AIR EMISSION AND ODOR CONTROL AT THE CITY OF LAS VEGAS WATER POLLUTION CONTROL FACILITY

The City of Las Vegas Water Pollution Control Facility (WPCF) is completing an expansion from 66 mgd to 91 mgd. Concurrent with the expansion, there has been an increase in development around the perimeter of the facility. This, coupled with the need to meet air quality requirements, and an increase in solids that will be coming into the WPCF from a new reclamation facility, has prompted the City to embark on an extensive air emissions and odor control program. The elements of this program have included the following:Air and liquid phase sampling to characterize emissionsComputer modeling to project the future extent of odors with future expansion and controlsAlternative analysis to determine the most appropriate control technologyObtaining appropriate air permitsCapital improvements for emissions and odor controlOperational adjustments to reduce emissionsAs a result of the study phase of work, the following odor control and air emission improvements have been constructed:Lining six digesters and covering scope boxes to reduce fugitive emissions from the digestersEnclosing and venting grit binsInstalling a 34,000 cfm soil media biofilter to treat air from an existing screening building and from existing primary sedimentation basinsCovering eight 180-foot diameter trickling filters with low profile aluminum dome coversInstalling seven 24,000 cfm multi-stage packed bed scrubbersExtending stacks on existing scrubbersReplacing open flame waste gas flares with two more efficient and higher capacity enclosed waste gas flaresInstalling a 34,000 cfm soil media biofilter and extensive ventilation to treat air from an expanded and improved dewatering buildingInstalling a 30,000 cfm soil media biofilter to treat air from new headworks facilityInstalling a 32,000 cfm soil media biofilter to treat air from new facility primary sedimentation basins and gravity thickenersIn addition to the capital improvements listed above, the following operational adjustments have also been made:Conversion from alum to ferric chloride at the head of the plant to reduce sulfide in the trickling filters and gravity thickenersConfining biosolids hauling to night time hours to limit off-site odors and the number of times during the day the doors to the dewatering building are openChanging the operating pressure and control of the digesters to reduce the number of uncontrolled digester gas releasesControlling the hours per year emission units are allowed to operate and the volume of natural and/or digester gas they are allowed to use to keep within allowable emission limitsAs a result of these improvements the City has been able to essentially eliminate off-site odors as evidenced by a dramatic decrease in the number of residential odor complaints and has been able to meet air emission requirements.