Ultimate anaerobic biodegradation of plastic materials in controlled slurry digestion systems
According to ISO 13975, the determination of ultimate biodegradability of plastic materials under anaerobic conditions in a controlled anaerobic slurry digestion system can be performed by measuring the volume of biogas produced using Gas Endeavour® and the amount of dissolved inorganic carbon (DIC) formed in excess of blank values. The instrument allows for continuous monitoring of released biogas with real-time temperature and pressure compensation, standardised measurement procedure, data interpretation and report. The level of biodegradability is calculated as the ratio of the sum of the net increase of produced biogas and DIC to the theoretical amount of evolved biogas.
The figure shows the comparison of anaerobic biodegradability of semicrystalline polylactic acid (PLA) and polyhydroxybutyrate (PHB) samples in anaerobic mesophilic condition. Cellulose is used as a positive control and biodegradation is 81% after 15 days with a standard deviation of only ±3% which well fulfils the validity criteria, i.e., >70% and <±20%. Biodegradation of PHB and PLA samples are 88 ±2% and only 5 ±2%, respectively after 40 days incubation, which clearly demonstrates the different biodegradability characteristic for PHB and PLA materials under anaerobic condition.