Rotten But Not Forgotten

Decomposition is the process of breaking down organic matter into basic chemical components of carbon, hydrogen, nitrogen, phosphorus, oxygen, etc. Decomposition is a complex process and serves many functions, including the formation of soil, the recycling of nutrients stored in the organic materials, and the reduction of high energy carbon compounds. Carbon, the basic building block of all living things, is recycled back into the environment when it is no longer a part of a living organism and decomposition takes place. During decomposition, nutrients that were used for the growth of plants and animals are discarded. Other organisms, known as decomposers, feed upon these nutrients, grow, die and become food for others. The process is cyclical, but the rate of decomposition is dependent upon the chemical composition of the various components, which are degraded at widely different rates.

The following graphic uses plant material as a decomposition model. Two concurrent processes are involved in decomposition: mineralization and humification of complex carbohydrates by soil organisms. Mineralization is when organic compounds are converted into inorganic forms and made available to meet the nutritional needs of organisms. Humification is the result of the activity of soil organisms upon residues. Humus resists further decomposition and, while it is not nutritional, it enhances the water holding, nutrient-supplying capacity of soil.

The decomposers responsible for this process include the following:

Bacteria are simple, microscopic organisms that begin the chemical stage of the decomposition process by secreting enzymes. They appear as rods, spheres or chains when viewed under a microscope. They live almost everywhere: in water, soil, and even the bodies of other organisms. They are the most numerous of all the decomposers and are capable of generating significant amounts of energy as heat. Millions of bacteria may be present in just a small sample of decomposing matter. All living things depend upon bacteria to maintain a healthy balance in nature and sustain life. Many plants need bacteria in the soil to survive. Some bacteria take nitrogen out of the air and change it into nitrates the plants can then use.

Fungi are organisms that produce networks of root-like structures and continue the chemical breakdown process. Fungi lack chlorophyll so they are unable to manufacture their own food from the raw materials around them. Instead, they get their nutrition from other plants or animals. Fungi are called parasites when their food is derived from living plants or animals, and saprophytes when the food comes from dead plant or animal matter. Their root structures, called mycelium, dissolve and collect nutrients. As mycelium spread throughout an area, they meet and form fruiting bodies. Fruiting bodies contain spores which produce the next generation. Mushrooms are an example of a fruiting body.

Actinomycetes are higher forms of bacteria and share many of the same properties. Their role in the decomposition process is similar to that of bacteria. They produce the thick "earthy" smell of decaying matter. Actinomycetes look something like spider webs, with long, thick filaments branching out.

Arthropods, physical decomposers, serve many purposes in the decomposition process. Some feed directly on bacteria, while others continue to break down the material into small sizes. Arthropods are larger and more complex than bacteria or fungi, and range in size from microscopic to relatively large. Beetles, sow bugs, centipedes and praying mantises are examples of arthropods.

Earthworms enter the decomposition process as the decaying matter becomes soil-like. They eat bacteria, fungi, protozoa and decaying organic matter. They enrich the humus by passing the matter through their bodies and producing castings. Castings, the waste of the earthworms, are rich in nutrients.

The microscopic organisms, bacteria, fungi, and actinomycetes do the majority of the work of decomposing matter, while the arthropods, earthworms and other small animals provide the finishing touches.

Bioremediation

Bioremediation is the use of microorganisms to remove environmental pollutants from soil, water or gases. The current implementation rate for bioremediation is 5-10% of all pollution treatments, but there is evidence to suggest that as research continues and advancements are made this percentage will increase significantly.

In a natural setting microorganisms decompose organic compounds using enzymes. Enzymes are protein molecules that control metabolism. Some of these enzymes can break down pollutants. Exploitation of this ability to biodegrade pollutants can greatly enhance the effective treatment of wastes from a variety of sources — hazardous, industrial, agricultural — and has applications for municipal solid wastes as well.

Bioremediation is most effective when used on natural carbon-rich substances called hydrocarbons. Hydrocarbons and the bacteria that are capable of degrading them are found in abundance in the environment. For example, there are bacteria found in soil that can degrade gasoline. Scientists can culture these bacteria to produce enough to effectively clean up a large gasoline spill and lessen the environmental impact caused by the cleanup process.

While bioremediation is often used to remove dispersed pollutants that have inadvertently entered the environment, industries have utilized bioremediation very effectively in treating wastewater and other industry by-products. There are also indications that bioremediation can assist in agriculture by removing toxins from soil.

The process does not work with every pollutant, i.e. the organisms are unavailable in large enough quantities to be useful or have not been identified, yet the possibilities of bioremediation are limitless. Some scientists are advocating genetically engineering microorganisms to be more effective, but there is much controversy surrounding the issue of genetic engineering and its long-term effects on the environment.