Vol. 15, No.1 (January 2017) – Preface
Understanding the Biodegradation of LAS in the Absence of Oxygen
Does LAS degrade under anoxic (no oxygen) conditions? This question has been asked for many years.For the majority of that time, the answer has typically been negative. This position has been based on thepoor performance of LAS in standard OECD 311 guideline studies (OECD 2006). The OECD guideline is based on the ISO standard 11734 (ISO 1995) which in turn was developed from the method described in ECETOC Technical Report No. 28 (ECETOC 1988). OECD 311 is considered a screening test and conducted using a high concentration of the test material. Biodegradation is usually not determined by chemical specific measurements, but rather though non-specific measurements such as total in organic carbon, carbon dioxide and methane production. The use of OECD 311 as the sole determination of anaerobic biodegradation has been criticized by a number of researchers. Recently, Bendt and Willing(2014) described the guideline as not being realistic especially in the case of surfactants. Two of their main critiques are that the guideline uses a low microbial density and the test material is the only carbon source available to the microbes both conditions of which do not occur in a normal wastewater treatment plant (WWTP) anaerobic digester.
While the norm over the years has been that LAS will not degrade anaerobically, research conducted over the last two decades has challenged that position. By using advanced and innovative methods, LASis showing the potential to be anaerobically degraded under certain conditions.
While articles investigating the topic of anaerobic biodegradation of LAS have been presented in anumber of past issues of the CLER Review (e.g. Volume 5, 1999; Volume 6, 2000 and Volume 11, 2007),this issue is dedicated to reviewing LAS anaerobic biodegradation research.
First, an article by Corada-Fernández and others from the University of Cadiz in Spain provides a review of the anaerobic biodegradation of LAS in marine sediments. As evidence of in-situ anaerobicbiodegradation, the authors cite the presence of LAS metabolites (sulfophenyl carboxylic acid (SPCs)) found in core samples at anoxic depths of marine sediments. Many of the sediments showed a trend of increasing SPC concentration with increasing depth while the concentration of LAS was correspondingly decreasing. Based on the results from field studies, the authors then describe degradation pathway for LAS which occurs under anoxic conditions.
The second article written by the Technical Director of CLER, John Heinze, is a comprehensive review ofthe results from all past studies using anaerobic bio-reactors including Batch Reactors, Up flow AnaerobicSludge Bed (UASB) Reactors, Continuous Stirred Tank Reactors (CSTR), Horizontal Anaerobic Immobilized Bed (HAIB) Reactors, Fluidized Biomass Reactors (FBR), Anaerobic Sequencing Batch Reactors (ASBR) and Expanded Granular Sludge Bed (EGSB) Reactors. Based on the author’s review of the studies, LAS can show high levels (>85%) of primary biodegradation (as measured by disappearance of LAS) with several of the reactor designs and conditions.
Despite the Scientific Committee on Health and Environmental Risks (SCHER) opinion in 2005 (SCHER2005) and confirmed in 2008 (SCHER 2008) that “poor biodegradability under anaerobic conditions is not expected to produce substantial modifications in the risk for freshwater ecosystems as the surfactant removal in the WWTP seems to be regulated by its aerobic biodegradability,” eco-labeling programs such as EU Ecolabel and Nordic Swan insists upon good anaerobic biodegradation. As such, it is hoped that the breadth and scope of anaerobic biodegradation research on LAS is taken into consideration for acceptability for eco-labeling.
Ricky A. Stackhouse
Council for LAB/LAS Environmental Research (CLER)
Bendt, T.,Willing, A. (2012) A New Method to Determine the Anaerobic Degradability of Surfactants: theAnBUSDiC Test. Environmental Sciences Europe 24: 38.
ECETOC (1988) European Chemical Industry Ecology and Toxicology Centre, Technical Report No. 28 –Evaluation of Anaerobic Biodegradation.
ISO (1995) International Organization for Standardization, ISO 11 734 Water Quality – Evaluation of theUltimate Anaerobic Biodegradation of Organic Compounds in Digested Sludge – Method by Measurementof the Biogas Production.
OECD (2006) Organization for Economic Cooperation and Development, Guideline for the Testing ofChemicals (2006) 311: Anaerobic Biodegradability of Organic Compounds in Digested Sludge: ByMeasurement of Gas Production, Paris.
SCHER (2005) Scientific Committee on Health and Environmental Risks, SCHER scientific opinion on“The Environmental Risk Assessment of non-Biodegradable Detergent Surfactants under AnaerobicCondition”, 25 November 2005.
SCHER (2008) Scientific Committee on Health and Environmental Risks, SCHER scientific opinion on “Anaerobic Degradation of Surfactants and Biodegradation of Non Surfactant Organic Ingredients”. 17 November 2008.