Biodegradability & Compostability

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 BPC Blue 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.

According to ISO 23977-2, the determination of aerobic biodegradation of plastic materials exposed to seawater can be performed by measuring the oxygen consumption or depletion caused by aerobic respiration of microorganisms from seawater or seawater with low amount of sediment using BPC Blue as a fully automated closed respirometer. During biodegradation of plastic materials, the consumed oxygen is measured continuously by BPC Blue and the biodegradability is calculated as the ratio of the consumed oxygen to the theoretical value. The experimental configuration using BPC Blue includes oxygen supply and the biodegradation process is not inhibited by the limitation of available oxygen in the headspace of test flask. It is therefore convenience to perform the analysis with a higher sample amount.

The figure displays the ongoing biodegradation over 110 days of incubation with continuous agitation at a temperature of 22 ±1 ^oC. The test period typically does not exceed 1 year and is considered valid if the degree of cellulose reaches at least 60% after 180 days. In the current study, the biodegradation of cellulose in seawater is only 9% ±4% after 110 days, whereas higher biodegradation rates of 43% ±8% (higher sample concentration) and 63% ±5% (lower sample concentration) can be observed for tests in seawater and marine sediment, respectively. These results clearly illustrate a lower degree of biodegradation in seawater only, due to the lower microbial density in seawater compared to a higher microbial density in sediment.

According to ISO 17556, the determination of ultimate aerobic biodegradability in soil can be performed by measuring the oxygen consumption or depletion caused by aerobic respiration of microorganisms using BPC Blue as a fully automated closed respirometer. The plastic materials, which is the sole source of carbon and energy, is mixed with the selected soil and incubated at temperature 22 ±1 ^oC. During biodegradation of plastic materials, the consumed oxygen is measured continuously by BPC Blue and the biodegradability is calculated as the ratio of the consumed oxygen to the theoretical value.

The low standard deviations can be observed for the cumulative oxygen consumption of both blanks and samples (lower than ±4% and ±9%, respectively). This supports a high level of confidence of the results obtained with BPC Blue. Accordingly, the validity criteria of ISO 17556:2019 are fulfilled (i.e., the positive control reached 60% biodegradation and BOD values of all blanks are within ±20%) and the PHB test material reached a 95% of biodegradation in 90 days.

According to ISO 14851, the determination of aerobic biodegradability of plastic materials in an aqueous medium can be performed by measuring oxygen consumption or depletion caused by aerobic respiration of microorganisms using BPC Blue as a fully automated closed respirometer. The plastic materials, which is the sole source of carbon and energy, is mixed with selected domestic wastewater, continuously agitated, and incubated at temperature 22 ±1 ^oC. During biodegradation of plastic materials, the consumed oxygen is measured continuously by BPC Blue and the biodegradability is calculated as the ratio of the consumed oxygen to the theoretical value.

The experimental configuration using BPC Blue includes oxygen supply and the biodegradation process is not inhibited by the limitation of available oxygen in the headspace of test flask. It is therefore convenience to perform the analysis with a higher sample amount. In the current study, the impact of sample concentration on the dynamic profile of biodegradability was demonstrated using microcrystalline cellulose. The validity criteria of ISO 14851 are fulfilled (i.e., all samples have > 60% biodegradability with standard deviations range from ±2.1% to ±9.8%, only ±3.5% for three blanks control which is far below the max limit ±20%) at the plateau phase within 60 days.  

According to ISO 17556, the determination of ultimate aerobic biodegradability in soil can be performed by measuring the oxygen consumption or depletion caused by aerobic respiration of microorganisms using BPC Blue as a fully automated closed respirometer. The plastic materials, which is the sole source of carbon and energy, is mixed with the sandy-loam soil and incubated at temperature 22 ±1 ^oC. 1.5 g plastic per 100 g soil was used for all plastic samples. During biodegradation of plastic materials over 200 days, the consumed oxygen is measured continuously by BPC Blue and the biodegradability is calculated as the ratio of the consumed oxygen to the theoretical value.

The extremely low relative standard deviations can be observed for the cumulative oxygen consumption of blank, cellulose positive control, PHB powder samples (±1.6%, ±2.5% and ±6.0%, respectively). This supports a high level of confidence of the results obtained with BPC Blue. Accordingly, the validity criteria of ISO 17556:2019 are fulfilled (i.e., the positive control reached 75.1% which is more than 60% at the end of the test) biodegradation and relative standard deviation of BOD values of all blanks are only ±1.6% which is far below ±20%). PHB powder material reaches about 100±10.2% of biodegradation in 100 days, but only 9.5±2.0% degradation for PHB granule over 200 days. PBS powder has 26.5±4.6% degradation in 200 days. No significant degradation can be observed for PLA granule and PLLA film over the full duration of incubation.

Article: “Mechanical, rheological and anaerobic biodegradation behavior of a Poly(lactic acid) blend containing a Poly(lactic acid)-co-poly(glycolic acid) copolymer”

Authors: Kosar Samadi, Michelle Francisco, Swati Hegde, Carlos A. Diaz, Thomas A. Trabold, Elizabeth M. Dell, Christopher L. Lewis
Polymer Degradation and Stability (2019) 170, 109018

Rochester Institute of Technology (United States)

AMPTS^® II was used to examine the thermophilic anaerobic biodegradation performance of PLA blends containing a highly degradable polymer.

The respiratory activity of the microorganisms in samples of soil, determined by measuring the biological oxygen demand, has long been related to soil fertility. BPC Blue could be used to follow soil respiration in real-time and compare the microbial activity of standard soils or soils of natural origin. For instance, activity of soil organisms was examined in the breakdown of soil organic matter, as well as using microcrystalline cellulose as a reference sample to evaluate various commercially available sandy-loam soils for biodegradation at temperature 22 ±1 ^oC. The purpose is to select suitable type of soil for performing biodegedability test according to ISO 17556.

The degradation curves illustrate the different kinetics of cellulose biodegradation in the different soils and show that the fastest initial degradation rate and the highest biodegradability were achieved with Soil B. Using Soil C as an example, it is possible to distinguish a lag phase (day 0 to 6), where adaption of the soil inoculum to the cellulose occurs, a degradation phase, in which the microorganisms metabolize the sample, and a plateau phase, in which the biodegradation has ended.

The test is considered valid for all soils investigated except Soil A, as the degree of biodegradation of microcrystalline cellulose reached more than 60% in less than six months and all the blanks are within ±20% of the mean at the end of the test (i.e., the standard deviations are less than ±4% for all blanks).

BPC Blue can be configured to evaluate aerobic biodegradability of polymer samples using home or industrial compost under a simulated composting environment like any home composting or controlled composting sites. The instrument allows for continuous and on-line monitoring of oxygen demand or depletion caused by aerobic respiration of compost bacteria. This arrangement should be served as a practical analytical tool of biodegradability evaluation under similar conditions of home composting or controlled composting facilities for internal study or research purpose. Microcrystalline cellulose is often used as a positive control for the test validation. In the current study, biodegradability test of microcrystalline cellulose samples is evaluated at two different concentrations under a simulated composting environment at 58^oC similar with a controlled composting condition. After the incubation of 100 days, the biodegradability of two cellulose samples is 87 ±8% and 62 ±11% for high and low concentrations, respectively. For the higher concentration cellulose sample, 72% biodegradability is achieved after 45 days. The validity criteria of ISO 14851 are fulfilled, i.e., the positive control reaches 70% after 45 days and the standard deviation of test result is within ±20%.

Article title: “Assessment of models for anaerobic biodegradation of a model bioplastic: Poly(hydroxybutyrate-co-hydroxyvalerate)”

Authors: Cecily A. Ryan, Sarah L. Billington, Craig S. Criddle
Bioresource Technology (2018), 227, 205-213

Dept of Civil and Environmental Engineering, Stanford University (United States)

Five kinetic models of anaerobic digestion are evaluated to determine their suitability for modelling of anaerobic biodegradation of the bioplastic poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV). AMPTS^® II was used to perform the actual anaerobic biodegradability analysis in order to produce kinetic degradation data for evaluating the model simulation.