How to reduce MBR membrane fouling and improve service life

MBR refers to a new wastewater treatment device that combines ultrafiltration and microfiltration membrane separation technology with bioreactors in wastewater treatment. This reactor combines the advantages of membrane treatment technology and biological treatment technology. Ultrafiltration and microfiltration membrane components, as drowning separation units, can completely replace secondary sedimentation tanks. Compared with traditional processes, this MBR process that combines membranes with biochemical reactions has significant advantages. MBR can be divided into two types: flat panel and roll type (FMBR/SMBR).

MBR membranes are mainly used in industrial wastewater reuse, reverse osmosis pretreatment, landfill leachate pretreatment, domestic wastewater reuse, secondary sedimentation tank effluent, heavy metal removal, process water, circulating water, and other aspects. Its advantages are: high effluent quality, no impact of influent water quality fluctuations, small footprint, longer activated sludge age, less sludge discharge, saving operating costs, and convenient replacement.

How to reduce membrane fouling and improve membrane service life?

Based on the characteristics of membrane materials and membrane separation, various aspects such as MBR design, process flow, and equipment operation are considered to minimize concentration polarization and membrane fouling. Based on theoretical research and practical applications both domestically and internationally, many effective experiences and methods have been accumulated to mitigate MBR membrane fouling.

(1) Effectively pretreat the feed liquid

Effective pre-treatment of the feed solution (raw water) is adopted to improve the water quality of the membrane component inlet, such as pre flocculation, pre filtration, or changing the pH value of the solution, to remove some solutes that can interact with the membrane.

(2) Changing the hydrodynamic conditions of the membrane surface

Improve the fluid dynamics conditions on the liquid side near the membrane surface, such as increasing the inlet flow rate or using cross flow methods to reduce concentration polarization, so that the intercepted solute is promptly carried away by the water flow. In addition, new membrane biological processes that are conducive to membrane fouling control can be studied and developed based on the reactor configuration, such as adding activated carbon to traditional MBR and combining membrane technology with biofilm fluidized bed to form a membrane biofilm fluidized bed process.

(3) Optimize operating conditions

① Control operation at critical membrane flux

Critical flux refers to the presence of a critical value in constant flux filtration under certain operating conditions. When the membrane flux exceeds this value, the transmembrane pressure (TMP) rapidly increases and membrane fouling rapidly develops; When the membrane flux is less than this value, the development of membrane fouling is very slow.

The critical membrane flux is related to hydraulic operating conditions, membrane separation operating modes, feed liquid properties, and inherent membrane properties. The concept of critical membrane flux is receiving increasing attention.

② Intermittent operation

In the submerged MBR, the intermittent suction operation mode aims to achieve a net flow rate of zero from the liquid to the membrane surface by regularly stopping membrane filtration, so that the sludge deposited on the membrane surface relaxes under the action of aeration bubbles and falls off the membrane surface, partially restoring the filtration performance of the membrane. The longer the suction process, the more pollutants accumulate on the membrane surface; The longer the suction stop time, the more reversible pollutants on the membrane surface will fall off, and the better the recovery of membrane filtration performance.

③ Enhanced aeration

Enhanced aeration can reduce the deposition of organisms on the membrane surface (i.e., reverse pollution); For blocking caused by soluble substances entering into membrane pores and irreversible pollution of gel layer on membrane surface, backwashing can effectively control membrane pollution.

④ Reasonably place membrane components

The placement of membrane components should consider the distance between the membrane components and the wall of the aeration tank, the distance between the membrane components and the air diffuser, and the distance between the membrane components and the reactor liquid level, the air diffuser and the bottom of the aeration tank, in order to ensure that water flows vertically upwards from the bottom of the tank, the membrane surface and the water flow are in uniform contact, and the downward water flow can be evenly distributed around the membrane unit, reducing concentration polarization as much as possible, which is conducive to slowing down the formation of sludge cake and promoting the detachment of sludge cake layer, and achieving the goal of delaying membrane pollution.