Bioremediation to restore contaminated soils

Every year, agricultural effluents, industrial waste, and industrial accidents contaminate surface waters, soils, air, aqueous streams, and reservoirs. A new composting technique, known as Compost Bioremediation, is currently being used to restore contaminated soils, manage stormwater, control odors, and degrade volatile organic compounds.

Compost Bioremediation refers to the use of a biological system of microorganisms, in mature compost, to sequester or destroy contaminants from water or soil. Microorganisms consume contaminants from soil, ground and surface water, and air.

The pollutants are digested, metabolized and transformed into humus and inert products, such as carbon dioxide, water and salts. It has proven effective in degrading or altering many types of contaminants, such as chlorinated and non-chlorinated hydrocarbons, wood preservative chemicals, solvents, heavy metals, pesticides, petroleum products, and explosives. Composts used in Bioremediation are referred to as custom-made or drawn, in the sense that they are specially made to treat specific contaminants at specific sites.

The ultimate goal in any remediation project is to return the site to its pre-contaminated condition, which often includes reforestation or revegetation to stabilize the treated soil. In addition to reducing pollution levels, compost advances its goal by facilitating plant growth. In this role, compost provides soil conditioning, and also provides nutrients to a wide variety of vegetation.

Soil bioremediation

Pollution of heavy metals

Dr. Rufus Chaney, a senior agronomic researcher with the US Department of Agriculture, is an expert in using compost methods to correct metal-contaminated sites. In Bowie, Maryland, for example, it found a high percentage of lead in soils adjacent to homes painted with lead-based paint. To determine the effectiveness of compost in reducing lead bioavailability in these soils, Chaney fed rats contaminated soil and contaminated soil mixed with compost. Both compost and soil trap lead, therefore reducing its bioavailability; soil treated with compost was more effective than untreated soil. In fact, the rats exhibited no toxic effects from lead-contaminated soil mixed with compost, while they did with the soil alone.

In another study, Dr. Lee Daniels and PD Schroeder of Virginia Polytechnic Institute, Blacksburg, Virginia, remediated a waste site contaminated with sand and sludge from a heavy metal mine.

The application of compost revitalized the soil for agricultural use. 20 tons per acre were applied for Dr. Grano production and 120 tons/acre for peanuts.

Organic contaminants

Dr. Michael Cole, an expert in the degradation of contaminants in soil, remediated soil containing 3000 parts per million (ppm) kl of dicamba herbicide to undetectable levels in 50 days. Cole mixed wood chips and mature compost into the soil to make the combined substrate, 10% (by volume) compost and wood chips, and 90% contaminated soil. According to Dr. Cole, dicamba eventually breaks down in the soil, but the process takes years rather than days. In addition to speeding up the Bioremediation process, using compost can also save money. The traditional method of remediation by landfilling and incineration can cost five times or more than composting technology. According to Dr. Cole, Compost Bioremediation, more than any other soil cleanup technique, results in enriched soil and leaves it in better condition than before it was contaminated.

Petroleum hydrocarbon pollution

At Seymour Johnson Air Force Base near Goldsboro, North Carolina, the soil is contaminated as a result of frequent jet fuel spills and excavation for underground fuel storage tanks. The base deals with a variety of petroleum contaminants, including gasoline, kerosene, fuel oil, jet fuel, hydraulic fluid, and motor oil.

In 1994, the base implemented a Bioremediation system using compost made from wood waste and turkey droppings. Previous remediation systems included lifting contaminated soil and taking it to a brick manufacturer, where it was incinerated at high temperatures. Compared to the cost of lifting, incinerating and purchasing clean soil, Bioremediation with compost saved the base US$133.000 in the first year. The use of compost also resulted in faster cleanup, since projects are completed in weeks instead of months.

Compost fungi produce a substance that breaks down petroleum hydrocarbons, allowing compost bacteria to metabolize it. A typical ratio consists of 75% contaminated soil, 20% compost and 5% turkey manure. A mechanical shovel mixes and stirs the piles to keep them aerated. After mixing, a vinyl nylon covers the piles to protect them from wind and rain, and to maintain proper humidity and temperature for optimal microbial growth.

Storm water management

It is the excessive water not absorbed by the soil after heavy rains. Core on surfaces such as roads, parking lots, building roofs, fields and gardens. On their journey to larger bodies of water (lakes, streams, rivers) those waters can carry a wide range of potentially environmental contaminants, such as metals, oils and greases, pesticides and fertilizers. These types of contaminants pollute rural waters, damage recreational and commercial fisheries, and degrade the beauty of waterways. This water, according to the US Environmental Protection Agency, must be treated before it is discharged into natural streams. To complete it, many municipalities and industries are turning to solutions that involve compost technologies instead of other much more expensive traditional treatments. There is, for example, a filter system that uses compost and that retains more than 90% of solids, 85% of fats and oils and around 85% of oils and fats.

Biofiltration vs. Bioremediation

Biofiltration involves physically separating particles based on their size.

Bioremediation by contrast implies a biochemical change, as the contaminants or pollutants are metabolized by microorganisms, and converted into harmless, stable constituents, such as carbon dioxide, water and salts.

*Translated and summarized by Bioagro
Source: EPA 530-f-97-042 (United States Environmental Protection Agency)

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