If you are not building mass, ...

If you are not building mass, then the bacteria are not acclimated, being starved and then overloaded organically, or you have some toxic and recalcitrant compounds.  I would reseed from another train (may want to make a jumped to pull off recirculation back to the train just in case it is needed in the future).  If you use POTW sludge in an industrial application, then count on 70% attrition of the bacteria, because you have changed their food source.  In any event you have to reseed.  In addition, I would use freeze-dried bacteria cultures from an abundance of different bio-enhancement companies (i.e. Novozymes), and possibly some micronutrients to top it off.  If there are NO cultures in this train as you say, then I am betting you have a toxic stream.  In that event, you may want to segregate the stream and perform Advanced Oxidation Process (there are several, but for specific toxicants and pollutants there are many papers in circulation as to which AOP has worked previously.  Now, there are always scavengers (whatever else is in your stream) and byproducts that can affect the AOP greatly.  That is just bench work  To shorten things up at the bench you can use algorithms for Simplex Optimization Methods.  This is a bit challenging unless you are a good math student, but there is enough written to give you a handful of choices.  Could cut down on testing by up to 10x.  Good luck and keep us posted.  Thanks, Sean L. Roop - Senior Water and Wastewater Consultant - Industrial and Engineering Consultants, LLC.