appropriate amount of membrane dispersant must be added to ensure the long-term safe and stable operation of the reverse osmosis system and extend the service life of the membrane. The feed water for the second-stage reverse osmosis is the treated water from the first-stage reverse osmosis. , Low hardness and alkalinity do not require the addition of scale inhibitors. According to calculations using specialized reverse osmosis software, the recommended dosage under 75% recovery rate is: 3ppm (based on feed water), daily dosage = Reagent concentration × Feed water volume ×24h≈8.64 kg (feed water volume calculated as 120m3/h )

II. PH Adjustment

        Adjustment pH The system uses X015 type diaphragm pump and 120L water tank. A solution with a concentration of 0 ． 1 ％～ 0 ． 5 ％ of Na0H is prepared in the water tank and added through a diaphragm pump. Adjust the alkali addition according to the treated water pH value and treated water conductivity to achieve a moderate value. Determine the addition concentration based on the actual conductivity of the secondary treated water. The diaphragm pump operates synchronously with the second-stage reverse osmosis.

General Principles for Adjusting Alkali Dosage

       1 When the conductivity rises sharply, it indicates that the alkali dosage is too high.

       2 When the conductivity is relatively stable but high, it indicates that the alkali dosage is too low.

       3 When the alkali dosage is too low and then increased, the conductivity drops sharply, but then rises again after reaching a certain level, indicating that the increase in alkali dosage is too large.

       4 If the alkali diaphragm pump scale cannot reach the alkali dosage even at maximum, it indicates that the alkali concentration in the tank is too low.

       5 If the alkali pump scale is below 20 and the adjustment sensitivity is too high, it indicates that the alkali concentration in the tank is too high.

III. Dosage of Bactericides

       1 Since the raw water is municipal tap water, the number of bacteria in the system is relatively low. However, as the temperature rises, , especially in summer, , it will affect the normal operation of the reverse osmosis membrane. , Therefore, a certain amount of bactericide should be added to control bacterial growth and protect the reverse osmosis membrane from microbial damage. This agent is continuously added to the system pretreatment to maintain the residual chlorine level in the feed water to inhibit bacterial growth. Therefore, the dosage should be determined based on the actual degree of biological contamination of the system. The recommended dosage is 2ppm ( based on feed water )。

       2 ), daily dosage for the desalination water treatment system = Reagent concentration × Feed water volume ×24h≈5.76 kg (feed water volume calculated as 120m3/h )

IV. Dosage of Reducing Agents

        1 To prevent oxidizing bactericides from entering the reverse osmosis membrane and oxidizing the membrane elements, a reducing agent dosing system is installed before the reverse osmosis system. The type of agent used is DCL95 . The specific dosage depends on the residual chlorine level in the feed water of the reverse osmosis system after adding the oxidizing bactericide. It is generally 3-5 times the residual chlorine level, with a dosage of 2ppm as the basis.

        2 Daily dosage for the desalination water treatment system = Reagent concentration × Feed water volume ×24h≈5.76 kg (feed water volume calculated as 120m3/h ). Note that excessive addition of reducing agents can also cause system fouling. Therefore, daily monitoring of residual chlorine is necessary to adjust the dosage ratio between oxidizing bactericides and reducing agents, ensuring that the reducing agent sufficiently reacts with oxidizing substances to prevent damage to the membrane elements without leaving excessive residue to cause additional pollution to the system.