Well I never.
Nicotine is a potent killer of bacteria. In test-tube studies, it can destroy more than a dozen types of bacteria, including ones that cause diseases.
Nicotine readily destroys a wide range of bacteria. Germs that cause tuberculosis, as well as gum and skin diseases, are all susceptible. So are bacteria that naturally reside on human skin and in people's mouths and gastrointestinal tracts.
One reason smokers are prone to gum disease is that the nicotine from their cigarettes eliminates protective microbes that normally ward off disease-causing bacteria that even the nicotine can't check.
It isn't clear how nicotine kills bacteria, but it has the potential to be used as a disinfectant.
Chewing tobacco is much more biodegradable than cigarette butts though. Butts really would be a no-no in a septic tank.