Biodegradation or Biodegradable Plastic means the total breakdown of a product (by microorganisms) to something found in nature. Some industry individuals compare the biodegradation of a leaf or a tree to plastic. It is important to understand that originally the leaf or tree was found in nature. Biodegradation of plastic takes a period of time. Plastic is found around the world and is the by-product of making oil. During the oil-making process, plastic engineers take 3% of the total composition of oil and make plastic or processing aids.
They turn monomers into polymers and take those polymers and turn them into plastic bags, bowls, etc. The amazing benefit of BioSphere is that it converts the plastic product (which is very slow at biodegradation) and turns it into a biodegradable product that shows biodegradation 100-200 times faster than regular plastic products. Biodegradation occurs by allowing the microbes to consume the macromolecules within the plastic and convert it (anaerobically) into CH4, CO2, biomass, and water. Water is left behind by microorganisms, even though most is utilized during the biodegradation process. Aerobic biodegradation, which occurs in both landfills and compost facilities, produces CO2, biomass, and water.
Biodegradability of Plastic
Biodegradation is different then compostable. The industry defines compostable to be Aerobic biodegradation in an industrial compost facility. These are different in home compost piles and commercial compost facilities. The reason for the industry definition of compostable products is further define biodegradation and to set it apart from biodegradation based on testing methods and standards. Composting in an industrial compost facility requires 140F to break down the polymer chain of polylactic acid (otherwise known as PLA).
Biodegradation in the United States is defined as anything that biodegrades based on microorganisms turning the product into organic material found in nature. ASTM D5511-12 is the testing method for plastic biodegradation, and the ISO 15985 is the standard for the test of anaerobic biodegradation of plastic materials internationally.
To determine if your product or package is biodegradable plastic you may need to perform some testing if the product company has not given you testing over your resin type or product. The ASTM D5511-12 and the ASTM D5526-12 are both tests to define biodegradation in anaerobic environments. To determine compostable products, you would need to do the Standard Test ASTM D6400 which is performed by the test ASTM D5338-12, which is for the Aerobic testing method for determining Aerobic biodegradation of plastic materials in an industrial compost facility only.
Currently the only test for home composting is done by the reduction of heat while performing the ASTM D5338, this also applies to municipal compost facilities. There are currently no industrial compost facilities around the world that maintain a 180 day time for composting at a constant 140F temperature, 130F is optimal temperatures for most compost facilities due to the different micro-organisms that live within the compost.
There are other biodegradation testing methods to determine Litter Biodegradation.
There are four key biological and chemical stages of anaerobic digestion:
In most cases, plastic is made up of hydrophobic polymers. Chains must be broken down into constituent parts for the energy potential to be used by microorganisms. These constituent parts, or monomers, are readily available to other bacteria. The process of breaking these chains and dissolving the smaller molecules into solution is called hydrolysis. Therefore, hydrolysis of these high-molecular-weight polymeric components is the necessary first step in anaerobic biodegradation. Through hydrolysis, the complex organic molecules are broken down into simple sugars, amino acids, and fatty acids.
Acetate and hydrogen produced in the first stages can be used directly by methanogens. Other molecules, such as volatile fatty acids (VFAs) with a chain length greater than that of acetate must first be catabolised into compounds that can be directly used by methanogens.
The biological process of acidogenesis results in further breakdown of the remaining components by acidogenic (fermentative) bacteria. Here, VFAs are created, along with ammonia, carbon dioxide, and hydrogen sulfide, as well as other byproducts. The process of acidogenesis is similar to the way milk sours.
The third stage of anaerobic digestion is acetogenesis. Here, simple molecules created through the acidogenesis phase are further digested by Acetogens to produce largely acetic acid, as well as carbon dioxide and hydrogen.
The terminal stage of anaerobic biodegradation is the biological process of methanogenesis. Here, methanogens use the intermediate products of the preceding stages and convert them into methane, carbon dioxide, and water. These components make up the majority of the biogas emitted. Methanogenesis is sensitive to both high and low pHs and occurs between pH 6.5 and pH 8. The remaining, indigestible material the microbes cannot use and any dead bacterial remains constitute the digestate.
A simplified generic, chemical equation, for the overall processes outlined above is as follows: C6H12O6 → 3CO2 + 3CH4