A study on volatile organic sulfide causes of odors at Philadelphiaʹs Northeast Water Pollution Control Plant

Volatile organic sulfide (VOS) causes of odors were studied at Philadelphiaʹs Northeast Water Pollution Control Plant between September 11 and November 25, 2003. Results showed that dimethyl sulfide (DMS) dominated the VOS pool whenever VOS concentration rose above the background level (<50 μg/L). Methanethiol was generally less than 10% of VOS and it was mainly found at sites with limited or reduced dissolved oxygen (DO). Dimethyl disulfide occupied 1% of the VOS and was often not detectable. Carbon disulfide was not detected. The concentrations of DMS varied by three orders of magnitude, ranging from <5 to 1260 μg/L. High concentrations of DMS, averaging 419 and ranging from <5 to 1000 μg/L, were generally found in return activated sludge. The DMS concentration in the primary effluent ranged from <5 to 729 μg/L and averaged 245 μg/L. Concentrations of DMS in the aeration tank (AT) with high DO were from <5 to 997 μg/L with an average of 250 μg/L. However, DMS concentrations in the AT representing anaerobic conditions were as high as 1260 μg/L. The estimated average purge efficiency of DMS was about 78%, which required a DMS production rate of 108 μg/L h−1 to keep the analyzed concentration in the AT. While a valid but weak statistical relationship between acetone and DMS was observed, there was no strong evidence to support that the methylation of hydrogen sulfide with acetone could be the mechanism for the DMS formation. Instead, DMS production was found to be associated with the characteristics of incoming wastewater. Thus, a VOS precursor was believed to be present in the incoming wastewater, which warranted a need for further investigation.