The main influencing factors on the pollution rate of surface water reverse osmosis water treatment equipment

Author: Hongjie Water

1、 Type of membrane material (acetate fiber membrane or polyamide membrane)

The common reverse osmosis membranes on the market are divided into CAB series (acetate fiber) membrane components or CPA series (aromatic polyamide) membrane components based on their materials. For difficult to treat surface water or wastewater systems, CAB membranes are often used instead of CPA membranes. The advantage of CAB film is that its surface is smooth and uncharged, which can reduce the deposition of pollutants during use and prevent microorganisms from sticking on its surface. CAB membrane has another advantage, which is that it can contain 0.3 to 1.0ppm of free chlorine in the feedwater during operation. Chlorine, as a disinfectant, can protect the CAB membrane from harmful bacteria and prevent fouling caused by the growth of microorganisms and algae. The CPA membrane itself is resistant to chlorine, but cannot tolerate its oxidation. Therefore, it is required to remove chlorine.

2、 Water flux:

The water production flux is the water production per unit effective area of the membrane surface, expressed in GFD (gallons per square foot per day) or LMH (liters per square meter per hour). There is a proportional relationship between the water flux produced by reverse osmosis equipment and the pollution rate. Low water flux leads to low pollution rate; On the contrary, as the water flux increases, the pollution rate increases. Reverse osmosis membrane elements with larger membrane areas can be selected to reduce water flux.

If the cleaning is done every three months or more, it indicates that the pre-treatment and reverse osmosis system design is reasonable. If the equipment needs to be cleaned once every 1-3 months, the process needs to be improved or additional equipment needs to be added.

3、 Lateral flow velocity:

The lateral flow rate is also an important factor affecting the pollution rate of reverse osmosis equipment. The higher the lateral flow rate of surface water supply and its generated concentrated water on the membrane surface, the slower the membrane fouling rate. This is because the high lateral flow rate of water reduces the sedimentation and accumulation of particulate matter on the membrane surface, while accelerating the diffusion rate of high concentration salt on the membrane surface to the main solution, reducing the risk of insoluble salt precipitation.

4、 Reverse osmosis cleaning:

Cleaning and maintaining reverse osmosis water treatment equipment can effectively prevent equipment contamination. The methods include concentrated water recycling, shutdown low-pressure flushing, and regular disinfection.

RO equipment produces water for flushing and short-term soaking of membrane components, which can reduce bacterial growth, dissolve pollutants on the membrane, or make it loose.

Concentrated water recirculation can increase the lateral flow rate and flush out pollutants on the membrane surface; But it increases the capacity of the RO feed pump and the salt content of the equipment's produced water.

Low pressure cleaning during equipment shutdown can flush pollutants and concentrated water out of membrane components, preventing microbial growth.

The purpose of regular disinfection is to control the growth of microorganisms between two cleanings.

5、 Structure of reverse osmosis membrane components:

Reverse osmosis water treatment equipment is used for well water and surface Water purification purification, and the membrane elements selected for the equipment are mainly roll type membrane elements. With comprehensive consideration of anti pollution ability of water supply channel, equipment space requirements, investment and operation costs and procurement, roll type membrane elements are superior to hollow fiber and plate frame structures. Designing a large membrane area is beneficial for reducing water flux, increasing lateral flow rate, and reducing equipment pollution rate.