Removal of organic matters, phosphates and nitrates present in pond wastewater using chemical coagulant solutions

The study aims to treat and remove of organic matters, phosphates and nitrates present in fish pond wastewater using chemical coagulants at different concentrations [FeSO₄, FeCl₃, and Al₂(SO₄)₃] through coagulation-precipitation. These effluents are discharged without any treatment. Fish pond wastewaters were subjected to a series of physicochemical and bacteriological analyses before and after treatment according to standard methods. The results of the main physicochemical and bacteriological characteristics of the fish pond wastewater released from a fish farm located in Taghit-Bechar (Southwest of Algeria) show values exceed the Algerian norms for liquid discharges. These values include organic matter (chemical oxygen demand (COD) = 285.42 mgO₂/L, biological oxygen demand (BOD) = 226.71 mgO₂/L, oxidizable materials (OM) = 56 mgO₂/L), total suspended solid (TSS) (45 mg/L), phosphate (2.60 mg/L), nitrate (80 mg/L), fecal coliforms (3.07 log MPN/100mL) and fecal streptococci (3.32 log MPN/100mL). The treatment results showed that the optimum concentration varies around 50 mg/L for ferric chloride and ferric sulfate, and 80 mg/L for aluminum sulfate. At these optimum doses, treatment yields are satisfactory for the abatement of organic pollution, namely; SS, OM, COD, and BOD₅ with a rate of 80%, 64.3%, 91%, and 84% for ferric chloride; 87%, 68.6%, 93%, and 86 for ferric sulfate and 95%, 71.5%, 96% and 87 for aluminum sulfate, respectively. Nitrate and phosphate removal performance was excellent, with removal rates of 92% and 97% for ferric chloride, 94% and 99% for ferric sulfate, and 95% and 98% for aluminum sulfate, respectively. The pollutant parameters tested appear to be better eliminated with ferric chloride in a pH range between 6 and 8 for organic matter (MO, COD, BOD), and between 8 and 10 for phosphates and nitrates. The best results were recorded for ferric sulfate and aluminum sulfate. However, the three coagulants effectively removed bacterial pollution indicators, such as fecal coliforms and fecal streptococci.