A study on volatile organic sulfide causes of odors at Philadelphia's Northeast Water Pollution Control Plant.

Volatile organic sulfide (VOS) causes of odors were studied at Philadelphia's 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 microg/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 approximately 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 microg/L. High concentrations of DMS, averaging 419 and ranging from <5 to 1000 microg/L, were generally found in return activated sludge. The DMS concentration in the primary effluent ranged from <5 to 729 microg/L and averaged 245 microg/L. Concentrations of DMS in the aeration tank (AT) with high DO were from <5 to 997 microg/L with an average of 250 microg/L. However, DMS concentrations in the AT representing anaerobic conditions were as high as 1260 microg/L. The estimated average purge efficiency of DMS was about 78%, which required a DMS production rate of 108 microg/Lh(-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.