Sustainable Removal of Nitrophenols by Rhizoremediation Using Four Strains of Bacteria and Giant Duckweed (Spirodela polyrhiza)

We examined the effectiveness of rhizoaugmentation for treating water contaminated with the nitrophenols (NPs), 2-NP, 3-NP, 4-NP, and 2,4-dinitrophenol (2,4-DNP) using NP-degrading bacteria. We used 2-NP-degrading Pseudomonas sp. (strain ONR1), 3-NP-degrading Cupriavidus sp. (MFR2), 4-NP-degrading Rhodococcus sp. (PKR1), 2,4-DNP-degrading Rhodococcus sp. (DNR2), and giant duckweed (Spirodela polyrhiza). The four bacterial strains readily colonized Spirodela roots, as approximately 1 × 10⁵ colony-forming units [CFUs] plant⁻¹ to 10⁶–10⁷ CFU plant⁻¹. The higher populations remained stable through five sequential 2-day degradation cycles and completely removed all four NPs within each cycle. The root–bacteria association also successfully treated wastewater effluent contaminated with NPs; 52–71 % of 2-NP and 100 % of 3-NP, 4-NP, and 2,4-DNP were removed within each of five 2-day cycles. These results demonstrate the potential of rhizoaugmentation to achieve efficient and sustainable treatment of NP-contaminated waters.