Abstract
The study aimed to investigate the ability of Pseudomonas stutzeri as biofilm (fixed mode) for decontaminating tannery wastewater based on the remarkable efficiency that planktonic P. stutzeri exhibited in the removal of all the contaminants during the batch treatment in a previous study. P. stutzeri were fixed on white stone as supporting material and tested as continuous treatment biofilm system for the tannery effluent at different flow rates (30-200 mL/h) for 5 h where samples were collected on hourly interval. Extremely high contaminants concentration of total suspended solids (TSS), total dissolved solids (TDS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), fat, oil and grease (FOG), ammonia (NH3), nitrates (NO3), chromium (Cr) and hydrogen sulphide (H2S) were determined in the raw tannery wastewater. The highest achieved removal efficiencies (RE(s)) by the proposed biofilm system after 5 h were 78.98%, 93.44% and 76.19% for TSS, BOD and FOG, respectively, at 30 mL/h while 82.60%, 25.09%, 97.67% and 38.30% were achieved for COD, NH3, Cr and H2S, respectively, at 200 mL/h. On the other hand, TDS, NO3 and total viable count of P. stutzeri increased with time (49.95%, 41.4% and 26.4 fold at 50, 30 and 200 mL/h, respectively) due to bacterial metabolic activity reaching their highest levels after 5 h. Results also revealed huge variations in the RE of all the tested parameters achieved by P. stutzeri biofilm system compared with those obtained by the control (bacteria-free system) confirming the efficient role of P. stutzeri in removing effluent contaminants. Fixation of P. stutzeri enhanced contaminants removal from the highly polluted tannery effluent and protected biofilm bacteria from effluent toxicity, death and the wash out as shown by higher RE(s) for all the tested parameters coupled with shortening of the treatment time (5 h) instead of 7 d in the batch treatment. Therefore, it is evident that the proposed biofilm system with the highly active bacterium P. stutzeri represents a very promising, renewable and cheap biotechnology for the treatment of wide range of contaminated effluents not only in the industrial sector but also for domestic and agricultural wastewater.