Problems with Microthrix Parvicella in WWTP

We are running a WWTP with a flow of 6 m3/s and we have problems with Microtrix Parvicella. We have carefully monitored DO, we've improved the aeration system, we applied chlorine, polymer, but we still have problems. Do you have information on some new treatment and monitoring of the growth control techniques? Thanks in advance for your help.