Effects of storage of a mature compost on its potential for biodegradation of plastics

Biodegradation of plastics was tested in the compost stored at -20degreesC, 4degreesC and 20degreesC for different periods. Viable cells in the compost stored at -20degreesC were expected to be fewer than those in the compost stored at 4degreesC and 20degreesC, because microbes may be under stress or even be killed due to the formation of ice crystals at the Subzero temperature. Mesophilic bacteria and mesophilic actinomycetes were fewer in number in the compost stored at 20degreesC than in the compost stored at the other two lower temperatures contrary to expectation. In contrast, both thermophilic bacteria and thermophilic actinomycetes were fewest in the compost stored at -20degreesC as was expected, indicating that thermophilic microbes were more susceptible to stress in the freezing conditions than the mesophilic ones. Activity of the exo-enzymes plausibly excreted by the microbes in the compost decreased as a result of the storage. Nevertheless, biodegradation of cellulose in the compost was almost independent of the storage time and temperature. In contrast, biodegradability of both polycaprolactone (PCL) and poly(butylene succinate) (PBS) depended strongly on the storage conditions. From the point of view that the existing standards for biodegradation tests of plastics in compost accept reproducibility of cellulose biodegradability as a criterion for the validity of the biodegradation tests, a new standard of the compost preparation should be provided to guarantee more reliable results on the biodegradability of plastics. (C) 2004 Elsevier Ltd. All rights reserved.