How to improve the efficiency of reverse osmosis system in drink water production

In order to improve the efficiency of reverse osmosis system, raw water must be pre-treated effectively. In view of the quality of raw water and the requirements of the main design parameters such as the recovery rate of the system, choosing the appropriate pre-treatment process can reduce the fouling, scaling and membrane degradation, thus greatly improving the system efficiency, the optimization of water yield, desalting rate, recovery rate and operation cost is realized.

1.Filter operation

The filter is mainly composed of filter container, filter material, valve, pipeline, pressure gauge and so on. During operation,

The raw water to be filtered enters the top of the filter, and the filtrate penetrates the filter layer and enters the water collection system at the bottom.

When the pressure difference between the inlet and outlet of the filter increases by 0.03~0.06Mpa, first backwash and then forward wash the filter to remove the sediment, and then backwash the filter.

It usually takes more than 10 minutes, and the large-diameter filter must also be scrubbed with an auxiliary air source. Frequent openings must be avoided

Machine and shutdown, because each sudden change in flow rate will release the material that has been deposited on the medium.

2.Chemical dosing (option)

Almost all of the reverse osmosis pre-treatment systems have dosing equipment. There are many chemicals that can be added to the water source. Specific chemicals should be selected according to the specific water source. The dosing device generally consists of a metering box, a metering pump, and a stirring device. Commonly added drugs mainly include bactericides, flocculants, scale inhibitors, PH adjustment and so on.

3. Anti-scalants

Anti-scalants can be used to control carbonate scale, sulfate scale and calcium fluoride scale, and there are generally three types of scale inhibitors: sodium hexametaphosphate (SHMP), organic phosphates and polyacrylates. Scale inhibitor is a kind of high-efficiency scale inhibitor and dispersant, especially suitable for RO system, NF and UF system with high content of Ba, Sr and F in feed water and serious scaling tendency of BaSO4, SrSO4 and CaF2. Ideal for normal operation.

4. Calculation of the dosage of the drug

The dosage of the scale inhibitor is generally 3-5 grams of the scale inhibitor stock solution per ton of water in accordance with the water intake. The stock solution is diluted with pure water at 1:10 and added to the anti-scalant medicine box, and then added by the metering pump.

First, know the maximum range and maximum pressure of the pump through the nameplate on the metering pump. The dosing amount can be calculated (dosing amount = dosing amount per stroke × frequency). The total dosage is linear with frequency (50% frequency = 50% dosage).

5. Precision filter (security filter)

Each reverse osmosis and nano-filtration system should be equipped with a filter element type security filter with a minimum pore size of less than 10 μm, which protects the membrane and high-pressure pump and prevents the possible damage of suspended particles, usually it is pre-treated Finally, we recommend using a pore size of 5 μm or less. The better the pre-treatment, the fewer cleaning times the RO/NF membrane needs. When the concentration of silicon in concentrated water exceeds the theoretical solubility, it is recommended that the filter pore size be selected to be 1 μm to reduce the interaction of silicon with iron and aluminum colloids.

The cartridge filter should be replaced in time before the pressure drop exceeds the allowable limit, but preferably not more than three months.

The filter element material must be a non-degradable synthetic material such as nylon or polypropylene, and the filter is fitted with a pressure gauge to indicate pressure drop in order to indicate the amount of contaminant trapped on the filter element.

Regular inspection of used filter elements provides contamination hazard alerts and useful information on the need for cleaning. If the pressure drop of the cartridge filter increases too rapidly, indicating a possible problem with the pre-treatment process or the water source, the cartridge filter provides only some short-term protection until countermeasures are taken.

The replacement steps of the precision filter element:

The security filter is managed by the combination of pressure drop and time, that is, when the pressure drop of the inlet and outlet water is greater than 0.05Mpa or runs for 1-3 months, the filter element is replaced. The steps to replace the filter element are as follows:

1. Turn off the pre-processing system.
2. Close the water inlet and outlet valves of the security filter.
3. Release the pressure from the exhaust valve.
4. Disassemble the top cover of the security filter.
5. Take out the old filter element and clean the inside of the filter.
6. Drain the water in the filter and install a new filter element.
7. Install the head, and the screw torque should be uniform during installation.
8. Turn on the raw water pump, open the water inlet valve, and exhaust from the exhaust valve.
9. If there is no leakage, open the water outlet valve.