Relevance of aquatic biodegradation tests for predicting degradation of polymeric materials during biological solid waste treatment

The aquatic biodegradability of cellulose and cellulose acetate with degrees of substitution (d.s.) in the range of 1.5 to 3.0, was compared with the mineralization under laboratory controlled composting conditions. In line with previous observations, it was found that cellulose acetates with d.s. ≤ 2.5 were readily mineralized to CO2 in the controlled composting test. The degradation rate was clearly affected by the degree of substitution (d.s. 1.5 > d.s. 2.5 > d.s. 3.0). Surprisingly, however, biodegradation of cellulose acetate materials was not observed in the aquatic Sturm test. Modifications of the pH and the inoculum source in an attempt to improve the activity of fungi and actinomycetes in the aquatic environment, did not increase CO2-evolution. It is concluded that the relevance of modified Sturm tests is limited for predicting complete biodegradation of polymeric materials during biological waste processing. For evaluation of the compostability of polymeric products or packaging materials, more relevant laboratory controlled composting tests should be used.