“Remediate” means to solve a problem, and “bio-remediate” means to use biological organisms to solve an environmental problem such as contaminated soil or groundwater. Biodegradation is nature’s way of recycling wastes, or breaking down organic matter into nutrients that can be used by other organisms. “Degradation” means decay, and the “bio-” prefix means that the decay is carried out by a huge assortment of bacteria, fungi, insects, worms, and other organisms that eat dead material and recycle it into new forms.

In a non-polluted environment, bacteria, fungi, protists, and other microorganisms are constantly at work breaking down organic matter. What would occur if an organic pollutant such as oil contaminated this environment? Some of the microorganisms would die, while others capable of eating the organic pollution would survive. Bioremediation works by providing these pollution-eating organisms with fertilizer, oxygen, and other conditions that encourage their rapid growth. These organisms would then be able to break down the organic pollutant at a correspondingly faster rate. In fact, bioremediation is often used to help clean up oil spills.

Biodegradation processes vary greatly, but frequently the final product of the degradation is carbon dioxide or methane.

The term is often used in relation to ecology, waste management, environmental remediation (bioremediation) and to plastic materials, due to their long life span. Organic material can be degraded aerobically, with oxygen, or anaerobically, without oxygen. A term related to biodegradation is biomineralisation, in which organic matter is converted into minerals.

Biodegradable matter is generally organic material such as plant and animal matter and other substances originating from living organisms.

Anaerobic biodegradation in landfill

Biodegradable waste in landfill degrades in the absence of oxygen through the process of anaerobic digestion. The byproducts of this anaerobic biodegradation are biogas and lignin and cellulose fibres which cannot be broken down by anaerobes (anaerobic microbes)
Engineered landfills are designed with liners to prevent toxic leachate seeping into the surrounding soil and groundwater. Paper and other materials that normally degrade in a few years degrade more slowly over longer periods of time. Biogas contains methane which has approximately 21 times the global warming potential of carbon dioxide. In modern landfills this biogas can be collected and used for power generation.

Methods of measuring biodegradation

Biodegradation can be measured in a number of ways. The activity of aerobic microbes can be measured by the amount of oxygen they consume or the amount of carbon dioxide they produce. Biodegradation can be measured by anaerobic microbes and the amount of methane or alloy that they may be able to produce.

Measurement of aerobic decomposition

The DR4 test or 4-day dynamic respiration index test is a test to measure the biodegradability of a substance over 4 days. The substance is aerated by passing air through it. This definition is used to dte the method from those where aeration is by diffusion of air into and out of the test material which is referred to as the SRI or static respiration index test.[1] Microbes are introduced to the test material whilst incubating it under aerobic conditions by aerating the mixture in a vessel through which air is blown. The microbes degrade the material producing CO2 as the product of biodegradation. This CO2 production can by monitored as a measure of the biodegradability of the test material and converted into oxygen consumption units.

Measurement of anaerobic decompostion

BMP100 test, 100 day biogenic methane potential test, is a test method that determines the biodegrability of biodegradable wastes under anaerobic conditions by measuring the production of biogas.

Under anaerobic methanogenic conditions the decomposition of organic carbon proceeds by producing biogas (containing methane and carbon dioxide)from the organic carbon. The amount of biogas production therefore measures directly the carbon which is mineralised.The test is set up in a small vessel containing the test substrate, a mineral aqueous medium and an inoculum of methanogenic bacteria taken from an active anaerobic digester. The test is monitored by collecting and measuring the biogas produced. The test is incubated for an extended period until gas production ceases which may be up to 100 days or more. The test therefore measures the complete degradation of the waste.

Plastics

Biodegradable plastics made with plastarch material (PSM), and polylactide (PLA) will compost in an industrial compost facility. There are other plastic materials that claim biodegradability, but are more often (and possibly more accurately) described as ‘degradable’ or oxi-degradable; It is claimed that this process causes more rapid breakdown of the plastic materials into CO2 and H2O.

Indicative lengths of degradation

(from http://www.worldwise.com/biodegradable.html)

  • Banana peel, 2 – 10 days
  • Cotton rags, 1 – 5 months
  • Paper, 2 – 5 months
  • Rope, 3 – 14 months
  • Orange peels, 6 months
  • Wool socks, 1 – 5 years
  • Cigarette filters, 1 – 12 years
  • Styrofoam cup, 1 – 100 years
  • Tetrapaks (plastic composite milk cartons), 5 years
  • Plastic bags, 10 – 20 years
  • Leather shoes, 25 – 40 years
  • Nylon fabric, 30 – 40 years
  • Plastic six-pack holder rings, 450 years
  • Diapers and sanitary pads 500 – 800 years

Source: Wikipedia, Enviromental Enquiry

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