Degradation and detoxification of high malachite green concentrations by an indigenous strain of Aeromonas sp. in batch and continuous reactor

Abstract

A previously isolated Aeromonas sp. strain capable of metabolizing Malachite Green (MG) was studied to determine the optimal conditions for its degradation in batch reactors. The effects of various parameters—including alternative carbon sources, medium pH, incubation temperature, and initial MG concentration—were evaluated. A continuous upflow fixed-bed biofilm reactor was then designed and inoculated with the strain to treat a synthetic MG-containing effluent. MG removal was monitored using spectrophotometric and chromatographic analyses, while toxicity and genotoxicity were assessed through Lactuca sativa and Allium cepa bioassays. In batch experiments, Aeromonas sp. degraded up to 1250 mg L⁻¹ of MG in the presence of alternative carbon sources (peptone, yeast extract, or glucose) with over 96% efficiency. The process remained effective across temperatures of 20–35 ◦C, pH values between 5 and 9, and NaCl concentrations up to 3 %. Chromatographic data suggested probable mineralization of the dye. The continuous reactor operated for 38 days without sterility or temperature control, achieving 99.95 % removal efficiency at an inlet concentration of 1400 mg L⁻¹, corresponding to an organic load of 777.8 g m⁻³ d⁻¹. Toxicity tests with Lactuca sativa and Allium cepa confirmed detoxification after both batch and continuous treatments. These results suggest that the selected Aeromonas sp. strain represents an efficient and cost-effective option for treating effluents and water containing high concentrations of Malachite Green.