Coconut husks and bacteria: a new recipe for cleaning explosive-contaminated soil

The Persistent Problem of Explosive Pollution

Military and industrial activities often leave behind a dangerous legacy of soil contamination. Two common secondary explosives, RDX Hexahydro-1,3,5-trinitro-1,3,5-triazine and HMX Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, are particularly troublesome. These compounds are toxic to humans, animals, and plants and are resistant to natural degradation. Because they do not bind well to soil, they can easily seep into groundwater, posing a widespread environmental and health risk. Traditional methods for cleaning up this contamination are often expensive, inefficient, and can produce their own harmful byproducts.

A Sustainable Solution from Waste

Researchers from the Centre for Fire, Explosive and Environment Safety, Defence Research & Development Organization and the Department of Environmental Science and Engineering, Guru Jambheshwar University of Science & Technology have developed an environmentally friendly alternative. They created a special "bioformulation" by combining an explosive-degrading bacterium, Arthrobacter subterraneus, with biochar. Biochar is a porous, carbon-rich material produced by heating biomass in the absence of oxygen. In this study, the team used a readily available waste product—coconut husks—to create the biochar, providing a sustainable carrier for the bacteria.

Putting the Bioformulation to the Test

The scientific team, including lead author Kirty Sharma and supervisors Praveen Sharma and Pritam Sangwan, conducted a laboratory experiment to assess the bioformulation's effectiveness. They prepared pots of garden soil and contaminated them with set concentrations of RDX and HMX, both separately and as a mixture. They then mixed their newly developed bioformulation into the soil and monitored the reduction in explosive levels over a 30-day period, comparing the results to contaminated soil left untreated.

Impressive Degradation Results

The study found that the bioformulation significantly accelerated the breakdown of the explosives. In soil containing 50 mg/kg of contaminants, the treatment removed up to 85.98% of RDX and 80.4% of HMX within 30 days. In contrast, the untreated control soils showed minimal reduction in the same timeframe. The results clearly demonstrated that the combination of biochar and bacteria was responsible for the effective cleanup. The formulation was slightly more effective at degrading RDX, which is known to be less chemically stable than HMX.

How the Mixture Works

The success of the bioformulation lies in the cooperative action of its two components. The porous structure of the coconut husk biochar provides a protective habitat for the Arthrobacter subterraneus bacteria, helping them survive and thrive in the toxic soil environment. The study confirmed that the bacteria could remain viable within the biochar for up to six months. Furthermore, biochar's sorptive properties attract and hold the explosive molecules, increasing their availability to the bacteria for degradation. As the bacteria metabolize the explosives, they produce byproducts like nitrite, the levels of which were observed to increase in the treated soil, confirming active biodegradation.

From Lab to Field

This new method offers a promising, eco-friendly approach to reclaiming land contaminated by military explosives. The use of a waste product like coconut husks makes the process sustainable and potentially cost-effective. An added benefit is that biochar is known to improve soil quality, so the remediation process could also prepare the land for future use, such as planting trees. The authors suggest that the next steps involve moving from the laboratory to real-world field trials to evaluate the bioformulation’s performance under more complex environmental conditions and to conduct comprehensive assessments of its ecological safety.

Corresponding Author:

Kirty Sharma

Original Source:

https://doi.org/10.1007/s44246-023-00068-y

Contributions:

Conceptualisation: Pritam Sangwan, Kirty Sharma; methodology: Pritam Sangwan, Kirty Sharma; formal analysis and investigation: Kirty Sharma; writing—original draft preparation: Kirty Sharma; writing—review and editing: Pritam Sangwan, Praveen Sharma, Kirty Sharma; funding acquisition: Praveen Sharma, Pritam Sangwan; resources: Praveen Sharma, Pritam Sangwan; supervision: Praveen Sharma, Pritam Sangwan.