I agree with most what has ...

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I agree with most what has already been said. I would make sure that you control your MLSS to give an F:M of around 0.1 a sludge age of a least 12 days. If the pH is around neutral and you have sufficient alkalinity you should have no problem re-establishing the nitrifier population. I would never buy nitrifiers, grow your own. If you need to add them, there is something wrong with the process; sort that out and they will return naturally within a week or so (depending on the operating temperature). Keep the DO above 2 mg/l initially and reduce depending on effluent quality once nitrification has stabilised. Let us know how you get on. If you lose nitrification under these circumstances then check for inhibition due to something in the influent (ISO 9509).

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1.The pH is changed from about 6.6 to  5.6.

2.The abnormal time have been two weeks, and the temperature is about 35℃.

3.we pump the sludge from other system (which is good to NH3-N reduction) as usually, but this time  the NH3-N reduction rate and MLSS is poor to improve .

4.we have increase the pH, from 5.6 to 6.0 (now), the target is about 7.

5.Could you kindly offer me the ISO 9509, thanks.

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Dear Lin. Is the wastewater domestic or industrial?

1. Do you know the cause of the pH drop? Is this the untreated wastewater or after treatment? You will not nitrify at pH 5.6

2. Is this wastewater temperature? You are on the edge of nitrification at 35oC. You will need sludge age of at least 12 days, preferably 18 days for full nitrification at this temperature.

3. If you have a sludge from another plant, this is good. But, the conditions need to okay. I suggest you raise the pH to at least 6.5. What is the alkalinity? You will need at least 300mg/l as CaCO3 for 40 mg/l NH3 and a minimum of 50mg/l after full nitrification to prevent pH drop, Do you denitrify and recover the alkalinity?

4. Is this pH increase after treatment or have you increased by manual alkaline addition?

5. ISO9509 is available on the internet

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