Oxidation ditch, .450 MGD design rate, .220 MGD flow. I have dosed the RAS with sodium hypochlorite and the filamentous immediately returns. Eventually there is nothing but filamentous left in activated sludge. After examining the reed bed drain effluent that flows to oxidation ditch, there isn't very many bugs but they all appear to be filamentous. I'm planning on putting a gallon of bleech a day into wet pit where reed bed drain pump is.
Maybe the chlorine dosage was not appropriate. It have to be adjusted with the load in your system as well as the type of filamentous bacteria that you have. You have many article on the subject on internet. I can suggest you one to help you with your problem.