Tips about Reverse Osmosis Treatment Plant

How often should the RO system be cleaned

In general, when the normalized flux decreases by 10-15%, or the system desalination rate decreases by 10-15%, or the operating pressure and the pressure difference between sections increase by 10-15%, the RO system should be cleaned. The cleaning frequency is directly related to the system pretreatment degree. When SDI15<3, the cleaning frequency may be 4 times a year; when SDI15 is about 5, the cleaning frequency may be doubled, but the cleaning frequency depends on each item actual situation on site.

What is SDI value

At present, the best technique for evaluating the possibility of colloidal pollution in the RO/NF system influent water is to measure the sedimentation density index (SDI, also known as the fouling index) of the influent water, which is an important parameter that must be determined before RO design. During RO/NF operation, measurements must be made periodically (2-3 times a day for surface water), and ASTM D4189-82 specifies the standard for this test. The water inlet of the membrane system is stipulated that the SDI15 value must be less than or equal to 5. Effective technologies for reducing SDI pretreatment are multi-media filters, ultrafiltration, microfiltration, etc. The addition of polydielectrics prior to filtration can sometimes enhance the ability of the physical filtration described above to lower the SDI value.

Difference between Reverse osmosis and Ion exchange

Under many influent conditions, it is technically feasible to use ion exchange resin or reverse osmosis, and the choice of process should be determined by economic comparison. In general, the higher the salt content, the more economical the reverse osmosis will be. The lower the amount, the more economical the ion exchange is. Due to the widespread popularity of reverse osmosis technology, the combination of reverse osmosis + ion exchange process or multi-stage reverse osmosis or reverse osmosis + other deep desalination technologies has become a recognized technical and economical more reasonable water treatment solution. For understanding, please consult the representative of the water treatment engineering company.

Difference between Reverse osmosis and Nanofiltration

Nanofiltration is a membrane liquid separation technology located between reverse osmosis and ultrafiltration. Reverse osmosis can remove the smallest solutes with a molecular weight of less than 0.0001 microns, and nanofiltration can remove solutes with a molecular weight of about 0.001 microns. Nanofiltration is essentially a low-pressure reverse osmosis, which is used in cases where the purity of the produced water after treatment is not particularly strict. Nanofiltration is suitable for the treatment of well water and surface water. Nanofiltration is suitable for water treatment systems that do not have a high desalination rate like reverse osmosis, but it has a high removal capacity for hardness components, sometimes called "softening membrane", the operating pressure of the nanofiltration system is low, and the energy consumption is lower than The corresponding reverse osmosis system.

Effect of chromium on RO membrane

Certain heavy metals such as chromium can catalyze the oxidation of chlorine, which in turn causes irreversible performance degradation of the diaphragm. This is because Cr6+ is less stable than Cr3+ in water. It seems that metal ions with high oxidation valences have a stronger destructive effect. Therefore, the concentration of chromium should be reduced in the pretreatment part or at least Cr6+ should be reduced to Cr3+.

Pretreatment for Reverse osmosis system

The usual pretreatment system is composed as follows: coarse filtration (~80 microns) to remove large particles, adding oxidants such as sodium hypochlorite, then precision filtration through a multi-media filter or clarifier, and then adding sodium bisulfite to reduce residual chlorine and other oxidants, Finally, install the security filter before the inlet of the high pressure pump. The role of the security filter is as the name implies, it is the ultimate insurance measure to prevent the damage of the impeller and membrane elements of the high-pressure pump by accidental large particles. Water sources with more suspended particulates usually require a higher degree of pretreatment to meet the specified water inflow requirements; water sources with high hardness content are recommended to use softening or adding acid and scale inhibitors. High water sources also require the use of activated carbon or anti-fouling membrane elements.

Can reverse osmosis remove microorganisms such as viruses and bacteria?

Reverse osmosis (RO) is very dense and has a very high removal rate of viruses, phages and bacteria, at least above 3log (removal rate >99.9%). However, it should also be noted that in many cases, microorganisms may still breed on the water side of the membrane, which mainly depends on the way of assembly, monitoring and maintenance. That is to say, the ability of a certain system to remove microorganisms depends on the key. It depends on the appropriateness of system design, operation and management rather than the nature of the membrane element itself.

How to remove silicon from water

Silicon exists in two forms in water, active silicon (monomeric silicon) and colloidal silicon (multi-component silicon): colloidal silicon has no ionic characteristics, but is relatively large in size, and colloidal silicon can be trapped by fine physical filtration processes, such as reverse Osmosis, which can also be reduced in water by coagulation techniques, such as coagulation-clarifiers, but separation techniques that rely on ionic charge characteristics, such as ion exchange resins and continuous electrodeionization (CDI) processes, are very effective at removing colloidal silica limited.

The size of active silicon is much smaller than that of colloidal silicon, so most physical filtration techniques such as coagulation clarification, filtration and air flotation cannot remove active silicon. The processes that can effectively remove active silicon are reverse osmosis, ion exchange and continuous Electrodeionization process.

How to know if the membrane be polluted

The following are common symptoms of pollution:

Under the standard pressure, the water production rate decreases. In order to achieve the standard water production rate, the operating pressure must be increased v the pressure drop between the influent and the concentrate increases v, the weight of the membrane element increases v the membrane removal rate changes significantly (increase or decrease)

When the element is taken out of the pressure vessel, pour water on the water inlet side of the upright membrane element, the water cannot flow through the membrane element, and only overflows from the end face (indicating that the water inlet channel is completely blocked).

More inquiries related to Reverse Osmosis Treatment Plant please contact:

Mob& Wechat& WhatsApp: (+86)13544774483

Email: sales010@water-sy.com

We will provide high-quality, all-round comprehensive professional services for project consulting, system design, manufacturing, installation and commissioning, personnel training, etc