[Hongjie Water] Seven Common Misunderstandings about Membranes

Misunderstanding 1:

The membrane water treatment equipment is a highly difficult to operate system. The automatic control requirements of the membrane water treatment system are much higher than those of conventional biochemical treatment systems, and many users mistakenly believe that the membrane system is difficult to operate. In fact, the operation of the membrane water treatment system is highly automated, and operations such as start/stop, dosing, and online flushing are all carried out by the PLC system program control, which can achieve unmanned operation. Only manual scheduled inspection and dispensing, periodic maintenance and cleaning are required, and there is basically no need for additional operating staff. The routine cleaning and maintenance of membranes can be mastered in just one day of training, and the difficulty is much lower than that of biochemical systems that require high comprehensive skills from employees.

There is a viewpoint that the one-time investment and depreciation replacement cost of membranes are high, and they can be bought but not used. In fact, with the development of domestic membrane manufacturing enterprises, the price of membranes is constantly decreasing. The use of MBR membrane system can save construction and land costs, reduce sludge volume and disposal costs, and has a high comprehensive cost-effectiveness, making it a good choice; For UF and RO systems, the economic benefits generated by achieving wastewater resource recycling far exceed the investment of the equipment itself. If the MBR membrane with lining or UF and RO membrane are combined for depreciation and replacement, the general depreciation cost of the membrane will not exceed 0.6 yuan/t of influent water, or even lower than the cost of adding chemicals per ton of influent water in the system.

Misunderstanding 3:

Membranes are delicate and easily damaged - some engineering companies, due to their lack of experience, have encountered problems with membrane breakage and scrapping in the design and construction of membrane systems, leading users to mistakenly believe that membrane products are difficult to maintain. In fact, the main issues arise from two aspects: process design and the membrane itself. Through reasonable pre-treatment design and safety protection design, high-quality lined reinforced PVDF film can be used for more than 5 years, and the replacement cycle of RO film is more than 3 years.

Misunderstanding 4:

Brand and RO quantity are more important than membrane area and system design. When establishing membrane systems, some enterprises excessively focus on whether the membrane is an imported product and lack awareness of the importance of system design. In fact, the performance of some domestically produced ultrafiltration membranes has approached or even reached international advanced levels, with a cost-effectiveness exceeding that of imported membranes. The problem of membrane system failures mostly comes from engineering design. Many users pay more attention to the number of RO membranes in membrane reuse systems, rather than the membrane area and system design of lined reinforced PVDF membranes in MBR and ultrafiltration components in pre-treatment. In fact, when using the MBR+RO or UF+RO dual membrane recycling process, the RO system operates well, often due to insufficient membrane area and unreasonable design of the pre-treatment MBR or UF, resulting in excessive inlet water quality of the RO system. In fact, the cost of some membrane products for pre-treatment itself exceeds that of RO membranes, such as MBR flat membrane, which is very high in cost.

Misunderstanding 5:

Membrane technology is a universal membrane technology, which is a unit treatment technology with characteristics such as low effluent turbidity, decolorization, desalination, and strong softening. However, when treating industrial wastewater, membrane technology usually needs to be combined with traditional physicochemical and biochemical treatment processes to better leverage the advantages of membrane deep treatment. Moreover, membrane water treatment often has the problem of concentrated water discharge, and it also requires supporting other technologies, which is not omnipotent.

Misunderstanding 6:

The more membranes there are, the better within a certain range. Increasing the number of membranes can improve the water production safety of the membrane system and reduce operating costs. However, as the number of membranes increases to a certain extent, the amount of water evenly distributed on the unit membrane decreases. The flow rate of cross flow filtration water on the membrane surface is lower than the critical value, and sediment on the membrane surface cannot be taken away, leading to increased fouling and blockage of the membrane, and a decrease in water production performance. Moreover, as the number of membranes increases, the required flushing water volume increases. If the flushing water pump and compressed air volume cannot meet the flushing volume requirements per unit membrane area, it is difficult to thoroughly flush, exacerbating membrane fouling, and affecting its water production performance, which is particularly important for MBR or UF membranes. In addition, as the number of membranes increases, the one-time membrane investment and depreciation cost of the system will also increase.

Misunderstanding 7:

RO membrane must use anti fouling membrane. In theory, anti fouling RO membrane is more suitable for wastewater reuse treatment than conventional RO membrane, but the selection of anti fouling membrane depends on its anti fouling mechanism. There are two types of anti fouling RO membranes: one is that the flow channel of the membrane is wider, less prone to blockage, and anti fouling. This type of membrane is widely applicable; Another method is to modify the surface of the RO membrane to make it negatively charged, positively charged, or electrically neutral. Based on the principle of electrical repulsion, pollutants with specific properties are not easily deposited on the membrane surface, thus achieving anti pollution characteristics. The performance of the latter in terms of pollution resistance largely depends on the characteristics of water quality. Due to the wide variety of additives in printing and dyeing wastewater, it is necessary to choose the appropriate type of anti fouling membrane with appropriate electrical properties based on the inflow characteristics of the RO system, otherwise it will be counterproductive. In addition, in wastewater reuse, due to the fact that the surface of the RO membrane is quickly covered by a layer of pollutants and homogenized, the electrical characteristics of the membrane itself are not distinct. Therefore, the actual effectiveness of its anti pollution needs to be studied. The price of anti fouling RO membranes is much higher than that of conventional RO membranes, and there are few ultra-low pressure anti fouling membranes, so they do not have significant comprehensive advantages in wastewater reuse.

The above is the "Seven Common Misunderstandings about Membranes" introduced by Hongjie Water, hoping to be helpful to you.