Odor Elimination Program
Background
In 2004, OWASA applied for and received a Special Use Permit (SUP) Modification from the Town of Chapel Hill for the upgrade and expansion of OWASA's Mason Farm Wastewater Treatment Plant (WWTP). In order to gain approval of the SUP, the OWASA Board adopted a Resolution reaffirming OWASA's goal of no off-site objectionable odors from the WWTP. The SUP Modification was then approved by the Chapel Hill Town Council on March 1, 2004, stipulating a requirement that OWASA eliminate off-site odor from the WWTP to the satisfaction of the Council and that OWASA regularly report to the Council on the progress of its off-site odor elimination program. Here is a link to our current Quarterly Report to the Town of Chapel Hill.
Work Already Accomplished
OWASA has invested extensively in its program to eliminate off-site odors at the WWTP. Capital investment to-date totals approximately $6.6 million, and the annual operating and maintenance costs for odor control are currently about $100,000. Major projects already completed include:
- Four separate studies to assess and determine the appropriate remedial actions for the various odor sources at the WWTP;
- Construction of a biofilter to treat exhaust air from the solids handling facility;
- Covering the solids storage basins and treating the exhaust air through a scrubber;
- Establishment of an in-house odor monitoring program, including the installation of hydrogen sulfide (H2S) monitoring equipment at various locations around the WWTP that provides automated monitoring and an alarm system for odors related to H2S;
- Covering and treating exhaust air from the new headworks structure; and
- Covering and treating exhaust air (via carbon filtration) at the influent and effluent splitter boxes leading to and from the primary clarifiers, intermediate pump station wet wells (#1 and #2), aeration basin influent channel, and all three primary clarifiers.
Remaining Work
The final capital project identified by the 2007 Black & Veatch Study as necessary to prevent objectionable odors from leaving the perimeter of the WWTP involves the partial covering and treatment of exhaust air at the WWTP's aeration basins (Phase III odor improvements). Funding constraints in recent years necessitated that OWASA delay the completion of this project and as a result, the Chapel Hill Town Council requested that OWASA commit to a specific completion date. In September 2009 the OWASA Board adopted a resolution committing to complete the Phase III Odor Control Project as soon as practical but not later than December 31, 2014.
OWASA's Fiscal Year (FY) 2012-2016 Capital Improvement Budget shows that OWASA will meet this commitment to the Council by completing the project in FY 2013 and 2014. The Phase III design was originally completed in January, 2009; however, the recently completed WWTP Hydraulic Capacity and Treatment Study indicated that OWASA needs to improve the aeration system in some portions of the WWTP's biological treatment process before proceeding with the Phase III Odor Improvements. This study also recommended, and OWASA subsequently implemented, certain improvements to the treatment process in the aeration basins which changed the odor “footprint” for this part of the treatment process. A field validation confirmed the WWTP Hydraulic Capacity and Treatment Study's computer modeling results, and an additional round of odor sampling and analysis confirmed the need to change the number and location of basins needed to meet the goal of no offsite odor (the earlier design included 8 of the 16 aeration basins; the project will be redesigned to cover and treat 10 of the basins). The redesign of the Phase III Odor Improvements project is expected to begin within the next few months in close coordination with the design of the aeration system improvements.