Secrets Uncover: How Does the MBR Membrane Work?

The MBR pool uses membranes to filtersludge-containing sewage in the biochemical reaction tank to achievesludge-water separation. On the one hand, the membrane intercepts themicroorganisms in the reaction tank. The concentration of activated sludge inthe pool reaches a very high level, so that the biochemical reaction ofdegrading sewage is carried out more quickly and thoroughly. On the other hand,due to the high filtration accuracy, the effluent is clear and transparent.High-quality water is obtained.

The organization and function of membranesystem

What does the MBR membrane system include?

MBR membrane module system includes waterproduction system, backwash system, cleaning system, membrane purge aerationsystem, control system, etc.

Purging (aeration) within the MBR membranearea has two functions: one is for air-water oscillation around the membranemodule to keep the surface clean, and the other is to provide oxygen requiredfor biodegradation.

The biodegraded water passes through theMBR membrane module by self-priming pump, and the filtrate is collected throughthe MBR collection pipe and sent to the fresh water pool. Through the efficientinterception of the membrane, all bacteria and suspended solids are retained inthe membrane pool, which can intercept nitrifying bacteria, and make thenitrification reaction proceed smoothly. At the same time, it can holdmacromolecular organic matter that is difficult to degrade, extend itsresidence time in the membrane reactor, and maximize biodegradation.

The membrane purge aeration system isintegrated at the bottom of the module to alleviate the sludge accumulationaround the membrane module. The remaining sludge is regularly dischargedthrough the sludge pump in the membrane area, which can control the concentrationof activated sludge and the existing time in the system.

At the same time, in order to ensure thatthe MBR membrane module has a good water flux and can continuously and stablyproduce water, a unique clean water backwash, maintenance cleaning andrestorative chemical cleaning procedures are designed to regularly clean themembrane module.

Key points of control for membrane systemoperation

Next, we are going to learn about some keypoints in the entire membrane system operation.

　　(1) Temperature

The temperature of sewage is changeable,the inoculated sludge can be used and kept in a lower operation load (Sludge).When the temperature of the raw sewage is less than 12℃, the nitrification ofthe biochemistry will be reduced, and the ammonia nitrogen index of themembrane system may exceed the standard.

　　(2) Aeration rate

In the early stage of aeration, the sludgehas not yet formed in large quantities. The flocculation performance of sludgeis not very good, and it is still in a discrete state. Coupled with the lowconcentration of sludge, microorganisms are easy to be in the endogenousbreathing state. So the amount of aeration should not be too large. It can becontrolled at about 1/2 of the normal value of the design, otherwise flocculentsludge is not easy to form.

　　(3) Microorganism

To monitor and inspect the sludge formationprocess, it is necessary to observe the SV30 and MLSS of the aeration tankmixture, but also to observe the biological phase of the sludge at any time andunderstand the growth of mycocolloids and indicator microorganisms. So as tomake necessary adjustments to the culture process according to the situation.

　　(4) Sludge reflux rate

The management of the sludge reflux systemadopts a constant return ratio. When the amount of inflow sewage changes, theamount of reflux sludge is adjusted accordingly. With this method, when theremaining sludge discharge is basically unchanged, the sludge level in MLSS,F/M and the aeration tank can be kept basically constant. Without changing withthe inflow sewage volume Q, to ensure a relatively stable treatment effect.

　　(5)Sludge discharge

The residual sludge discharge is few due tothe MBR process used in this project. With the stable operation of the system,the amount of sludge will gradually increase. The sludge concentration needs tobe adjusted according to the needs of process adjustment. The daily amount ofsludge discharge and the discharge time are closely related to theconcentration of pollutants and the amount of influent water, which should becarried out according to the process analysis. The remaining sludge of the MBRsystem is directly discharged by the membrane tank. The concentration can reachabout 8000~12000 mg/L. Compared with the sludge discharge of the traditionaldual sedimentation tank, its dewatering and settlement performance are worse,and the operating parameters, including the amount of sludge intake, dosage,conditioning intensity and time, need to be flexibly adjusted to ensure stableoperation.

Membrane system supporting equipment

　　1.Equipment description: The equipment roomis mainly for placing membrane modules, water production systems and otherequipment. In addition, the auxiliary systems, such as backwashing system,cleaning system, membrane aeration system, control system and other systems,are set up to ensure the operation of the system and the stability of effluentquality.

The water production system is equippedwith a self-priming pump, and a single membrane corresponds to a priming pump.If the rate of water is small, the number of pumps can be decreased. It isrecommended to set up a vacuum pump to help the priming pump start and reducethe workload at the beginning of the pump's operation. The customer can alsoset up a compressed air system as the air source for pneumatic valves in sewageplants (except for electric valves designed).

Several membrane cells can share onebackwash pump. PLC control is adopted to backwash multiple membrane cells inturn.

The membrane cleaning system can be dividedinto two parts: the maintenance chemical system and the recovery chemicalsystem.

Maintenance chemical systems (alkalinewashing) include sodium hypochlorite storage tank, sodium hypochlorite dosingpump, sodium hypochlorite discharge pump; Maintenance chemical systems(pickling) include oxalic acid (or citric acid) feeders, oxalic acid (or citricacid) storage tanks, oxalic acid (or citric acid) dosing pumps. Alkalinewashing and pickling are recommended to set the cleaning cycle in the controlsystem, and the cycle can be adjusted at any time.

The restorative chemical system can bedivided into automatic dosing and manual dosing, and it is recommended toconfigure the automatic system to control the dosing agent concentration moreaccurately. The dosing pumps of the two cleaning systems are supposed to haveone standby, if the concentration of chemical solution in the storage tank istoo low, 2 sets can be started at the same time.

2.Control objectives: each system worksstably and can run automatically; The membrane system works well; The flow rateand negative pressure are stable, and can run according to the set flow; Eachpneumatic valve (electric valve), liquid level meter, turbidity meter, flowmeter and other instruments work normally and accurately; The membrane cleaningsystem is normal and effective;

3.Basic operating parameter settings:

Set value of water production in each membranepool: negative pressure limit < -60 kPa; Monitoring effluent SS to meet thedesign requirements;

Water production/backwashing time of eachmembrane tank: 9 min / 1 min or 8 min / 2 min (according to different sewagetypes)

Backwash method: according to the periodicsetting of water production, each 6 cycles of water production for backwashing.