Chlorine Dioxide Odor Scrubber Overview:
Chlorine dioxide has been used for odor control for over 30 years in the rendering industry. As a chemistry, chlorine dioxide has several advantages over what had been the predominate choice for treating room and process odors in the rendering industry.
- Chlorine dioxide is a very fast acting oxidant and works at a very low dosage rate. Where chlorine (Bleach) levels often need to be in the 10-50 ppm range in the circulation water, chlorine dioxide is fed to a residual of 1 -2 ppm in the scrubber water going to the spray nozzles.
- Chlorine dioxide can be used very effectively in a pH range from 4 – 9.5 due to the oxidation potential not changing throughout this pH range. This allows chlorine dioxide to be used in systems that require both alkaline (ammonia and amines) and acidic gases (hydrogen sulfide). In these situations, an acid scrubber could be followed by an alkaline scrubber while still using a single oxidant. Alternatively, bleach is an acidic gas that is volatile at pH levels below 8.
- At pH levels of 8-9.5 bleach is a very weak oxidizer. This means that in air scrubbers the concentration of bleach may need to be very high to get the oxidation potential of the water to above 500 mV ORP (~5-50 ppm). With chlorine dioxide, the same ORP can usually be reached with just a 1-2 ppm residual at a pH of 9.5.
- Chlorine does not create aldehydes like bleach does (oxidation of alcohols) and as a result, a scrubber changing over to chlorine dioxide will see a drop in VOC levels coming from the scrubber. If VOC’s are a concern, replacing bleach and caustic with chlorine dioxide will likely reduce the VOC emissions from the air scrubbers.
- Chloramines are formed when bleach is used with ammonia present. Chloramines are very odorous and toxic. High intensity rendering odors should never be treated with bleach. Chlorine dioxide does not react with ammonia. When treating ammonia air streams, the scrubber pH should be maintained at a pH level of 4.0 -5.0. Complex amines will be oxidized by chlorine dioxide at this pH and ammonia, which is not reactive with chlorine dioxide, will stay in the scrubber as a weak acid (NH4+)
- TMA (trimethylamine) is the foul fish odor that is present in all rendering air scrubbers and is not oxidized by bleach. However, chlorine dioxide will oxidize TMA to TMA=O which is highly soluble in water. Bleach will not react with TMA.
- In rendering applications with high levels of grease in the air, fouling of the packing is common. In many applications, the bacteria that are supported by the buildup on the packing increase odor! This can be especially true when hydrogen peroxide or non- oxidizing programs are used (detergents). Chlorine dioxide is the best bactericidal product that can be used for combating bacteria slime. Keeping packing free of slime growth is a benefit of chlorine dioxide where in some plants cleaning of the packing has gone from a monthly occurrence to yearly saving a great deal of maintenance cost. Chlorine dioxide applications are approved to treat bio slime in process waters such as air scrubbers.
Case Histories in Rendering:
The following cases are current rendering plants utilizing chlorine dioxide.
- Rendering plant beef and poultry room air scrubbers: Two 90,000 SCFM air scrubbers in northwest rendering plant currently use chlorine dioxide for both scrubbers. Control limits are ORP reading >60 pH 8-10. The feed rate of chlorine dioxide to the scrubber spray headers is 2 ppm with a residual of .5 to 1 ppm in the scrubber water basin. Odor control improved greatly when these control parameters were utilized.
- Fish food manufacturing plant: A fish food manufacturing plant in the northwest was treating cooked fish odors with acid in the scrubbers at a pH of 2. There was no oxidizer being used since chlorine would quickly become volatile and cause a release of chloramines. TMA was the main odor agent and was saturating the scrubber water and releasing into the air. Odor complaints were in the hundreds. Chlorine dioxide was fed to the scrubber and the pH was adjusted to 4-5. This treated the TMA and the odor complaints were eliminated. The feed rate of chlorine dioxide is 4 ppm with a residual of 1 ppm going to the spray header.
- Chicken Rendering: A chicken rendering plant uses chlorine dioxide in three scrubbers. The high intensity scrubber is kept at a low pH to remove the amines and ammonia. The room air scrubber is run at a neutral pH and the feather scrubber is run at a high pH to handle organic sulfur compounds. All three are effectively using chlorine dioxide at all three pH ranges. Chlorine dioxide is the only chemical that has this capability.
Gulf Coast Environmental Systems has extensive experience providing odor and pollution control solutions to the rendering industry. If you have questions about this solution, please contact our team at firstname.lastname@example.org or 832.476.9024