The test method of composting in vermiculite is unaffected by the priming effect

Glucose, starch, and cellulose can increase the biodegradation of the compost used as a solid matrix in the biodegradation test under composting conditions (priming effect). The enhanced evolution of carbon dioxide determines an overestimation of the biodegradation of the starch- and cellulose-based materials and, in some cases, values higher than 100% can be reached. The work has verified that using activated vermiculite, an inorganic matrix, the priming effect can be reduced, improving the reliability of the test method. Glucose, the most effective primer, causes the attainment of biodegradation values significantly higher than 100% in mature compost while this does not happen in activated vermiculite. Since all the initial carbon present in the activated vermiculite is converted into CO2 within the test period, we conclude that a substantial priming effect cannot occur for the lack of organic carbon. Furthermore, by measuring in parallel both the consumption of glucose and the CO2 evolution, the yield of CO2 production ( ) was determined. In no case a value higher than 1, a clear indication of priming effect, was found