Sampling method, biodegradability tests

ISO 10210 2012 Plastics - Methods for the preparation of samples for biodegradation testing of plastic materials... 

During a soil burial biodegradation test for 27 months, samples specimen were withdrawn at time intervals and characterized by means of structural and thermal analysis. This method allows to watch any progress of oxidative degradation as a direct effect of the incubation in an active microbial environment. 

The Vin otte soil biodegradation certification specifies that two types of tests are performed on the plastic samples. The first test procedure for modified EN 13432 standard specifies that a satisfactory rate of biodegradation of the plastic material is under soil burial conditions between 20°C and 30°C for 24 months, that is, more than 90% of the carbon in the original plastic sample is converted into CO2 as measured by a CO2 respirometer or wet chemistry methods. The details of the test procedures are listed in ISO 14855, ISO 14851, ISO 14852, or ISO 17566 test methods. 

State of the polymer (visual assessment, calculation of the loss of mass, tensile testing, etc.) compared with the samples on the non-inoculated and the sterile media (Fignre 14.6). This strictly empirical method was not intended to show the biodegradability of materials in contact. The norm NF EN ISO 846 describes this methodology, but these kinds of tests are insufficient to show the biodegradability of the tested material, as they are too prone to subjective interpretation. However, they can be useful to show and reinforce other types of tests (particnlarly respirometric). 

The method is simple to apply, but it requires that the tests are repeated as many times as samples carried out by the ATP assays. It is not possible to establish the dynamics or the final rate of biodegradation with this method. However, interesting results are often obtained that appear to show that pre-treated PE with additives promotes bacterial activity and thus a faster biodegradation of PBAT-starch or PL A [LEM 12]. The method uses seleeted micro-organisms according to unspecified criteria. There is therefore a bias, as the whole microbial spectram is not covered, and it is not representative of natural phenomena, whieh could explain these results that are often difficult to explain. 

Gas evolution tests are popular test methods because they are relatively simple, rapid (days to weeks) and sensitive. A direct measure for mineralisation is determined, and water-soluble or insoluble polymers can be tested as films, powders or objects. Furthermore, the test conditions and inoculum can be adjusted to fit the application or environment in which biodegradation should take place. Aquatic synthetic media are usually used, but also natural sea water or soil samples can be applied as biodegradation environments. A prerequisite for these media is that the backgroimd COa-evolution is limited, which excludes the application of real composting conditions. Biodegradation under composting conditions is therefore measured using an inoculum derived from matured compost with low respiration activity . ... 

Proper methods for the preparation of test samples that can be used for the determination of the ultimate aerobic and anaerobic biodegradability of plastic materials in an aqueous medium, soil, controlled compost or anaerobic digesting sludge have been standardized. These should result in an improved reproducibility of the test results during the assessment of the biodegradability (79). 

These methods are similar to a BOD test, using bacterial activity for their measurement and consequently responding strongly to easily biodegradable material. Many researchers use a monoculture how well this approximates a mixed culture s response will depend mainly on the sample. Some researchers have had trouble obtaining reproducible results from sensors that use mixed microorganisms from activated sludge. 

Another application is to rapidly infer biodegradability of samples from the COD tests. This is commonly accomplished by establishing a correlation between COD and BOD. This method has been found successful when the proportions and types of materials in a wastewater remain relatively constant. For example, BOD in domestic wastewater samples from 5-day BOD tests can be approximated as BODj = 0.476 COD. 

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