Daily Inspection of Toray Submerged Membrane Module for MBR(Manual)

May 27, 2021


Daily recording of the values associated with these parameters will be helpful in determining the current condition of the MBR system. Operational data should be analyzed daily to serve as a guide for preventative maintenance. Take action to correct any unfavorable operational trends before more serious conditions develop. In addition, it is beneficial to inspect all system components for correct and smooth operation on a weekly basis.

(1)   Diffused air conditions
Check the air flow rate and blower discharge pressure of the air supply line to the MBR air diffuser. Too low of an air flow rate can result in membrane clogging. Too high of an air flow rate can result in element damage. Try and keep the air flow rate per module between recommended ranges. If the recommended air flow rate cannot be achieved, stop filtration and check the air supply piping for leaks, incorrect valve positions, blower inefficiency or possible air line restrictions. In the case where multiple MBR modules are located in the same tank check that diffused air is being evenly distributed between each MBR module. If uneven air distribution is observed conduct an air diffuser cleaning.

If the scouring air flow rate drops or becomes extremely irregular or if air supply is stopped, then immediately stop filtration to prevent membrane clogging.

(2)   Trans-membrane pressure
Check the trans-membrane pressure (TMP) frequently. When the TMP increases by 5 kPa (50 mbar) at a constant filtrate flow rate, it is time to initiate a membrane element chemical cleaning. A sudden increase in the trans-membrane pressure suggests that the membrane surfaces are clogging. Clogging can be caused by abnormal diffused air distribution, too high flux rate, too high MLSS concentration or deteriorating sludge properties. If TMP values are increasing, check the MBR operating conditions and the biological condition of the sludge. Take necessary actions to correct operating conditions and then perform a chemical cleaning of the elements.

(3)   Activated sludge characteristics
The activated sludge of the membrane bioreactor should be self-cohesive and free from odor. The color of healthy activated sludge is typically brown, however this color can differ among plants, depending on wastewater composition, organic load etc. If an unexpected change is observed in sludge characteristics, check current operating conditions such as BOD load, MLSS concentration, DO, pH, temperature and/or wastewater composition, and take appropriate corrective actions.

(4)   Water temperature
The desirable water temperature is 15 degree C to 40 degree C. If the temperature is out of this range and the activated sludge properties are not optimum, it is recommendable to install a temperature control device to cool or heat the liquid.

(5)   DO
The aeration tank and the membrane tank should be kept in an aerobic condition. If DO is less than 1.0 mg/L, take necessary actions such as increasing the air-flow rate of the biological aeration unit, or lowering the sludge concentration by increasing the excess sludge discharge rate. In the case where the air supply for biological aeration requirements and air piping for membrane scouring comes from the same blower, do not exceed the recommended range of membrane scouring air flow rate to the diffuser. To increase DO concentration of the liquid within the membrane tank adjust the separate biological aeration system.

(6)   pH
The recommended pH range is 6 to 8. If pH is out of this range and the activated sludge properties are not optimum for filtration, adjust the pH by gradually adding acid or alkali.

(7)   MLSS
MLSS concentration in the membrane tank is recommended to be between 7,000 to 18,000 mg/L. If MLSS is too low, increase the MLSS concentration in the membrane tank by reducing the sludge discharge rate. If the MLSS concentration is too high, check the RAS (return activated sludge) flow rate. If it is determined that the RAS flow rate is too low increase the RAS flow rate to the proper value. If RAS flow rate is correct, increase excess sludge discharge rate.

(8)   Water levels
Check to confirm that the water levels of the membrane tank are being maintained within the recommended values. If it is determined that the levels are not as per the design, check the following: level control devices, level control circuits, filtrate pump VFD controls, activated sludge feed control valve, membrane flux rate. Take corrective action as necessary.

(9)   Sludge viscosity
It is recommended that the sludge be no higher than 100 mPa.s (measured by B-type viscometer) or 250 mPa.s (measured by C-type viscometer). If the sludge viscosity is too high, check MBR operating conditions and biological conditions, such as F/M ratio, and take necessary corrective actions.

(10)  Sludge filterability
Paper filtration method is a simple and reliable method to determine the filtration properties of the sludge. See the method described in the attached document. Toray recommends conducting paper filtration test and measurement of TOC and/or turbidity of filtered water routinely. In the case an abrupt decrease in filterability is recorded and/or increase in TOC/turbidity, check the operating and biological conditions, and take appropriate action based on those findings.

(11)  Pretreatment system
In addition to the operating parameters for the Toray Submerged Membrane Module for MBR, check the status of the pretreatment systems (particularly the screening device) frequently. At regular intervals remove any accumulated trash that may accumulate on the screening device.

This content does not intend to guarantee the results of application of the information provided herein or the safety and the compatibility of this product.
Before using this product, the user is asked to check for its safety and compatibility with the intended purpose.
This content is subject to revision from time to time.
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This content is extracted from “Submerged Membrane Module for MBR TORAY “MEMBRAYTM” Instruction Manual”(the Manual).  Please refer to other contents stated in the Manual.
( https://www.water.toray/knowledge/manual/ )