Standard testing carbon dioxide evolution

ISO 9439,1999, Water quality - Evaluation of ultimate aerobic biodegradability of organic compounds in an aqueous medium - Carbon dioxide evolution test International Standard ISO 9439 1999(E), International Oiganization for Standardization (ISO),... 

ISO 9439 2000(E), Water Quality - Evaluation of Ultimate Aerobic Biodegradability of Organic Compounds in Aqueous Medium - Carbon Dioxide Evolution Test, International Organization for Standardization, Geneve, Switzerland, 2000. 

The evolution of carbon dioxide was monitored by gas chromatograph (Hewlett-Packard model 5890) equipped with an HP thermal-conductivity detector and a Hayesep 100-120-mesh packed column (10 m X 3.2 mm). Helium was the carrier gas, and its flow rate was 28 mL/min. In each run, 0.5 mL of the gas mixture in the headspace was withdrawn from the test tube by using a pressure-lock gas syringe and injected into the GC column. The calibration curve was made by acidifying a known amount of potassium bicarbonate in the reaction tube under conditions similar to those of the corresponding experimental conditions. Standard carbon dioxide gas (Supelco) was used to confirm the formation of carbon dioxide. 

Notwithstanding the difficulties of testing in anaerobic environments, several laboratory methods, as indicated earlier, have been developed. These measure carbon dioxide and methane evolution. The ASTM standard was developed on the basis of work from Europe (28) and is widely used for these polymers (29). Several variants on this method reported for example by Barlaz and co-workers (30) for a variety of polymers including polyesters, acrylates, cellulosics, and others are used. Similarly, the earlier pioneering work of McCarthy and co-workers is also useful (31). 

Anaerobic tests generally follow biodegradation by measuring the increase in pressure and/or volume due to gas evolution, usually in combination with gas chromatographic analysis of the gas phase [83, 84]. Most aerobic standard tests apply continuous aeration the exit stream of air can be directly analysed continuously using a carbon dioxide monitor (usually infrared detectors) or titrimetrically after sorption in dilute alkali. The cumulative amount of carbon dioxide generated, expressed as a percentage of the theoretically expected value for total conversion to CO2, is a measure for the extent of mineralisation achieved. 

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