The aim of the study was to analyze and assess the possibility of using a two-stage filtration system with ceramic membranes: a 3-tube module with 1.0 kDa cut-off (1st stage) and a one-tube module with 0.45 kDa cut-off (2nd stage) for treating effluent water from a juvenile African catfish aquaculture. The study revealed that during the 1st filtration stage of the effluent water, the highest degrees of retention were obtained with respect to: suspended solids SS (rejection coefficient RI=100%), turbidity (RI=99.40%), total iron (RI=89.20%), BOD5 (RI=76.0%), nitrite nitrogen (RI=62.30%), and CODCr (RI=41.74%). The 2nd filtration stage resulted in a lower reduction degree of the tested indicators in comparison to the 1st filtration stage. At the 2nd stage, the highest values of the rejection coefficient were noted in for the total iron content (RIV=100%), CODCr (RIV=59.52%; RV=64.28%, RVI=63.49%) and turbidity (RIV and RV = 45.0%, RVI=50.0%). The obtained results indicate that ceramic membranes (with 1.0 and 0.45 kDa cut-offs) may be used in recirculation aquaculture systems as one of the stages of effluent water treatment.

Aquaculture plays a great role in producing foodstuffs, sustaining inland capture fisheries and providing employment. The key to future development in pond aquaculture is diversification of production technology, intensity, and function connected to increasing the environmental value of pond areas. New production systems involve a combination of intensive and extensive pond culture, increasing productivity and improving nutrient utilisation and fish species diversification. The most important principle of these systems is the possibility to use the wastes from intensive aquaculture as the input for extensive, environment-friendly fish production. These systems were proven to be profitable and sustainable in tropical and subtropical areas. However, for temperate climatic conditions, such data are scarce. For this reason, we decided to discuss modifications that, in our opinion, can be applied in an extensive part of the integrated intensive-extensive system in temperate climatic conditions in order to increase the overall productivity of the pond aquaculture.