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What Is Reverse Osmosis And How Is It Used?

What is Reverse Osmosis and How is it Used?

Reverse osmosis (RO) is a membrane filtration technology that removes organic and inorganic contaminants from water. RO systems are simple to operate, modular for ease of installation, and can be integrated with existing filtration or ion exchange systems to achieve high purity water. Reverse osmosis is also used for treatment of industrial wastewater and implementation of closed loop and zero liquid discharge systems. If you need deionized water or ultrapure water for your processes, are looking to reduce water consumption and recycle wastewater, or need a technology that can remove PFAS, reverse osmosis may be a good option.

How does it Work?

Naturally, by the process of osmosis, water flows through a semipermeable membrane from lower to higher salt concentration. Reverse osmosis uses pressure to force water containing organic and inorganic contaminants through semipermeable membranes to produce highly purified water.

The key component of reverse osmosis is in the semipermeable membrane that comprises each RO filter unit. The most common membrane used is thin film composite (TFC) materials placed on top of a stronger substrate. TFC membranes are typically configured with three layers to provide high rejection of contaminants, high filtration rates, and good mechanical strength. Each membrane is wound tightly within a pressure vessel and can provide a large filtration surface area. Filtration surface area depends on feed spacers within the membrane, which can vary based on design factors such as feedwater characteristics1.

Contaminants that are separated from purified water are concentrated in a waste stream known as RO reject or “brine”. RO systems use cross-flow filtration, sending filtered water out one side and reject out the other, to provide self-cleaning of membranes. In a typical industrial application 80% – 85% of feedwater is purified2; however, removal efficiency depends on flow rate, pressure, solute concentration, and other conditions that should be considered when designing a RO system.

What does it Remove?

The power of reverse osmosis lies in its capacity to remove dissolved solids or TDS with >95% removal efficiency. Dissolved solids include any minerals, salts, metals (including copper, cadmium, chromium, lead, iron, zinc, etc.), and cations or anions (calcium, magnesium, chlorides, sulfates, etc.) dissolved in water.  This includes organics (organic compounds, BOD, COD, microorganisms, etc.) and even emerging contaminants like perfluoroalkyl substances or PFAS. Research shows reverse osmosis can remove a wide range of PFAS with >90% removal efficiency3.

Water Reuse & Closed Loop Systems

In combination with filtration and other treatment technologies, reverse osmosis can be used to treat process wastewater and water for reuse in production processes. Wastewater recycling and water reuse has been adopted in many industries (food & beverage, semiconductors, metal finishing, chemical manufacturing, pharmaceuticals, etc.) to improve process efficiency and reduce water consumption. Industrial wastewater recycling and water reuse not only decreases a facility’s water footprint but can provide additional benefits including:

  • Reducing water usage costs
  • Reducing or eliminating discharge / disposal costs
  • Progress towards sustainability goals

Loureiro can support evaluation for creating a closed loop or zero liquid discharge system, where all wastewater from your production process is either reused or concentrated to reduce off-site disposal costs. Some benefits of a closed loop system are:

  • Achieving a higher water use efficiency
  • Eliminating wastewater regulatory requirements
  • Progress towards sustainability goals

Loureiro can provide industrial wastewater treatment system design, construction, permitting, and commissioning for a turnkey solution.

Deionized & Ultrapure Water

Many industrial processes (electroplating, metal finishing, chemical manufacturing, pharmaceutical, etc.) need deionized or ultrapure water to meet production quality standards. Deionized (DI) water contains very low concentrations of mineral ions (calcium, chloride, etc.) and ultrapure water is used when the industrial process requires a very strict water quality standard. Reverse osmosis can be combined with additional filtration and ion exchange polishing to provide ultrapure water that meets production standards.

Conclusion

Reverse osmosis can be a cost-effective treatment option to produce high quality water for use in industrial processes and can be an integral part of a water reuse / wastewater recycling system.

Loureiro can support with design and installation of reverse osmosis skid systems, operation and maintenance support, industrial wastewater closed loop evaluations, and water reduction evaluations. If you are interested in using reverse osmosis or any associated services you can contact our team by completing the form on our industrial wastewater page.

References:

  1. Bartels C., M. Hirose, H. Fujioka. Performance Advancement in the Spiral Wound RO/NF Element Design. Oceanside, CA. 2007.
  2. United States Environmental Protection Agency. Drinking Water Treatability Database: Membrane Separation. tdb.epa.gov/tdb/treatmentprocess?treatmentProcessId=-2103528007
  3. United States Environmental Protection Agency. Reducing PFAS in Drinking Water with Treatment Technologies. 2018. www.epa.gov/sciencematters/reducing-pfas-drinking-water-treatment-technologies
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