Nitrogen and COD removal from tannery wastewater using biological and physicochemical treatments

Abstract

An integrated wastewater treatment was evaluated for nitrogen and COD removal from a tannery effluent. The system was conformed by the combination of a biological treatment using a sequencing batch reactor (SBR) followed by a physicochemical treatment based in a coagulation-flocculation process. The contaminants in the tannery wastewater had average concentrations of 1546 mg COD·L-1, 200 mg TKN·L-1 and 121 mg N-NH4+·L-1. The duration of a complete SBR operation cycle was 12 h. Dissolved oxygen (DO), pH and oxidation-reduction potential (ORP) were used to monitor biological nutrient removal process in the reactor. In addition, densities of nitrifying and denitrifying microorganisms in the mixed liquor were evaluated during the biological treatment. During physicochemical treatment, the concentrations of FeCl3.6H2O and sour brine (agroindustrial waste used as adjuvant) were 2.7 and 100 g·L-1, respectively (doses were 60 and 5 mL·L-1, respectively). Results show the integrated treatment system was effective to produce an effluent suitable for discharge into water bodies, according to the Venezuelan environmental regulations. Average effluent concentrations were 303 mg COD L-1, 35.1 mg TN·L-1 and 0.5 mg N-NH4+·L-1, giving COD, TN and N-NH4+ removals of 80%, 82% and 99.6%, respectively. Profiles of ORP, DO and pH were efficient ways to monitor the evolution of biological nutrient removal and real-time control can be implemented in order to optimize the SBR operation. Finally, density of nitrifying bacteria was greater than density of denitrifying bacteria during biological treatment.