Mineral bed composting test

In an effort to combine the possibilities and advantages of both types of tests, a novel test method was developed in which the compost matrix is replaced hy a mineral, inert medium [8,9]. In this novel test procedure the carrier matrix consists of vermiculite, which is a type of expanded clay mineral with an overall physical structure and waterholding capacity behaviour very similar to compost. This medium is inoculated with a compost extract and mineral medium is added. The inert matrix should permit the extraction and determination of metabolites and biomass. 

The novel method using vermiculite, a mineral inert matrix, has been included in a new edition published in 2005 ISO 14855-1 Determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions — Method by analysis of evolved carbon dioxide Part 1 General method. 

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A drawback of using complex degradation environments such as mature compost is that simultaneous characterisation of intermediate degradation products of determination of the carbon balance is difficult due to the presence of a great number of interfering compounds. To overcome this, an alternative test is currently under development based on an inoculated mineral bed based matrix . ... 

Tosin, M., Degli-lnnocenti, F. and Bastioli, C., 1998, Detection of a toxic product released by a polyurethane-containing film using a composting test method based on a mineral bed. J. Environ. Polym. Degr. 6 79-90. 

A variant of this method, uses a mineral bed, i.e., vermiculite inoculated with thermophilic microorganisms obtained from compost with a specific activation phase, instead of a mature compost. This variant is designed to yield the percentage of carbon in the test substance converted to carbon dioxide and the rate of conversion. 

The absence of an extra carbon source also prevents the phenomenon of a priming effect in a mineral bed test. The addition of a readily degradable and energy-rich test material in a conventional controlled composting test sometimes results in an extra stimulated activity... 

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