Method of mitigating MBR membrane contamination
According to the separation characteristics of membrane materials and membranes, various links such as MBR design, process flow and equipment operation and operation are taken into consideration to minimize concentration polarization and membrane fouling. At home and abroad, on the basis of theoretical research and application practice, many effective experiences and methods of mitigating MBR membrane fouling have been accumulated.
(1) Effectively pretreat the feed solution
The effective pretreatment of the feed liquid (raw water) is used to improve the water quality of the membrane module influent, such as pre-flocculation, pre-filtration or changing the pH of the solution, to remove some of the solute that can interact with the membrane.
(2) Change the hydrodynamic conditions of the membrane surface
Improve the fluid mechanics conditions on the liquid side near the membrane surface, such as increasing the influent flow rate or using cross-flow methods, etc., to reduce the concentration polarization, so that the retained solute is taken away in time by the water flow. In addition, from the reactor configuration, we can research and develop new membrane bioprocesses that are conducive to membrane fouling control, such as the addition of activated carbon in traditional MBR, the combination of membrane technology and biological fluidized bed to form a membrane biofluidized bed process.
(3) Improvements in Membrane Materials and Optimization of Membrane Components
The membrane material, pore size, and hydrophobicity of the membrane surface all affect the rate of membrane fouling to some extent. Membrane materials commonly used in MBR are polyfluorene, polypropylene grease, polyvinylidene fluoride, polyolefins and the like. The study also found that the characteristics of the membrane module, such as the tightness, length, and diameter of the membrane, also affect the filtration performance of the membrane. Therefore, the optimized design of the membrane module is also an effective way to delay the membrane fouling.
(4) Optimize operating conditions
1 Controlled operation at critical membrane flux
Critical flux means that there is a critical value in constant flux filtration under defined operating conditions. When the membrane flux is greater than this value, the transmembrane pressure (TMP) rapidly rises, and membrane fouling develops rapidly; When the amount is less than this value, the membrane fouling develops very slowly.
Critical membrane flux is related to hydraulic operating conditions, membrane separation mode of operation, feed liquid properties, and intrinsic properties of the membrane. The concept of critical membrane flux is getting more and more attention.
2 intermittent operation
In the submerged MBR module, the mode of operation using intermittent suction is intended to stop the membrane filtration at regular intervals, so that the net flow rate from the liquid to the membrane surface is zero, so that the sludge deposited on the membrane surface acts as an aeration bubbler. It relaxes so that it is detached from the film surface and the filtration performance of the film is partially recovered. The longer the pumping process is, the more the pollutants accumulate on the membrane surface; the longer the stoppage time is, the more the reversible contaminants on the membrane surface fall off, and the better the membrane filtration performance is.
3 Strengthen aeration and backwash
Enhanced aeration can reduce organisms deposited on the membrane surface (ie, contaminant reversibility), and backwash can effectively control membrane fouling for irreversible fouling due to blockage caused by the entry of dissolved substances into the membrane pores and the gel layer on the membrane surface.
4 Reasonably place the membrane module
The placement of the membrane module should take into account the distance between the membrane module and the wall of the aeration tank, the distance between the membrane module and the air diffuser, and the distance between the membrane module and the reactor surface, the air diffuser and the bottom of the aeration tank. In order to ensure the vertical flow of water from the bottom of the pool, the film surface and the water flow evenly, so that the downward flow of water can be evenly distributed around the membrane unit, to reduce the concentration polarization as much as possible, is conducive to slow down the formation of mud cake and promote the cake layer The shedding will achieve the purpose of delaying membrane fouling.
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