What are the feed water requirements for reverse osmosis equipment? And what are the required instruments for the equipment

Reverse osmosis Equipment water intake to pay attention to：

Bacteria: chlorination can be used to sterilize and disinfect, but the residual chlorine content must not exceed 0.1mg/L, otherwise it will oxidize the membrane element, residual chlorine can be used to remove the chlorine of sodium metabisulfite or activated carbon, in the presence of dissolved oxygen 1kg of chlorine needs to be 3kg of sodium metabisulfite, the water temperature is low and the pH is low when the sterilization effect is better

Iron content: the oxidation rate of iron depends on the iron content, the concentration of dissolved oxygen in the water and pH, the higher the pH the faster the oxidation rate, therefore, reduce the pH value can prevent oxidation, the maximum allowable iron content of feed water and the relationship between the oxygen content and pH is shown in the table below:

Particulate matter: No particulate matter larger than 5um is allowed to enter the high pressure pump and reverse osmosis components, this must be ensured to avoid damage to the equipment.

SDI and turbidity: SDI must be less than 5, the smaller the better, turbidity should be less than 0.2NTU (maximum allowed 1NTU).

Oil and grease: Oil and grease are not allowed in the water.

Organic matter: Organic matter in water has the most complicated effect on RO membrane, activated carbon filtration can be used to reduce the concentration of organic matter.

SiO2: Concentrated water is not allowed to precipitate SiO2, when it is oversaturated, it may polymerize and form insoluble colloidal silicon or silica gel and cause scaling. At 25℃, the solubility of amorphous silicon is 100mg/L, the solubility varies linearly with temperature, 0mg/L at 0℃, and increases to 160mg/L at 40℃, and it is only silica gel that is dissolved at neutral pH, and the solubility of amorphous is greater than that of neutral solution under alkaline solution, mainly due to the ionization of silicic acid, however, in the presence of aluminum, the solubility may be reduced a lot due to the fact that due to the very small solubility of aluminum silicate.

Reducing the SiO2 content can be done by controlling the system recovery; using lime softening or adding more ferric chloride and sodium aluminate to the clarifier; and also by temperature control.

Anti-scaling: CaCO3, CaSO4, BaSO4, CaF2 scale must be prevented.

Generally by reducing the system recovery rate, to avoid exceeding the solubility product; the use of ion exchange softening to remove calcium ions; add acid to remove carbonic acid or bicarbonate ions; add scale inhibitors.

Water temperature: reverse osmosis membrane more water temperature have certain requirements, composite membrane general inlet water temperature control in 0-45 ℃.

The highest feed water pressure: reverse osmosis membrane components have certain requirements for the highest pressure of the feed water.

Maximum water inlet volume of each membrane: reverse osmosis membrane has certain requirements on the maximum water inlet volume, see the design manual.

Ratio of Concentration and Transmission Water: Considering the membrane’s dirt-holding and other aspects, there are certain requirements for the concentration and transmission water of each membrane.

Reverse osmosis equipment needs which commonly used instrumentation

In order to make RO device can run safely and reliably, easy to monitor the operation process, should be equipped with the necessary instrumentation and control devices, generally need to install the instrumentation are temperature meter, flow meter, pressure meter, conductivity meter, oxidation potential meter, chlorine meter, pH meter, specific as follows:

1. temperature meter:

Feed water temperature meter, because the water production is related to the temperature, so it needs to be tested in order to find out the standardized water production, large-scale equipment should be recorded, in addition, the temperature exceeds 45 ℃ will damage the membrane element, so the raw water heater system should be set up to exceed the limit of the alarm, over the limit of the automatic drainage and shutdown RO protection.

2. Pressure gauge:

The feed water pressure gauge, the first section RO effluent pressure gauge, and the drain pressure gauge are used to calculate the pressure drop in each section and to standardize the water production and salt transmission rate. Salt transmission rate, water yield and Δp are used to analyze RO performance issues.

The 5um filter should be installed with inlet and outlet pressure gauges, and when the pressure drop reaches a certain value, the filter element needs to be replaced.

Inlet and outlet pressure gauges for feed pumps, inlet and outlet pressure switches are used to shut down the pump when the inlet pressure is low and to stop the pump when the outlet pressure is high.

3. flow meter:

Product water flow meter in operation to detect the amount of water produced, each section should be installed separately, in order to standardize RO performance data. Product water flow rate should be indicated, totalized and recorded. Concentrated water drainage flow meter in operation to detect the amount of drainage, should be indicated cumulative and record. From the product flow rate and drainage flow rate can be calculated from the sections of the water supply, recovery rate and the recovery rate of the entire RO, feed water flow meter is mainly used for RO dosage of automatic adjustment, in addition to indicating the cumulative signal should also be given for proportional adjustment.

4. conductivity meter:

Feed water conductivity meter, water conductivity meter indicates and records the conductivity of water: alarms can be set, and the desalination rate can be calculated from the conductivity of feed water and the conductivity of produced water.

5. pH meter

When acid is added to the feed water to prevent CaCO3 from forming scale, a pH meter should be installed in the feed water after acid is added.

6. chlorine meter

Chlorine meter is installed in the feed water to control the chlorine content of the feed water.

7. oxidation potential meter

After adding sodium bisulfite to eliminate residual chlorine feed water should be equipped with redox point meter, there should be an indication of records, exceeding the limit alarm.