Why is it recommended not to use MBR technology for rural sewage treatment?

Author：

With the advancement of the times, sewage treatment stations have gradually become popular in rural areas in China. Although there is currently no unified effluent standard for township sewage treatment plants, many village and town sewage stations have set extremely high discharge standards at the beginning of construction, even comparable to urban sewage treatment plants. Under such high standards, village and town sewage stations have adopted diverse treatment processes, such as contact oxidation, AAO, artificial wetlands, biological turntables, SBR, MBBR, MABR, MBR, FBBR, etc. Among them, MBR process is highly favored due to its advantages in treatment efficiency.

MBR, also known as membrane bioreactor, is a new type of wastewater treatment system that combines membrane separation technology with biological treatment technology. It uses membrane components to replace traditional biological treatment technology's secondary sedimentation tanks, reducing tank capacity and footprint, making it particularly suitable for sewage stations with limited land resources, technology, and personnel. However, with a deeper understanding of the MBR process, we have found that it is not applicable to all rural sewage treatment plants for the following reasons:
Firstly, the construction investment and operating costs of MBR process are relatively high. The expensive price of membrane components makes the engineering cost of MBR process 30% -50% higher than that of conventional activated sludge process. For rural areas with relatively tight funds, purchasing sewage treatment equipment is already a significant expense. In addition, the high cost during the operation of the MBR process, such as the addition of two membrane flushing fans, has led to an increase of 200-400% in operating power consumption, and a water and electricity consumption of 1-3 degrees per ton, making it difficult for many areas to bear their operating costs.
Secondly, the sewage characteristics of villages and towns are also important factors affecting the application of MBR technology. The incomplete construction of pipeline networks in some areas has led to low sewage collection rates and low hydraulic loads. In addition, rural sewage often contains water with a low carbon to nitrogen ratio. This water quality characteristic, when using MBR process, can easily lead to loose structure and reduced activity of activated sludge, thereby accelerating membrane pore blockage and increasing the frequency of membrane washing. In the long run, MBR membranes will face frequent washing operation negative pressure rise offline washing cycles until they are scrapped.
Furthermore, the phenomenon of disputes between owners and membrane manufacturers is not uncommon. Due to the difficulty in achieving the designed membrane flux in practical applications, or membrane damage caused by improper membrane washing methods, both parties often have their own opinions and it is difficult to reach a consensus. In fact, the actual water production of MBR membrane process often only reaches half of the membrane manufacturer's designed flux, which further highlights its limitations in application.
In addition, there are many components used in the MBR film process, which also increases the frequency of faults. Once a malfunction occurs, on-site personnel often find it difficult to quickly locate the cause of the problem, leading to difficulties in maintenance. For example, a malfunction of the liquid level gauge may cause the inlet pump to continue running, resulting in flooding of the pool; The failure of the membrane fan may cause the MBR production water pump to operate without aeration, accelerating membrane blockage and even scrapping. Therefore, high requirements are placed on instruments, and it is best to choose imported or domestic first tier brand instruments.
Finally, the MBR process performs weakly in removing nitrogen and phosphorus from wastewater. Due to the need for a large amount of gas to scrub the membrane surface during the operation of the MBR membrane process, a large amount of oxygen is carried during the sludge reflux process in the membrane tank, resulting in poor treatment efficiency for domestic sewage with low BOD load and high dissolved oxygen. When the effluent index requires a high level of total nitrogen and phosphorus, a large amount of carbon sources and phosphorus removal agents need to be added, thereby increasing operating costs.
In summary, although MBR process has certain advantages in sewage treatment, its high investment and operating costs, sensitivity to sewage characteristics, disputes with membrane manufacturers, high failure frequency, and weak nitrogen and phosphorus removal ability make it unsuitable for application in some rural sewage plants. Therefore, when choosing a sewage treatment process, it is necessary to comprehensively consider various factors and choose the process that is most suitable for the local actual situation.