GIRE-097-2-2
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sludge characteristics, check the operating condition, such as BOD load, MLSS
concentration, DO, pH, temperature and/or wastewater component, and take appropriate
actions.
(4) MLSS
MLSS concentration in the membrane submerged tank should be normally 7,000 to 18,000
mg/L. If MLSS is too low, please decrease excess sludge discharge rate. If MLSS is too high,
please check the return activated sludge flow rate and if it is low, please increase the RAS
rate at proper value. If RAS rate is proper, please increase excess sludge discharge rate.
(5) Sludge viscosity
It is desirable that the sludge viscosity is not higher than 250 mPa
・
s (Measured by C-type
viscometer). If the sludge viscosity is too high, please check the operating condition and
biological condition, such as F/M ratio, and take necessary actions.
(6) DO
Any point in the aeration tank and the membrane submerged tank should be kept at oxic
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 lower the sludge concentration by increasing excess
sludge discharge rate. In case the blower and air piping for membrane scouring is not
separated from the biological aeration system, control the membrane scouring air flow rate at
fixed value without being affected by DO control in oxidation process.
(7) pH
The desirable pH range is 6 to 8. If pH is out of this range and the activated sludge property
is not good, please adjust pH by gradually adding acid or alkali.
(8) Liquid temperature
The desirable liquid temperature is 15 degree C to 40 degree C. If the temperature is out of
this range and the activated sludge property is not good, it is recommendable to install
temperature control device to cool or heat the liquid.
(9) Liquid level
Check the liquid level of the membrane submerged tank is kept in the appropriate range. If
this requirement is not met, check the situation of the control system, particularly the
