Odors treatment: Biological technologies

Abstract

Physical-chemical waste gas cleaning techniques have proven their effi ciency and reliability and will continue to occupy their niche, but several disadvantages remain. Among them are high investment and operation costs and the possible generation of secondary waste streams. With biological waste treatment techniques, reactor engineering is often less complicated and consequently costs are less. In addition, usually no secondary wastes are produced. Biological methods are nonhazardous and benign for the environment. Possible drawbacks are restricted knowledge about the biodegradation processes, limited process control, and relatively slow reaction kinetics. Anyway, the biological methods for the removal of odors and volatile organic compounds (VOCs) from waste gases are cost-effective technologies, when low concentrations (below 1-10 g/m-3) are to be dealt with (Kosteltz et al., 1996). Therefore, decision making can be based merely on economical analysis. Like the treatment of liquid effl uents, gaseous streams will be more often considered for biological treatment. For organic compounds, the biological reaction can be described as: CHO + O2 + nutrients C5 H7 O 2 N (cell dry weight) + CO2 + H2O + heat When heteroatoms are present (e.g., chlorine, sulfur), end-products like HCl or H2SO4 can be formed. For effi cient pollutant removal, target pollutants have to be suffi ciently biodegradable and bioavailable. A major advantage in the case of odor treatment is that biocatalysts have high affi nity for the substrates, which allows effi cient treatment of low infl uent concentrations. Biocatalysts also operate at room temperature and they have innocuous fi nal products (e.g., carbon dioxide and water). Provided that you have the right inocula, microorganisms can metabolize almost every compound there is. In general, odors consist of a very complex mixture of volatile organic as well as inorganic compounds. The most relevant compounds regarding odors in the food industry are nitrogencontaining compounds (ammonia, amines, amides, and more complex molecules like indole and scatole), reduced sulfur compounds (hydrogen sulfi de and volatile organic sulfur compounds) and VOCs like alcohols, aldehydes, volatile fatty acids, and phenols. Most are easily biodegradable. © 2006 Springer Science+Business Media, LLC.