Biotreatment of simulated tannery wastewater containing Reactive Black 5, aniline and CrVI using a biochar packed bioreactor

Abstract

Azo dyes and hexavalent chromium (CrVI) are common pollutants in wastewater generated by the leather processing industry. This study was designed to develop a treatment strategy that can simultaneously remove azo dyes, their byproducts and CrVI using a biochar packed bioreactor. Various feedstock materials were evaluated, after which, biochar produced from pyrolysis of corn cobs at 400 °C was selected as a packing material for the reactor, based on its large surface area (1275 m² g⁻¹), microporosity (2–5 μm), and ability to support microbial biofilm formation. In the bioreactor experiments, simulated tannery wastewater containing 100 mg L⁻¹ Reactive Black-5 azo dye and 10–100 mg L⁻¹ aniline (byproduct of azo dye) was treated in the presence and absence of CrVI using the bacterium Pseudomonas putida strain KI. The results showed complete biodegradation of Reactive Black 5 (100 mg L⁻¹) within 5 h. Strain KI could also reduce 100 mg L⁻¹ dye and 10 mg L⁻¹ CrVI simultaneously in 24 h in a 2 L continuous packed bed bioreactor. Complete biodegradation of aniline (byproduct of Reactive Black 5) in the bioreactor was obtained within 24 h in the absence of CrVI, whereas degradation was decreased to 84% in the presence of CrVI. LC-MS analysis confirmed the biodegradation of Reactive Black 5 and aniline. This study clearly illustrates the feasibility of using bacterial strains having multifaceted functions for the biological treatment of tannery wastewater in bioreactors containing pyrolyzed carbon (biochar) as a support matrix for the bacterial cells.