Composting simulation testing is a controlled laboratory procedure that reproduces the thermophilic aerobic composting environment to evaluate how completely and how rapidly materials biodegrade, generating essential data for compostability certification and sustainable product development. This technical guide explains the testing principles, applicable standards such as ISO 14855 and ASTM D5338, sample requirements, evaluation parameters, and typical industrial applications.
Technical Overview
Composting simulation testing, also referred to as controlled composting biodegradation testing, is a laboratory-scale experiment designed to replicate the conditions of an industrial aerobic composting process. The test measures the ultimate biodegradability of materials—particularly biodegradable plastics and organic packaging—by quantifying the carbon dioxide evolved when microorganisms metabolize the test material under optimized temperature, moisture, and aeration conditions.
The fundamental principle of the method is mass-balance-based carbon tracking. The test material is mixed with a mature compost inoculum rich in active microbial communities and incubated in sealed or semi-sealed reactors, typically maintained at 58 °C ± 2 °C. Compressed, carbon-dioxide-free air is passed through the reactors at a controlled flow rate, and the carbon dioxide produced by microbial respiration is captured and quantified using infrared gas analysis, titration, or gravimetric absorption columns. The measured cumulative carbon dioxide is compared against the theoretical carbon dioxide (ThCO₂) that would be released if the entire organic carbon content of the sample were mineralized, yielding a biodegradation percentage over time.
A valid test requires parallel control vessels, including a blank vessel containing only inoculum to subtract background respiration, a reference vessel containing microcrystalline cellulose to confirm inoculum activity, and replicate test vessels to ensure statistical reliability. Under major international standards, the reference material must achieve more than 70% biodegradation within the test period, and the blank respiration must remain stable for the results to be considered valid.
Testing Samples
Biodegradable Plastics and Polymers
This category covers the majority of samples submitted for composting simulation testing, including polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS and PBSA), polyhydroxyalkanoates (PHA and PHB), polycaprolactone (PCL), and starch-based or cellulose-based polymer blends. Samples may be supplied as granules, powders, films, sheets, or molded articles depending on the intended evaluation.
Packaging and Consumer Products
Finished goods such as compostable shopping bags, food packaging films, disposable cutlery, food containers, coffee capsules, tea bags, straws, and agricultural mulch films are frequently tested to demonstrate end-of-life performance. Testing finished products, including their inks, adhesives, and barrier coatings, provides a more realistic assessment than testing raw resin alone.
Fibers, Nonwovens, and Hygiene Products
Biodegradable nonwoven fabrics, wet wipes, sanitary products, and textile substrates are evaluated to verify their disintegration behavior and biodegradation kinetics in composting environments.
Coatings, Adhesives, and Additives
Bio-based and biodegradable coatings applied to paper and board, laminating adhesives, printing inks, and processing additives may be tested individually or as integral components of a composite structure.
Natural Materials and Biomass Products
Plant fibers, agricultural residues, molded pulp products, and other lignocellulosic materials are tested to characterize decomposition rates and to support compostability claims for natural-fiber-based product lines.
Before testing, all samples must be characterized for total dry solids, volatile solids, and total organic carbon content, because these values directly determine the theoretical carbon dioxide used in biodegradation calculations. Depending on the applicable standard, samples may be cryogenically milled to a defined particle size to reduce physical heterogeneity and improve reproducibility.
Testing Items
Composting simulation experiments typically comprise the following evaluation items:
- Ultimate aerobic biodegradation degree, expressed as the percentage of evolved carbon dioxide relative to theoretical carbon dioxide over the incubation period.
- Biodegradation kinetics, including time-course curves, the time required to reach 60% and 90% biodegradation, and lag-phase duration.
- Degree of disintegration, determined by sieving composted material through a 2 mm screen and calculating the percentage of sample mass lost or fragmented.
- Volatile solids and dry solids content of the sample and inoculum, used for carbon balance calculations.
- Elemental analysis for heavy metals and regulated substances, including arsenic, cadmium, chromium, copper, mercury, nickel, lead, and zinc, which must remain below statutory limits in compostability schemes.
- Ecotoxicity assessment of the resulting compost, typically involving seedling emergence and growth tests on higher plants and, where required, acute earthworm toxicity tests.
- Compost quality parameters such as pH, electrical conductivity, ammonium nitrogen, total nitrogen, phosphorus, potassium, and magnesium.
- Visual and morphological observations, including photographic documentation of disintegration progress and, where applicable, residual fragment counting.
Testing Methods
ISO 14855-1 Controlled Composting Biodegradation Test
ISO 14855-1 specifies the determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions by measuring evolved carbon dioxide. Test vessels containing a mixture of test material and compost inoculum are incubated at 58 °C with controlled humidity and aeration for up to six months, with carbon dioxide monitored continuously or at defined intervals. This method forms the scientific backbone of most industrial compostability evaluation programs.
ISO 14855-2 Modified Gravimetric Variant
ISO 14855-2 describes a laboratory-scale variant using smaller reactors in which carbon dioxide is absorbed in alkaline traps and quantified gravimetrically, offering a compact and cost-effective approach suitable for screening and comparative studies of multiple formulations.
ASTM D5338 Aerobic Biodegradation Under Controlled Composting Conditions
ASTM D5338 is the North American counterpart to ISO 14855, specifying an incubation temperature of 58 °C and requiring inoculum derived from well-aerated municipal or synthetic compost. It is widely referenced in certification schemes such as ASTM D6400 for compostable plastics sold in North America.
ISO 16929 and EN 14045 Pilot-Scale Disintegration Test
These standards assess the degree of disintegration of plastic materials under defined composting conditions in a pilot-scale reactor. Samples are exposed to a realistic thermophilic composting cycle for twelve weeks, after which the compost is sieved and the fragmentation of the material is quantified. A disintegration rate of at least 90% is generally required.
ISO 20200 and EN 14806 Laboratory-Scale Disintegration Test
These methods evaluate disintegration under laboratory-controlled composting conditions using a synthetic compost matrix, providing a repeatable screening tool for material developers before committing to pilot-scale trials.
Ecotoxicity Methods Following OECD and EN Guidelines
Compost generated during simulation trials may be subjected to plant growth tests in accordance with OECD 208 and Organisation-based terrestrial toxicity protocols, comparing germination rates and biomass yields against control compost to confirm the absence of phytotoxic effects.
A typical experimental workflow proceeds as follows:
- Sample homogenization, milling where appropriate, and characterization of dry solids, volatile solids, and carbon content.
- Preparation of mature, active compost inoculum with verification of its microbial activity through a cellulose pre-check.
- Charging of reactors with defined ratios of test material to inoculum, alongside blank, reference, and replicate vessels.
- Incubation at 58 °C with continuous aeration using carbon-dioxide-free air, maintaining moisture content within the specified window.
- Periodic measurement of evolved carbon dioxide, temperature, airflow, and pressure, with moisture and pH adjustments as needed.
- Calculation of cumulative biodegradation curves and application of validity criteria before reporting final results.
Applications
Composting simulation testing serves a wide range of industrial, regulatory, and scientific purposes:
- Industrial compostability certification against EN 13432, ASTM D6400, ISO 18606, and AS 5810, which are prerequisites for labeling products as compostable in many jurisdictions.
- Research and development of new biodegradable polymer formulations, plasticizers, and additives, where biodegradation curves guide iterative material optimization.
- Regulatory compliance and market access, including conformity demonstration under evolving packaging and single-use plastic regulations in Europe, North America, and the Asia-Pacific region.
- Verification of environmental marketing claims, providing scientifically defensible evidence for statements such as "industrially compostable" or "biodegradable under composting conditions."
- Quality control for converters and brand owners seeking to confirm that incoming resin lots or finished goods consistently meet declared biodegradability specifications.
- Academic research into polymer degradation mechanisms, microbial ecology of composting, and the environmental fate of bio-based materials.
- Support for accredited third-party laboratories and certification bodies in evaluating manufacturer submissions through standardized, reproducible test data.
FAQ
What biodegradation threshold must a material achieve to pass a composting simulation test?
Under EN 13432, ASTM D6400, and related schemes, a material must reach at least 90% biodegradation in absolute terms, or at least 90% of the biodegradation achieved by the cellulose reference, within a maximum incubation period of six months under industrial composting conditions.
How long does a complete composting simulation experiment take?
The biodegradation phase typically runs for 45 to 180 days depending on the material's degradation kinetics and the applicable standard. When disintegration, ecotoxicity, and chemical characterization are included as part of a full compostability assessment, the overall program may span six to nine months.
What is the difference between biodegradable and compostable?
Biodegradable describes a material's general capacity to be broken down by microorganisms, without specifying a timeframe or environment. Compostable is a stricter claim requiring demonstrated biodegradation, disintegration, and absence of ecotoxic effects within a defined composting environment and timeframe, verified through standards-based testing such as the experiments described in this article.
Can finished products be tested, or only raw polymer resins?
Both can be evaluated. Certification programs increasingly require testing of the final article as placed on the market, including any additives, inks, adhesives, and coatings, because these components can significantly influence overall biodegradation and disintegration performance.
Why is the test performed at 58 °C rather than ambient temperature?
A temperature of 58 °C represents the thermophilic phase of industrial composting, where microbial activity is highest and decomposition rates are accelerated. Testing under these conditions simulates real-world industrial composting facilities and produces results within a practical laboratory timeframe.
What happens if the reference cellulose fails to reach 70% biodegradation?
If the reference material does not achieve the required biodegradation level, the inoculum is considered insufficiently active and the test is deemed invalid. The experiment must then be repeated using a freshly prepared or reactivated compost inoculum before any conclusions can be drawn about the test material.