PM07 Pollutant Chemistry Transport, Cycling and Fate
Exhibit Hall
8:00 AM - Monday
(PM102) Retrospective analysis of LAS monitoring data to estimate current and future exposure from treated effluents and validate laboratory based estimates of removal.
Federle, T1, Itrich, N1, 1 The Procter & Gamble Company, Cincinnati, OH, USA
ABSTRACT- Linear alkylbenzene sulfonate (LAS) is one of the most commonly used and intensely studied chemicals found in commerce today. Since the advent of modern HPLC analytical methods in the mid-1980s, there have been multiple studies that have monitored levels of LAS in wastewater influent and wastewater treatment plant effluents. These data are important for validating the assumptions used for predicting wastewater levels of a chemical based upon usage volume and per capita water use as well as estimating removal from laboratory test results. In addition, they can provide a basis for developing a probabilistic model to estimate effluent concentrations of LAS for different usage, which have fluctuated by more than 150% during the period in which the monitoring studies were conducted. Measured LAS levels are available for more than 90 wastewater samples in the U.S. and Europe. Measured concentrations ranged from 5 to 115% of their corresponding predicted concentration based upon usage volume and water use, with only two measurements exceeding their predicted levels. The average ratio of measured to predicted LAS was 0.45 with the 90th percentile ratio being 0.63. Such low ratios reflect the conservative nature of the estimates as well as biodegradation of LAS in the sewer. LAS removal has been measured in 50 activated sludge plants, which represent the most common and important type of treatment. LAS removal in well operating activated sludge plants ranged from 97.8 to >99.9% with the average removal being 99.3%. The 10th percentile level for removal was 98.0%. For comparison, the predicted removal of LAS based upon realistic laboratory activated sludge die-away and continuous activated sludge tests range from 99.4 to 99.7%, which correspond to the 40th to 60th percentiles for monitored removal. Combining the distributions for the ratios of measured to predicted wastewater concentration and those for removal in a probabilistic model predicts that there is a 90% certainty that LAS in effluents from an activated sludge plant will not exceed 0.0083% of that predicted to be present in wastewater based upon volume and water usage. Thus, in 2002 when annual LAS usage was 289,000 and 344,000 mtons in U.S. and Europe, respectively, there was 90% certainty that effluent levels were below 62 
g/L in the U.S. and 107 g/L in Europe.
Key words: Probabilistic Exposure, LAS, Wastewater, Surfactant