Analysis of Priority Alkyl Aryl Sulfonates (AAS) in Wastewater 2018

In 2018 samples of raw influent and final effluent wastewater from fourteen municipal wastewater treatment plants at various locations in Canada were analyzed for priority alkyl aryl sulfonates (AAS) using the methods developed by Van Stempvoort and Brown (2018). The analyses included seven homologues of linear alkyl benzenesulfonates (ABS), nine homologues of branched ABS, and six homologues of alkyl-phenoxybenzene-sulfonates (APBS). The latter included five homologues of monoalkyldiphenylether disulfonates (MADS) and one monoalkyldiphenylether sulfonate (MAMS) homologue.

In the samples of raw influent wastewater from the fourteen treatment plants, the concentrations of linear ABS (total) ranged from 349 to 2701 µg/L, the concentrations of branched ABS (total) ranged from 20 to 126 µg/L, and the concentrations of APBS (total) ranged from 0.9 to 13.6 µg/L (Table 7). These are apparently the first published reports of the detections of APBS in wastewater. Generally the samples of final effluent from the same plants had much lower concentrations: the linear ABS ranged from 0.25 to 900 µg/L, the branched ABS ranged from below detection to 58 µg/L, and the APBS ranged from below detection to 4 µg/L. The APBS appeared to be the most resistant to loss during wastewater treatment. The most effective wastewater treatments were those that involved either aeration or advanced treatment including biological nutrient removal. Two treatment plants that had primary treatment only, and were sampled after heavy rains, had the highest AAS concentrations in the final effluent. The relative abundances of both linear ABS and branched ABS homologues in the raw influent wastewater suggest that they are derived primarily from commercial linear ABS products, which contain branched ABS as impurities. During wastewater treatment, the inferred losses (decreases in concentrations) of both linear ABS and branched ABS tended to increase with increasing carbon number.

APBS were detected in all wastewater samples; five homologues of MADS were detected in raw influent wastewater at average concentrations ranging from 0.02 to 3.95 µg/L. Four of the MADS homologues were detectable in final effluent samples at average concentrations ranging from 0.04 to 0.74 µg/L. The MAMS C12 homologue was detected in 59% of the raw influent samples and a few of the final effluent samples. The ratio of the relative abundance of the MADS and MAMS homologues detected in the raw influent was very different than what was measured in the commercial APBS product that was analyzed (Calfax DB-45).

Equipment blanks collected as quality control samples indicated contamination by linear ABS and branched ABS, probably derived from a cleaning agent used to prepare the sample containers. For future analyses of AAS in wastewater, we recommend that sample containers be used that have not been exposed to detergents or other cleaning agents that contain surfactants.