Controlled composting test

The maximum test duration in principle is 6 months, while a typical minimum duration is 45 days. CO2 production is continuously measured. After subtracting the background CO2 production from the blank compost inocnlnm (withont any additional carbon source), the percentage of biodegradation is determined by the net amount of carbon of the test item that is converted to CO2. A positive reference control, cellulose, is tested in parallel to check the activity of the inocnlnm. Strict requirements are imposed on the results for cellulose in order to validate the test. The test item is preferably added in the form of a fine powder. 

Other norms similar to ISO 14855 inclnde ASTM D5338-11, EN 14046 and JIS K 6953. 

---

Laboratory test of biodegradability [ISO 14855 (controlled composting test or equivalent)]... 

Fig. 1 Controlled composting test of Ecoflex yields >90% conversion to CO2 after 80 days...

CO2, a blank compost inoculum without an additional carbon source (polymer sample) is simultaneously tested under the same conditions. The CO2 content of the exhaust air of both vessels is compared. After subtracting the CO2 evolution of the blank inoculum, the CO2 evolution related to the test polymer is monitored and plotted as a biodegradation curve (see Fig. 1). Finally, the activity of the compost inoculum in the controlled composting test is validated using a cellulose reference instead of the polymer. In Fig. 1, the biodegradation curve of Ecoflex is depicted. After 80 days, 90% of the theoretical CO2 evolution is reached. Thus, Ecoflex is ultimately biodegradable according to the ISO standard for compostable polymers (ISO 17088), which requires 90% of the theoretical CO2 evolution within 180 days. 

Standard tests in solid conditions are rare. Petri dishes do not determine mineralization but only the resistance of a material to selective exposure to microorganisms and thus are not relevant for the problem of waste elimination. Controlled composting tests are more representative of the natural environment (i. e. waste management treatment). 

Pagga, U., Beimbom, D.B., Boelens J., and De Wilde, B 1995, Determination of the aerobic biodegradability of polymeric material in a laboratory controlled composting test. Chemosphere 31 4475-4487. 

The composting test method based on activated vermicuUte was proposed as a comprehensive system for the assessment of the environmental impact of compostable polymers [1, 2]. Vermicnlite, a clay mineral, can be activated (by an inoculation with an appropriate microbial population and fermentation) and used as a sohd matrix in place of mature compost in the controlled composting test. The formula of vermicnlite is (MgJ e,Al)3(Al,Si)40io(OH)2.4H20. The results obtained with two materials (cellulose and a starch-based blend) indicated that activated vermicnlite affected neither the biodegradation rate nor the final biodegradation level. 

PLA PLLA (poly(L-lactide)) -laboratory synthesized Controlled composting test (prEN14046) CO2 evolution measurement Biodegradation 92% ( 17%) for PLLA in 202 days (56% in 150 days) Whatman Chromatography paper as positive control [24]... 

BAK 1095, commercial polyesteramide based on caprolactam, butanediol and adipic acid was fonnd to be completely biodegradable according to German compostability standard DIN 54900 [113], Biodegradability of laboratory synthesized poly(esteramide) was studied in the controlled composting test according to EN 14046 standard [114], It was found that poly(esteramide) meets the biodegradation criteria of the standard. 

The evolution of CO2 or CH4 from a substrate represents a direct parameter of mineralisation. Therefore, gas evolution tests can be important tools in the determination of the biodegradability of polymeric materials. A number of well-known test methods have been standardised for aerobic biodegradation, such as the (modified) Sturm test [70-75] and the laboratory controlled composting test [76-79] ... 

The testing procedure is slightly different the Controlled Composting Test . DIN 54900 (in press) defines Biodegradable polymers and measures the ecotoxicity and heavy metal content. The method will be very similar to the CEN standard. 

Figure 5.4 Schematic layout of controlled composting test...

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... 

---