In view of the many misunderstandings that many people have about the membrane at present, these misunderstandings are particularly explained here (technical dry goods, every point is the truth)

1.1 misunderstanding 1: membrane water treatment equipment is a highly difficult operating system

The automatic control requirements of membrane water treatment system are much higher than those of conventional biochemical treatment system, and many users mistakenly believe that the membrane system is difficult to operate. In fact, the operation of membrane water treatment system is highly automated. The start-up, shutdown, dosing and on-line flushing operations are all performed by PLC system program control, which can be unattended. It only requires manual regular patrol inspection, dispensing, periodic maintenance and cleaning, and basically does not need to add additional operating staff. The routine cleaning and maintenance of membrane can be mastered in one day of training, and the difficulty is far lower than that of biochemical system which requires high comprehensive skills of employees.

1.2 misunderstanding 2: large investment, affordable

It is believed that the one-time investment, depreciation and replacement cost of membrane is very high, which can be bought but not used. In fact, with the development of domestic membrane manufacturing enterprises, the price of membrane is declining. MBR membrane system can save the cost of civil engineering and land occupation, reduce the sludge volume and sludge disposal cost, and is a good choice with high comprehensive cost performance ratio; For UF and RO systems, the economic benefits generated by the waste water 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 depreciation cost of the membrane will not exceed 0.6 yuan / T of water inflow, or even lower than the dosing cost of the system per ton of water inflow.

1.3 misunderstanding 3: the membrane is delicate and easy to be damaged

S - due to lack of experience in some engineering companies, the membrane systems designed and constructed have problems such as broken wires and scrapped membranes, and users mistakenly believe that membrane products are difficult to maintain. In fact, the main problems come from the process design and the membrane itself. Through reasonable pretreatment design and safety protection design, the high-quality lined enhanced PVDF membrane can be used for more than 5 years, and the replacement cycle of RO membrane is more than 3 years.

1.4 misunderstanding 4: brand and RO quantity are more important than membrane area and system design

When establishing membrane system, some enterprises pay too much attention to whether the membrane is an imported product, and do not understand the importance of system design. In fact, the performance of some domestic ultrafiltration membranes has approached or even reached the international advanced level, and the cost performance ratio exceeds that of imported membranes. The failure of membrane system mainly comes from engineering design.

Many users pay more attention to the number of RO membranes in the membrane reuse system, rather than the membrane area and system design of lined enhanced PVDF membranes in MBR and ultrafiltration modules in pretreatment. In fact, when the mbr+ro or uf+ro double membrane recycling process is adopted, the RO system operates well, which is often related to the insufficient membrane area and unreasonable design of the pretreatment MBR or UF, resulting in the excessive inflow water quality of the RO system. In fact, the cost of some membrane products for pretreatment is higher than that of RO membrane, such as MBR flat membrane, which is very high.

1.5 misunderstanding 5: membrane technology is omnipotent

Membrane technology is a unit treatment technology, which has the characteristics of low turbidity, decolorization, desalination and softening. However, when treating industrial wastewater, membrane technology usually needs to be combined with traditional physicochemical and biochemical treatment processes to give better play to the advantages of membrane advanced treatment. Moreover, membrane water treatment usually has the problem of concentrated water discharge. It also has the needs of supporting other technologies, which is not omnipotent.

1.6 misunderstanding 6: the more the membrane, the better

In a certain range, increasing the number of membranes can improve the water production safety of the membrane system and reduce the operation cost. However, when the number of membranes increases to a certain extent, the amount of water evenly distributed on the unit membrane decreases, and the flow velocity on the membrane surface of cross flow filtration is lower than the critical value, so the deposited debris on the membrane surface cannot be taken away, resulting in the aggravation of membrane pollution and blockage and the decline of water production performance. Moreover, with the increase of the number of membranes, the required washing water volume increases. If the washing water pump and compressed air volume cannot meet the washing volume requirements per unit membrane area, it will be difficult to wash thoroughly, aggravate membrane pollution and affect its water production performance, which is particularly important for MBR or UF membranes. In addition, when the number of membranes increases, the one-time membrane investment and depreciation cost of the system will also increase.

1.7 misunderstanding 7: RO membrane must use anti pollution membrane

Theoretically, anti fouling RO membrane is more suitable for wastewater reuse than conventional RO membrane, but the selection of anti fouling membrane depends on its anti fouling mechanism. There are two types of anti pollution RO membranes: one is that the flow channel of the membrane is wider, which is not easy to be blocked and anti pollution. This kind of membrane is generally applicable; The other is to modify the RO membrane surface so that the RO membrane is negatively charged, positively charged or electrically neutral. According to the principle that electrical properties repel each other, pollutants with specific properties are not easy to deposit on the membrane surface, so as to achieve anti pollution characteristics. The anti pollution performance of the latter depends largely on the characteristics of water quality. Due to the wide variety of additives in printing and dyeing wastewater, it is necessary to select the appropriate type of anti pollution membrane according to the inflow characteristics of RO system, otherwise it will backfire. In addition, in wastewater reuse, because the RO membrane surface will be quickly covered by a layer of pollutants and homogenized, the electrical characteristics of the membrane surface itself are not distinct, so its actual anti pollution effect needs to be discussed. The price of anti pollution RO membrane is much higher than that of conventional RO membrane, and there are few ultra-low pressure anti pollution membranes, so it has no significant comprehensive advantages in wastewater reuse.