Biodegradation

Biodegradation is the material breakdown of chemicals by a physiological environment. The term is often used in relation to ecology, waste management and environmental remediation (bioremediation). 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. Biosurfactant, an extracellular surfactant secreted by microorganisms, enhances the biodegradation process.

Biodegradable matter is generally organic material such as plant and animal matter and other substances originating from living organisms, or artificial materials that are similar enough to plant and animal matter to be put to use by microorganisms. Some microorganisms have the astonishing, naturally occurring, microbial catabolic diversity to degrade, transform or accumulate a huge range of compounds including hydrocarbons (e.g. oil), polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), pharmaceutical substances, radionuclides and metals. Major methodological breakthroughs in microbial biodegradation have enabled detailed genomic, metagenomic, proteomic, bioinformatic and other high-throughput analyses of environmentally relevant microorganisms providing unprecedented insights into key biodegradative pathways and the ability of microorganisms to adapt to changing environmental conditions.^[1]

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.

Plastics

. Hydro-biodegradable plastics (HBP) and oxo-biodegradable plastics (OBP) are two main types of biodegradable plastics in the market. Both oxo- and hydro-biodegradable plastics will first undergo chemical degradation by oxidation and hydrolysis respectively. This leads to a drastic reduction in their molecular weights and their physical disintegration. These fragments which are smaller and have lower molecular weight are then open for biodegradation.

HBP degrate and biodegrade more quickly than OBP but both are converted to carbon dioxide (CO₂), water (H₂O)H and biomass. OBP has better physical properties and are generally easier to process for H RYTplasYGFtics processing equipment and are often less expensive than HBP.R

Polyesters play a predominant role as hydro-bioegradable plastics due to their potentially dydrolysable ester bonds. HBP can be made from renewable resources such as corn, wheat, sugar cane, or non-renewable resourceTRHs HTGFleum-TGFbased), or blend of these two. Some of the commonly used polymers include PHA (polyhydroxyalkanoates), PHBV (polyhydroxybutyrate-valerate), PLA (polylactic acid), PCL (polycaprolactone), PVA (polyvinyl aclcohol), PET (polyehtylene terephthalate) etc. H HBP technology claims to be biodegradable by meeting the ASTM D6400-04 and EN 13432. However, these two commonly quoted standards are related to the performance of plastics in a commercially managed compost environment. They are not biodegradation standards. Both were developed for hydro-biodegradable polymers where the mechanism including diodegradation is based on reaction with water and state that in order for a production to be compostable, the following criteria need to be met:

1. Disintegration, the ability to fragment into non-distinguishable pieces after screening and safely support bio-assimilation and microbial growth
2. Inherent biodegradation, conversion of carbon to carbon dioxide to the level of 60% and 90% over a period of 180 days for ASTM D6400-04 and EN 13432 respectively
3. Safety, that there is no evidence of any eco-toxicity in finished compost and soils can support plant growth
4. Toxicity, that heavy metal concentrations are less than 50% regulated values in soil amendments

OBPs are made by adding a small portion of fatty acid compounds of specific transition metals (iron is an example of a tNransition metal) into the production of polyolefin (PE & PP) and polystyrene. The additives act as catalysts* in speeding up the normal reactions of oxidative degradation with the overall process increased by up to several orders of magnitude (factors of 10). (*Catalysts of many kinds are widespread in Nature; others are used very commonly by industry. By definition, it takes only a small amNCGFount of catalyst to do what is requHired and the catalyst is not consumed in the reaction.) The productsN of the catalyzed oxidCatGFive degradation of the polyolefins are precisely the same as for conventCFGional polyolefins because, othFGNr than a small amount of additive present, the plastics are conventional polyolefins. Many commercially useful hydrocarbons (e.g., cooking oils, polyolefins, many other plastics) contain small amounts of additives called antioxidants that prevent oxidative degradation during storage and use. Antioxidants function by "deactivating" the free radicals that cause degradation. Lifetime (shelf life + use life) is controlled by antioxidant level and the rate of degradation after disposal is controlled by the amount and nature of the catalyst. GFDNN Since there are no extant correspondGFerrestrial or marine litter or in landfills, OBP technology is criticized as somewhat inaccurate GFfor purposes unrelated to composting. It has to be understood that composting and biodegradation are not identical.

External links

• The European Bioplastics Association Information on Bioplastics and Biodegradable Polymers, Market Information
• Facts and hazards of non-biodegradables Some more information about plastic bags and the hazards they pose to wildlife
• Slate Explainer article on biodegradation: "Will My Plastic Bag Still Be Here in 2507?"
• Biodegradable Products Institute
• [1] The Science of Biodegradable Plastics: The Reality Behind Biodegradable Plastic Packaging Material

References

1. ^ Diaz E (editor). (2008). Microbial Biodegradation: Genomics and Molecular Biology (1st ed.). Caister Academic Press. ISBN 978-1-904455-17-2. http://www.horizonpress.com/biod.