Membrane pollution refers to the condition that the pollution components in the sludge mixture in the membrane and tubular reactor interact with each other, resulting in absorption, agglomeration, deposition, etc. in the membrane pore or membrane surface, thus causing the rise of membrane transmembrane working pressure (constant current power supply mode) or the decrease of membrane flux (constant pressure mode).
There are many components in the active sludge management system, including waste water cultivation substrate, methanogens, microbial strains, somatic cells, somatic fragments and their microbial strains metabolic substances, such as extracellular polymers (EPS) and solubility microbial strains (SMP), as well as various organic chemistry and organic matter solubility components, Theoretically, each part contributes to membrane pollution.
The pollution caused by the adhesion and agglomeration of components in the activated sludge management system in the membrane pores is called internal pollution; The pollution caused by the accumulation or accumulation on the membrane surface is called external pollution.
It must be emphasized that, MBR membrane There are "mud cake layer" pollution and "suspected glue layer" pollution in the external pollution of. Sludge cake layer pollution refers to the pollution caused by the accumulation of many sludge flocs on the membrane surface; The suspected glue layer pollution is the adhesion and agglomeration of some small particle components, such as colloidal solution components, EPS, SMP and other components on the film surface. The particle size of this component is generally widespread, and it is impossible to control this component well without film surface accumulation.
In the MBR operation, once the mud cake layer is polluted, the system software will rapidly increase with the working pressure or the flux will significantly decay coefficient. MBR will reach the operation terminal in a short time, and membrane cleaning must be carried out. However, in the long-term operation link, this mud cake layer pollution, which is considered "reversible", will gradually link up to "irreversible", endangering the long-term stable operation of the system software.
Although some scholars think that the mud cake layer pollution can have the effect of blocking fine and fine particles, it is generally necessary to try to prevent the connection of mud cake layer during the actual operation of MBR. What the suspected glue layer pollution produces is the whole process of the slow rise of membrane fouling friction resistance, which is mainly manifested in the slow rise of working pressure in the actual operation mode of constant current power supply, and the slow decline coefficient of flux in the actual operation mode of constant pressure power supply.
In addition, at this stage, there are still objections to the scientific research and understanding of the advantageous pollutants in MBR, but it is generally believed that the colloidal solution composition and microbial species in the tubular reactor are the key pollutants that cause pollution in the long-term operation of MBR, Moreover, the railway bridge and complexation between organic positive ions and organic compounds will cause more serious pollution.
In MBR, membrane pollution is related to three parts: membrane raw materials, characteristics of sludge mixture and its control operation standards. Therefore, MBR's membrane pollution control is also focused on the above three levels, namely, the research and development of membrane raw materials/membrane components with excellent performance, the control of sludge mixture characteristics, and the improvement of actual operation standards.
Membrane raw materials and membrane components are the key to MBR and other membrane separation technology processes, and are one of the main factors endangering membrane pollution in membrane separation technology processes. The selection of membrane raw materials and membrane components with excellent performance and anti pollution is an immediate and reasonable way to reasonably control membrane pollution. Therefore, a variety of membrane products with various materials and membrane components have emerged in the market at this stage. In terms of membrane raw materials, membrane pore, diameter, hydrophilicity/hydrophobicity, Zeta potential difference, membrane surface roughness and membrane surface functional group isomerism will all cause harm to membrane pollution.
In the whole process of preparing excellent membrane raw materials, the hazards of each physical performance parameter on the membrane surface must be fully considered. At present, the improvement of the performance of membrane raw materials includes two ways: membrane surface modified materials and membrane itself modified materials.
Specifically, it includes:
① Water absorption improvement, such as plasma solution, drug soaking drying, etc;
② Anti pollution factor plus or thermal polymerization, such as detergent factor plus, nanocomposites, surface UV/y direct thermal polymerization, etc;
③ Positive charge decoration on film surface;
④ Improvement of membrane diameter, porosity, surface roughness, etc. In general, MBR medium membrane raw materials are expected to have the characteristics of strong water absorption, high negative charge, uniform diameter and low surface roughness.
In addition, it is worth mentioning that some cheap plates, such as non tarpaulin, screen silk, stainless steel screen mesh, polyester mesh, etc., can be used to produce dynamic membrane on the plate for filtration and separation, which not only achieves good actual stripping effect, but also can prevent serious problems of traditional membrane pollution. This kind of membrane plate cleaning is also very convenient. Naturally, the optimization of membrane components and their modules is also important for the rational control of membrane fouling.
The characteristics of mixed liquor are another key factor that may harm membrane pollution, including sludge concentration value, sludge composition (fiber composition, colloidal solution, solubility composition, SMP, EPS, organic positive ions, etc.), sludge particle size, sludge viscosity, sludge beneficial bacteria, etc. The relationship between the characteristics of mixed solution and membrane fouling is very complex, and there are some disagreements and differences in the scientific research results.
