What is the principle of biological deodorization method?

Biological deodorant is used in biological deodorization which is to fix the selected deodorant microorganisms on the carrier and oxidize and degrade the malodorous pollutant through a certain
biochemical pathway. The deodorization process of biological deodorant is a comprehensive process of gas diffusion and biochemical reaction. The deodorization mechanism can be divided into three stages.
First, the malodorous pollutants contact with water and dissolve in water or adhere to the surface of water. Second, the malodorous pollutants dissolved in water were absorbed into microorganism cells.
The malodorous pollutants which are insoluble in water are first attached to the surface of the microbial body, decomposed into soluble substances by secreting extracellular enzymes by the microbial, and then absorbed into the cell. Finally, microorganisms decompose and utilize the malodorous pollutants as nutrients for metabolism to eliminate the odor.

1. Removal of odorous sulfur-containing gases
   H2S is the main component in odorous sulfur-containing gases. Beggiatoa and Thiobacillus aerobic bacteria, as well as Chlorobium and Chromatium photosynthetic bacteria are used to remove H2S. These species of bacteria, through vulcanization, can oxidize H2S to substances such as elemental sulfur or sulfate, thus achieving the removal of H2S.
   Aerobic bacteria can oxidize H2S to sulfate and obtain energy. Photosynthetic bacteria are anaerobic bacteria utilizing H2S as a hydrogen donor for CO2 reduce through cyclic photophosphorylation under anaerobic light conditions to realize the H2S oxidation to sulfur element or further oxidation to sulfate.
2. Removal of odorous nitrogen-containing gases
   NH3 is the main target for the removal of odorous nitrogen-containing gases. The traditional biological denitrification process includes nitrification and denitrification. First, ammonia nitrogen is oxidized to nitrite by chemotrophic bacteria such as Nitrosobacteria. Nitrite can be oxidized to nitric acid by self-healing bacteria, such as Nitrobacter. Then, nitrite was converted into gaseous nitrides N2 and N2O by anaerobic denitrifying bacteria such as Bacillus Licheniformis, Paracoccus Denitrifican and Pseudomonas.
   Recently, the discovery of Pseudomonas, Alcaligenes Faecalis, Bacillus subtilis and Pseudomonas Putida has made it possible for the aerobic denitrifying bacteria which have two types of living style to live efficiently in one reaction system. Meanwhile, many heterotrophic nitrifying bacteria also have aerobic denitrification, such as Paracoccus denitrificans GB17 and Pseudomonas SP. The discovery of these new functional strains provides a theoretical basis for the research and development of new denitrification technologies.
3. Removal of hydrocarbon odorous gases
   Hydrocarbon odorous gases mainly come from petrochemical industry. It can be successfully degraded by Pseudomonas, Achromobacter, Corynebacterium and Candida. Hydrophobic surfaces outside the microbes are formed through the pili or the outer capsule of lipids or proteins, which are randomly attached by oil droplets in water. Some microorganisms can also secret glycolipids, lipoproteins and glycoproteins to emulsify oil droplets into many tiny particles, thus expanding the surface area of insoluble hydrocarbons in water and facilitating the adhesion of microorganisms. Notably, some emulsifiers can promote the degradation of some hydrocarbons as well. Hydrocarbon odorous gases include aliphatic and aromatic hydrocarbons. Both aliphatic and aromatic hydrocarbon degradation pathways are rapidly catalyzed by dehydrogenase or oxygenase in microorganisms.
4. Removal of odorous oxygen-containing gases
   Odorous oxygen-containing organic gases, such as aldehydes and phenols, are easily soluble in water, and the removal principle of such odorous gases by microorganisms is similar to that of hydrocarbon odorous gases, which is mainly through the efficient catalytic degradation by enzymes.
   The common phenolic pollutants, such as phenol, bisphenol A, nonylphenol and pentachlorophenol, can be degraded by Rhizobium, Fusarium and Candida. The decomposition is catalyzed by Oxygenases or dehydrogenases in microorganismsto reduce phenolic pollutants into CH4, CO2 and other harmless end products. Formaldehyde can be degraded by Pseudomonas Putida and P. Aeruginosa. The key enzyme to catalyze formaldehyde degradation is formaldehyde dehydrogenase. In the presence of glutathione and NAD+, formaldehyde is oxidized into formic acid which is then converted into CO2 by formic acid dehydrogenase.