In this post, I am going to discuss the microbiology of atmospheric treatment and how these towers all work on a biochemical level. In general, the towers are all based on a biofilm growing on a support media. The media allows for biofilm development with the biofilm receiving energy from sulfides and volatile organics. The other nutrients, pH controls, oxygen and moisture are maintained via water recirculation over the media.
Biologically the towers usually support two distinct communities of microbes.
First, are the chemo-autotrophic organisms that oxidize reduced sulfur species for energy and use carbon dioxide as their carbon source. This group is often referred to as Thiobacillus, Starkeya, or Thiosphaera sp. This group of microbes can oxidize reduced sulfur into elemental and sulfate forms. This process releases acids which are often associated with concrete degradation. In the biotower, we manage the pH to keep it in the ideal range for sulfide oxidizing microbes usually a pH of 3.5 – 6.5.
A second group of microbes that can metabolize short-chain volatile fatty acids (acetic, butyric, propionic) and mercaptans are also present. This group of microbes are often discussed as we often view odors as coming from H2S. However, in many systems the organic acids are a greater problem. In this case the biotower will favor the heterotrophic organisms which required a slightly higher ideal pH. Usually these microbes thrive from 6.0 – 8.5.
Additionally, several organisms are known to both degrade short chain volatile organics and oxidize sulfides. In some biofilters, it is beneficial to add concentrates of these cultures to rapidly colonize the media with a biofilm capable of addressing both the sulfide and organic acids. This ability to add cultures is obviously beneficial in reducing startup time, but it is also an effective option in building a biofilm in filters with high seasonal loading variation or where the biofilm integrity was compromised by mechanical failure.