Bioremediation of petroleum refinery wastewater using constructed wetlands: A focus on microbial diversity and pollutant degradation

Abstract

Horizontal flow constructed wetlands were evaluated for the treatment of synthetic petroleum refinery wastewater (PRW), with and without Typha latifolia. The synthetic PRW was formulated with a chemical oxygen demand (COD) of 1528.43 ± 125.8 mg/L, and contained diesel, phenol, 49.94 ± 1.48 mg/L of NH₄⁺-N, 142.86 ± 4.26 mg/L of S²⁻, and 265.75 ± 4.28 mg/L of SO₄²⁻. The constructed wetlands (CW) were acclimated for 50 days under continuous flow, followed by three operational phases with varied hydraulic retention times. The synthetic PRW simulated with chemical oxygen demand (COD) of 1528.43 ± 125.8 mg/L, containing diesel and phenol, 49.94 ± 1.48 mg/L of NH₄⁺-N, 142.86 ± 4.26 mg/L of S²⁻, and 265.75 ± 4.28 mg/L of SO₄²⁻. The CW was acclimated for 50 days with continuous flow, followed by three different operational phases with varied hydraulic retention times. Effluent COD in unplanted and planted CW systems were 74.44 ± 16.05 mg/L and 56.67 ± 0.14 mg/L, respectively, with NH₄⁺-N removal rates of 75 % and 92 % over 7 days. S²⁻ removal resulted in solid sulphur deposition and increased the SO₄²⁻ concentration. Microbial dynamics revealed that Proteobacteria, Bacteroidetes, and Firmicutes were the dominant phyla, with genera such as Pseudomonas, Acinetobacter, and Bacillus identified as the key hydrocarbon-degrading bacteria. Gas chromatography-mass spectrometry (GC-MS) analysis confirmed the removal of hydrocarbons, with a reduction in the number of hydrocarbon compounds and generation of intermediate compounds in the effluent. This study highlights the potential application of HFCWs for the treatment of PRW by leveraging the synergistic effects of microbial activity and plant-mediated processes to enhance pollutant removal efficiency.