Enhancing remediation of RDX-contaminated soil by introducing microbial formulation technology coupled with biostimulation

Abstract

The degradation of Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) through bioaugmentation and biostimulation was investigated. Aqueous phase experiment established the potential of Kinneretia asachharophila strain 12853 in invigorating the RDX-degradation. The microbe denitrified 75.7% RDX from the minimal salt medium by utilizing it as a nitrogen source based on nitrite production. High-Performance Liquid Chromatography (HPLC) and Liquid Chromatography-Mass Spectrometry (LCMS) analyses confirmed the presence of methylenedinitramine (MEDINA) and 4-nitro-2,4-diazabutanal (NDAB) as intermediate metabolites. The microbe formulated into powder and beads showed 29% and 14% loss in viability, respectively, after a storage period of 3 months at 25 °C. The third type of formulation, i.e., water-dispersible granules (WDG), retained 98.52% viability at similar experimental conditions. The microcosm studies revealed a 40% RDX degradation in soil using WDG, while unformulated fresh cultures showed 29% degradation. The process became 1.9–2.4 times more efficient when WDG coupled with stimulants, wheat straw, or sucrose (0.5% w/w). We recorded first-order degradation kinetics with an RDX soil half-life of 16.54–24.15 days. The current study demonstrates the enhanced RDX remediation from the contaminated soil using a robust microbial formulation compatible with wheat straw as an organic stimulant.