Influence of inocula on the results of biodegradation tests

A series of biodegradation tests were carried out according to the standard test method ISO 14851 in order to compare the performance of different activated sludge inocula on different plastic materials (polycaprolactone and starch-based material). Cellulose was used as positive control. Inocula were derived from two municipal wastewater treatment plants (Novara and Pero-Milan) and from the treatment plant of a pharmaceutical company. Both municipal sludges were used as such and after a period of acclimation to both compounds. The results were in some cases significantly different. The starch-based material was degraded to similar or higher extents than PCL with municipal sludge. Industrial sludge gave good results with both materials (PCL = 100%; starch-based material = 89%), but was less active towards cellulose. Such results raise some questions about the opportunity of also using other reference materials besides cellulose for biodegradation tests. Acclimation did not provide the expected results.