ASSESSMENT OF BIODEGRADABILITY OF PLASTICS UNDER SIMULATED COMPOSTINGCONDITIONS IN A LABORATORY TEST SYSTEM

An automated laboratory-scale test system was developed for measuring the aerobic biodegradability of degradable plastics under simulated co mposting conditions. Biodegradation was monitored by measuring microbi al carbon dioxide formation and oxygen consumption. Completeness of bi odegradation was assessed in an aquatic test by conducting a carbon ma ss balance. The percentage of plastic carbon degraded to carbon dioxid e, biomass and water-soluble byproducts were determined. The rate of b iodegradation under simulated composting conditions was measured in a fixed-bed system with mature compost. A time-dependent temperature pro file was applied to simulate the natural self-heating of a composting process. The aquatic test was conducted at a constant temperature of 3 0 degrees C as well as with a temperature profile. The rate of biodegr adation was significantly higher in the aqueous environment. Equal deg rees of mineralization were reached in the aquatic and the fixed-bed s ystem only if the same temperature profile was applied. Conducting the aquatic test at a constant temperature of 30 degrees C less microbial carbon dioxide formation was observed. However, a carbon mass balance revealed that taking into consideration the portion of the plastic's carbon incorporated into biomass, a similar degree of biodegradation w as reached. Consequently, the measurement of microbial carbon dioxide production is not sufficient to assess the extent of biodegradation of plastics. In the heterogeneous matrix 'compost', it is not feasible t o assess the completeness of biodegradation due to limited possibiliti es to analyze degradation intermediates and biomass growth. Therefore, a new fixed-bed system with an inert, carbon-free packing material wa s developed. The inert material was inoculated with an aqueous eluate from compost. First results showed biodegradation rates similar to a c ompost environment. Copyright (C) 1996 Elsevier Science Limited.