Sustainability 2021, 13, 1654. https://doi.org/10.3390/su13041654 www.mdpi.com/journal/sustainability
Pilot-Scale Composting Test of Polylactic Acid for
Nobuyuki Kawashima *, Tadashi Yagi and Kouya Kojima
Mitsui Chemicals, Inc., 1-5-2 Higashi-Shimbashi, Minato-ku, Tokyo 105-7122, Japan;
firstname.lastname@example.org (T.Y.); email@example.com (K.K.)
* Correspondence: firstname.lastname@example.org; Tel.: +81-3-6253-2923; Fax: +81-3-6253-4247
Abstract: The chemical industry and subsequent value chain of plastics are facing significant chal-
lenges from the viewpoints of resource conversion and environmental burden. Now is the time to
explore the future direction of plastics, which will require an integrated scheme using resource cir-
culation, carbon neutrality, and a social system to promote after-use treatment under the concept of
a circular economy. Polylactic acid (PLA) should help reduce greenhouse gas (GHG) emissions as a
biobased material and contribute to waste management after use due to its biodegradability if man-
aged properly. That is, it will be necessary to treat biodegradable products appropriately in closed
systems such as composting facilities after use and recovery. To realize the implementation of fully
approved composting facilities in society, simply evaluating biodegradability in the laboratory is
insufficient. In this study, a pilot-scale test using PLA under actual composting conditions was con-
ducted in accordance with both international standards and domestic evaluation methods. The re-
sults not only confirm its biodegradability and disintegration, but also demonstrate that the pres-
ence of a biodegradable plastic product has a negligible impact on the composting process. The
obtained compost did not adversely affect plant germination or growth, demonstrating its safety
and high quality. Such a multifaceted perspective makes this study unique and useful for creating
a social framework.
Keywords: PLA; biodegradability; composability; pilot-scale compost; circular economy; social im-
In the early 1990s, biodegradable plastics
[1,2] attracted attention as a potential solu-
tion for waste treatment problems associated with the shortage of landfills and environ-
mental concerns, which were represented by fur seals entangled in fishing nets. Although
extensive development was conducted, market growth was slower than biodegradable
plastics manufacturers expected because sorting biodegradable products from non-bio-
degradable products was not trivial, and the necessary infrastructure to treat biodegrada-
ble products appropriately was not well developed.
The Kyoto protocol reinvigorated interest in biobased plastics such as polylactic acid
 since they should contribute to a reduction in greenhouse gas (GHG) emissions
as they are renewable plant resources as opposed to fossil fuel resources. Around 2005,
market growth was slowing due to various reasons: difficulty collecting and sorting prod-
ucts, insufficient properties compared with alternative products such as polyethylene ter-
ephthalate (PET), use of edible resources, and decreased cost competitiveness with fossil
fuel resources caused by a decline in oil prices. It was ironic that regulations and social
systems developed for environmental protection hindered advances in innovative envi-
ronmentally sound products .
Citation: Kawashima, N.; Yagi, T.;
Kojima, K. Pilot-Scale Composting
Test of Polylactic Acid for Social
Implementation. Sustainability 2021,
13, 1654. https://doi.org/10.3390/
Academic Editors: Vincenzo Torretta
and Chunjiang An
Received: 14 December 2020
Accepted: 1 February 2021
Published: 4 February 2021
Publisher’s Note: MDPI stays neu-
tral with regard to jurisdictional
claims in published maps and insti-
Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license
Sustainability 2021, 13, 1654 2 of 20
In 2015, the Sustainable Development Goals (SDGs) were adopted. To achieve these
goals, the chemical industry is expected to transfer raw material sources from fossil fuel
resources to renewable resources as well as reduce GHG emissions via an integrated
lifecycle from raw materials to waste treatment after use. Furthermore, from the perspec-
tive of a circular economy , it is necessary to build a social system that promotes not
only resource circulation, including recycling of plastic products, but also carbon neutral-
ity and effective waste treatment after use. After an extended hiatus, PLA is once again
gaining momentum because it should contribute significantly to GHG emission reduction
and environmentally sound waste treatment together with organic waste [4,6,7]. How-
ever, PLA alone cannot solve such environmental problems. In addition to the viewpoints
of carbon footprint and LCA from raw materials to disposal, it is necessary to evaluate
PLA from the viewpoints of edibility (whether it is edible or not) and SDGs, including
human rights and land use.
Currently, the estimated global PLA production capacity is about 300,000 tons, of
which Corbion Total produces 75,000 tons, NatureWorks produces 150,000 tons, and
China manufactures several tens of thousands of tons. Although current PLA manufac-
turing technology employs the lactide method [7,8], a direct polycondensation method of
lactic acid has been demonstrated at the semi-commercial level [3,7,9]. The operating rate
and actual sales volume are unknown. However, there is a shortage of goods globally.
The claim of reducing GHG emissions is emphasized from the viewpoint of carbon
neutrality as it is derived from biomass rather than biodegradability. It is unknown
whether recovery or composting after use is performed to take advantage of its biodegra-
dability. However, cases of closed systems are becoming more common (e.g., Furano City,
Lark Burger). Biodegradable plastics, including PLA, can help reduce the environmental
load if properly collected and treated after use. However, the word biodegradable may
promote littering, which is a moral hazard.
PLA holds promise for containers and packaging, garbage bags, and agricultural ma-
terials such as mulch. Its compost is expected to play an important role in disposing of
these products. However, for social implementation, that is, acceptance at composting fa-
cilities, demonstrating its biodegradability on the laboratory scale is not enough. For com-
mercial-level use of biodegradable plastic products, the quality and safety of the resulting
compost, as well as its degradability and disintegration, must be confirmed on the pilot
scale to model an actual composting facility and an environmentally sound composting
process. In addition, good growth of agricultural products using the obtained compost
must be established. Although many papers were published from the early 1990s to 2019
relating to the biodegradability of PLA in compost as well as the quality and safety of the
resulting compost, few papers reported a comprehensive and holistic approach on the
pilot scale that included an evaluation of plant growth.
The purpose of this study is to demonstrate the importance of a pilot-scale compost-
ing test, rather than a laboratory test, to show that composting is the proper treatment
method for social implementation after using packaging made of PLA contaminated with
food waste. The degradability of the product, impact on the composting process, and qual-
ity and safety of the obtained compost were examined. As a result, we confirmed that both
biodegradability and disintegration are demonstrated under actual composting condi-
tions on the pilot scale, and the presence or absence of PLA products does not affect the
composting process. Furthermore, the obtained compost is high quality and safe and does
not show adverse effects on plant growth. This type of comprehensive pilot-scale compost
test should be useful to design a social system to treat organic waste together with biode-
gradable products after use.
Sustainability 2021, 13, 1654 3 of 20
2. Materials and Methods
2.1. PLA Sample and Compost Raw Materials
2.1.1. Standard Biodegradability Test of PLA in Compost
According to ISO 14855 , in the basic test, which indicates the biodegradability of
PLA, PLA powder and mature compost from a compost facility in Hayakita-cho, Hok-
kaido, were used at 58 ± 2 °C. ISO 14755  was later modified into ISO 14855-1  and
ISO 14855-2 , although the basic principles remained the same.
2.1.2. Biodegradability and Disintegration of PLA Products in the Pilot-Scale Compost
PLA film-laminated paper plates, which are a BPS certified Green Plastic #216 pro-
vided by Tohcello, were used in the pilot-scale compost test. BPS was formerly the Biode-
gradable Plastics Society, but its name changed to the Japan Bioplastics Association
(JBPA). Green Plastic is the brand name of the biodegradable plastics. The plates were
composed of a 40 μm-thick PLA film made from LACEATM (Mitsui Chemicals) and a pa-
per part made from 100% pulp paper with a weight of 320 g/m2 (Figure 1).
In accordance with ISO 16929 , the raw material for compost was wood chips as
an auxiliary material, horse and animal waste as return compost, and plant-based waste
as a substitute for fermentation with artificial garbage. Table 1 shows the composition
ratios of these compost raw materials.
Figure 1. PLA film-laminated paper plates as a test sample.
PLA pellets were provided by Mitsui Chemicals and processed into PLA film by
Tohcello. PLA film was laminated with 100% pulp paper. Then, the PLA film-laminated
paper was thermoformed into plates.
Table 1. Formation of the composting materials.
Component Description Weight (wet, kg)
Feed for rabbits (solid compounded feed) 9
Supplied compost Horse dung compost product 40
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Auxiliary raw material Larch 10
2.2. Test Equipment and Processing Conditions
2.2.1. Biodegradability Standard Test of PLA in Compost
In the standard model of ISO 14855 , about 100 g of a sample is put into about 600
g of compost. Figure 2 shows a newly developed small-scale model. In this model, about
5 g of a sample was put into 100–500 g of compost. The temperature was kept at 58 ± 2 °C.
CO2 generated by biodegradation was absorbed by the alkaline solution and measured by
Figure 2. Scheme of the laboratory-scale compost apparatus according to ISO 14855.
2.2.2. Biodegradability and Disintegration of the PLA Product in Pilot-Scale Compost
Each fermenter was a 180 L metal columnar drum (without a stirring mechanism)
equipped with a blower with an airflow meter, non-dispersive infrared absorption
(NDIR)-type CO2 concentration meter, thermometer, and other measurement equipment
(Figure 3). Table 2 summarizes the list of auxiliary apparatus.
Figure 3. Scheme of the pilot-scale compost apparatus principle.
Sustainability 2021, 13, 1654 5 of 20
Table 2. List of auxiliary apparatus used in the pilot-scale compost experiment.
Apparatus Device Description
Air supply Blower Roots-type blower
Air flow meter Flow-rate control type airflow meter with a needle valve
Air supply pipe PVC loop-type air supply pipe
Gas meters CO2 meter NDIR gas meter
Collection device Diffused gas collector made of PET
Selection switch Electromagnetic valve
Mist separator Liquid displacement type
Recorder Intermittent recorder (also used for temperature)
Thermometer Temperature sensor JIS Pt100 platinum temperature measurement resistor
Recorder Intermittent recorder (also used for gas)
Fermenters, which contained 170 L of compost raw materials, were prepared and
divided into two zones (Figure 4). In the test zone, PLA samples (1.1 kg) were added to
the fermenter (Figure 5). In the blank zone, the fermenter did not contain PLA samples.
To confirm the validity, each zone was duplicated. After the test was completed, the con-
tents of the fermenter in each treatment area were sieved to separate particles of non-
disintegrated PLA samples with a diameter greater than 2 mm, and as a result the residual
rate of PLA samples was measured. The maximum test treatment period was 80 days.
However, biodegradation was completed within about 60 days. The test ended after con-
firming that fermentation had stopped, which was determined when fermentation condi-
tions such as CO2 concentration and temperature no longer changed over time.
The temperature depended on the heat generated by biodegradation of the compost.
External heat was not added.
Table 3 summarizes the measured items.
Table 3. Measured items.
Item Method Measurement Frequency and Remarks
Daily, continuous measurement
Top: 15 cm from the surface
Center: 40 cm from the surface
CO2 concentration Gas detector, NDIR Daily, continuous measurement
40 cm from the surface
O2 concentration Gas detector
Daily, frequency varies with the change in the
40 cm from the surface
NH3 concentration Gas detector
Daily, frequency varies with the change in the
40 cm from the surface
Water content Weight method Weekly, at the time of turning
Ignition loss Weight method Weekly, at the time of turning
pH Glass electrode Weekly, at the time of turning
EC Glass electrode Weekly, at the time of turning
C/N2 ratio C/N meter Weekly, at the time of turning
Contents volume Calculated value Weekly, at the time of turning
Contents weight Direct weighing Weekly, at the time of turning
Amount of water added Direct weighing At the time of water addition
Sustainability 2021, 13, 1654 6 of 20
Figure 4. Photo of the pilot-scale compost apparatus. (left) Two drums are the blank zone without
PLA samples and (right) two drums are the test zone with PLA samples. All drums were
equipped with an air blower, gas concentration meter, and thermometer. Drums were placed on a
Figure 5. PLA test sample in the pilot-scale compost apparatus.
Test sample: PLA film-laminated paper plates were put into the compost after cutting
into 5 × 5 cm pieces.
The test zone contained the PLA sample, whereas the blank zone did not. Table 1
shows the compost raw materials. The PLA sample was a PLA film-laminated paper plate
cut into 5 × 5 cm2 pieces. Table 4 shows the conditions.
Table 4. Operating conditions (according to ISO 16929 ).
Item Operation Condition
Agitation/turning Drum contents were spread on the sheet, stirred manually, and returned to the drums each week.
Air supply 5 to 25 L/min/m3 (Value was set such that the oxygen concentration in the compost was above 5%).
Water addition Water was added such that the water content of the compost would not fall below 50% when turning the compost.
Nitrogen control Urea solution was added to compensate for the drop in the nitrogen concentration due to the addition of water.
Sustainability 2021, 13, 1654 7 of 20
2.3. Measurement Items
2.3.1. Biodegradability Standard Test of PLA in Compost
The CO2 generated by biodegradation was measured according to ISO 14855 .
2.3.2. Biodegradability and Disintegration of PLA Product in Pilot-Scale Compost
The tests measured the following: temperature, CO2, O2, NH3, water content, loss on
ignition, pH, electrical conductivity (EC), carbon/nitrogen ratio, content volume, content
weight, and added water weight. At the end of the test, the PLA sample residual rate was
measured. For the compost input, the elution test described in the Waste Management
and Public Cleaning Act was conducted . For the treated compost, the water, nitrogen,
and heavy metal contents were analyzed according to the items described in the Fertilizer
Regulation Act in Japan .
The blank zone and test zone were each measured twice and graphed with their av-
erage values. They appear on the graph as an error bar and a circle of the average value.
Items were measured to confirm whether composting progressed smoothly. For ex-
ample, the ignition loss and EC indicated whether or not the compost was suitable as fer-
tilizer by evaluating the degree of decomposition of organic matter and salt concentration.
On the other hand, the carbon/nitrogen ratio determined the balance between carbon and
nitrogen as a fertilizer. Composting proceeded as usual even if PLA was present.
2.4. Plant Growth
Finally, the effect of the resulting compost on the germination and growth of Japa-
nese komatsuna (Japanese mustard spinach) was evaluated. The resulting compost was
used as a fertilizer. B-1 and B-2 were obtained from compost without the PLA sample. T-
1 and T-2 were grown in the compost with the PLA sample based on the test method 
of plant growth. This method measures toxicity against plants and is regulated by the
Ministry of Agriculture, Forestry and Fisheries in Japan No. 1943 (18 April 1984). Ko-
matsuna seeds were buried in each type of fertilizer to observe the effects of the presence
of the PLA sample.
3. Results and Discussion
3.1. Biodegradability Standard Test of PLA in Compost
Tracing the biodegradability of PLA powder using the amount of CO2 generated in the
mature compost confirmed that about 88% of the PLA decomposed in 90 days (Figure 6).
Figure 6. Biodegradability index of the PLA powder measured by the amount of CO2 emission
according to ISO 14855.
Sustainability 2021, 13, 1654 8 of 20
3.2. Biodegradability and Disintegration of PLA Products in the Pilot-Scale Compost
3.2.1. Changes in the Temperature and Gas Concentration in the Fermenter
The temperature during the test period was measured at the top (Figure 7) and center
of the fermenter (Figure 8). The blank and test zones did not differ significantly as both
showed a temperature of 65 °C or higher for a minimum of 48 h at the early stage of fer-
mentation. Hence, the compost meets the test standards of ISO 16929 and the epidemio-
logical conditions of Japan.
Figure 7. Change in the average temperature at the top (15 cm from surface) of the fermentation drum.
Figure 9 shows the daily change in CO2 content in both the blank and test conditions.
The content initially increased, but then decreased rapidly. From 10–50 days, the content
was 0–5%, but it settled at around 1% or less after 50 days. There are some points that do
not overlap in the data of the blank zone and the test zone, but when comparing the be-
havior before and after, there is no significant difference between the two zones.
Sustainability 2021, 13, 1654 9 of 20
Figure 8. Change in the average temperature at the center (40 cm from the surface) of the fermentation drum.
Figure 9. Change in the average CO2 content with time.
Sustainability 2021, 13, 1654 10 of 20
Figure 10 plots the daily change in O2 content. As O2 consumption was intense at the
beginning of fermentation, it dropped to less than 10%. After 10 days, it stabilized at over
10% of the O2 content by adjusting the air supply rate. Similar to the trends of CO2 content,
although there are some irregular points, the blank and test zones did not differ signifi-
Figure 10. Change in the average O2 content with time.
The NH3 concentration in the fermenter was initially high but decreased after 20 days
(Figure 11). The data from the large error bar at around the 40 day mark may appear ir-
regular, but when comparing it to the decomposition behavior of the two zones at other
periods, there were no significant differences.
The similar trends in the temperature, CO2, O2, and NH3 concentrations in the blank
and test zones indicate that the presence of the PLA film did not affect the composting
3.2.2. Property Changes to the Fermentation Mass in the Fermenter
The test (treated) and blank (untreated) zones did not significantly differ with regard
to water content, pH, EC, and residual amount of ignition during the test period (Figures
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Figure 11. Change in the average ammonia concentration with time.
Figure 12. Change in water content with time.
Water Content (%)
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Figure 13. Change in pH with time.
Figure 14. Change in electrical conductivity with time.
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Figure 15. Change in ignition loss with time.
Figures 16 and 17 show the weight per container and bulk specific gravity measured
during the test period, respectively. The test and blank zones showed similar results.
These results further demonstrate that the presence of PLA film-laminated paper did not
affect the composting process.
Figure 16. Change in weight with time.
Ignition Loss (%)
Sustainability 2021, 13, 1654 14 of 20
Figure 17. Change in bulk specific gravity with time.
3.2.3. Residual Rate of the PLA Sample at the End of Test
To investigate the residual rate of PLA samples, the compost after the test was passed
through a 2 mm sieve. The PLA sample remaining in the compost with a diameter of 2
mm or more was 0.054 kg, and the residual rate was 5.23% compared with the input PLA
sample by dry weight. Table 5 shows the average weight of each zone at the end of the
test. Overall, 94.8% of the PLA sample, which weighed 1.031 kg at the time of input, de-
composed. Furthermore, fermentation did not vary significantly between the blank and
test zones. These results provide additional evidence that the presence of PLA film-lami-
nated paper does not affect the composting process.
Table 5. Weights before and after the test.
Non-Treated Zone Treated Zone
Average weight of the compost (dry weight) 59.95 kg (29.26 kg) 60.05 kg (31.67 kg)
Average weight of the test specimen
Before charge (water content) 1.1 kg (6.3%) = 1.031 kg as dry
After test (water content) 0.067 kg (24.82%) = 0.054 kg as dry
Residual rate of the test specimen 5.23% (compared in dry weight)
3.2.4. Quality of Inputs and Composted Products
The elution test of the input materials was conducted based on the Waste Manage-
ment and Public Cleaning Act  in Japan. As shown in Table 6, the results were all
below the requirements for heavy metals, organophosphorus compounds, and other reg-
Table 6. Analysis results of items specified in the Waste Management and Public Cleaning Act
(unit: 10−3 kg/m3).
Analysis Item Blank 1 Blank 2 Test 1 Test 2 Standard Value
alkyl mercury compounds <0.0005 <0.0005 <0.0005 <0.0005 not detected
mercury or its compounds <0.0005 <0.0005 <0.0005 <0.0005 ≤0.0005
cadmium or its compounds <0.002 <0.002 <0.002 <0.002 ≤0.3
lead or its compounds <0.01 <0.01 <0.01 <0.01 ≤0.3
organophosphorus compounds <0.001 <0.001 <0.001 <0.001 ≤1
chromium (VI) compounds <0.05 <0.05 <0.05 <0.05 ≤1.5
0 5 10 15 20 25 30 35 40 45
Specific Gravity (kg/L)
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arsenic or its compounds 0.031 0.030 0.031 0.030 ≤0.3
cyan compounds <0.1 <0.1 <0.1 <0.1 ≤1
polychlorinated biphenyls <0.0005 <0.0005 <0.0005 <0.0005 ≤0.003
trichloroethylene <0.001 <0.001 <0.001 <0.001 ≤0.3
tetrachloroethylene <0.001 <0.001 <0.001 <0.001 ≤0.1
dichloromethane <0.001 <0.001 <0.001 <0.001 ≤0.2
carbon tetrachloride <0.001 <0.001 <0.001 <0.001 ≤0.02
1,2-dichloroethane <0.001 <0.001 <0.001 <0.001 ≤0.04
1,1-dichloroethylene <0.001 <0.001 <0.001 <0.001 ≤0.2
cis-1,2-dichloroethylene 0.004 <0.001 <0.001 <0.001 ≤0.4
1,1,1-trichloroethane <0.001 <0.001 <0.001 <0.001 ≤3
1,1,2-trichloroethane <0.001 <0.001 <0.001 <0.001 ≤0.06
1,3-dichlorobenzene <0.001 <0.001 <0.001 <0.001 ≤0.02
benzene <0.001 <0.001 <0.001 <0.001 ≤0.1
thiuram <0.006 <0.006 <0.006 <0.006 ≤0.06
simazine <0.003 <0.003 <0.003 <0.003 ≤0.03
thiobencarb <0.01 <0.01 <0.01 <0.01 ≤0.2
selenium or its compounds <0.002 <0.002 <0.002 <0.002 ≤0.3
The composted products were analyzed by the test method based on the “Fertilizer
Regulation Act” . Table 7 shows the nutrient contents (e.g., moisture content, total ni-
trogen, total phosphoric acid). Table 8 shows the level of toxic items regulated by the Fer-
tilizer Control Law (e.g., arsenic, cadmium, mercury). The results confirm that the com-
post is suitable for use as fertilizer.
Table 7. Analysis results of nutrient items specified in the Fertilizer Control Law.
Analysis Item Unit Blank 1 Blank 2 Test 1 Test 2
Water content % 44.5 44.2 43.8 44.0
Total nitrogen amount % 1.54 1.57 1.36 1.44
Total phosphoric amount % 0.96 0.99 0.96 0.96
Total potassium amount % 1.58 1.64 1.67 1.66
Total copper amount mg/kg 23.1 22.4 23.9 23.9
Total zinc amount mg/kg 77.3 80.0 78.8 75.0
Total lime amount % 0.88 0.86 0.91 0.88
Organic carbon % 11.4 11.4 10.8 11.2
Carbon/nitrogen ratio 7.4 7.3 7.9 7.8
Table 8. Analysis results of toxic items specified in the Fertilizer Control Law (Unit: %).
Analysis Item Blank 1 Blank 2 Test 1 Test 2 Standard Value
Arsenic 0.0010 0.0007 0.0009 0.0009 <0.005
Cadmium <0.000005 <0.000005 <0.000005 <0.000005 <0.0005
Mercury 0.00003 <0.000002 0.00003 <0.000002 <0.0002
Nickel 0.003 0.003 0.008 0.007 <0.03
Chromium <0.005 <0.005 <0.005 <0.005 <0.05
Lead <0.001 <0.001 <0.001 <0.001 <0.01
3.2.5. Confirmation of Effects on Plant Germination
Finally, based on the practical test method  of plant growth, which measures the
toxicity against plants and is related to the scope of ISO16929 , we confirmed the effect
of the PLA sample-treated compost on plant germination. There were two test groups to
grow komatsuna or Japanese mustard spinach. The control samples were grown in ferti-
lizer from the pilot-scale compost without the PLA sample (B-1 and B-2), while the tests
were grown in fertilizer from the pilot-scale compost with the PLA sample (T-1 and T-2).
The komatsuna seeds were buried in each type of fertilizer. After three weeks, good
growth was observed in both groups. Additionally, neither group showed abnormal
Sustainability 2021, 13, 1654 16 of 20
growth (Table 9). Hence, the compost-treated product with the PLA sample did not in-
duce harmful effect on plants, demonstrating its suitability as a good compost product.
Table 9. Test results of plant growth in fertilizer from pilot-scale compost.
Zone Rate of Germination Results of Growth Abnormality
2 Weeks (cm)
3 Weeks (cm)
B-1 100.0 100.0 100.0 5.0 7.7 16.5 None
B-2 98.3 98.3 98.3 5.2 8.2 18.7 None
T-1 98.3 98.3 98.3 4.8 7.5 15.3 None
T-2 98.3 98.3 98.3 5.7 7.6 16.2 None
3.2.6. Insight from the History of PLA Degradation in Compost
Prior to our experiments, we surveyed the literature from 1992 to 2019 to analyze
previous research on pilot-scale biodegradability and safety of the resulting compost.
Many papers published from the 1990s to the early 2000s were related to the promotion
of PLA polymers’ biodegradability [17–25]. Some studies also worked to improve the me-
chanical properties by producing copolymers  or blending with other biodegradable
polymers [20,24] and additives . Other studies reported direct and simple biodegra-
dability testing of PLA [26,27], and socially implementable biodegradability experiments
using compost [28–30]. However, full-scale studies on the biodegradability and disinte-
gration results utilizing existing real composting facilities for commercially available PLA
products only began to appear around 2005.
In 2006 and 2007, papers were published demonstrating the degradability of a variety
of commercial PLA products in compost such as cheese packaging , carpet and fiber
products , bottles, trays and deli-containers , and knives and packaging . In
one study , three commercially available forms of PLA packaging and containers were
exposed to real composting conditions at Michigan State University under ambient expo-
sure conditions. Degradation in a real composting facility was monitored by visual in-
spections, gel permeation chromatography, differential scanning calorimetry, and ther-
mal gravimetric analysis. The authors noted the need to address the compostability of
these packages under real composting conditions for social implementation since the
standard methodology of evaluating biodegradability in simulated composting condi-
tions has limitations. They also showed that the compostability of the complete package
in real composting conditions may take longer than a simple piece of polymer.
Professor Narayan, who is a leader in research on biodegradable polymers, and col-
leagues have published many papers regarding biodegradability. Among these, two pa-
pers compared ASTM/ISO tests with realistic composting conditions in 2007  and 2009
. Based on their disintegration tests on real compost (fresh compost) using PLA bottles,
they pointed out that standard test methods such as ISO 14855 only answer whether a
plastic is biodegradable . Standard methods do not answer the question of whether it
is fully biodegradable in an actual compost facility. This follows on from ISO 17088, which
was announced in 2008 and revised in 2019 .
From industrial and business perspectives, major consumer goods companies have
documented  that it is pointless to use PLA and other biodegradable plastic products
unless they are properly processed in a composting plant. Without proper composting,
they will not contribute to waste reduction.
In 2017, a paper was published that questioned the decomposability of compost in
actual facilities, even if decomposition is demonstrated on the laboratory scale . They
argued that compost facilities vary in operational methods, and the actual degradability
depends on the form. As the above studies show, it is important to confirm biodegrada-
Sustainability 2021, 13, 1654 17 of 20
bility in actual composting facilities as social implementation of bioplastics with biode-
gradable properties such as PLA progresses. All the messages delivered by the above pa-
pers are similar to the one that this paper tries to convey.
There are few examples demonstrating the safety of PLA by assessing plant growth
in the literature. A paper in 2019 questioned the safety of micro and nanoparticles, which
is a concern during decomposition of PLA products, including their additives . In
many practical available resins, various additives are used in the manufacturing process.
Hence, it is necessary to investigate whether such additives decompose in real compost.
Additionally, we need to evaluate the safety of the decomposed material and the resulting
compost. However, it appears that few studies demonstrate the method and results of
such a comprehensive and holistic approach on the pilot scale.
3.2.7. Influencing Elements Affecting the Biodegradability Time in Compost
To date, the biodegradability of PLA in compost has been demonstrated on the la-
boratory scale according to ISO 14855 . Consistent with our previous paper , this
study shows that more than 80% of PLA biodegrades in 80 days using mature compost
(Figures 2 and 6). According to the paper by M. Kunioka et al. on the Biodegradability
Evaluation of Polymers by ISO 14855-2 , they found that 80% or more of the powder
was biodegraded after 50 days . In contrast, when a sample is shaped into PLA cups,
it takes 100 days or more to reach a minimum of 80% decomposition. Hence, the sample
shape affects decomposition time.
ISO 14855 tracks the biodegradability by the amount of CO2 generated . On the
other hand, this study used ISO 16929, which assesses the contents of the fermenter after
testing and sieving . The decomposition rate was subsequently calculated by compar-
ing the dry weight of the remaining PLA sample and the original PLA sample. Such a
comparison is challenging. Here, if degradation is considered to be complete at the time
when the temperature, CO2 concentration, and weight in the container stopped changing,
it means that 94.8% of the PLA sample was degraded in 50–60 days. Comparing the above
results in laboratory-scale and pilot-scale studies, the degradability on the laboratory scale
and the pilot scale was at least equivalent when considering the sample shape, and sug-
gest a slightly faster degradation time on the pilot scale.
3.2.8. Holistic Approach and Social Implementation
This study investigates both the biodegradability and disintegration property of the
product in the compost. The PLA samples did not adversely affect the composting pro-
cess. The quality and safety of the obtained compost were maintained. Such results are
difficult to obtain in a laboratory-scale test. However, the pilot-scale test provided results
suitable as a proof of concept for social implementation. That is, a pilot-scale test was used as
a holistic approach to demonstrate the feasibility compost facilities to process PLA products.
PLA products have been used in two major global events for social implementation:
the Kassel project [42–45] and the Aichi EXPO . The Kassel project ran from 2001 to
2002 in the city of Kassel, Germany. PLA film-laminated paper plates were used in a su-
permarket. After use, they were collected, sorted, and safely composted. During the Aichi
EXPO in Japan, single-use and compostable tableware made from PLA was used in the
food court and composted after use. In both cases, vegetables were grown in the resulting
compost. Beside the global events described above, garbage bags made of PLA were in-
troduced in Kosaka Town, Akita Prefecture, and Furano City [47,48]. Organic waste was
also collected from homes in Hokkaido and treated in composting facilities. The resulting
compost was used as fertilizer in domestic farms. Additionally, some companies have fo-
cused on the closed system, which is beyond the involvement adopted in business models
based on related holistic approaches and is drawing attention from the viewpoint of a
circular economy. In Colorado, USA, a hamburger chain minimized the use of packaging
and containers, and introduced biobased and biodegradable packaging and cups made of
Sustainability 2021, 13, 1654 18 of 20
paper and PLA . The environmental contribution was not made through use of the
material itself but rather the recovery and composting treatment implemented after use.
PLA film-laminated paper, which was used as the test sample representing commer-
cial products, does not affect the fermentation status of the composting process. However,
it does satisfy the various conditions shown in the “Plastic disintegration under compost-
ing conditions” described in ISO 16929. In addition, the elution test of the input materials
meets the requirements specified in “Waste Management and Public Cleaning Act”, and
an analysis of the obtained compost based on the “Fertilizer Regulation Act” indicates that
it does not suffer from quality problems. Adverse plant growth did not occur even if the
compost contained residual residues of the PLA sample. Consequently, composting treat-
ment of the organic waste together with biodegradable plastics such as PLA will contrib-
ute to a circular economy by adding value to waste. This comprehensive and holistic pilot-
scale demonstration test shows that the composting process of PLA products after use is
effective in social implementation and meaningful for creating a social framework.
Author Contributions: Conceptualization, methodology, formal analysis, and supervision by T.Y.
and N.K.; writing—original draft preparation by K.K. and N.K.; writing—review and editing by
N.K. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Acknowledgments: The authors thank Shin Fukuda, Shingo Shibata, Kiyoshi Ito, Ken Migita, and
Toshie Sato for their support and insight. The authors also thank Tadahisa Iwata, The University of
Tokyo and Hiroyasu Yamaguchi, Osaka University for their advice and instruction.
Conflicts of Interest: The authors declare no conflict of interest.
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