Solutions to common problems in reverse osmosis operation

01 Microbial contamination
Symptoms: decreased water production, decreased desalination rate, and increased pressure difference.
Phenomenon: Bacterial and microbial growth is severe, and after the membrane shell is opened or the membrane components are dissected, viscous substances are attached to the inside of the membrane shell, the membrane surface, and the inlet channel, accompanied by a foul odor.
Reason:
The incoming water is rich in nutrients, such as TOC and COD, which are relatively high;
Not sterilized or insufficiently sterilized, the influent contains microorganisms;
Excessive dilution of scale inhibitors and severe contamination of the medicine box;
Delayed flushing after shutdown, resulting in bacterial and microbial contamination;
Excessive addition of reducing agent causes the growth of anaerobic bacteria.
Solution:
Set up sterilization equipment or adjust dosage to prevent microbial contamination of raw water;
Adjust the dosage of reducing agent;
Using non oxidizing fungicides, such as DBNPA for periodic impact sterilization;
Disinfect the entire system, including pre-treatment and membrane, to prevent re contamination;
Use strong alkaline cleaning with a pH of 12-13 for recovery, and NaOH+Na-SDS or Na4EDTA cleaning can also be used.
02 Inorganic scaling pollution
Symptoms: decreased water production, decreased desalination rate, increased pressure difference, and heavier membrane components.
Phenomenon: Scaling often occurs in the last stage.
Reason:
The raw water has high hardness, pH, and alkalinity values, as well as high content of calcium, barium, strontium, and sulfate ions;
Changes in water quality, such as changes in inlet pH;
The RO system has a high recovery rate, exceeding the solubility of inorganic salts;
Incorrect selection of scale inhibitor;
Insufficient dosage of scale inhibitor.
Solution:
Analyze the composition of scale;
Adjust the pH value of the inlet water, such as adding acid;
Reduce the hardness of incoming water, such as softening;
RO system recovery rate should be reduced
Adjust the amount of scale inhibitor added or replace the scale inhibitor
Acid is used to remove carbonate scale, but sulfate scale is difficult to clean and recover. NaOH+Na4EDTA or Na-SDS is used for cleaning.
03 Iron pollution
Symptoms: Decreased water production and reduced desalination rate.
Phenomenon: After the pressure vessel is opened, the end face of the membrane element turns reddish brown. After the membrane element is dissected, the surface of the membrane turns reddish brown.
Reason:
High iron content in raw water;
Corrosion of pipelines or pressure vessels in pre-treatment systems
Solution:
Using aeration flocculation to remove iron from raw water;
Replace or maintain equipment;
Use Na2S2O3 or H3PO4 and citric acid to clean and recover.
04 Organic pollution
Symptoms: decreased water production, decreased desalination rate, and increased pressure difference.
Reason: Oil in the feed water; Cation coagulation for pretreatment.
Solution: Adjust the preprocessing process. Clean the membrane components.
05 Colloidal contamination
Symptoms: decreased water production, decreased desalination rate, and increased pressure difference.
06 Sediment particle pollution
Symptoms: decreased water production, decreased desalination rate, increased pressure difference, and inlet water pressure.
Phenomenon: Mud and sand particles accumulate at the inlet of the first few membrane components in the first section.
Reason:
The raw water is contaminated;
Insufficient preprocessing;
Improper use of coagulants. Inappropriate pre-treatment dosage and excessive use of flocculants result in secondary flocculation;
The flocculant is incompatible with water quality;
There are compatibility issues with water treatment agents.
Solution:
Check the pre-treatment process and adjust the working conditions;
Adjust the type and dosage of coagulant;
Add special scale inhibitor;
Clean the membrane components.
07 Membrane oxidation
Symptoms: Increased water production, decreased desalination rate, and stable pressure difference.
Phenomenon: After dissecting the membrane components, the experimental solution in Fujiwara's experiment turned pink, and atomic spectroscopic chemical analysis (ESCA) found chlorine or bromine elements.
Reason:
Excessive addition of pre-treatment oxidizing fungicides;
Reduced agent failure or insufficient dosage.
Solution:
Anatomic analysis;
Strictly control the inlet ORP value;
The membrane element is irreversibly damaged and difficult to repair, so the membrane element can only be replaced.
08 Membrane damage
Symptoms: Increased water production, decreased desalination rate, and increased pressure difference.
Phenomenon: Severe pollution at the inlet end, fiberglass shell ruptures along the axial direction, and the inlet grid protrudes. After membrane dissection, bubbles and layering appear on the surface of the membrane.
Reason:
Incorrect operation, resulting in back pressure, such as forgetting to open the production water valve after cleaning, etc;
Excessive inlet pressure difference;
Metal oxidants or other particulate impurities in the water supply cause surface wear of the membrane;
Solution:
Operate according to regulations and strictly prevent back pressure;
Improve pre-treatment, clean in a timely manner, and prevent excessive pressure difference;
Replace the membrane components.