A plastic is biodegradable when the degradation results from the action of naturally occurring microorganisms such as bacteria, fungi, and algae. Biodegradability is the ability of material to be utilized as a carbon source by microorganisms and converted safely into carbon dioxide, biomass and water. The procedure is performed in an anaerobic digester environment that represents highly anaerobic environmental conditions analogous to that of a Landfill. The samples are placed within containers that are positioned underneath a large diameter effluent discharge pipe flowing at a fairly constant rate and temperature.
The samples are completely covered in the liquid waste and remain fully immersed under the highly anaerobic effluent. The continuous flow of anaerobic effluent passes through the test vessel causes the samples to degrade.
Plastics have been widely used because of their lightweight, inertness, and low cost. With the increasing use of plastics, their disposals have become a major environmental issue. The disposal of plastics, especially those used in packaging, give a serious challenge to waste management. Conventional methods of plastic waste management such as land-filling, recycling and incineration have proved inadequate. Biodegradable plastics are now emerging as one of the available options to solve such environmental issues. The industrial development of new biodegradable plastics and compostable plastics has been accompanied by the parallel development of suitable standard test methods
Currently, composting is an important method of organic waste management. The biodegradation of biodegradable plastics in the composting is simple, reliable and inexpensive test to assess the aerobic biodegradability of polymeric materials in a compost environment.
Two ASTM standard methods are designed to evaluate the ability of aerobic biological reaction systems to degrade specific components in the vessels under controlled conditions. The first method, ASTM D 5338-98 (03) standard is designed to determine the degree and rate of aerobic biodegradation of plastic materials on exposure to a controlled composting environment under laboratory conditions. Although it is quite expensive, this method is mainly used for biodegradation test. The second method, ASTM D 5988-03 standard is a method to determine the degree and rate of aerobic biodegradation of synthetic plastic materials in contact with soil, or mixtures of soil and nature compost under laboratory conditions. This method is inexpensive and easier than that of the ASTM D 5339-98 (03) standard but is not favored as same as ASTM D 5338-98 (03).