How Reverse Osmosis is used to produce purified water

When large bottled water companies boast about their water being filtered with reverse osmosis, they probably don’t tell us the science behind how the process works. If you are like many consumers of pure drinking water who don’t know how reverse osmosis works, this article explains how reverse osmosis is used to produce purified water. And how the Epochem reverse osmosis filtration technology works so that you know why you enjoy healthy drinking water 

First, we will start with the primary definition of osmosis, and then we use it to understand reverse osmosis.   Osmosis describes the diffusion of the solvent through a semipermeablesemipermeable membrane. Suppose a semipermeable membrane (permeable to water but not a solute) separates pure water from water in which solute is dissolved. In that case, water molecules will diffuse across the membrane into the region of higher solute concentration. The hydrostatic pressure required to resist the movement of solvent molecules in this way is osmotic pressure. This is one of the fundamental colligative properties of a solution—that is, it depends on the number rather than the osmotically active particles in a solution, which may be complete molecules or dissociated ions.

Osmotic pressure in an ideal solution is affected by temperature and volume2:


where P is the osmotic pressure, n is the number of particles, R is the gas constant, T is the absolute temperature, and V is the volume. We can calculate the number of particles(n) by multiplying (mass of solute/molecular weight of solute) by the number of particles into which the solute dissociates.

What is Reverse Osmosis?

Reverse Osmosis (RO) is a modern water purification technology that uses a semi-permeable membrane in the separation of ions, unwanted molecules, and larger particles from drinking water. The result is that the solute is retained on the pressurized side of the membrane. The pure solvent is allowed to pass to the other side.

Reverse osmosis is a water purification, uses a semipermeable membrane (synthetic lining) to filter molecules that are not wanted and large particles such as contaminants and sediments like chlorine, salt, and dirt from drinking water. It gets water to clean down to a molecular level, allowing drinkable pure water. In addition to removing impurities and residues, it also eliminates microorganisms – we do not want to drink.

The technology behind reverse osmosis to filter water

In reverse osmosis, the technology design creates applied pressure to overcome the osmotic pressure and push the water from a high concentration of contaminants to a low concentration of pollutants. This means it’s being forced in reverse, and the contaminated water is trying to move into the pure water, but because it must pass through a filter first, the contaminants get trapped, and only the pure water passes through; resulting in the cleanest possible drinking water – which is what we want. Reverse osmosis creates the cleanest drinking water ever, and that is why this technology is promoted immensely for the production of drinking water.

Reverse osmosis typically involves four stages of filtration: a sediment filter, pre-carbon block, reverse osmosis membrane, and post-carbon filter. The sediment filter removes the largest particles, like dirt, sand, and rust, to prevent clogging of the subsequent filters. The pre-carbon filter uses activated carbon to prevent anything larger than a speck of flour from passing through and attract and bond with positively charged ions to avoid chemical compounds, like chlorine and chloramines, from passing through to the third filter. The reverse osmosis membrane then removes molecules heavier than water, such as sodium, high levels of lead, dissolved minerals, and fluoride. Finally, the post-carbon filter polishes the water.

Carbon Filtration process 

Carbon filters remove contaminants through adsorption. Adsorption means that pollutants are attracted to the surface of the activated carbon and held to it, much the same way a magnet attracts and retains iron filings.

Carbon filters also act as a catalyst to change the chemical composition of some contaminants. Activated carbon is ideal for removing chlorine, organic chemicals such as pesticides, THMs like chloroform, and many VOCs that are components of gasoline, solvents, and industrial cleaners. Ion exchange resins are also used in water purification.

Why is Reverse Osmosis Beneficial?

Another known method for water filtration is carbon filtration; as explained above, the carbon filtration process involves using carbon filters to remove contaminants from water. Reverse osmosis differs from carbon filtration in that it can rid the water of up to 99.9% of all contaminants and sediments, or particles as small as .001 micron. In contrast, carbon filtration can only remove particles as small as 1 micron. Your local tap water could be award-worthy clean when it leaves the municipal plant, but as it travels miles from the plant to your glass, it could pick up a host of contaminants, even the water from our boreholes at home may have a lot of contaminants or it may have a naturally high number of total dissolved solids (TDS) in the water, so it would be best to get a reverse osmosis filtration system to ensure that your water does not have any contaminants

Requirements for a safe RO system

The technical requirements of reverse osmosis (RO) system, according to the FDA, are:

Technical Requirements of a RO System

Several basic technical requirements of a RO system are:

  • Feedwater should be adjusted to proper pH and be prefiltered. The amount of TDS and suspended materials in the feed water after prefiltration should be controlled within the designed limits.
  • Feedwater and product water should be monitored for microbiological quality. The system should be disinfected when microbiological quality levels are exceeded.
  • All system components should be mechanically cleaned before disinfecting. Appropriate tests should be performed to assure that chemicals used in disinfection are completely removed from the system.
  • The use of filters or ion-exchangers down stream of RO modules should be avoided.
  • The RO system should be designed for continuous flow without traps, dead ends, and pipe sections to collect stagnant water.
  • The chemical and microbial quality of water should be tested at predetermined intervals during a production cycle. In-line conductivity probes should be installed at key points for continuous monitoring of water quality.
  • The equipment should be qualified and the RO system should be validated periodically, as well as operated and maintained according to manufacturer’s instructions so that it can consistently produce water with acceptable quality.

The Epochem RO technology system meets all the technical requirements above.

Frequently asked question about Reverse Osmosis plant installation in Nigeria

Yes, we already have a plant fully available in Nigeria

Reverse Osmosis works by using a high-pressure pump to increase the pressure on the salt side of the RO and force the water across the semi-permeable RO membrane, leaving almost all (around 95% to 99%) of dissolved salts behind in the reject stream.

Reverse osmosis helps in removing many types of suspended and dissolved species from water. It helps in removing bacteria and removes the impurity of the water. In the process of reverse osmosis desalination, pressure is applied to overcome the osmotic pressure which is driven by all the chemical potential solvents

Water treatment with ion exchange resins

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