Wet Scrubbing

Wet scrubbing is another widely used technology for odor control. Most wet scrubbers for odor control employ reactive chemicals. Reactive scrubbing involves the removal of odorous materials by neutralization, oxidation, or other chemical reactions. Odor removal by any liquid-gas process is a function of the solubility of the chemical compound in the liquid phase, the total effective gas-liquid contact area, the concentration of the odorous chemical compound in the gas stream, and the residence time of the gas stream in the scrubber.

Atomized mist scrubbers and packed scrubbers are both capable of providing large gas-liquid contact areas for gas absorption. In a mist scrubber, pneumatic nozzles use a high-velocity compressed air stream to atomize a chemical solution into 5- to 20-^m-diameter drops, providing a large contact area. Unlike packed scrubbers, mist scrubbers do not clog even if the gas stream contains large particles. In a packed scrubber system, the chemical solution is often recirculated. As a result, the water and chemical consumption is significantly reduced.

For more complex odor problems caused by a mixture of odorants, multiple stages of scrubbers utilizing different chemicals in each stage are often used. Figure 5.27.1 shows a multiple-stage scrubber installed to control odorous emissions from a wastewater sludge treatment facility. The system uses sulfuric acid in the first-stage, cocur-rent, coarse-packing, packed-tower scrubber to remove ammonia and particulates; a caustic/hypochlorite solution in the second-stage, cocurrent, horizontal-mist scrubber to remove or reduce sulfur compounds and VOCs; and a weak caustic solution in the third-stage, cross-flow, packed-bed scrubber to remove the remaining odorants, especially those chlorine compounds generated in the second-stage scrubber. The control system also uses a 50-ft-tall stack to enhance the dilution of the remaining odorants during plume dispersion (Ponte and Aiello 1993).

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