Degradation of some EN13432 compliant plastics in simulated mesophilic anaerobic digestion of food waste

Abstract

The research looked at the anaerobic biodegradation of 9 different bioplastics, all of which were commercially available and certified in Europe as compostable packaging material compliant with the biodegradation and other requirements of the EN13432 standard. A combination of testing strategies was used to assess the degree of degradation both under batch conditions, and in a simulation in which the plastics and food waste were fed daily to a digester for a period of 147 days. Two non-biodegradable plastics were used as controls, and verified the robustness of the sampling regime and the recovery of the plastic film, with errors of <1% in the final balance. The simulation allowed quantification of the weight loss of the plastics and determination of a decay coefficient for the different materials, which was then used to estimate long-term degradation. Use of a biochemical methane potential (BMP) batch test allowed estimation of the conversion of carbon into gaseous products. There was no evidence that any of the plastic films inhibited the anaerobic digestion process when continuously fed to digesters, although some inhibition occurred when the most readily degradable materials were tested at higher concentrations in batch mode. There were some interesting differences between results from the various measures of plastic degradation in the batch and simulation experiments, with batch testing in most cases suggesting a higher degree of degradation than was achieved in a semi-continuous system at a solids retention time of 50 days. The exceptions to this were two plastics that appeared to show rapid weight loss in the simulation experiment. BMP test results confirmed this was not through biological conversion of the bioplastic to gaseous carbon products, and was therefore probably due to physical disintegration. It was concluded that, of the 9 bioplastics tested, only 4 showed substantial biodegradability under anaerobic conditions. Further evidence to support the mechanism of biodegradation was obtained by microscopy, and photomicrographs using different techniques are included to illustrate the process. Even the most degradable materials would not break down sufficiently to meet the physical contaminant criteria of the UK PAS110 specification for anaerobically digested material, if fed to a digester at 0.5% of the input load on a volatile solids basis.

Methodologies to assess biodegradation of bioplastics during aerobic composting and anaerobic digestion: A review

“…The final weight values were then used to obtain an empirical firstorder decay reaction to provide an estimate of the destruction of the bioplastics in compost. The five studies carried out on different bioplastic materials and at temperature lower than 37°C show a biodegradation not higher than 35% (Zhang et al, 2018).…”

“…Figure 3 summarizes the results of studies reported in Table 5, obtained for biodegradation of bioplastics under anaerobic conditions for different temperatures and duration. The graph shows that no significant results were found under mesophilic conditions, independently of the duration of the test (Gómez and Michel, 2013;Massardier-Nageotte et al, 2006;Zhang et al 2018). However, on raising the temperature to 55°C, higher percentages were gained (Yagi et al, 2010(Yagi et al, , 2013.…”

“…After weighing each retained fraction of bioplastic pieces, a granulometric curve can be assessed, and a model of the disintegration process in time can be elaborated (Lavagnolo et al, 2017). Under anaerobic conditions, in addition to the previously mentioned methods, Zhang et al (2018) applied a modified version of CEN/TC BT 151 WI: the fraction retained on the sieve was washed with tap water and tokens were recovered by hand. They were then air dried for 3-4 days, counted and weighed.…”

Effect of Bio-Based Products on Waste Management

“…Regarding the current level of the presence of bio-based waste in the stream of the biowaste according Zhang et al [51], it is not possible to quantify additional biomethane production as a result of bio-based waste addition in the semi-continuous digestion trial, even where a high degree of degradation of the bio-based waste was observed, as the relative proportion of gas production from the bioplastics is low in comparison to that from food waste. This is inevitable unless a much higher plastics loading is used than is likely to occur in a real mixed biowaste stream.…”

Degradation of Plastics under Anaerobic Conditions: A Short Review

“…It was found that the starch in these composites biodegrades only partially, as it is limited if a discontinuous matrix of starch is present [120]. For composites based in a biodegradable matrix, different biodegradation rates ranging from 10.2% to 53% were reported [121][122][123]. Table 3 summarizes the results for biodegradation under anaerobic digestion conditions, showing only those where respirometric tests were used to assess the process.…”