Effect of ethoxylate number and alkyl chain length on the pathway and kinetics of linear alcohol ethoxylate biodegradation in activated sludge

Abstract

Batch activated-sludge die-away studies were conducted with various pure homologs to determine the effect of ethoxylate number and alkyl chain length on the kinetics of primary and ultimate biodegradation of linear alcohol ethoxylates. The 14C-(ethoxylate) homologs C14E1, C14E3, C14E6, and C14E9 were used to investigate the effect of ethoxylate number, and 14C-(ethoxylate) homologs C12E6, C14E6, and C16E6 were used to examine the effect of chain length. Activated sludge was dosed with a trace concentration (0.2 microM) of each homolog, and the disappearance of parent, formation of metabolites, production of 14CO2, and uptake into solids were monitored with time. Ethoxylate number had little effect on the first-order decay rates for primary biodegradation, which ranged from 61 to 78 h(-1). However, alkyl chain length had a larger effect, with the C16 chain-length homolog exhibiting a slower rate of parent decay (18 h(-1)) compared to its corresponding C12 and C14 homologs (61-69 h(-1)). Ethoxylate number affected the mechanism of biodegradation, with fission of the central ether bond to yield the corresponding fatty alcohol and (poly)ethylene glycol group increasing in dominance with increasing ethoxylate number. Based upon the measured rates of primary biodegradation, removal of parent during activated-sludge treatment was predicted to range between 99.7 and 99.8% for all homologs except C16E6, which had a predicted removal of 98.9%. Based upon the measured rates of ultimate biodegradation, removal of ethoxylate-containing metabolites was predicted to exceed 83% for all homologs. These predictions corresponded closely with previously published removal measurements in laboratory continuous activated-sludge systems and actual treatment plants.

Environmental Safety of the Use of Major Surfactant Classes in North America

“…In a more recent set of definitive studies, Itrich and Federle (2004) and Federle and Itrich (2006) evaluated the effect of ethoxylate number and alkyl chain length as well as position of the radiolabel on the kinetics of primary and ultimate biodegradation of linear AEs in activated sludge. The 2004 study shows that ethoxylate number has little effect on the first-order primary biodegradation rate for EO 1–9 , which ranged from 61 to 78 hr −1 .…”

“…The most important advances were facilitated by advances in radiolabel ( 14 C) synthesis and analysis of parent compounds. For example, the use of LC-and TLC-RAD techniques to measure parent compounds at extremely low concentrations allowed for more accurate determinations of biodegradation rate constants (Steber and Wierich, 1987; Steber et al, 1988; Nuck and Federle, 1996; Nielsen et al, 1997; Itrich and Federle, 2004; Federle and Itrich, 2006) and sorption coefficients (Kerr et al, 2000; McAvoy and Kerr, 2001; van Compernolle et al, 2006). …”

Evaluation of Biodegradability and Biodegradation Kinetics for Anionic, Nonionic, and Amphoteric Surfactants

“…Some researchers have estimated biokinetic parameters for PAE, although not for Neodol 23-5 ® specifically. Of note is that PAEs containing different numbers of ethoxylates and alkyl chain lengths will exhibit different growth kinetics (Itrich and Federle 2004). Zhang et al (1999) studied the growth kinetics of a PAE, Witconol, and determined that b m was 0.11, lower than 0.19+/−0.078 as determined for PAE in Neodol 23-5 ® , and K s was 2,450 mg/l as cobalt active thiocynate substance.…”

“…However, surfactants are characterized by high molecular weight and complex structures and thus biodegradation pathways are often multi-step processes (Jimenez et al 1991;van Ginkel 1996). Metabolites formed during surfactant biodegradation may degrade more slowly than the parent compound (Griffiths et al 1986;van Ginkel 1996;Bokern and Harms 1997;Bennie 1999;Itrich and Federle 2004). The fate of surfactants in biological treatment systems is becoming increasingly important as water reuse systems become more common and regulations for trace contaminant release by wastewater treatment plants are more stringent.…”

Essai n° 314 : Essais de simulation pour évaluer la biodégradabilité de produits chimiques rejetés dans les eaux usées

“…Les essais peuvent être conçus en vue d'une évaluation précise de la biodégradation de produits chimiques tant nouveaux qu'existants (6,7,8,9,10,11) rejetés en continu ou par intermittence dans les eaux usées. Dans certains cas, les constantes cinétiques ainsi obtenues peuvent être intégrées dans les modèles d'exposition utilisés en évaluation des risques.…”