Removal and environmental exposure of alcohol ethoxylates in US sewage treatment.

Alcohol ethoxylates (AE) are a common nonionic surfactant employed in consumer and industrial detergents worldwide. Commercial AE are typically complex mixtures composed of > 100 homologous compounds with varying alkyl chain lengths and varying numbers of ethylene oxide (EO) units. Recent improvements in analytical methodology have enabled accurate measurement of the entire AE mixture in sewage treatment plant (STP) influents and effluents, including alkyl chain lengths from 12 to 18 carbons with a range of ethoxylation from 0 to 18 EO units. These improved analytical methods were used to measure AE concentrations at nine sites representative of sewage treatment processes and geographical locations. These new data will make possible a more accurate assessment of environmental risk for AE in the United States. The results indicate that all AE homologues are effectively removed (> 99%) in the most common treatment types. Individual STP total AE effluent concentrations ranged from a low of 0.92 microg/L for activated sludge to a high of 15.6 microg/L for a trickling filter process. For the purpose of representing a national average distribution, an average-flow-weighted wastewater treatment plant effluent concentration was determined for each AE component. The total-flow-weighted average AE effluent concentration was 3.64 microg/L.

Monitoring of environmental fingerprints of alcohol ethoxylates in Europe and Canada.

Recent improvements in methodology for the determination of alcohol ethoxylates (AE) in effluents now enable measurement of the full range of AE components, at ng/L levels, in the same analysis. This approach was deployed in effluent monitoring of biofilm and activated sludge wastewater treatment plants from Europe (n = 12) and Canada (n = 8) receiving predominantly municipal effluent. Individual component or "environmental fingerprint" analyses for alkyl carbon numbers C12-C18 and ethoxylate numbers 0-18 were conducted using a derivatization procedure with liquid chromatography/mass spectrometry determination. The AE results were very similar with an overall mean level of 5.7 microg/L (range 1.0-22.7 microg/L). The major contribution to the total AE content was from fatty alcohol, which constituted, on average, 43% of the total. The exposure data can then be corrected to account for alcohol derived from sources other than AE and for sorption to particulate matter to determine AE concentrations in undiluted effluents. These data can be used with site-specific dilution information to estimate river water exposure in mixing zones and then to determine aquatic risk by integrating normalized AE effect concentrations determined through quantitative structure-activity relationships.

Predicting the sorption of fatty alcohols and alcohol ethoxylates to effluent and receiving water solids.

Alcohol ethoxylates (AEs) are an important group of nonionic surfactants. Commercial AEs consist of a mixture of several homologues of varying carbon chain length (Cx) and degree of ethoxylation (EOy). The major disposal route of AE is down the drain to municipal wastewater treatment plants that discharge into receiving surface waters. Sorption of AE homologues onto activated sludge and river water solids is an important factor in assessing exposure of AE in the environment. This study presents the experimental determination of sorption coefficients for a wide array of AE homologues including five alcohols under environmentally relevant conditions and combines these data with literature data to generate a predictive model for the sorption of AEs in the environment. These results demonstrate that sorption can be effectively modeled using a log Kd vs. Cx and EOy predictive equation having the form log Kd = 0.331C - 0.00897EO - 1.126(R2 = 0.64).

Risk assessment approach for untreated wastewater using the QUAL2E water quality model.

This paper presents a novel approach for assessing the risk of consumer product ingredients in surface waters that receive untreated wastewater. The approach utilizes the water quality simulation model QUAL2E for predicting the impact caused by conventional pollutants, as well as the exposure concentration of consumer product ingredients. This approach invokes an impact zone concept whereby the receiving water can be thought of as a natural wastewater treatment system. After the river has recovered via self-purification, the ecosystem is then assessed by traditional risk assessment methods. This approach was validated using data collected from the Balatuin River, which is located in the Philippines. Results from this study support the use of QUAL2E for assessing the risk of consumer product ingredients in riverine systems receiving untreated wastewater.

Integration of aquatic fate and ecological responses to linear alkyl benzene sulfonate (LAS) in model stream ecosystems.

An integrated model stream ecosystem fate and effect study of dodecyl linear alkylbenzene sulfonate (C(12)LAS) was performed in the summer and fall of 1996. The study addressed responses of periphytic microbes, immature benthic fauna including abundance, drift, and emergence of adult insects in a 56-day exposure. Exposures ranged from 126 to 2978 microg/L and were continuously presented in a single-pass, flow-through test system. Microbial heterotrophs acclimated to C(12)LAS exposure quickly (14 days) and biodegraded C(12)LAS at all concentrations. Blue-green algae responded by increasing in abundance with increasing C(12)LAS concentration. Invertebrates responded by increased drift and reduced benthic abundances at concentrations exceeding 293 microg/L. Emergence at 927 microg/L also declined relative to the control. Adverse responses for mayflies and chironomids were indicated using univariate statistical techniques. Multivariate techniques indicated these taxa plus mollusks, aquatic worms, caddisflies, and stoneflies were impaired at some concentrations. Bioavailability of C(12)LAS was investigated in streams as a function of the total suspended solid load in the water column driven by local weather and watershed patterns. A continuous bioavailability model indicated exposure was reduced by an average of 8.5+/-8.9%. A model ecosystem no-observed-effect concentration (NOEC) was concluded to be 293 microg/L based on measured water column exposure and adjusted to 268 microg/L by the bioavailability model. A literature review of 13 available model ecosystem studies was conducted and NOEC conclusions were adjusted by a structure-activity relationship to a dodecyl chain length (sulfophenyl position and distribution being ignored due to lack of information in the reviewed studies). Lentic studies (n=7) were found to have higher NOECs than lotic studies (n=6) and were more variable. Mean NOECs+/-SD for all studies, lentic studies only, and lotic studies only were 3320+/-6040, 5720+/-7640, and 530+/-430 microg/L, respectively. Interpretation of results for anomalies from specific studies suggests the importance of experimental design, use of laboratory versus natural surface water, biological complexity of the test system, and physical test system design as relevant factors for consideration. The specific results of the new model ecosystem study presented in this article can be well defended on the basis of a robust experimental and physical design and because the system contained a diverse and sensitive aquatic community. A low or no uncertainty factor could be applied to the result.

How adaptation and mass transfer control the biodegradation of linear alkylbenzene sulfonate by activated sludge.

We use a nonsteady-state model to evaluate the effects of community adaptation and sorption kinetics on the fate of linear alkylbenzene sulfonate (LAS) in batch experiments conducted with activated sludge that was continuously fed different concentrations of LAS. We observed a sharp decrease in the biodegradation rate between 30 and 60 minutes and the presence of an LAS residual at the end of the batch experiments. The modeling analysis indicates that these phenomena were caused by relatively slow inter-phase mass transport of LAS. The modeling analyses also showed that the amount of LAS-degrading biomass increased when the continuous activated sludge was fed a higher LAS concentration. Although community adaptation to LAS involved accumulation of more LAS degraders, the increase was not proportional to the feed concentration of LAS, which supports the concept that LAS degraders also utilized portions of the general biochemical oxygen demand (BOD) fed to the continuous activated sludge systems.

Evaluation of an inactivation procedure for determining the sorption of organic compounds to activated sludge.

A batch method was developed and validated for determining the sorption coefficient (Kd) of biodegradable organic compounds to activated sludge solids using a nonspecific analytical technique, total organic carbon (TOC) analysis. In this method, activated sludge solids were first inactivated by lyophilization and dry heat (103 degrees C) and then washed to remove any dissolved organic carbon released during the inactivation procedure. The inactivated sludge solids were exposed to a range of concentrations of different test compounds in synthetic wastewater until equilibrium was achieved (< 2 h). The amount of test compound sorbed to the solids was then determined by measuring TOC levels in centrifuged supernatants. Results revealed that the sorption coefficients (Kd values) for four detergent chemicals in inactivated sludge solids using TOC analysis were in good agreement with values determined in fresh activated sludge using radiolabeled materials. These Kd values are suitable for use in estimating environmental exposure concentrations and for developing screening-level models to assess the removal of organic compounds by sorption and settling during activated sludge wastewater treatment.

A simplified modeling approach using microbial growth kinetics for predicting exposure concentrations of organic chemicals in treated wastewater effluents.

Various mathematical relationships have been used to assess exposure concentrations of organic chemicals when emissions occur via wastewater treatment. These relationships range from a simple removal factor calculation to more sophisticated approaches using kinetic based mathematical models. While these existing approaches have been used by decision makers to screen new chemicals for exposure assessments, they all have limitations in the predictive capabilities. Thus, a simplified modeling approach grounded in sound scientific fundamentals that utilizes relatively easy to obtain input parameters is needed. In this paper a simplified modeling approach that utilizes microbial growth kinetics was developed for predicting effluent concentrations in secondary biological wastewater treatment systems. Receiving water predicted exposure concentrations (PEC) are assessed by using a dilution factor. One advantage of this approach is that it allows for wastewater treatment plant effluent concentrations, and therefore receiving water exposure levels, to be predicted with a minimum amount of experimental data. It also provides quantitative data that can be used to assess the relative biodegradability of different chemicals for use in regulatory and risk assessment activities.

Effect of mineral and organic soil constituents on microbial mineralization of organic compounds in a natural soil.

This research addressed the effect of mineral and organic soil constituents on the fate of organic compounds in soils. Specifically, it sought to determine how the associations between organic chemicals and different soil constituents affect their subsequent biodegradation in soil. Four C-labeled surfactants were aseptically adsorbed to montmorillonite, kaolinite, illite, sand, and humic acids. These complexes were mixed with a woodlot soil, and CO(2) production was measured over time. The mineralization data were fitted to various production models by nonlinear regression, and a mixed (3/2)-order model was found to most accurately describe the mineralization patterns. Different mineralization patterns were observed as a function of the chemical and soil constituents. Surfactants that had been preadsorbed to sand or kaolinite usually showed similar mineralization kinetics to the control treatments, in which the surfactants were added to the soil as an aqueous solution. Surfactants that had been bound to illite or montmorillonite were typically degraded to lesser extents than the other forms, while surfactant-humic acid complexes were degraded more slowly than the other forms. The desorption coefficients (K(d)) of the soil constituent-bound surfactants were negatively correlated with the initial rates of degradation (k(1)) and estimates of CO(2) yield (P(o)) as well as actual total yields of CO(2). However, there was no relationship between K(d) and second-stage zero-order rates of mineralization (k(o)). Microbial community characteristics (biomass and activity) were not correlated with any of the mineralization kinetic parameters. Overall, this study showed that environmental form had a profound effect on the ultimate fate of biodegradable chemicals in soil. This form is defined by the physicochemical characteristics of the chemical, the composition and mineralogy of the soil, and the mode of entry of the chemical into the soil environment.