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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.

Following the culturing of post‐juvenile African catfish, wastewaters were purified using single and integrated processes. Iron coagulant (IC), aluminium coagulant (AC), lanthanum modified bentonite (LMB) and ceramic membranes (NF – nanofiltration) were each tested in single processes, while the combination of IC + NF and AC + NF were used in the integrated process tests. Among the single processes, membrane filtration was the most effective in purifying the aquaculture effluent. The total suspended solids (TSS) were removed entirely and there was a near‐complete removal of turbidity (99.2%), as well as effective removal of Al and Fe (80.8% and 67.4% respectively). Precipitating agents overall removed TSS most faithfully, from 37.5% removal with AC, through 50.2% with IC, to 62.3% with LMB. Using integrated processes, the highest removal efficacy was recorded for TSS (100%) and turbidity (99.7% – IC + NF; 99.9% – AC + NF). Additionally, integrated processes attained a 96.8%–98.4% removal of NO2‐‐N. This study confirms the possibility of using IC, AC and LMB in chemical purification of effluents from recirculating aquaculture systems (RAS). However, due to their low removal efficacy for nitrogen and phosphorus, it is preferable to use NF or integrated processes – membrane filtration combined with chemical precipitation, methods which proved to be most effective for water purification in RAS. [ABSTRACT FROM AUTHOR]