There is a lot of discussion on micropollutants such as pharmaceuticals, chlorinated organics, pesticides/herbicides, and even common things such as artificial sweeteners. The biggest issues are these xenobiotics (not naturally occurring compounds) are passing through biological treatment without degradation. So, a lot of effort is being directed at finding bacteria that can degrade these compounds. In traditional microbiology, we pften screen organisms by sole-carbon source testing. In sole-carbon source testing, you look for microbes that can initate biodegradation of the target compound. Often we can find strains that grow on the target compound. For more difficult compounds, we may need to a cometabolism component. If organisms exist that can degrade these compounds, why are the difficult to treat in wastewater, soils, and groundwater? Here are a few possible explanations:
- The most discussed reason is that target concentrations are too low for supporting the organisms. At concentrations in the ppb (parts per billion), there is often too little of the compound for direct degradation. In this case you need to evaluate cometabolism where a non-specific enzyme starts decomposition.
- Another cause could be that moving from a sole-carbon source environment to one with other available "energy" sources will change microbial behavior. In the presence of easy-to-degrade substrates (sugars, starches, etc), we often see microbes conusmer the "easy" compounds first. This leaves low energy yeilding compounds unaltered. Think of this as similar to giving kids a choice of candy or broccoli. Which one would most kids select... of course you know it is candy.
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