The reverse osmosis system includes three parts: raw water pretreatment, reverse osmosis device and post-treatment. RO system has its specific requirements for raw water pretreatment. Due to the wide variety of raw water and its very complex composition, according to the requirements of the raw water quality and the recovery rate of RO system and other main process design parameters, select a suitable pretreatment process system to reduce the fouling and scaling of RO membrane, and prevent the reduction of RO membrane desalination rate and water production rate, especially for the current water shortage and deteriorating water quality, select a correct pretreatment system, It will directly affect the function of the whole water treatment system. It is well known that the RO system fails to run, most of which are caused by the imperfect function of the pretreatment system. In order to ensure the normal operation of the reverse osmosis process, the raw water must be strictly pretreated.

The main factors that reduce the performance of reverse osmosis membrane are:

1. The membrane undergoes chemical degradation, such as the destruction of aromatic polyamides by oxidizing agents such as chlorine and strong acids and alkalis;

2. Scaling of insoluble salt on membrane surface;

3. The membrane is blocked by influent suspended solids and colloid;

4. Adhesion and erosion of membrane microorganisms, fungi, algae, etc. cause fouling and membrane degradation;

5. Macromolecular organics block membrane fouling and small molecular organics are adsorbed by membrane.

The efficiency and service life of reverse osmosis are closely related to the raw water pretreatment effect. The purpose of pretreatment is to minimize the pollution, scaling and damage of the influent to the membrane, so as to optimize the water yield, desalination rate, recovery rate and operation cost of the system. Therefore, good pretreatment is very important for the long-term safe operation of RO plant. Its purpose is subdivided into:

1. Remove suspended solids and reduce turbidity;

2. Control the growth of microorganisms;

3. Inhibit and control the deposition of slightly soluble salt;

4. Adjustment of inlet water temperature and pH;

5. Removal of organic matter;

6. Precipitation control of metal oxides and silicon.

Objectives of reverse osmosis membrane pretreatment

In order to ensure the water recovery rate of the reverse osmosis system, the quality of the permeate water, the stability of the permeate water flow, the minimization of the operating costs, and the optimization of the service life of the membrane, it is necessary to carry out perfect pretreatment. The specific objectives are:

1. To prevent pollution on the membrane surface, suspended solids, microorganisms, colloidal substances and organic substances must be removed as far as possible, so as to prevent these substances from depositing on the membrane surface or blocking the water flow channel of the membrane element;

2. To prevent scaling on the membrane surface, that is, the deposition of insoluble salts such as CaCO3, CaSO3, BaSO3, SrSO3, CaF2 and iron, manganese, aluminum and silicon compounds on the membrane surface must be suppressed as much as possible;

3. Prevent the membrane from physical and chemical damage, that is, try to avoid the impact of high temperature, extreme acidic water or alkaline water, oxidant, etc. on the membrane.