Abstract: The Philadelphia Water Department (PWD) has for six-years intensively studied the odor characteristics of its biosolids cake to identify effective mitigative measures for odor control. Between 2001 and 2006, PWD, working with Bucknell University and several other research partners, demonstrated that biosolids odors arise from the release of total volatile organic sulfur compounds (TVOSC) during protein metabolism, when shear forces within centrifuges both release food for decomposition and suppress methanogenesis. A peak odorant intensity results several days after dewatering. Concentrations of TVOSCs may at times be six orders of magnitude above the ED50 concentration. No single mitigative measure provides compelling control over odorant production. Examined alternatives include 1) addition of chemical conditioners (ferric chloride); 2) use of alternative dewatering polymer products; 3) changes to centrifuge operational parameters (speed and torque); 4) treatment after post-dewatering with various mineral, alkaline and enzyme products; 5) evaluation of storage and effects of freezing/thawing and wetting/drying on odors; 6) supplementation of digesters with nutrients and enzymes. Steps PWD has taken in response are: matching the point of low odor in biosolids to its use at sensitive sites; blending high carbon coal ash to reduce odorant emissions; providing temporary covered storage of piles to prevent rainfall capture and biosolids freezing
