> When 2,3-butanediol (2,3-BDO) is produced through microbial fermentation, common byproducts include ethanol, acetoin (acetylmethyl-carbinol), lactic acid, acetic acid, formic acid, succinic acid, CO2, and H2, depending on the microorganism and fermentation conditions, with acetoin and diacetyl being key intermediates in the pathway.

The intermediate diacetyl appears to have a potentially major side effect which, at scale, may make it a non-starter.

> Inhalation of vapors can cause bronchiolitis obliterans, a severe and irreversible lung disease, leading to coughing, wheezing, and shortness of breath, notes CDPH

Are there any microbial derived biofuels in wide deployment today? I have assumed that the practicalities of cleanly growing industrial quantities of chemicals will never be cost competitive vs an inorganic process.

There are already inorganic mechanisms to synthetically generate petroleum feed stocks from air/water, so would be happy to hear the state of the art.