Sustainable removal of nitrophenols by rhizoremediation using four strains of bacteria and giant duckweed (Spirodela polyrhiza)

Abstract

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.