Anaerobic biodegradability testing

At AIMPLAS, we perform tests to evaluate the performance of plastic materials under anaerobic biodegradation conditions by simulating the conditions of anaerobic reactors and determining whether or not a plastic is biodegradable under these conditions. We also optimize anaerobic biodegradation processes by adjusting the nutrients needed to improve biogas production and the biodegradation of polymers.

What is anaerobic biodegradation?

Because sustainability and environmental pollution are growing concerns in society, replacing conventional plastic materials with biodegradable plastics may help reduce pollution in different ecosystems, thus improving waste management.

Biodegradation of plastic materials depends on the environment where the material is broken down. A material can be biodegradable in a medium such as compost, but not in soil because of the different conditions of each medium, such as temperature, the absence or presence of oxygen, and the density of microorganisms.

Anaerobic digesters are widely used in sectors such as the cattle, agriculture and wastewater industries. Plastic materials can end up in digesters, so it’s necessary to know how these materials perform under representative anaerobic digestion conditions.

Anaerobic digestion

In anaerobic digestion, organic matter is broken down under anaerobic conditions (i.e. in the absence of oxygen) through the action of different microorganisms.

Anaerobic digesters can work at mesophilic conditions (37°C) or thermophilic conditions (52°C). Digesters under thermophilic conditions are more efficient in terms of degradation of organic matter and biogas production.

The products obtained from degradation include new biomass, as well as biogas, a mixture of methane (CH₄), carbon dioxide (CO₂) and traces of hydrogen sulphide, which has great potential for producing electricity and heat.

Anaerobic digestion stages

The process is divided into four stages:

Hydrolysis, in which microorganisms secrete extracellular enzymes into the medium to break down long-chain molecules so they can be assimilated by other microorganisms.
Acidogenesis, in which acidogenic microorganisms transform shorter chain molecules into volatile fatty acids such as propionic, acetic and valeric acid.
Acetogenesis, in which volatile fatty acids are transformed into acetate.
Methanogenesis, in which methanogenic microorganisms use acetic acid, dihydrogen and carbon dioxide to obtain methane and carbon dioxide as end products.

Standards for evaluating anaerobic biodegradation

Different standards have been issued to evaluate the performance of plastic materials under anaerobic biodegradation conditions, such as ASTM D5511 and its European equivalent, UNE-EN ISO 15985, in which the biodegradation of plastics is tested under optimal anaerobic conditions.

The test is designed to be performed in a short period of time (15 to 30 days) since it aims to imitate anaerobic digesters, which do not usually work with retention times of more than 30 days.

Biodegradation monitoring is carried out by measuring the production of biogas during the test. The amount produced can be used to calculate the amount of organic carbon released as biogas, as well as the biodegradation rate during the test.