Chemical dosing system is indispensable for seawater desalination plant as there are many impurities in the water as we know. So it is required to add chemicals in the pre-treatment process of seawater desalination RO system, so as to kill bacteria, remove the smell, color and other particles. In general, what we add are flocculant, bactericide, reductant, antiscalant, etc. They are common chemicals in seawater desalination plant. And thus each kind of chemical has different its feature and function, thereby, it is necessary to differentiate which kind of chemical we need to add.

Flocculant (PAC or FeCl3) for seawater desalination plant:

The flocculant is mainly to gather the particles dispersed in the water for easy to remove in the sand filter, so as to meet the requirements of the membrane inlet water quality (turbidity <1NTU, SDI < 5). The dosage of flocculant is about 2.5?5ppm of raw water flow. And dosing pump is connected to feed water pump. Automatically alarm and stop the pump when the tank level is low.

Bactericide for seawater desalination plant:

There are a lot of microorganisms, bacteria and algae in seawater. The growth of bacteria and algae in the sea water and the growth of the microorganism will not only bring many troubles to the water supply facilities but also directly affect the normal operation of seawater desalination equipment and process pipeline, so it is required to carry out the disinfection of sea water. Typical bactericide is classified into oxidizing and non-oxidizing.

  • Oxidizing bactericide is usually named as a strong oxidizing agent, which is strong enough to kill microorganisms in the water. Typical oxidizing bactericides are liquid chlorine, sodium hypochlorite, copper sulfate and other chemical agents.
  • Non-oxidizing bactericide is not to kill the microorganisms, but to the special part of the microorganisms, so it is not affected by reductant substances. Non-oxidizing bactericide is usually chlorophenols and quaternary ammonium salt. The killing effect of non-oxidizing bactericide is good and enduring. It is less affected by the reduction of hydrogen sulfide, ammonia and other substances, and also less affected by the pH in the water.

Reductant for seawater desalination plant:

Oxidizing bactericide is constantly added to the RO pre-treatment process, and free chlorine is controlled 0.2-0.4 ppm. However free chlorine of RO inlet requirement is requested less than 0.1 ppm, so it is required to add reductant to control free chlorine when seawater entering into RO system.

Antiscalant for seawater desalination plant:

Before pre-filtered water entering into RO system, adding antiscalant is to prevent RO concentrated side fouling to ensure that the membrane module still maintains good permeability in the long-term operation, and effectively prolong membrane lifespan and improve the stability of the production quality of reverse osmosis system. Antiscalant is mainly used in reverse osmosis system, it can effectively prevent the deposition of colloidal and inorganic salt in the membrane surface, strongly control the sulfate and effectively prevent the formation of iron on the reverse osmosis membrane.

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