Anaerobic Biodegradability Assessment: Standards, Methods, and Applications

Anaerobic biodegradability assessment is a laboratory-based evaluation that quantifies how completely organic materials, such as biodegradable plastics, packaging, chemicals, and organic waste, are decomposed by microorganisms in oxygen-free environments, producing methane and carbon dioxide as biogas. Guided by internationally recognized standards such as ISO 14853, ISO 15985, ISO 11734, ASTM D5210, and ASTM D5511, this testing service provides essential data for compostability certification, environmental claim substantiation, anaerobic digestion optimization, and regulatory compliance.

Technical Overview

Anaerobic biodegradability assessment measures the extent to which microorganisms in oxygen-free environments can break down an organic material into methane (CH4), carbon dioxide (CO2), water, and new microbial biomass. Unlike aerobic biodegradation, which relies on oxygen respiration, the anaerobic process proceeds through a sequential consortium of reactions: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. The final gaseous products, methane and carbon dioxide, serve as direct quantitative indicators of mineralization.

In a typical test, the material is incubated with an anaerobic inoculum (usually digested sludge from a wastewater treatment plant or an anaerobic digester) in sealed vessels under mesophilic conditions, generally around 35°C. The biogas volume and composition are monitored over time, and the degree of biodegradation is calculated as the percentage of theoretical biogas production (ThGP) or as a carbon balance converting the organic carbon of the test material into CH4 and CO2, including dissolved inorganic carbon in the liquid phase.

This assessment is critical for industries developing biodegradable polymers, compostable packaging, environmentally safe chemicals, and for facilities operating anaerobic digesters. It supports certification schemes such as EN 13432 and ASTM D6400, validates marketing claims for biodegradability, and helps predict material behavior in landfills, anaerobic digesters, and sludge treatment systems. Accredited third-party laboratories routinely perform these tests under Good Laboratory Practice (GLP) principles to ensure data reliability and regulatory acceptance.

Testing Samples

Biodegradable Plastics and Polymers

This category includes PLA (polylactic acid), PHA/PHB (polyhydroxyalkanoates), PBS, PBSA, PBAT, starch-based blends, cellulose derivatives, and bio-based composite materials. Samples may be supplied as resins, granules, powders, films, sheets, fibers, or finished molded products, and are typically reduced to a defined particle size to ensure homogeneous and reproducible degradation.

Packaging and Consumer Products

Food packaging, shopping bags, refuse bags, disposable cutlery, plates, cups, coffee capsules, agricultural mulch films, paperboard coatings, adhesives, and printing inks are frequently evaluated to verify their compatibility with anaerobic digestion or landfill end-of-life scenarios and to support compostability certification.

Chemicals, Surfactants, and Formulations

Organic compounds such as surfactants, detergent ingredients, lubricants, cosmetic and personal care ingredients, pharmaceuticals, and agrochemical intermediates are screened for ultimate anaerobic biodegradability as part of environmental fate assessment, chemical registration, and ecolabel documentation.

Organic Waste and Digestion Feedstock

Food waste, sewage sludge, animal manure, agricultural residues, energy crops, and other biomass substrates are tested to determine their biochemical methane potential (BMP), which informs digester design, process optimization, and energy recovery projections.

Testing Items

The core scope of an anaerobic biodegradability evaluation typically covers the following parameters:

• Ultimate anaerobic biodegradability, expressed as percent biodegradation relative to theoretical gas production or total organic carbon
• Cumulative biogas volume and pressure evolution over the incubation period
• Biogas composition analysis, quantifying CH4 and CO2 by gas chromatography (GC-TCD or GC-FID with methanizer)
• Dissolved inorganic carbon (DIC) determination in the liquid phase for complete carbon balance
• Theoretical gas potential (ThGP) calculated from elemental analysis (C, H, O), COD, or TOC data
• Total solids (TS) and volatile solids (VS) characterization of both sample and inoculum
• Biodegradation kinetics, including lag phase, degradation rate, and plateau identification
• Optional disintegration assessment, mass loss measurement, and residue analysis
• Supporting monitoring parameters such as pH, volatile fatty acids (VFA), and ammonia to confirm process stability

Testing Methods

ISO 14853 — Aqueous Low-Solids Anaerobic System

ISO 14853 determines the ultimate anaerobic biodegradability of plastic materials in an aqueous medium inoculated with digested sludge. Test vessels are incubated at 35 ± 2°C, and the degree of biodegradation is calculated from the carbon converted to CH4 and CO2, including dissolved inorganic carbon. The test is valid when the reference material, microcrystalline cellulose, achieves a biodegradation level above 70%.

ISO 15985 / ASTM D5511 — High-Solids Anaerobic Digestion

These methods evaluate biodegradation under high-solids, static anaerobic digestion conditions that simulate dry digestion or accelerated landfill environments. Samples are mixed with dewatered digestate, incubated at approximately 35°C, and the generated methane and carbon dioxide are quantified to compute the percentage of carbon mineralized. This route is widely used for biodegradable plastics intended for waste treatment through dry anaerobic digestion.

ASTM D5210 — Municipal Sewage Sludge Method

ASTM D5210 measures the anaerobic biodegradation of plastic materials in the presence of municipal sewage sludge. The extent of biodegradation is determined by monitoring the conversion of sample carbon into carbon dioxide and methane, providing a practical simulation of sludge digestion conditions.

ISO 11734 / OECD 311 — Organic Compounds in Digested Sludge

ISO 11734 addresses water quality evaluation of the ultimate anaerobic biodegradability of organic compounds in digested sludge by measuring biogas production, while OECD Guideline 311 provides a harmonized framework for measuring gas production from chemicals in digested sludge, commonly applied in environmental hazard profiling and chemical safety dossiers.

General Test Workflow

All methods follow a consistent quality-controlled design: the sample is characterized and prepared to the required particle size; inoculum is collected from a actively running anaerobic digester and pre-conditioned; test, blank (inoculum only), and reference (cellulose or another positive control) vessels are prepared in replicate; vessels are incubated with periodic gas volume and composition measurement; and results are corrected for blank activity, checked against validity criteria, and reported with full carbon balance documentation.

Applications

• Supporting compostability and biodegradability certification programs, including EN 13432, ASTM D6400, and ISO 17088, where anaerobic digestion data may complement aerobic composting results
• Research and development of biodegradable polymers, allowing formulation screening, additive evaluation, and comparative performance benchmarking
• Substantiation of environmental marketing claims and prevention of greenwashing through objective, standards-based evidence
• Environmental risk assessment for chemicals under frameworks such as REACH and OECD screening programs
• Biochemical methane potential (BMP) testing to optimize feedstock selection and process design for anaerobic digestion plants
• Landfill gas generation modeling and evaluation of material behavior in oxygen-limited disposal environments
• Municipal solid waste policy compliance, including requirements for biodegradable bags, foodservice ware, and organic waste diversion programs
• Quality control and lot release testing for biopolymer resin producers and converters

FAQ

What is the difference between aerobic and anaerobic biodegradability testing?

Aerobic testing measures mineralization to CO2 in the presence of oxygen, usually under composting or aqueous conditions. Anaerobic testing measures conversion to CH4 and CO2 in oxygen-free conditions. The two pathways involve different microbial communities and yield different products, and many certification programs request both datasets to characterize a material across realistic end-of-life scenarios.

How long does an anaerobic biodegradation test take?

Most tests run between 30 and 60 days, continuing until biodegradation reaches a plateau as required by the applicable standard. Slow-degrading materials, thermophilic variants, or complex multi-layer products may require extended incubation to reach a definitive endpoint.

What is considered a passing result?

Acceptance thresholds depend on the framework. For test validity, reference materials such as cellulose must typically exceed 70% biodegradation. As a general benchmark, results at or above 60% indicate substantial biodegradability, while composting-oriented certification schemes under EN 13432 and ASTM D6400 require at least 90% disintegration and biodegradation, for which the anaerobic test data serve as supporting evidence.

How do I choose between ISO 14853 and ISO 15985?

Select ISO 14853 when the intended environment is a wet, low-solids anaerobic digester or sludge treatment system. Select ISO 15985 or ASTM D5511 when the material is destined for high-solids dry digestion or landfill-like conditions. For soluble chemicals and wastewater-relevant substances, ISO 11734 or OECD 311 is generally more appropriate.

What sample form and quantity are required?

Laboratories typically request 20 to 100 grams of material, preferably as powder, granules, or small film pieces with particle size below approximately 5 mm, along with information on composition and organic carbon content. Elemental analysis or TOC data are needed to calculate the theoretical gas potential accurately.

Can laboratory results predict real-world behavior?

Standardized anaerobic tests represent optimized, controlled laboratory conditions and provide a rigorous comparative basis. Actual degradation rates in landfills or digesters may vary with temperature, moisture, microbial community, and retention time, so results are best interpreted as a scientifically standardized measure of intrinsic biodegradation potential rather than an exact field prediction.