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What Reverse Osmosis Pretreatment Processes are Used for Seawater Desalination?

Dec. 25, 2022


Reverse osmosis filtration is currently the most commonly used desalination technology for seawater desalination. It mainly uses reverse osmosis membranes to intercept inorganic salts, metal ions, organic substances, minerals, colloids and other impurities in seawater, so that seawater can be desalinated into fresh water for human consumption. In addition to the reverse osmosis membrane, the pretreatment of reverse osmosis is also very important, which also plays a decisive role in the service life and filtration efficiency of the reverse osmosis membrane. Seawater desalination reverse osmosis pretreatment process mainly includes coagulation, flocculation, dissolved air flotation, multimedia filtration and microfiltration process.

1. Coagulation, Flocculation and Dissolved Air Flotation Processes

After the seawater is transported to the storage tank through high-pressure pumps and pipelines, it first passes through the coagulation tank and flocculation tank to coagulate and flocculate the suspended matter and colloids and other impurities in the seawater, forming sediment and sinking to the bottom of the tank. The supernatant flows into the dissolved air flotation tank to further remove suspended particles, organic matter, colloids, algae and other impurities in the seawater, and then pump the treated seawater to the multimedia filtration system for the next step of filtration.


2. Multimedia Filtration Process

The filter medium of the multi-media filter generally uses quartz sand, manganese sand and activated carbon, etc. The main function of the quartz sand and manganese sand multimedia filter is to further remove suspended particles, colloids, microorganisms, metal ions in seawater. The activated carbon filter is mainly used to absorb organic substances, suspended substances, colloids, chlorinated free substances, etc. in seawater, so as to reduce the turbidity and color of water and improve water quality.


3. Microfiltration Process

The main function of microfiltration process is to intercept particulate impurities in water and prolong the service life of downstream reverse osmosis membrane elements. Due to the high salt content in seawater, stainless steel filter housings will be corroded by seawater, so the equipment in the microfiltration system generally uses FRP filter housing with strong corrosion resistance. Filter consumables usually choose High Flow Filter Cartridges, Melt Blown Cartridges or PP Filter Bags with 5 micron.

FRP High Flow Filtration System

The FRP high flow filter system is composed of FRP high flow filter housing and High Flow Filter Cartridge. In order to meet the different requirements for the space used, the way of assembly and installation and the water flow, HONGTEK provides various models of FRP high flow filter housings, such as VRP Series Single High Flow Filter Housing, MRP Series Multi High Flow Filter Housing and Horizontal FRP High Flow Filter Housing.


FRP Depth Filtration System

The FRP depth filtration system is composed of FRP cartridge filter housing and Melt Blown Filter Cartridges. In order to meet the different requirements for water flow in different regions and projects, HONGTEK also provides a variety of FRP filter housing with different specifications, such as 5 rounds x 20 inch, 5 rounds x 30 inch, 5 rounds x 40 inch, 12 rounds x 30 inch, 12 rounds x 40 inch, 22 rounds x 40 inch, etc.


FRP Bag Filtration System

The FRP bag filtration system is composed of FRP bag filter housing and Size #2 PP Filter Bag. The single and multi FRP bag filter housings provided by HONGTEK can not only meet the water flow requirements of different project sites, but also increase flexibility in filter design. At present, our FRP multi bag filter housings are available in 3 rounds, 4 rounds, 5 rounds, 6 rounds, 7 rounds, etc.


When designing the FRP filtration system, HONGTEK recommends to choose our existing FRP filter housing according to the water flow required by the system. If the available space on the project site is limited or our single unit of FRP filter housing could not meet the water flow requirements of the system, we suggest that you choose the appropriate specification from the same FRP filter housing of our existing specification according to the actual situation of the project site, and connect them in parallel to meet the requirements of the project.

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