Novel device for aerobic biodegradability testing of natural and/or synthetic polymers, copolymers or mixtures in an aqueous medium.

Anticipating a market opportunity in the field of eco-friendly products, a number of companies have marketed materials purported to be biodegradable (e.g. thermoplastic starch products; starch synthetic aliphatic polyester blends etc.)

As any marketable plastic products, these new ones must also meet the performance requirements as well as normative criteria set by the International Standards Organisation (ISO) standards by which European biodegradable plastics are currently assessed.

Therefore, our aim was to develop a device suitable for different tests and able to function with a high degree of autonomy that limits labour costs. It was also very important to reach a higher scientific accuracy through auto-calibration and continuous validation.

Tests in this device can currently be run under the following ISO standards:
ISO 14855 (aerobic biodegradation under composting conditions)
ISO 14852 (aerobic biodegradation in an aqueous medium)

Both standards specify methods to measure the amount of CO2 evolved for the determination of the degree of aerobic biodegradability of polymers.

The Umic Lab I (fig. 1) is an automatic measurement system monitoring various factors such as CO2, temperature, relative humidity and air flow.
The device can hold up to 18 vessels of 3L total volume which are pressure and temperature resistant and all the connections are air tight.
The use of a closed bed reduces energy requirement to maintain a stable temperature.
Each vessel is made independent from the other vessels by its own pressure regulator and, in the case of ISO 14852, with its own stirring plate.
Gas switching system, sensor array, pressure and flow regulation systems are installed inside the incubator with the vessels avoiding by this way any condensation problems.
The control and monitoring software has been developed by Wetlands in the Labview environment (NI). Data are automatically transferred and can be treated easily by common software like Excel®.

The conditions used in this equipment are designed to determine the potential biodegradability of polymers or give an indication of their biodegradability in natural environments.

Method – ISO 14852

The vessels contain a test mixture with a working volume of 2L. The test mixture contains an inorganic medium, the organic test material as the sole source of carbon and energy with a concentration between 100 mg/L and 2000 mg/L of organic carbon, and activated sludge as the inoculum containing about 10-6 cfu/mL. Cellulose a well defined biodegradable polymer is used as a positive control with comparable TOC, form and size of the test sample. The mixture is constantly agitated using magnetic stirrers and aerated with air at a constant flow rate of 400 mL/min over a period of time depending on the biodegradation kinetics. The CO2 evolved during the microbial degradation is determined by the CO2 analyser with an IR detector. Each experimental analysis is performed in duplicate as per the guidelines. The test is considered complete (max period 6 months) when a constant level of CO2 is attained.

Initial data (fig. 2) obtained from the system have shown significant amount of CO2 produced in the positive control (cellulose) compared to the test and blank in the first three weeks of the experiment. The test and the blank vessels have started producing CO2 but not in a significant amount compared to the positive control. The data is also comparable to the visual changes observed (fig. 3 & 4) in the vessels, whereby the control vessels have turned from white to brown in colour indicative of microbial growth. The amount of evaporation observed in the vessels is minimal which limits the intervention during the running of the experiment.

The device has shown to function autonomously with limited intervention. Sensor integrities and validation values were maintained throughout the period. Values measured showed a high degree of accuracy and small variability was observed between vessels.

This device therefore can be used by both research centres and testing & certification laboratories for biodegradability testing.