A water treatment system comprises a reactor (10) having a first zone (11) and having a second zone (12). A water inlet (21) for receiving an intake water flow is provided to said first zone (11) and a water outlet (22) is present for discharging an output water flow from said second zone. Bubble generator means (50) generate, during operation, gas bubbles, particularly micro bubbles, and mix these with the intake water flow. Foam removal means (30) are used for separating and evacuating a foam layer (16) floating at a waterline (15) of said second zone (12). These foam removal means comprise a foam collection device (33) having an entrance (31) beyond a level of said foam layer and having a foam outlet (32). The reactor is provided with water level control means that maintain said waterline (15) within said reactor and said foam layer (16) below a level of said entrance (31) of said foam collection device (30). Said water level control means enable raising said waterline substantially to beyond a level of said entrance of said foam collection device, thereby discharging said foam layer at least substantially from said waterline.
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