As nature fresh water resource is limited, sea water plays an important part as a source for drinking water. The use of reverse osmosis is becoming the accepted standard for desalination. Reverse osmosis (RO) system has been used for many years to remove dissolved substances from seawater, with mixed success. Water feed must be pretreated to remove organics, algae, and fine particles that, in most cases, cause RO systems to foul prematurely. Pretreatment systems capable of providing a filtrate with low SDI and turbidity values are of critical important for RO applications.

MS® provides a cost-effective and typical pretreatment method with these process multi-media filters with coagulation, followed by active carbon filters and cartridge filters.

• The performance targets for pretreatment system are defined as follow: SDI<5.0, best<3.0
• Turbidity<1.0, best<0.3
• No chlorine and similar oxides, such as ozone
• No other chemicals that may damage the RO systems

Fig.1 RO Treatment Process

1. Coagulant

A coagulation/sedimentation process was paired with the multi-media filter to improve the water quality of the filtrate in terms of SDI and turbidity. The most commonly used coagulants are ferric or alum salts to destabilize particles in the raw feed water.

• aluminum sulfate：pH 6.0-8.5
• Ferric chloride：pH 3.5-11.0
• iron sulfate：pH 4.0-11.0

2. Polymer

Coagulation was followed by flocculation, a mixing technique promoting the aggregation of the destabilized (coagulated) particles and as an aid to sedimentation and filtration.

• PAC (polyaluminium chloride): pH 6.0-8.5
• PFS (Polymeric ferric sulfate) : pH 6-9

3. Multi-media filtration

Multi-media filtration could efficacious remove the suspended solids in the feed, reduces turbidity and SDI value. Surface loading rates for the media filtration are selected based on industry standard design criteria and quality of feed. The type of filtration media typically utilized includes anthracite，sand，and other traditional media.

• Anthracite：effective diameter 0.7-0.8mm
• Sand ：effective diameter 0.35-0.5mm

4. Carbon filtration

Active carbon could adsorb dissolved organic and chlorine, has widely used for RO pretreatment system. This process is similar to Multi-media Filtration. Active carbon must be periodic sterilization used steam or hot water.

5. Scale inhibitor

When insoluble salt is concentrated in excess of its solubility limit, it will occur at the membrane surface of reverse osmosis. The main insoluble salts in natural water are CaCO3, CaSO4, SiO2，and so on. Inhibitor can prevent carbonate, sulfate, and calcium fluoride scale.

• Inorganic polyphosphate: sodium hexametahposphate, Sodium tripolyphosphate, etc.
• Polymer：Organic phosphonae，polyacrylic acid, polymarelic acid, etc.

6. Cartridge filtration

Cartridge filters are utilized as additional protection for the RO membrane elements to capture any final particles or suspended solids that many enter the feed stream. The cartridge filters are to capture relatively large particles (>5μm) that many plug the membrane. Cartridge filters are replaced when suspended solids plug the filter and increase the differential pressure above a desired level.

MS® can supply a variety of cartridge filters for RO pretreatment. MS® cartridge filters are an excellent choice as a pre-filter to protect more expensive RO system.

• MS® Micropure Classic Series Melt Blown Cartridge Filter: 1/5μm

MS® Micropure Classic Series Melt Blown Cartridge Filter is pure polypropylene depth filter, graded pore structure enhances dirt holding capacity and long service life. MS® Micropure Classic Series Melt Blown Cartridge Filter offer better protection of RO membrane systems.

• MS® polypure W/polypore Calssic Cartridge filter: 1/5μm

MS® polypore W Cartridge Filter is especially designed to provide over 50% filtering area than traditional pleated cartridge filters. It uses fibers of varying diameters to produce a pore size distribution from upstream to dowmstream. Very high contaminant holding capacity and all polypropylene construction could bring longer service life, save your cost imperceptibly.

MS® polypore Classic Cartridge Filter is ideally suited for the removal of agglomerate particles and gels. Deep, wide pleats for long service life in liquids with high levels of suspended solids and designed for reverse flow cleaning and construction optimized for consistent performance under variation in flow.

• MS® String Wound cartridge filter AquaPure Classic/GP Series: 1/5μm

MS® string wound cartridge filter is a kind of deep filter cartridge, which is made of the textile fabric string preciously winding onto the multi-hole axies according to the specific technology.

MS® String Wound cartridge filter AquaPure Classic is high efficiency but low in price for equipment installation cost saving.

MS® String Wound cartridge filter AquaPure GP is structured loose outer layers and tight inner layers which can offer true depth filtration for high dirt holding capacity.

• MS® FiltraPure Series Cartridge Filter: 1/4/10μm

The MS® FiltraPure Cartridge Filter, a pleated cartridge which can be backwashed, could directly installed into existed housing, no need for any changes.

• MS® 600FlowPure Series Cartridge Filter:1/3/5μm

MS® 600FlowPure-MH Series: MS® 600FlowPure-MH cartridge filter is designed to be used in different housing. It can be used for a variety of hardwares and for different flow rate request. The large diameter with big filter area insures to reduce the number of filter cartridges and the dimension of housing required.

MS® 600FlowPure-HF Series: MS® 600FlowPure-HF cartridge filter has a 6 inch/152mm large diameter, and is coreless, single open-with an inside to outside flow pattern. The large diameter with big filter area insures to reduce the number of filter cartridges and the dimension of housing required. The long service life and high flow rate in low investment and less manpower in many applications.

MS® 600FlowPure-BC Series: MS® 600FlowPure-BC Series cartridge filter combines the performance advantages of cartridge filters with the ease use of bag filter systems. It offers unique combination of benefits and unmatched economics. The pleated media increases the effective filtration area with high flow and long service life.