Foam Control in WWTP

Foam Control in WWTP

What is the best ​chemical ​treatment to ​reduce foaming ​caused by ​filamentous ​bacteria in ​wastewater ​plants? The process in the plant where I work is composed of classic primary sedimentation, denitrification before oxidation, secondary sedimentation and disinfection. When the temperature of sewage inlet drops down to 15°C there is a gradual increase of foam growth in the oxidation. The operating conditions in the anoxic selector are HRT=3.5-4 h without flow equalisation. At the moment we’re dosing AlCl3 to coagulate PO42- and reduce the foaming. Please find the attached picture of bacteria viewed with a microscope.  What kind of chemical products should I use to eliminate or reduce the foaming? In the area where I live and work we can’t use NaOCl. Thanks and Best Regards, Matteo