OECD Guidelines Test No.311

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Anaerobic biodegradability of organic compounds in digested sludge

OECD 311 test guideline, which is based on ISO 11734 (1995), describes a screening method for the evaluation of potential anaerobic biodegradability of organic chemicals under specific conditions, i.e., in an anaerobic digester at a given time and range of concentration of microorganisms. Because a diluted sludge is used with a relatively high concentration of test substance and the duration of the test typically is longer than the retention time in anaerobic digesters, the conditions of the test do not necessarily correspond to the conditions in anaerobic digesters, nor is it applicable for the assessment of anaerobic biodegradability of organic chemicals under different environmental conditions. Sludge is exposed to the test substance for up to 60 days, which is longer than the normal sludge retention time (25 to 30 days) in anaerobic digesters, though at industrial sites retention times may be much longer. Complete anaerobic biodegradation can be assumed to occur if 75%-80% of theoretical gas production is achieved. The high ratios of chemical to biomass used in these tests mean that a chemical which passes is more likely to be degraded in an anaerobic digester. Additionally, substances which fail to be converted to gas in the test may not necessarily persist at more environmentally realistic substance-to-biomass ratios.

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Read more about OECD Test No. 311 at oecd-ilibrary.org.

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