Circular Cross Section Horizontal Airflow Vertical Bed Dry Media Odor Scrubber Design Considerations for Easy Operation and Maintenance

King County's Wastewater Treatment Division (KC-WTD) standardized its dry media scrubber systems to utilize the horizontal airflow vertical bed (HAVB) configuration (Figure 1). This was done due to the relative ease the HAVB configuration provides for media removal and replacement relative to the traditional deep bed configurations and other designs. With almost thirty HAVB scrubbers in service and more than 18 years of experience with this configuration King County staff have refined their standard design based on lessons learned about scrubber vessel geometry, media bed retention system design, drainage, and maintenance access. KC-WTD staff have recently received reports from others in the wastewater industry that some utilities are still having difficulties with the operation of the HAVB configuration. The aforementioned lessons, design details and insights will be shared in this paper in the hope that others may benefit from KC-WTD's experience and avoid such difficulties. The HVAB circular cross section configuration allows spent media to be removed easily with a vacuum truck (Figure 2) and replaced easily by dropping replacement media in via large access hatches (Figure 3). However, if the media fill ports are not appropriately dimensioned with respect to the vessel diameter, gaps may form between the media and the vessel wall which will allow foul air to bypass the media and escape treatment which can lead to odor impacts. KC-WTD staff have developed, and will share in this paper, a simple means of avoiding the problem by comparing the fill port dimensions, vessel diameter media's angle of repose (Figures 4 and 5). KC-WTD has also encountered problems with media bed retention system failures, accessing the scrubber interior to perform routine maintenance and repair of internal scrubber features, drainage of condensate, media sampling port design and other issues that have caused difficulties both in the operation and maintenance of HAVB dry media scrubbers. The lessons learned from these problems have allowed the refinement of KC-WTD's HAVB design standard that operate successfully. It is hoped that by sharing these lessons and solutions that were developed will help others who choose to incorporate the HAVB dry media scrubber configuration into their odor control systems.