chiwatec informs reverse osmosis membrane cleaning machine technology

Chemical cleaning of reverse osmosis membrane system (RO membrane cleaning)

Run data normalization:

When the system is started, the permeate flow rate, salt permeability and pressure drop of the RO membrane should be recorded (inlet water pressure minus concentrate water pressure). These records are used to establish a baseline to monitor the system and determine appropriate cleaning times.
Salt permeability is usually calculated using total dissolved solids (TDS) or conductivity of influent, product and concentrate. The ratio of the TDS (or conductivity) of the produced water to the average TDS (or conductivity) of the influent and concentrated water in the system is the salt penetration rate. The equation when calculating with TDS is as follows:
Average TDS = (TDS influent + TDS concentrate) ÷ 2
Salt permeability (%) = TDS product water × 100 ÷ TDS average
When comparing the current permeate flow with the permeate flow at the beginning of the start-up, it is important to normalize the operating data to allow for a more accurate comparison of system performance under different operating conditions. The effect of inlet water temperature on permeate flow is very important, therefore, in order to obtain comparable data, system operators must consider temperature effects.

Choice of cleaning agent:

pollutantsCleaning fluid formula
In weak washIn strong wash
Inorganic colloidal contaminants12
Calcium carbonate scale, calcium sulfate, barium sulfate, strontium sulfate scale21
Microorganisms, Natural Organic Matter (NOM)12

YS-1 cleaning agent is mainly used to remove scale, and different specific pollutants are cleaned with different cleaning agents.
YS-2 cleaning agent is mainly used to remove microorganisms or organic pollutants.
Usually the order of cleaning is to perform YS-1 cleaning first, then YS-2 cleaning. In some cases, if the contaminants are mainly organics or microorganisms, YS-2 can be washed first, then YS-1 can be washed, and YS-2 can be washed last.
If system performance does not return to its original level after cleaning, then a more detailed study of the contamination and measures to prevent contamination are required.

The relationship between pH value of cleaning solution and water temperature limit

Membrane TypeCleaning Solution pH
45°C35°C (T>30°C)Below 30°C

Cleaning solution formulations provide cleaning solutions by adding a certain weight (or volume) of chemicals to 25 gallons (100 liters) of clean water (RO product water or water without free chlorine). Solutions are prepared in proportions of all chemicals and water. The solvent is RO product water or deionized water, free of free chlorine and hardness. Before the cleaning liquid enters the membrane element, it is required to be thoroughly mixed, and the pH and temperature should be adjusted according to the target value. The conventional cleaning method is based on a cycle of cleaning with a chemical cleaning solution for 1 hour and soaking with an optional chemical for 1 hour.

The minimum cleaning temperature limit is 21°C and the maximum temperature limit is shown in the table below.

No.Main componentDosagepH adjustment valueMaximum temperature
2YS-2(100%) Granular100L9-1140

During the cleaning process, contaminants will consume the cleaning chemicals, the pH will change as a result, and the cleaning effectiveness of the chemicals will be reduced. During chemical cleaning, it is necessary to monitor the change of pH value at any time and adjust the pH value in time. Generally, when the measured pH value deviates from the set value by more than 0.5, it is necessary to add chemicals.

One of the following situations occurs, the membrane element should be cleaned immediately

  1. After the initial flow rate is stable, if the permeate flow rate drops by 5~15%, the membrane element needs to be cleaned, assuming that the pollution density index (SDI) of the RO process influent is less than 5.0.
  2. When the salt permeability of the RO membrane element increases by 30%~40%, the cleaning of the membrane element should also be considered. For example, if the salt penetration rate increases from 5% of the initial value to 7%, it means that the salt penetration rate has increased by 40%. Note: Sharp changes in permeate flow rate or salt permeability may also be caused by other factors, such as defective O-rings or failure of leaky seals causing bypass of concentrated water.
  3. Standardized differential pressure rises by 25%.

Precautions before cleaning

  1. The drug safety form and drug description obtained before using the drug
  2. When operating, wear safety glasses, gloves and overalls;
  3. Calibrate the pH meter before use;
  4.  Estimate the volume of cleaning solution used;
  5. Ensure that all cleaning chemicals are completely dissolved and mixed before the cleaning solution enters the system;
  6. The temperature and pH range of the cleaning solution meet the specified values.

Xi’an CHIWATEC Water Treatment Technology is a high-tech enterprise specialized in various water processing devices. Aside from these individual products, which cover a number of types and series, we can also help with related comprehensive engineering projects. Thanks to our hard work and dedication upon our founding, we are now one of the fastest-developing water treatment equipment manufacturers in Western China.

Further reading:

Filmtec RO membrane bw30365

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