A large pork processing plant in the Midwest uses two air washers in series to scrub hot gases from its cooker and hair hydrolyzer. As the hot gases from its operation are emitted, they are swept first into a cyclone separator venturi, where well water is sprayed into the stream of hot gases to cool, and separate the solids from the stream. Odors generated in the cooking operation and from the well water itself escape into the air, resulting in odor-related complaints from the neighboring community. Community complaint meetings were being held, and the plant needed a working solution within one week.
Hot gases escaping from the scrubbers contained hydrogen sulfide (H2S). Originally, the plant relied on a program of chlorine and caustic to treat the scrubber recirculating water. The recirculating water’s pH was elevated to 10 to keep gases from flashing. The chlorine was used to oxidize the organic and inorganic odors.
This program caused the calcium in the recirculating water to deposit on the plastic fill, which resulted in channeling of the recirculating water in the scrubbers. This channeling limited the water and gas contact and permitted odors to escape. In addition, at the higher pH of 10 the chlorine lost its effectiveness. The low chlorine level and water channeling led to microbiological fouling.
Veolia initiated a scrubber scale and biofoulant cleanup program, consisting of combination gaseous chlorine, and sodium bromide program controlled with an ORP meter. This program was augmented with a biopenetrant/ biosurfactant (DeposiTrol* SF series product) to aid the oxidants in removing biofoulants. Calcium carbonate deposition was stopped by a special inhibitor program (DeposiTrol PY series product) which removed scale and inhibited scale formation. The chlorine was fed to the scrubber basin, causing the pH to drop and calcium carbonate to become less of a problem.
To rid the system of the odors, a complete survey of the scrubber stacks and rendering areas was made. A ProSweet OC series product was set up to feed into the scrubber venturi. Levels of H2S decreased from highs of 25 ppm (mg/L) to lows of 0-3 ppm (mg/L) in the air scrubbers. After the H2S odor decreased, a nonhydrogen sulfide odor became present. For this type of odor, another ProSweet OC series product, an odor neutralizer, was used.
Reduction of odors eliminated neighboring community complaints. In addition, clean scrubbers permitted better water and gas scrubbing. As sulfide levels lowered, unpleasant odors were neutralized and scaling was eliminated. Regular testing and adjusting of the feed points helped ensure continued success of the odor control program.