What are the key Components of a Reverse Osmosis (RO) System?
A Reverse Osmosis (RO) System is made up of many components that work like cogs in a clock to desalinate or filter water from its inherent impurities. Below are some of the main components of an RO System:
Feed pump of an RO System
A feed pump is required to drive raw water through the pretreatment system and on to the inlet of the high-pressure pump. The pump type and material is selected based on the type and source of water.
The sizing of the Feed pump is dependent on the required feed water flow, pressure required for prefiltration system & also to compensate pressure loss across the pipes & filters. Often the operating conditions are relatively unknown, so the pump is selected considering a safety margin. The feed pump may also be used to backwash the multimedia filter if designed so.
Multi Media Vessels are selected / designed based on the inlet water flow and filtration velocity with respect to the type and source of water. A MMF (Multimedia Filter) System is used to reduce the level of suspended solids (turbidity) from incoming feed water.
The Multimedia filter might need to be back-washed daily or upon differential pressure of 1-1.5 Bar across the filter, to flush out large particles, sediments and reduce chances of bacterial growth.
Antiscalant Dosing System
The Antiscalant injection system consists of an injection pump and dosing tank. The pump is often electronically controlled. The dosing rate depends on the raw water quality, flow and desired dosage of the chemical.
Dosing of antiscalant into the feed water delays / prevents scaling on the membrane surface. Antiscalant dosing should be carried out on the water before it reaches the RO membranes - to break up sulfate precipitates, calcium carbonate, and other mineral fouling.
Micro Filtration units
One or multiple microfiltration units may be located within the System. These could be Bag or Cartridge filters of varying micron ratings. Similar to the multimedia filter, the micro filtration units help arrest sediments and suspended solids that can harm the RO membranes.
Cartridge Filter are periodically replaced or cleaned, on the basis of the type of filter used and the inlet water quality, or upon a differential pressure of 0.5-1.0 Bar across the filters.
System Pump in an RO System
A high-pressure pump acts like the heart of the System, allowing pressurized water flow through the RO membranes. The treated water is fed by means of the high-pressure pump into the RO membranes, obtaining permeate or product water and high pressure brine rejection. The High Pressure Pump selection varies with respect to the type of water and its TDS. In case of Sea Water application where the pressure varies from Approx. 25-80 Bar, energy recovery systems are integrated with the HPP (high pressure pump) to reduce the power consumption of the system. Altering the operating pressure slowly and ensuring motor rotation is correct are some preventive methods to keep the high-pressure system in check.
Pressure Vessels in an RO System:
A pressure vessel is a tubular device inside which reverse osmosis membrane elements are housed. For spiral wound elements the pressure vessel is often referred to as the pressure tube. Multiple membrane elements can be installed inside a pressure vessel. A suitable vessel would have to be selected in such cases. Pressure vessels vary based on the number of membranes housed and on the required design system pressure. Good quality pressure vessels offer years of trouble-free operation and require no maintenance.
The RO Membranes:
Osmosis occurs when two solutions with different concentrations are separated by a semipermeable membrane. In RO water purification systems, the osmotic pressure is overcome using hydraulic pressure, which is applied using a pump to the concentrated side, allowing clean water to pass to the next stage.
If designed for use in gulf waters, it is essential to design and select adequate membrane type and quantity, as the salinity of gulf waters is known to be exceptionally high.
Chemical Cleaning of the membrane is to be conducted periodically, upon a significant drop in the normal flow rate or upon a pressure drop of 2 Bar across the Pressure Vessel. Daily flushing of membranes is advisable to remove any contaminants on the membrane surface.
The criteria to determine when the membranes should be replaced varies from site to site. The most common reason for the replacement of RO membrane elements is that they are no longer producing the desired permeate quality. Permeate quality is affected by the feed salinity, flux rate, temperature, recovery, fouling, membrane age, and many other factors. Changing one of these variables can often lead to increased or decreased permeate quality.
Advanced Watertek offers a wide variety of membranes from reliable and reputed manufactures like Dow Filmtec, Hydranautics, and Toray.
Post treatment is an optional stage if undesirable taste, odor, or gases are seen present after the RO treatment stage. Post-treatment includes chemical addition to adjust water quality, blending a controlled amount of raw water with permeate before disinfection and distribution to increase the TDS, or even removal of existing ions from the product water. Type of Post treatment depends on the required product water quality.
Fail-Safe Devices in the RO System:
Fail-safe devices are added as an additional level of security and risk prevention for the system. For example, the high pressure pump is protected via a low-high pressure control switch which will trip the motor at a threshold value. An overload relay is also provided to protect the motor.
These fail-safe devices are essential features of a reliable water treatment system, reducing risk of downtime and need for maintenance, and increasing the life of the system.
Monitoring Instruments in the RO System:
Proper monitoring of the RO system will prolong the life of the entire system. Some of the common monitoring instruments an RO system is equipped with are:
Low Pressure Gauge: The pressure indicator should be provided, maintained and monitored regularly as per design specifications to ensure the proper functioning of the system.
Flow Meters: The flow meter measures the flow rate of permeate & reject line. Accurate & calibrated level indicators are required to monitor and control both permeate and reject flow of the system.
High Pressure Gauge: The high pressure gauge indicates the pressure at the point of entry at the first pressure vessel and also at the reject line. Depending on the design of the system, the gauge will indicate the ideal pressure to be maintained to deliver your desired output. A constant operating pressure is recommended to maintain the life of the system.
Total hour Run Meter: As the name suggests, this monitors the total time the system is running.
Pressure Control Valve of the RO system:
In reverse osmosis, the water travels from high concentration to low concentration, but because that does not happen naturally, pressure must be applied to the high concentration side of the membrane to force water molecules to the other side.
If designed so, the system operating pressure is regulated with the use of pressure control valve. It is always advisable to turn the valves slowly during pressure adjustment and flow control.
The operating pressure is subject to the salinity and the temperature of the raw water. Assuming salinity is constant, the higher the temperature, the lower the pressure and lower the temperature, the higher the pressure.
Piping across the RO System
The RO system consists of multiple piping, including low and high pressure piping, fittings & Valves. Advanced Watertek uses high-quality stainless-steel pipes and accessories with anti-corrosive properties for high pressure piping. This helps maintain the pipes despite high salinity and harsh conditions.
Periodic preventive maintenance of your system & equipment helps maintain the product water quality and increase the life span of the system. Reach out to our After Sales team for a consultation on your RO Maintenance.
Skid of Container of the RO System:
The entire Reverse Osmosis Sea Water Desalination unit is built either on a steel skid or inside a container to protect the system. Advanced Watertek used high-quality stainless-steel skid or thermally insulated containers for their systems.