Anaerobic biodegradation performance evaluation determines how completely plastics, organic chemicals, and packaging materials decompose in oxygen-free environments such as anaerobic digesters, landfills, and sewage sludge systems, by quantifying the biogas (methane and carbon dioxide) they generate. This article explains the governing ISO, ASTM, and OECD test standards, the types of samples evaluated, the measured parameters, laboratory procedures, and typical acceptance criteria used by accredited third-party laboratories. It serves as a practical technical reference for engineers, product developers, and quality managers planning or interpreting anaerobic degradation studies.
Technical Overview
Anaerobic biodegradation is the breakdown of organic substances by microorganisms in the absence of molecular oxygen. Unlike aerobic (composting) degradation, which yields carbon dioxide, water, and biomass, anaerobic degradation proceeds through hydrolysis, acidogenesis, acetogenesis, and methanogenesis, ultimately producing a biogas mixture composed primarily of methane (CH4) and carbon dioxide (CO2), together with a small fraction of new microbial biomass and residual solids.
Anaerobic degradation performance evaluation quantifies this process under controlled laboratory conditions. A test material is incubated with an anaerobic inoculum—typically derived from a municipal or industrial anaerobic digester, or from digested sewage sludge—at mesophilic temperature (commonly 35 ± 2 °C). The volume and composition of the biogas evolved over the test period are measured and compared with the theoretical gas production (ThGP or ThBiogas) calculated from the material's total organic carbon content. The resulting biodegradation percentage indicates how completely the carbon in the sample has been converted to biogas.
This evaluation is critical for several reasons. It supports verifiable environmental claims for biodegradable plastics and packaging, predicts material behavior in landfills and anaerobic digestion facilities, screens chemicals for environmental persistence, and estimates the methane yield (energy recovery potential) of organic feedstocks. The internationally recognized frameworks include ISO 11734, ISO 14853, ISO 13975, ISO 15985, ASTM D5511, ASTM D5526, and OECD Test Guideline 311.
Testing Samples
Biodegradable Plastics and Polymers
Polylactic acid (PLA), polyhydroxyalkanoates (PHA/PHB), polybutylene succinate (PBS/PBSA), polybutylene adipate terephthalate (PBAT), starch-based blends, cellulose films, and other bio-based or compostable polymer formulations are the most frequently tested materials. Test specimens may be supplied as powders, granules, films, or finished product cuttings to ensure adequate surface area for microbial attack.
Packaging Materials and Consumer Products
Food packaging, bags, cups, cutlery, closures, labels, and cushioning materials are evaluated to substantiate end-of-life claims under anaerobic disposal scenarios and to support compliance with packaging recovery frameworks such as EN 13432 and ISO 18606, where anaerobic treatability data may be required.
Organic Chemicals and Surfactants
Detergent ingredients, surfactants, solvents, and specialty organic compounds are screened for ultimate anaerobic biodegradability as part of environmental hazard assessment and chemical registration dossiers, typically following OECD 311 or ISO 11734.
Lubricants, Hydraulic Fluids, and Greases
Environmentally acceptable lubricants (EALs) and rapidly biodegradable fluids are tested to demonstrate performance in oxygen-limited soil and sediment compartments where accidental release may occur.
Textiles, Fibers, and Nonwovens
Natural and regenerated fibers, wet wipes, hygiene products, and geotextiles are assessed for disintegration and gas evolution in slurry or high-solids anaerobic systems.
Coatings, Adhesives, and Inks
Coating residues, adhesive layers, and printing inks applied to biodegradable substrates are tested to confirm they do not inhibit the anaerobic decomposition of the finished article.
Testing Items
Depending on the selected standard and the client's objectives, an anaerobic biodegradation study typically reports the following items:
- Degree of ultimate anaerobic biodegradation, expressed as a percentage of theoretical biogas production (% ThGP)
- Cumulative biogas volume and the complete biogas production curve over time
- Biogas composition, including methane (CH4) and carbon dioxide (CO2) content and the CH4/CO2 ratio
- Biodegradation kinetics, including lag phase duration, maximum biodegradation rate, and time to plateau
- Degree of disintegration, mass loss, and changes in physical appearance or molecular weight
- Dissolved organic carbon (DOC) removal, where the method includes liquor analysis
- Process monitoring parameters such as pH, volatile fatty acids, alkalinity, and volatile solids
- Inhibition screening, verified by confirming that the reference material and inoculum perform normally in the presence of the test substance
Testing Methods
ISO 14853 — Aqueous Anaerobic System for Plastics
This method determines the ultimate anaerobic biodegradation of plastic materials in a dilute aqueous medium inoculated with digested sludge, usually at 35 ± 2 °C. Biogas generation is monitored manometrically (pressure increase) or volumetrically over 30 to 90 days, and gas composition is analyzed by gas chromatography or infrared analysis. Biodegradation is calculated against the theoretical biogas potential derived from the carbon content of the polymer.
ISO 15985 — High-Solids Anaerobic Digestion
ISO 15985 evaluates plastics under high-solids anaerobic digestion conditions (typically above 20% total solids), which simulate industrial dry digestion and the active phase of landfill bioreactors. Gas evolution is collected and measured over an extended incubation, providing a realistic estimate of degradation in concentrated digestate environments.
ISO 13975 — Controlled Slurry Digestion
This standard assesses the ultimate anaerobic biodegradation of plastics in controlled slurry digestion systems at reduced solids concentrations, bridging the gap between dilute aqueous tests and high-solids digestion. It is well suited to materials destined for wet anaerobic treatment plants.
ISO 11734 — Organic Compounds in Digested Sludge
ISO 11734 is a screening method for the ultimate anaerobic biodegradability of organic compounds. The test substance is incubated with washed digested sludge in sealed vessels, and gas production is compared with both a blank control and a reference compound to establish the biodegradation level.
ASTM D5511 and ASTM D5526 — Anaerobic Digestion and Accelerated Landfill
ASTM D5511 determines the anaerobic biodegradation of plastic materials under high-solids anaerobic digestion conditions, while ASTM D5526 evaluates materials under accelerated landfill conditions with longer incubation and larger reactors. Both methods are widely used in North America for biodegradability claims related to landfill disposal.
OECD 311 — Anaerobic Biodegradability in Digested Sludge
OECD Test Guideline 311 measures gas production from chemicals incubated with digested sludge at low biomass concentration. A substance is generally considered ultimately biodegradable under anaerobic conditions when gas production reaches or exceeds approximately 60% of the theoretical value within the test period.
Common Laboratory Procedure and Validity Criteria
All methods follow a consistent workflow: preparation and pre-conditioning of the inoculum; determination of sample carbon content; parallel setup of test vessels, blanks (inoculum only), positive controls (microcrystalline cellulose), and, where relevant, abiotic and toxicity controls; incubation at controlled mesophilic or thermophilic temperature; periodic measurement of gas volume and composition; and final calculation of biodegradation percentage. A test is considered valid when the blank gas production remains low, the cellulose reference achieves at least 70% biodegradation, and the replicate coefficient of variation stays within the limits specified by the standard. While absolute thresholds vary by standard and certification scheme, a biodegradation level of 70% or more relative to cellulose within the test period is the commonly accepted benchmark indicating that a material is effectively mineralized under anaerobic conditions.
Applications
Anaerobic biodegradation performance data are used across many industries and decision contexts:
- Substantiation of biodegradable and eco-label claims for plastics, packaging, and disposables
- Assessment of material behavior in landfills and estimation of methane generation potential
- Evaluation of feedstock suitability and biogas yield for anaerobic digestion and energy recovery facilities
- Environmental fate and persistence screening for chemical registration and regulatory dossiers
- Verification that lubricants and functional fluids meet environmentally acceptable product specifications
- Research and development screening of new polymer formulations, additives, and processing aids
- Academic studies of polymer-microbe interactions and methanogenic degradation pathways
FAQ
What is the difference between aerobic and anaerobic biodegradation testing?
Aerobic tests, such as those based on ISO 14855 or ASTM D5338, measure oxygen consumption or CO2 evolution in composting environments rich in oxygen. Anaerobic tests exclude oxygen entirely and measure methane and CO2 production in sealed vessels. The two pathways involve different microbial communities, yield different end products, and can produce substantially different biodegradation percentages for the same material.
How long does an anaerobic biodegradation test take?
Typical incubation periods range from 30 to 90 days for aqueous and slurry methods such as ISO 14853, ISO 13975, and OECD 311, while high-solids and landfill-simulation methods such as ASTM D5526 may extend beyond 90 days or even up to one year. The test continues until the biogas production curve reaches a plateau.
What result is considered a pass?
Although each standard and certification scheme defines its own limits, a common acceptance criterion is biodegradation reaching 70% of the theoretical gas production, or 90% of the level achieved by the cellulose reference material, within the test duration. OECD 311 applies a lower threshold of approximately 60% for chemicals.
How much sample is required for testing?
Sample requirements depend on the method: dilute aqueous tests may need only a few grams of material, while high-solids reactor tests can require several hundred grams. Carbon content analysis is also needed for accurate calculation of theoretical biogas production.
Which standard should be selected for a specific product?
The choice depends on the disposal environment and claim being made. Plastics intended for anaerobic digestion facilities are usually tested to ISO 14853, ISO 13975, ISO 15985, or ASTM D5511; landfill-related claims typically rely on ASTM D5526; and organic chemicals are screened under OECD 311 or ISO 11734. Consulting an accredited third-party laboratory during the design of the study ensures that the method, controls, and acceptance criteria align with the intended regulatory or marketing purpose.