When plant managers at a large Miami water treatment facility were dissatisfied with the occasional noxious odors emanating from their sludge loading area, they asked the process engineering experts at CH2M Hill to study the problem and come up with an advanced scrubbing system that would improve air quality by substantially reducing hydrogen sulfide levels and simultaneously cutting maintenance costs…and to design the system not only to conform to existing environmental regulations, which their operating system did, but to meet projected regulations which were even stricter.

And that's exactly what they did. The new four-stage scrubbing system they designed, has been achieving 99.9% reduction in sulfide levels, and 99.5% in odor measured by inlet and outlet odor values. According to Yvonne Picard, PE, the responsible CH2M Hill process engineer, the design of a cost effective, low maintenance odor control system requires close attention to the selection of flow control equipment that can withstand the two highly corrosive chemicals required for the scrubbing action: sodium hydroxide and sodium hypochlorite. All chemical feed lines were specified in CPVC, chlorinated polyvinyl chloride, and the ductwork in FRP, fiber reinforced plastic. The storage tanks were specified in FRP. Because of the dynamic hydraulic action within transfer and recirculation pumps, however, the material specifications established were more demanding.

The six recirculation scrubber pumps in the system required to deliver these corrosive chemicals, with pH values ranging from 3-12, at 650gpm against a 30' TDH, were designated as Vanton polypropylene horizontal centrifugal thermoplastic units conforming to ANSI process pump standards. (Figure 1) The stainless steel shafts were to be completely sleeved in KYNAR* PVDF (polyvinylidene fluoride) to isolate it from the fluid. The same strict material specifications were established for the caustic sodium hydroxide recycle pump required to deliver NaOH at 500gpm against a 16' TDH.

There were also two wet pit centrifugal sump pumps in the system for handling the caustic soda and chlorine solutions (Figure 2). These were specified as Vanton thermoplastic designs with wetted components furnished in polypropylene, but the immersed columns were required to be schedule 80 KYNAR* PVDF pipe. The pumps were required to deliver the chemicals at 200gpm at 13 TDH.

Complete details on this installation are available from the Vanton Technical Library. Contact Vanton Pump & Equipment Corp. and ask for TL-143...

eProduct Number 438