Measurement of biodegradability

The development of reliable measures of potential biodegradability is a key requirement in order to identify the potential environmental impacts of the increasing use of more sophisticated organic compounds. 

In essence, the test procedure requires introducing a sample of the organic material into a healthy bacterial suspension under controlled conditions and measuring the time or rate at which a suitable end point is achieved. 

As with all biological systems, controlling variables to give reproducible results requires a lot of standardisation. A detailed background of the development of biodegradability testing in relation to surfactants is given in Karsa and Porter [5], Painter [6] and Swisher [7]. 

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Tag K, Lehmann M, Chan C, Renneberg R, Riedel K, Kunze G (2000) Measurement of biodegradable substances with a mycelia-sensor based on the salt tolerant yeast Arxula adeninivorans LS3. Sensors Actuators B67 142-148... 

Renneberg R, Kwong WK, Chan C, Kunze G, Riedel K (1999) Rapid measurement of biodegradable substances in water using novel microbial sensors. In Advances in biosensors, JAS Press, pp 195-213... 

Measurement of Biodegradation. Numerous studies have documented the aerobic biodegradability of various AS compounds (see ref. 12). Most of these studies used methylene blue active substance (MBAS) and other colorimetric determinations, change in surface tension, foaming capacity, and sulfate formation as an indication of primary AS degradation. 

WPCF (Water Pollution Control Federation - Biodegradability Subcommittee). 1967. Required characteristics and measurement of biodegradability. ]. Water Pollut. Control Fed. 39 1232-1235. 

To obtain a consistent data set for comparison of biodegradability of different surfactants, we compiled first-order rate constants k for disappearance of surfactants measured in river water obtained in river die-away studies, as quantitative measures of biodegradability. In our comparison, we assumed that the solids concentrations in the different experiment were equally low and that surfactant disappearance therefore can be ascribed to biodegradation. We also assumed that the variation in [Cbio] in the different studies is negligible. The results are discussed in the following sections. 

Ribas, F., J. Frias, F. Ventura, L. Mohedano, and F. Lucena. 1995. Assessment of biological activity and fate of organic compounds in a reactor for the measurement of biodegradable organic carbon in water. Journal of Applied Bacteriology 79 558-568. 

Kaplan, L. A., F. Ribas, J. C. Joret, C. Volk, J. Frias, and F. Lucena. 1996. Measurement of Biodegradable Organic Matter with Biofilm Reactors. AWWA Research Foundation, Denver. 

As SCOUR is an alternative measure of biodegradable load, it has been illustrated in fig 7 for the same simulation. The SCOUR profile (fig 8) is closely related to the DO profile (fig 6). The latter, however, is directly measurable, and the oxygen transfer coefficient does not have to be estimated. 

Cozzarelli 1. M., Eganhouse R. P., Godsy E. M., WarrenE., and Bekins B. A. (2001b) Measurement of biodegradation of hydrocarbons in situ under different redox conditions. In 20th Int. Mtg of Organic Geochemistry, 10-14 Sept. 2001, 2pp. 

Figure 14.8 Experimental measurement of biodegradability using International Standards. (Reproduced with permission from [1], Copyright 2012, American Chemical society.)...

In spite of being developed for the measurement of biodegradation, ISO 14855 has also been proposed and used for the evaluation of disintegration. Nonetheless, this method is less suitable as it has been demonstrated to give false positive and several false negative results for disintegration. 

C. Chan, M. Lehmann, K. Tag, K.M. Lung, G. Kunze, K. Reidel, B. Gruendig, and R. Rermeberg. Measurement of biodegradable substances using the salt-tolerant yeast Arxula adeninivorans for a microbial sensor immobilized with poly(carbamoyl)sulfonate (PCS). Part I. Construction and characterisation of the microbial sensor. Biosens. Bioelectron., 14 131-138,1999. 

The obvious direct measure of biodegradation of a polymer will be the loss of polymer from the system. This measure essentially assesses the early stage of biodegradation when a high polymer material is broken down into a low polymer, an oligomer or a non-polymeric product. 

The percent conversion of the carbon in the polymer into carbon dioxide is a good measure of biodegradation of a polymer. In the case of an anaerobic process, methane or some other product might be measured in place of (or in addition to) carbon dioxide. 

Most norms and standards are dealing with a testing procedure, e.g., measurement of biodegradation by following a certain parameter in a given environment. In such cases, the main purpose of the norm is to harmonise test conditions, e.g., temperature, nutrients, pH, concentration of test substance, concentration of inoculum, etc. Some norms however are related to required properties for a certain characteristic and the necessary criteria and pass levels. Typical examples are the compostability norms, which comprise several aspects for which each specific criteria and pass levels are defined. 

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