Reverse Osmosis Systems: The “Magicians” of Water Treatment

Reverse osmosis (RO) is a sophisticated physical filtration using a semi-permeable membrane and pressure difference, the dissolved salts in water, heavy metal ions, microorganisms, organic matter, bacteria and other impurities in the water to effectively separate and remove impurities in the water.

What is semi-permeable membrane and pressure difference?

Reverse osmosis membrane is an artificial semi-permeable membrane that simulates biological semi-permeable membrane. It utilizes its small pore size (approximately 0.0001 microns), which is much smaller than the size of viruses, bacteria and most dissolved salts, to trap impurities on the outside of the membrane. Water molecules enter without any problems, thus filtering out pure or ultrapure water.

Pressure differential is a process whereby a pressure higher than the osmotic pressure of the solution is applied in order to separate the impurities from the pure water, “pushing” the water from a highly concentrated solution to a less concentrated solution.

How does reverse osmosis remove impurities?

1. The first step, the water enters the pre-treatment
The water is first sand filtered to remove larger suspended solids, particles and organics, and to prevent membrane clogging.
 

It then goes through carbon filtration to improve water quality and oil rates.

In the last step of pre-treatment, the water enters the softening/dosing tank to be softened.

2. In the second step, the water is pressurized and filtered by a high-pressure pump, so that the water flows into the reverse osmosis membrane. Pure water is formed.

3. In the third step, the reverse osmosis membrane retains the impurities.

4. The fourth step, post-treatment
Pure water is mineralized, sterilized or pH-adjusted as required to meet the water quality requirements of different applications.

Practical Cases

Community Water Supply System

A reverse osmosis plant was introduced in a rural suburb of Jinshui District, Zhengzhou, Henan Province, China, to purify highly fluoridated groundwater into pure water that meets drinking water standards. The fluoride content has been reduced from 5 ppm to 0.5 ppm, solving the health problems of local residents who had been drinking highly fluoridated water for a long time.

Seawater desalination system

Qingdao Desalination Project, a large reverse osmosis desalination plant was built to produce 500,000 cubic meters of fresh water per day to meet the domestic water needs of about 1 million people. The salt content of the raw seawater is about 35,000 ppm, and after treatment the salt content of the fresh water is reduced to less than 500 ppm, which is in line with the drinking water standard.