M parvicella is a typical ...

M parvicella is a typical foaming causing bacterium, but it has some weak points, that you can use to get read of it. 1) normally it affects doemstic plants and it increases dramatically in winter  when the temperature drops below 15,0 °C 2) you must avoid to tackle the problems when its level in activated sludge is too high 3) Collect the scum and dispose  it (never send it back in the plant) 4) Aluminum polycloride is effective, as Muna already said  (and it precipitates phosphorus as well). 4)  The basic strategy is in monitoring the bacterium presence since summer and intervene with Aluminum PC, or dose it continuosly (reminding to alternate with iron chloride (if you use it) to avoid acclimation phenomena. Many positive experiences have been recently collected in this IWA Book:

Rossetti S., Tandoi V., Wanner J. (2017), Eds: Activated Sludge Separation Problems: Theory, Control Measures, Practical Experiences – Second Edition, IWA Publishing.

Good luck!!!! Valter