The purpose of reverse osmosis membrane pretreatment

  Reverse osmosis systems consist of three parts: pretreatment of raw water, reverse osmosis equipment, and post-treatment. RO systems have specific requirements for the pretreatment of raw water. Due to the wide variety and complex composition of raw water, appropriate pretreatment processes should be selected based on the raw water quality and the main process design parameters such as RO system recovery rate. This minimizes membrane fouling and scaling, preventing a decrease in RO membrane desalination rate and water production rate. Especially with the current trend of dwindling water resources and deteriorating water quality, selecting the correct pretreatment system directly impacts the functionality of the entire water treatment system. It is well known that most RO system failures are due to incomplete pretreatment system functionality. To ensure the normal operation of the reverse osmosis process, strict pretreatment of the raw water is necessary.

The main factors that reduce reverse osmosis membrane performance are:

1. Chemical degradation of the membrane, such as the destruction of aromatic polyamide by oxidants like chlorine and strong acids and bases;

2. Scaling of sparingly soluble salts on the membrane surface;

3. Membrane fouling by suspended solids and colloids in the feed water;

4. Fouling and membrane degradation caused by the adhesion and erosion of microorganisms, fungi, and algae;

5. Membrane fouling by macromolecular organic matter and adsorption of small molecular organic matter by the membrane.

Reverse osmosis efficiency and lifespan are closely related to the effectiveness of raw water pretreatment. The purpose of pretreatment is to minimize the pollution, scaling, and damage of the membrane by the feed water, thereby optimizing the system's water production, desalination rate, recovery rate, and operating costs. Therefore, good pretreatment is crucial for the long-term safe operation of the RO unit. The specific purposes are:

1. Removal of suspended solids to reduce turbidity;

2. Control of microbial growth;

3. Inhibition and control of sparingly soluble salt deposition;

4. Adjustment of feed water temperature and pH;

5. Removal of organic matter;

6. Control of metal oxide and silicon precipitation.

Goals of Reverse Osmosis Membrane Pretreatment

To ensure the stability of the reverse osmosis system's water recovery rate, permeate water quality, permeate water flow rate, minimization of operating costs, and optimization of membrane lifespan, thorough pretreatment is necessary. The specific goals are:

1. Prevent membrane surface fouling; that is, remove suspended solids, microorganisms, colloidal matter, and organic matter to prevent these substances from depositing on or fouling the membrane element's water flow channels;

2. Prevent membrane surface scaling; that is, inhibit the deposition of sparingly soluble salts such as CaCO3, CaSO3, BaSO3, SrSO3, CaF2, and iron, manganese, aluminum, and silicon compounds on the membrane surface;

3. Prevent physical and chemical damage to the membrane; that is, avoid the effects of high temperatures, extremely acidic or alkaline water, and oxidants on the membrane.