Effective waste management is key in sustaining the cradle-to-cradle principle by reducing waste to a minimum and by re-using waste as raw material. Application of this concept in the poultry industry can be found in the production of feather meal from feathers. Keratin is a key protein in feathers which can be extracted and processed for the production of protein-rich animal feed. Keratin however has a rigid cellular structure made out of sulphur bridges. Processing feathers to a digestible feed is therefore accompanied by the release of organic and inorganic volatile compounds with an unpleasant odour. To reduce the negative odorous impact on the environment, the feather processing company subjects the odorous gas to an air treatment installation. The installation consists out of a slightly acidic scrubber, followed by an alkaline oxidative scrubber, a condenser and two activated carbon filters.
To determine the effectiveness of the air treatment installation, different activated carbon pilot set-ups were constructed through which process air of the animal feed production was sent. Composition of the in- and outgoing flow of each set-up was weekly investigated via TD-GC-MS, along with the achieved removal efficiency. An investigation method by means of pH measurements was also introduced to monitor the reduction in adsorption capacity of the activated carbon of each set-up.
pH measurements indicated that acidification only gives an indication of saturation when the ingoing airflow is sufficiently rich in acidic compounds. For the set-ups with non-impregnated activated carbon, chemical analysis demonstrated that removal of the alkaline oxidative scrubber and adding dry process air both resulted in faster breakthrough. This effect was more pronounced in case of very high H2S- and SO2-concentration in the ingoing airflow, which resulted in accelerated acidification and saturation. Because the added dry process air was strongly polluted, the influence of relative humidity on the lifespan of a carbon bed could not be determined. Comparison of impregnated and non-impregnated activated carbon demonstrated that impregnation provides a greater buffer for H2S and SO2, but a lower removal efficiency for organic odour components. Consequently, this type of carbon should rather be considered as an alternative to the alkaline oxidative scrubber than to the currently used activated carbon filters. A financial analysis showcased that the use of an impregnated activated carbon filter is more economical, and that replacement of the alkaline oxidative scrubber could be considered.