Reverse Osmosis: A water purification process - WorldOChemicals

Reverse Osmosis: Water Treatment Process

Category : Process
Published by : Data Research Analyst,

Reverse Osmosis (RO) is a water purification methodology that removes ions, molecules and other larger particles from drinking water using a semipermeable membrane. The process of removing salt from seawater or desalination is done by reverse osmosis.

History of Reverse osmosis:

The process of Reverse Osmosis by using semipermeable membrane was observed first in 1748 by a French clergyman and physicist Jean Antoine Nollet.

The University of California at Los Angeles was the first to investigate in 1950, desalination of seawater using semipermeable membranes. In the 1950s, researchers from both the University of California and the University of Florida successfully produced fresh water from seawater.

Cape Coral, Florida in 1977 became the first municipality in the US to use the reverse osmosis process on a large scale.

By the end of 2001, around 15,200 desalination plants came into operation worldwide, out of which 20% of them were in the U.S.

How does Reverse Osmosis work?

Formally, RO is the process of forcing a solvent to a region of low soluble concentration from high solute concentration region through a semipermeable membrane by applying pressure.

The typical single pass seawater RO system consists of:

  1. Intake: To set up RO system you need an intake pump at the source of the water to be purified.

  2. Pre-treatment: This step includes removal of solids, sediments, carbonic acid from the water so as to protect the membrane. This step also includes dosing of oxidizing biocides like chlorine to kill bacteria.

  3. High-pressure pump: The high-pressure pump is required to let the water pass through the membrane. Pressure for brackish water typically ranges from 225 to 376 psi and in the case of seawater it ranges from 800-1180 psi.

  4. Membrane: In membrane assembly there is a pressure vessel with a membrane, allowing feed water to be pressed against the membrane. RO system membranes are made in a range of configurations, but the two most common configurations are spiral-wound and hollow-fiber.

  5. Energy recovery: Energy recovery is used to reduce the energy consumption. Much amount of energy input of the high-pressure pump can be recovered by the concentrate flow and efficient energy recovery device.

  6. Remineralisation and pH adjustment: Stabilization of desalinated water is done to protect downstream pipelines and storage, generally by adding lime or caustic soda to prevent corrosion. Liming material is used to maintain pH between 6.8 to 8.1 so that meets the potable water specifications.

  7. Disinfection: Reverse osmosis is an effective blockade of pathogens, but post-treatment assures secondary protection against downstream and membranes problems. To sterilize pathogen which has bypassed the RO process, disinfection by means of UV lamps can be employed.

Where is RO used?

  1. Drinking water purification: Around the world, drinking water systems in households include RO step, are generally being used for purifying water for drinking and cooking purpose. The reverse osmosis water purification unit (ROWPU) is designed for military use, which is a self-contained water treatment unit providing potable water from almost any source of water.

  2. Water and wastewater purification: Reverse osmosis water processors are used to purify rainwater collected from storm drains, which is then used for irrigation and industrial cooling and other such purposes as a solution to water shortage problem. In industries, RO removes minerals from boiler water at power plants. Reverse osmosis is also used to purify brackish groundwater and effluent.

  3. Food industry: Reverse osmosis is an economical operation of concentrating food liquids such as fruit juices. RO is largely used for the production of whey protein powders and for concentrating milk to reduce shipping costs, in the dairy industry. This process is also used in the wine industry.

  4. Maple syrup and hydrogen production: A maple syrup producer uses this process to remove water from the sap before boiling it down into syrup. The use of reverse osmosis process lets 75-90% of the water to be removed from the sap, resulting in reduced energy consumption. Sometimes reverse osmosis is used in small-scale hydrogen production to prevent the formation of minerals on the electrodes surface.

  5. Reef Aquariums: For an artificial mixture of seawater, many reef aquarium keepers use RO systems.

  6. Window cleaning: An increasingly popular technique of cleaning windows is “water-fed pole” system. With this system windows are scrubbed with purified water, using a brush on the end of a long pole, wielded from the ground level.