Why is your membrane product losing treatment capacity and needing frequent replacement?

After the membrane system has been running for a period of time, sometimes the treatment capacity decreases significantly and fails to reach the designed capacity. The reasons for this phenomenon are mainly related to the working environment of the membrane system, selection and design, installation and construction, operation and management, and the performance of membrane products. In addition, with the membrane system (MBR, UF or R0) itself also has a certain relationship. Very important point: membrane product performance For UF system, the membrane itself anti-pollution and hydrophilicity of the flux has a greater impact on the flux, flux value is low after running for a period of time, MBR, UF processing capacity is reduced. In this regard, we can use strong anti-pollution, cleaning and good recovery lined with enhanced PVDF membrane, combined with gas washing without breaking the wire, the cleaning effect is very good. As for the MBR system, we should use the lined MBR membrane with permanent hydrophilicity and non-filamentation to ensure the water production and water quality.

Other important influencing factors:
1、Working environment
Inlet water temperature is lower than the design temperature (common in seasonal changes), will lead to a decline in the performance of the membrane water; water quality in the pollutant type, concentration and viscosity of the water body changes will also lead to the membrane permeability is lower than the expected value. To solve these problems, the need for the beginning of the membrane system design, taking into account the minimum annual water temperature and water quality fluctuations, in the selection of the membrane area to leave a certain margin of safety.
2, selection design
Due to the lack of design experience, too much consideration of the cost of the selected membrane area is not enough safety margin, the membrane of the water flux is estimated too high and so on, will make the membrane can not reach the design capacity. Whether it is MBR membrane, UF membrane or R0 membrane, must ensure that enough membrane area.

Insufficient pressure and uneven fluid distribution, resulting in water or air flow bias flow, will also affect the overall membrane performance, especially for UF systems and Ro systems.
For RO systems, low flow rates at the membrane surface can lead to contaminant deposition and cause clogging.
The solution is to improve the pump, water and air circuit design, so that multiple sets of membranes can handle the load, to avoid part of the membrane overload water production, and part of the membrane does not play a role.
If the cleaning and maintenance function is not enough design, especially no water flushing function, can be improved through the gas wash, water wash and drug wash design, set the appropriate flushing frequency and volume of water and other parameters to be resolved. No pre-filtering protection facilities before entering the membrane will lead to clogging of the membrane system.
The solution is: for MBR system, add 13 mm ultra-fine grid; for UF system, add 100 um level coarse filter; for R0 system, add 5 um level precision filter.
UF and RO system, there will be microbial slime clogging, affecting the normal production of water membrane.
The solution is: additional ultraviolet sterilizer or add biocides; for RO membrane system, the use of non-phosphorus scale inhibitors, slow down the growth of microorganisms; regular cleaning and maintenance of the system.
Pre-treatment capacity design is too low or the effect of deterioration, resulting in deterioration of the water quality into the membrane, the membrane system, especially the RO system has a great impact.
The solution is: improve the pretreatment to ensure that the membrane system water quality; for UF system, improve its pre-filter effect; for RO system, to ensure that the water pollution index (SDI) qualified.
3, installation and construction
Membrane system manufacturing and installation process, not timely cleanup of debris will lead to excessive residual impurities, thereby affecting the membrane water production performance. Especially welding slag, sharp or filamentous material, etc., which can lead to serious damage to the membrane filament, diaphragm. For MBR membrane, the pool needs to be cleaned of impurities before entering the water; for UF and RO systems, the first section of the piping system will be flushed before running the pre-filter, and then enter the water.
4、Operation management
The correct addition of pharmaceuticals, especially scale inhibitors, is very important to the RO system. In addition, according to the working conditions, timely flushing or take a drug wash to restore membrane performance. Inexperienced design leads to too high a recovery rate, or artificial operation over the design recovery rate, will also lead to a decline in membrane processing capacity. The UF system can be used for staggered flow filtration rather than dead-end filtration; RO membrane to increase the concentration of water discharge, reduce the recovery rate, reduce the number of membranes in series or increase the return flow.

Membrane life is shortened or need frequent cleaning

Membrane life cycle is reflected in two aspects:
First, the membrane itself is permanently damaged, can no longer produce sufficient quantity, quality of water, need to be able to solve;;.
Secondly, the membrane is temporarily damaged by severe contamination, need frequent cleaning to restore the water production capacity, the actual use of time and cleaning cycle is shorter, it is difficult to adapt to the production requirements. The problem can be solved from the process design, such as improving the quality of the membrane itself, and at the same time strengthen the environment, manufacturing construction and operation management.

1、Design
Inadequate protective design can lead to irreversible damage to the membrane. According to the different types of damage, the solution is also different. Such as: to avoid membrane filament, membrane was scratched, can choose to lined with reinforced PVDF membrane, and add a pre-filter; to prevent RO membrane oxidation by oxidizing substances, add ORP instrumentation and reductant automatic dosage device; in order to prevent overpressure physical damage, can be added to the pressure protection facilities; in order to prevent the membrane filaments, membrane by the rupture of the impact of water hammer, need to be designed to slow down the details of the water hammer.
Lack of design experience or too save on material costs, will cause the actual selection of the membrane area is seriously inadequate; unit area of overloaded operation, serious pollution, but also need to be cleaned frequently. For this reason, the membrane area needs to be selected according to the stable membrane flux design, inexperienced water quality, the need to verify the design data through the pilot test.
For the RO system, the number of membranes in series is too much, will also lead to serious contamination of the latter part of the membrane and difficult to clean and restore. The solution is to rationalize the design of the number of series of RO membranes, when using two-stage RO design, the design of segmented cleaning. In addition, the pretreatment capacity is small, resulting in membrane feed water quality exceeds the standard, forced operation, will also shorten the service life of the membrane. In this regard, the need to improve the pre-treatment process to ensure that the membrane system feed water quality meets the requirements.

2, membrane products
UF / MBR membrane if the use of conventional homogeneous membrane filament, easy to break the wire, anti-pollution and aging resistance is poor, backwash and tensile strength is low. Recommended selection of long life, high tensile strength lined with reinforced PVDF membrane. RO membrane flow channel is small, poor anti-pollution diaphragm, should try to use wide flow RO membrane, according to the water quality of targeted selection of anti-pollution membrane.
3, manufacturing, construction
Manufacturing and installation process, the membrane system mixed with debris, especially sharp foreign objects, will scratch the membrane wire, membrane. The solution is: for MBR membrane with liner, need to clean up the impurities in the pool and then into the water; for UF and RO system, must first rinse the front section of the piping system, run the pre-filter, and then into the water.
4、Operation management
Failure to correctly or timely dosing, especially RO system scale inhibitor dosing is not timely, will lead to serious clogging of the membrane. Under the premise of correct design, correct operation and maintenance according to the operating procedures.
Membrane systems operating under high differential pressure can lead to breakage of ultra-microfiltration membrane filaments and damage to RO membrane sheets. For this reason, it is necessary to inspect the trans-membrane pressure difference and the pressure drop of the membrane group, and carry out restorative cleaning in time according to the working condition, and prevent the operation of over-pressure difference. Chemical cleaning, strong acid, strong alkali and strong oxidizing agents will cause irreversible chemical damage to the membrane. Therefore, the operator needs to master the chemical cleaning process, avoid strong acid and alkali environment; RO membrane is strictly prohibited to use strong oxidizing agents cleaning.
5, the environment
Water temperature is higher than 45 ℃, will shorten the service life of the membrane. Generally need to control the water temperature below 40 ℃, if necessary, take cooling measures. For RO system, wastewater contains strong oxidizing substances or easy to precipitate substances, will lead to shorten the membrane life cycle. When designing the system, consider from its safety point of view, increase the pretreatment safety margin, add protective shutdown design, can avoid triggering such problems.

High operating cost of membrane system
1、Select ultra-low pressure reverse osmosis membrane
Conventional reverse transmissive membrane operating pressure of 1.3 ~ 1.5 MPa, ultra-low pressure reverse osmosis membrane operating pressure of about 0.8 MPa or even lower (closely related to the water temperature), can save more than 30% of power consumption. For large-scale RO system, the basic membrane can offset more than 70% of the annual depreciation costs, savings are more significant.
2, high pressure pump with frequency converter
High-pressure pump with frequency converter in addition to slowing down the water hammer when the pump starts, but also by setting a reasonable operating pressure, reduce the valve throttling energy consumption, at least quarterly energy savings of more than 15% throughout the year.
3, reasonable calculation of scale inhibitor dosage through the analysis of water quality data, optimize the dosage of pharmaceuticals, usually save 20% or even higher pharmaceutical costs.
4、Appropriately increase the number of membrane, reduce operating pressure by appropriately increasing the membrane area, can to a certain extent reduce the operating pressure of the membrane, reduce power consumption.
5, MBR or UF produced water and RO water mixing
RO water quality is better, usually can be mixed with a certain proportion of water with lined MBR membrane or UF membrane, to improve the system recovery rate, reduce the scale of operation of the RO system, thereby saving operating costs.