Anaerobic degradation testing is a laboratory-based evaluation that determines how completely and how quickly organic materials, plastics, and chemicals break down by microbial action in oxygen-free environments such as anaerobic digesters and landfills. By measuring biogas (methane and carbon dioxide) evolution against theoretical values, the test provides quantitative evidence of biodegradability for certification, regulatory compliance, and product development. This article explains the technical principles, applicable standards such as ISO 14853 and ASTM D5511, sample types, test procedures, and common applications.
Technical Overview
Anaerobic degradation testing (also referred to as anaerobic biodegradation testing) assesses the ultimate biodegradability of organic materials when microorganisms decompose them in the absence of oxygen. In these oxygen-free environments, consortia of anaerobic bacteria and archaea convert organic carbon primarily into biogas, a mixture of methane (CH4) and carbon dioxide (CO2), along with small amounts of biomass and soluble residues.
The test is performed in sealed serum bottles or anaerobic reactors containing a mineral medium and an inoculum, typically derived from digested municipal sewage sludge or actively operating anaerobic digesters. The test material is introduced as the sole or supplementary carbon source, and cumulative biogas production is monitored over the incubation period. The degree of biodegradation is calculated as the ratio of measured biogas to the theoretical biogas production (ThBP), which is derived from the carbon content of the test material.
Two principal test configurations exist: low-solids aqueous systems, which simulate anaerobic sludge digestion, and high-solids systems, which simulate accelerated landfill or dry anaerobic digestion conditions. Validity of the test is confirmed through reference materials (such as cellulose, which must typically exceed 70% biodegradation), blank controls, and inhibition controls. Incubation temperatures are generally mesophilic (35 °C ± 2 °C), although thermophilic conditions (approximately 52–55 °C) may be specified for certain high-solids methods.
Testing Samples
Plastic Materials and Biopolymers
Biodegradable plastics such as polylactic acid (PLA), polyhydroxyalkanoates (PHA), polybutylene succinate (PBS), polybutylene adipate terephthalate (PBAT), and starch-based blends are frequently evaluated to quantify their anaerobic biodegradation performance in digestion or landfill scenarios.
Packaging Materials and Films
Flexible films, rigid containers, coatings, and multilayer packaging structures are tested to support environmental claims, ecolabel applications, and end-of-life assessments for packaging intended to enter anaerobic treatment streams.
Chemicals and Organic Compounds
Surfactants, detergents, lubricants, solvents, and other organic substances are screened for ultimate anaerobic biodegradability as part of environmental hazard and risk assessment programs.
Textiles, Fibers, and Nonwovens
Natural fibers, regenerated cellulose fibers, and biobased synthetic textiles are tested to evaluate degradation behavior after disposal in oxygen-limited environments.
Agricultural and Consumer Products
Mulch films, seed coatings, wet wipes, disposable hygiene products, and other items with potential landfill exposure are commonly submitted for anaerobic biodegradation evaluation.
Testing Items
Typical parameters determined during an anaerobic degradation test include:
- Ultimate anaerobic biodegradability, expressed as the percentage of theoretical biogas production
- Cumulative biogas volume and production rate over time
- Methane (CH4) and carbon dioxide (CO2) composition of evolved biogas
- Biochemical methane potential (BMP) of the test material
- Dissolved inorganic carbon (DIC) in the liquid phase for aqueous methods
- Disintegration and mass loss of the material after exposure
- pH, volatile fatty acids, and inhibition assessment of the digestion system
Testing Methods
Anaerobic degradation testing is conducted according to internationally recognized standards published by ISO, ASTM International, OECD, and their national adoptions. The most commonly applied methods include:
- ISO 11734 — Water quality; evaluation of the ultimate anaerobic biodegradability of organic compounds in digested sludge by measurement of biogas production
- ISO 14853 — Plastics; determination of the ultimate anaerobic biodegradability of plastic materials in an aqueous system by measurement of biogas production
- ISO 15985 — Plastics; determination of the ultimate anaerobic biodegradability under high-solids anaerobic-digestion conditions by measurement of biogas production
- ISO 13975 — Plastics; determination of the ultimate anaerobic biodegradability in controlled slurry digestion systems by measurement of biogas production
- ASTM D5210 — Determining the anaerobic biodegradation of plastic materials in the presence of municipal sewage sludge
- ASTM D5511 — Determining anaerobic biodegradation of plastic materials under high-solids anaerobic-digestion conditions
- ASTM D5526 — Determining anaerobic biodegradation of plastic materials under accelerated landfill conditions
- OECD 311 — Anaerobic biodegradability of organic compounds in digested sludge
A standard test sequence involves preparing the inoculum, pre-conditioning it if required, dispensing defined amounts of test material into replicate vessels, incubating under controlled temperature with continuous or periodic agitation, and measuring pressure increase or gas volume at defined intervals. Gas composition is verified by gas chromatography or infrared analysis. Tests run until a plateau in biogas production is reached or for the fixed duration specified by the method, typically 30 to 60 days or longer for slow-degrading materials. Many national standards, including GB/T series adoptions, are technically equivalent to the ISO methods above.
Applications
Anaerobic degradation test data are used across multiple industries and regulatory contexts:
- Supporting biodegradable and compostable product certifications and ecolabel applications that include anaerobic digestion pathways
- Regulatory compliance demonstration for packaging, chemicals, and plastic products in international markets
- Research and development of new biopolymers, formulations, and additives with improved end-of-life performance
- Predicting material behavior in landfills and municipal anaerobic digestion facilities
- Environmental risk assessment and chemical registration submissions
- Comparative benchmarking of competing materials under standardized, reproducible conditions
- Substantiating environmental marketing claims with scientifically defensible laboratory evidence
FAQ
What is the difference between aerobic and anaerobic degradation testing?
Aerobic testing measures mineralization to carbon dioxide in the presence of oxygen, simulating composting or soil environments. Anaerobic testing measures conversion to methane and carbon dioxide in oxygen-free systems, simulating anaerobic digesters, landfills, and anoxic sediments. The inocula, apparatus, measured gases, and calculation basis all differ between the two approaches.
How is the biodegradation percentage calculated?
The measured cumulative biogas production (CH4 plus CO2, and dissolved inorganic carbon where applicable) from the test vessel is corrected for blank inoculum activity and divided by the theoretical biogas production calculated from the material's total organic carbon content. The result is expressed as a percentage of ultimate anaerobic biodegradation.
How long does an anaerobic degradation test take?
Most methods run for 30 to 60 days, or until biogas production reaches a plateau. Slow-degrading materials, accelerated landfill simulations, and thermophilic high-solids studies may extend to several months. Incubation typically occurs at 35 °C ± 2 °C under mesophilic conditions.
What validity criteria must a test satisfy?
A test is considered valid when the cellulose reference material achieves more than 70% biodegradation, blank biogas production remains low and stable, replicate vessels show acceptable agreement, and system pH remains within the range supporting healthy methanogenic activity.
How much sample is required for testing?
Generally, 10 to 100 grams of material is sufficient depending on the selected method and the number of replicates, though specific requirements vary with reactor volume, solids content, and target concentration. Materials are usually tested in powdered, granulated, or film form to ensure representative surface area.
Does a high anaerobic biodegradation result guarantee degradation in a real landfill?
No. Laboratory tests use optimized inocula, controlled temperature, and finely divided samples, so results represent intrinsic biodegradation potential rather than field performance. Actual landfill degradation depends on moisture, pH, temperature, microbial community, and material geometry. Test reports should always be interpreted together with the stated conditions and limitations of the applied standard.