Bioremediation of Explosive Contaminated Soil

John Gomez

Mr. Sterling

MicroBio.

Bioremediation of explosive contaminated soil

"It has been estimated that there are thousands of explosives-contaminated sites within the United States, and even a greater number in Europe and the Soviet Union."(2) TNT (2,4,6- trinitrotoluene) is one of the most popular explosives used by military forces, and due to improper handling and disposal techniques TNT and its derivatives, have polluted environments to levels that threaten the health of humans, livestock, wildlife and, entire ecosystems. TNT is known to have many health effects on animals as well as humans. As stated by The Agency for Toxic Substances and Disease Registry, "Workers involved in the production of high explosives experienced many harmful health effects as a result of exposure to 2,4,6-trinitrotoluene at their jobs. These effects included disorders of the blood, such as anemia, and abnormal liver function." (1)

Treatment of the contaminated soil has usually been handled through incineration, which is costly and does not always guarantee that the pollutants have been completely destroyed. Therefore new techniques such as bioremediation have been developed as a safe cost effective alternative to treating pollutants such as TNT. (3)

Fundamentals of Bioremediation

Bioremediation is a new, efficient, environmentally friendly, and low-cost technology, which uses microorganisms to clean up soil contaminated with heavy metals and organic contaminants such as solvents, crude oil, explosives, and other toxic compounds from contaminated environments.

Mechanism:

Bioremediation works by taking complex organic compounds such as TNT, which are made up of carbon, nitrogen, oxygen, and hydrogen. When combined with regular compost ingredients such as manures, sawdust, straw, and fruit and vegetable processing wastes, the explosives become broken down into harmless chemical forms.(3)

Bioremediation methods are classified into two categories: Composting, and bioslurries.

Composting:

According to the EPA's Fact Sheet on Composting of Soils Contaminated by Explosives, the process of composting operates as a result of naturally occurring microorganisms breaking down the explosive contaminants in the soil. Using the contaminants as "food," the microorganisms convert them into harmless substances consisting primarily of water, carbon dioxide, and salts. In addition to this food source, microorganisms require nutrients, such as carbon, nitrogen, phosphorous, and potassium, in order to thrive, digest, and reproduce. To provide these nutrients in sufficient quantities, soil amendments, such as manure and potato waste, are added to the contaminated soil.(3)The most common type of composting used for bioremediation of TNT contaminated soil is Windrow composting. The US Army Environmental Center report on Cleanup Technology: Bioremediation of Explosives-Contaminated Soil, describes windrow composting as the following. "Windrow composting mixes the soil with compost in long piles known as windrows. To facilitate the microbial growth, amendments such as wood chips, manure, straw, alfalfa, and other agricultural products are added. Windrows are used to facilitate aeration of the compost and are turned periodically using a compost turner. Moisture content, windrow oxygen level, and temperature are easily monitored. During a field demonstration conducted by USAEC at UMDA, TNT reductions were as high as 99.7% at 30% soil in 40 days of operation, with the majority of removal occurring in the first