Mitsubishi STERAPORE 5700 Series Instruction Manual page 21

3-1-2 Acid Cleaning
Although NaClO cleaning effectively removes organic contamination, it has no effect on inorganic
contamination. Cleaning only with NaClO will result in inorganic matter causing a rise in trans membrane
pressure. Perform acid cleaning once a year if the product is used for municipal wastewater treatment.
Either the same process as recovery cleaning or chemical soak cleaning process is used in acid cleaning.
If the trans membrane pressure is high after cleaning with NaClO, perform recovery cleaning according to the
following procedure. See Table 3-1 for the standard injection amount and injection time.
1. Adjust the acidic solution and put it into the dilution water tank.
2. Activate the dilution water pump and inject the solution from step 1. into the membrane
module.
Refer to "Chemical soak cleaning (Off line cleaning)" (p.19) for the chemical soak cleaning procedure. See
Table 3-1 for the standard injection amount and injection time.
With a small module, it is possible to inject chemicals by preparing a chemical tank in addition and connecting
it to the filtration line, taking advantage of the difference in water level between the membrane tank and the
chemical tank (See Figure 3-3). It is recommended to make the difference in water level 1 m or greater.
WAR NI NG
Mixing sodium hypochlorite (NaClO) and acid releases chlorine gas, which is very dangerous. Do not
mix these chemicals under any circumstances.
Type of cleaning
Maintenance
cleaning (NaClO)
Recovery
cleaning (NaClO)
Recovery cleaning
(acid)
Chemical soak cleaning
(NaClO)
Chemical soak cleaning
(acid)
＊1 2 L/m
2
(membrane surface area) + α (connection pipe volume)
＊2 Recommended value: Initial trans membrane pressure (negative pressure) -15 kPa
STERAPORE 5700 Series (FF) Instruction Manual
Table 3-1 Types of Chemical Cleaning
Cleaning frequency
Depends on design flux.
At most once a week
Once every 3 months or when the trans
membrane pressure reaches the upper
2
＊
limit
Once a year
When trans membrane pressure is not
restored by maintenance/recovery
cleaning.
When problems such as clogging
occur.
When trans membrane pressure is not
restored by maintenance/recovery
cleaning
Effective chlorine
concentration
(for NaClO)
NaClO 2 L/m
300 to 500 mg/L
NaClO 2 L/m
3,000 mg/L
Oxalic acid or citric acid 2 L/m
1 to 2 wt%
NaClO Enough to
3,000 mg/L immerse a
module
Oxalic acid or citric acid Enough to
1 to 2 wt% immerse a
Hydrochloric acid or module
sulfuric acid
0.1 to 0.6N
Chapter 3 Chemical Cleaning
Injection Injection and
amount immersion time
2 1
+ α ＊
Injection time: about
15 to 30 minutes
2 1
+ α ＊
Injection time: about
30 minutes
Settling time: about
90 minutes
2 1
+ α ＊
Injection time: about
30 minutes
Settling time: about
90 minutes
About 6 to 24 hours
About 2 to 4 hours
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