BIODEGRADABILITY ASSESSMENT OF ORGANIC SUBSTANCES AND POLYMERS Strategies to evaluate biodegradability: application to chlorinated herbicides S. Sanchis & A. M. Polo & M. Tobajas & J. J. Rodriguez & A. F. Mohedano Received: 28 June 2013 /Accepted: 30 August 2013 # Springer-Verlag Berlin Heidelberg 2013 Abstract The biodegradability of nitrochlorinated (diuron and atrazine) and chlorophenoxy herbicides (2,4-D and MCPA) has been studied through several bioassays using different testing times and biomass/substrate ratios. A fast biodegradability test using unacclimated activated sludge yielded no biodegradation of the herbicides in 24 h. The inherent biodegradability test gave degradation percentages of around 20–30 % for the nitrochlorinated herbicides and almost complete removal of the chlorophenoxy compounds. Long-term biodegradability assays were performed using se- quencing batch reactor (SBR) and sequencing batch mem- brane bioreactor (SB-MBR). Fixed concentrations of each herbicide below the corresponding EC 50 value for activated sludge were used (30 mg L -1 for diuron and atrazine and 50 mg L -1 for 2,4-D and MCPA). No signs of herbicide degradation appeared before 35 days in the case of diuron and atrazine and 21 days for 2,4-D, whereas MCPA was partially degraded since the early stages. Around 25–36 % degradation of the nitrochlorinated herbicides and 53–77 % of the chlorophenoxy ones was achieved after 180 and 135 days, respectively, in SBR, whereas complete disappearance of 2,4- D was reached after 80 days in SB-MBR. Keywords Biodegradability . Herbicides . Respirometry . SBR . SB-MBR . Zahn–Wellens Introduction In the last decades, the generation of new synthetic substances has led to increasing pollution problems due to their chemical structure, recalcitrance to biodegradation, or even toxicity to the microorganisms. The assessment of the toxicity and bio- degradability of these xenobiotics is of great interest in order to evaluate both their potential impact in the environment and the suitability of a biological treatment. Although toxicity and poor biodegradability are concepts sometimes used as equiv- alent in the literature, they are not necessarily linked, since some substances which are regarded as toxic compounds can be biodegraded at concentrations below their EC 50 (Polo et al. 2011). Among the existing bioassays for determining the biode- gradability of a certain pollutant are three types of standard- ized tests published by the Organization for the Economic Co- operation and Development (OECD): ready biodegradability (OECD 1993a), inherent biodegradability (OECD 1992), and simulation tests (OECD 1993b), which are based on the evaluation of overall parameters such as total organic carbon (TOC), chemical oxygen demand (COD), and biological ox- ygen demand (BOD). A comparative study analyzing the range of applicability of these assays was reported by Pagga (1997). Both ready and inherent biodegradability tests last for 28 days and differ in the inoculum concentration used. Ready biodegradability tests present the most restrictive operational conditions (Reuschenbach et al. 2003), since they are used to determine the possibility of degradation of a certain com- pound in the environment. In general, these assays could be useful to compare the biodegradability of different xenobi- otics, but they underestimate the degradation potential of the environmental systems. Inherent biodegradability assay (Zahn–Wellens test) is less restrictive, so it is commonly used for predicting the fate in a wastewater treatment plant (WWTP) (Lapertot et al. 2008; Ballesteros Martin et al. Responsible editor: Robert Duran S. Sanchis (*) : A. M. Polo : M. Tobajas : J. J. Rodriguez : A. F. Mohedano Sección Departamental de Ingeniería Química, Universidad Autónoma de Madrid, Carretera Madrid-Colmenar Viejo Km 12.700, 28049 Madrid, Spain e-mail: sonia.sanchis@uam.es Environ Sci Pollut Res DOI 10.1007/s11356-013-2130-y