All of the comments below ...

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All of the comments below have merit and awareness of their expertise.  Several things must be brought up.

1. No decisions on any approach can be made until you get a DNA of the microbes present in the current conditions. 

2. You must take into consideration the Temperature of the Water and therefore the best species of Microbes that will work in these conditions.

3. Use a DO meter to measure the amount of DO in the system. There are methods to increase the DO (Dissolved Oxygen) which will excite the exponential growth of the Microbes.

4.  Take a vertical profile of the sludge and dirty water (high TSS) levels of the system and send to your lab for evaluation of what is present in this system, such as Nitrogen, Phosphorus, etc, etc... 

5. once you have a cross section of what is in there, you can then begin to approach a cure for what ails you.  I believe you will have to supply both aerobic  as well as anaerobic Microbes.