To evaluate the efficiency of the membrane to remove the small-est fraction of the particulates from the recirculating system, the level of turbidity and number of colloids (particles smaller than1 m) were investigated. Results of the analysis of the content of colloidal particles and turbidity for the duration of the test in both the cRAS and mRAS pilot plants are shown in Fig. 2. The number of colloidal particles (Fig. 2 a) and turbidity (Fig. 2 b) was significantly lower in the cultivation tanks for the mRAS alternative at the set filtration rate. Highest values measured during the experiment were38% reduction in number of colloidal particles (25 dph) and 77%reduction in turbidity (30 dph). From the result it is evident that inthe process configuration which includes the membrane filtration,an improved water quality is obtained with respect to turbidity andfraction of colloidal material