Vol.:(0123456789) 1 3 International Journal of Environmental Science and Technology https://doi.org/10.1007/s13762-020-02783-0 ORIGINAL PAPER Optimization of process parameters for degradation of HMX with Bacillus toyonensis using response surface methodology A. Meda 1  · P. Sangwan 2  · K. Bala 1 Received: 9 September 2019 / Revised: 22 May 2020 / Accepted: 26 May 2020 © Islamic Azad University (IAU) 2020 Abstract Contamination of soil and water with explosive compounds like octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX or commonly known as high melting explosives) is increasing day by day due to their extensive use all over the world. High level of contamination has been found near military sites, explosive manufacturing facilities, war-lands, mines and exercise ranges. Remediation of such contaminants is necessary as they may have adverse impact on biotic as well as on abiotic envi- ronment. Present study was carried out with an objective to optimize the variable process parameters for the degradation of HMX in aqueous phase by indigenously isolated bacterial strain, Bacillus toyonensis from an actual HMX contaminated site in North India using response surface methodology. The relationship among varying initial concentrations of HMX, microbial inoculum size and degradation time was revealed in the current study. Results showed that 87.7% degradation was achieved at 2 mg/L initial HMX concentration with inoculum size of 4% on 15th day. High regression coefcient value (0.9878) further supported predictability of experimental data. Nitrite and nitrate concentrations estimated during the experiment indicate breakdown and degradation process of HMX. Findings of this study concluded that Bacillus toyonensis can be a potential microorganism to degrade HMX and can be used for microbial remediation of HMX contaminated sites. Keywords Explosive · HMX · Bacillus toyonensis · Microbial remediation · Response surface methodology Introduction Octahydro-1, 3, 5, 7-tetranitro-1, 3, 5, 7-tetrazocine (HMX, high melting explosive) is a heterocyclic nitramine, which is commonly used for military applications. It can enter the environment during the process of manufacturing, trans- port, usage and demilitarization. It is an important part of military applications and is classifed as non-carcinogenic by US Environmental Protection agency (1998). However, researchers revealed its toxicity efects on laboratory animals (Cuthbert et al. 1985; Greenhough and McDonald 1985). Further exposure of HMX in diferent mammalian species can cause convulsions, nausea and loss of consciousness (Wilson 1985). Many animal studies have indicated that HMX afects liver and central nervous system and can get accumulated in kidney, liver, brain and heart, even can cause mortality and histopathalogical lesions in animals (Johnson and Reddy 2015). Fate and transport of explosives have been described by earlier researchers in detail (Lotufo et al. 2009). HMX has shown low adsorption and high mobility in soil, which can lead to ground water contamination (Zheng et al. 2009). It can lead to reduction in microbial diversity of soil resulting in reduced natural degradation potential of such contaminants (Gong et al. 2002), thus can also adversely afect the soil profle and suitability for farming in the areas near military bases. US Environmental Protection Agency (USEPA 2018) has recommended the lifetime safe drinking water standards for HMX as 0.4 mg/L. Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) is known to be less stable than Tri nitro toluene (Hawari et al. 2000). Harkins et al. (1999) treated HMX in water Editorial responsibility: Jing Chen. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13762-020-02783-0) contains supplementary material, which is available to authorized users. * P. Sangwan pritam@cfees.drdo.in 1 Biofuels Research Laboratory, Discipline of Biosciences and Biomedical Engineering, Indian Institute of Technology Indore, Indore, India 2 Centre for Fire, Explosive and Environment Safety, Defence Research and Development Organization, New Delhi, India