FIELD TESTING OF SENSING DEVICES FOR INTEGRATION INTO AUTOMATIC SCRUBBER CONTROLS

BACKGROUND Incoming hydrogen sulfide and odor loading to foul air scrubbers at wastewater treatment plants varies throughout the day and from minute to minute. A constant chemical feed rate into the make-up flow of a scrubber cannot adequately treat odorous spikes, which can result in objectionable odors to the surrounding community. Alternatively, chemicals are grossly overused if feed rates are targeted to treat the peak loading levels and have a strong chemical scent. To better treat spikes, and reduce odorous puffs of air, the Orange County Sanitation District (OCSD) installed automated control systems on 27 of its scrubbers. These systems sense both hydrogen sulfide and chlorine. Depending on the loading and output, the chemical feedrates are adjusted according to input parameters. Odor complaints declined by 65%, and chemical usage decreased up to 40%. OCSD will be constructing new odor control facilities and set out to investigate other options to the existing systems. In the new facilities, the programmable logic will reside within OCSD's control system. Due to this change, many of the features of the existing system would no longer be needed, but there were no options to obtain a reduced-cost unit without the built-in software control technology. There were a few devices available that met OCSD's needs on paper, however, for such a large investment, a field test was preferred before specifying a device in a capital improvement project.