Water Research 37 (2003) 1571–1582 A critical comparison of respirometric biodegradation tests based on OECD 301 and related test methods Peter Reuschenbach a , Udo Pagga a , Uwe Strotmann b, * a BASF Aktiengesellschaft, Laboratory of Ecological Studies GV/TC Z570, D-67056 Ludwigshafen, Germany b Department of Environmental Technology, Fachhochschule Gelsenkirchen, University of Applied Sciences, Neidenburger Str. 10, D-45877 Gelsenkirchen, Germany Received 8 January 2002; received in revised form 14 June 2002; accepted 22 October 2002 Abstract Biodegradation studies of organic compounds in the aquatic environment gain important information for the final fate of chemicals in the environment. A decisive role play tests for ready biodegradability (OECD 301) and in this context, the respirometric test (OECD 301F). Two different respirometric systems (Oxitops and Sapromats) were compared and in two of ten cases (diethylene glycol and 2-ethylhexylacrylate) differences were observed indicating that thetestsystemsarenotalwaysequivalent.For2-ethylhexylacrylateandcyclohexanonewecouldnotstatedifferencesin the extent of biodegradation with a municipal and industrial inoculum whereas for cyclohexanone the degradation rate was faster with a municipal inoculum. Allylthiourea (ATU) proved to be an effective inhibitor of nitrification processes and did not affect the heterotrophic biodegradation activity. Modelling of biodegradation processes could be successfully performed with a first-order and a modified logistic plot. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Biodegradation; Mathematical modelling; OECD 301 tests; Ready biodegradability; Respirometry 1. Introduction Over past 40 years, the fate of chemical pollutions in the environment has become an important issue. Methods for investigating and monitoring biodegrada- tion processes have been developed [1]. Most efforts haveconcentratedonthefateofchemicalsintheaquatic environment, especially in wastewater treatment pro- cesses. Although the elimination of chemicals from the aquatic environment may occur by abiotic processes such as adsorption, hydrolysis and photolysis, the complete conversion of organic chemicals to inorganic products is due to microbial biodegradation processes. During these ultimate biodegradation processes the organic matter is converted into CO 2 ,H 2 O, inorganic salts, microbial biomass and organic metabolites [2]. Nearly20yearsago,in1981theOECDfirstpublished its guidelines for testing the biodegradation of chemicals which were updated 1993 [3]. In the mean time, also a number of biodegradation standards of the Interna- tional Organisation of Standardisation (ISO) [4], which are to some extent similar to the OECD guidelines, have been created. An overview gives ISO 15462 and Pagga [5]. In the OECD guidelines biodegradation tests are divided into three principal categories: tests for ready biodegradability, tests for inherent biodegradability and simulation tests. The most important tests for practical use are the tests for ready biodegradability. These are the most stringent tests, offering only limited opportu- nities for biodegradation and acclimatisation of the inoculum. The ready biodegradability tests are based on the removal of organic compounds measured as dissolved *Corresponding author. Tel.: +49-209-9596-142; fax: +49- 209-9596-144. E-mail address: uwe.strotmann@fh-gelsenkirchen.de (U. Strotmann). 0043-1354/03/$-see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII:S0043-1354(02)00528-6