The City of Davenport has used biofiltration to control odors from its wastewater treatment facilities for years. Todd Williams presents a case study on Davenport, Iowa during WEF’s Odor and Pollutants 2014 conference in Miami, Florida to show the benefits of upgrading the existing biofiltration system.

By: Todd Williams, Deputy Leader of CH2M HILL’s Global Wastewater Technology Practice

Todd Williams will present his paper, “Davenport Compost Facility Odor Control Improvements”, co-authored by Scott Plett, at the Water Environment Federation’s (WEF) Odors and Air Pollutants 2014 conference in Miami, FL on Sunday, June 1 at 9:30 a.m. Get a complete list of CH2M HILL’s participation in the event.

Odor control is a big deal for local communities and something that wastewater treatment facilities must consider in order to remain a good neighbor, and biofiltration, the technology that helps composting facilities control odor, has been declared one of the best available control technologies on the market.

Since 1995, the City of Davenport, Iowa has been successfully composting wastewater residuals and yard wastes from Scott County, Iowa using biofiltration at their award-winning enclosed aerated static pile composting facility.

From the beginning, odor control has been one of the core values of this facility. Davenport’s original facility was sized to process 140 wet tons per day of wastewater biosolids, five days per week. The facility also routinely processes 100,000 cubic yards of yard wastes annually. Odors at the facility are controlled by collecting and treating exhaust air from the compost building and process air from the aerated static pile through eight organic media (wood chip based) biofilter cells with a combined capacity of 210,000 cubic feet per minute.

In its 18 years of operation, the City of Davenport’s compost facility has only received one odor complaint, which was the result of a broken odor collection duct (something that was easily repaired). This achievement can be credited to the facility’s original biofiltration technology and the operational controls by the operations staff.

To keep odor controlled, the biofiltration system requires periodic media replacement, approximately every 4-6 years, which is not only time consuming but expensive. In order to minimize media change-out time and evaluate non-wood chip based alternatives, the City of Davenport contracted CH2M HILL to perform a feasibility study to evaluate alternatives for upgrading the biofiltration system. Seven alternatives were evaluated for cost effectiveness and operator preferences to achieve better airflow distribution and reduce media change-out time, including:

  • Keep the existing filter
  • BacTee™ aeration floor(new media support) with organic media
  • BacTee™ aeration floor with engineered inorganic media
  • BacTee™ aeration floor with lava rock media
  • HDPE (high density polyethylene) pipe in concrete with organic media
  • HDPE pipe in concrete with lava rock media
  • Risers and grates in concrete with organic media

Due to capital and life-cycle costs, ultimately, it was recommended that the city incorporate a system consisting of high density polyethylene pipes imbedded in a concrete pad. This solution makes it easy for the city to change out media and lava rock and wood chips can be used interchangeably. Additionally, this option helps reduce the overall biofilter footprint by 25% over the existing system, which opens space for future use or expansion.

Based on the results of the initial study, CH2M HILL completed design of the new biofilter system including reducing the number of biofilter cells from eight to four. Construction of the first cell is in progress with the next three to follow. This solution will provide the compost facility with reliable odor control for the next 20-30 years.

Todd Williams has spent 33 years working in environmental engineering, with operating and design experience and specific emphasis in residuals and biosolids management. Todd has made numerous presentations and is a contributing author for several articles and books significant to biosolids and residuals management, composting, and odor control including the recently published WEF/WERF/EPA Solids Process Design and Management Manual. Todd is an engineering graduate of Virginia Tech and is the past Chair of the Water Environment Federation’s Residuals and Biosolids Committee. Todd works out of CH2M HILL’s Richmond, Virginia office where he serves as Deputy Leader of CH2M HILL’s Global Wastewater Technology Practice.