Biological treatment of fish pond wastewater using selected bacteria in laboratory-scale batch culture: a case study of a farm in Taghit, Bechar (Southwestern Algeria)

This study evaluates the efficiency of biological treatment of fish pond wastewater (FPWW) using a laboratory-scale aerobic bioreactor inoculated with two bacterial strains—Pseudomonas aeruginosa and Bacillus cereus—isolated from dairy plant sludge. These strains were selected for their high biodegradation potential and applied to separate bioreactors, each containing 2 L of FPWW. A non-inoculated bioreactor served as the control. Over a two-week period at 25 °C, key water quality parameters were monitored, including biochemical oxygen demand (BOD5), chemical oxygen demand (COD), organic matter, nitrate, phosphate, sulfate, pH, fecal coliforms, and fecal streptococci. Initial analysis of untreated FPWW revealed that several parameters exceeded WHO and environmental discharge limits. BOD5 and COD levels were 160.75 mg/L and 231.5 mg/L, well above the respective limits of 30 mg/L and 75–100 mg/L. Organic matter (OMC) measured 110 mg/L, indicating a high load of biodegradable pollutants. Nitrate (154.96 mg/L) and phosphate (2.72 mg/L) exceeded effluent standards of 20–50 mg/L and 1 mg/L, respectively. Sulfate reached 328.85 mg/L, above the 250 mg/L guideline. Fecal coliforms and fecal streptococci were detected at 3.12 and 3.18 Log₁₀ MPN/100 mL, both exceeding the acceptable limit of < 3 Log₁₀ MPN/100 mL. Only pH remained within the acceptable range at 7.8 (6.5–8.5). After treatment, significant pollutant reductions were observed in the inoculated samples compared to the control. Fecal coliforms and fecal streptococci were reduced by 39.1–67.95% and 41.82–53.46%, respectively, versus 14.74% and 35.85% in the control. Organic matter decreased by 84–87.64% in treated samples, compared to 45.46% in the control. BOD5 and COD reductions ranged from 79.15 to 86.25% and 85.31 to 92.06%, respectively. Both bacterial strains proved effective in improving wastewater quality, with Bacillus cereus showing superior performance. These findings highlight the potential of biological treatment as a cost-effective, eco-friendly method for managing FPWW and demonstrate the suitability of these bacterial strains for future applications in bioremediation and sustainable aquaculture wastewater management.