(273g) Trash to Treasure: Converting Nitrogen Pollutants into Industrial Chemicals

To realize the circular bioeconomy, low cost and efficient methods must be developed that simultaneously prevent societal wastes from becoming environmental pollutants, while upcycling wastes to useful chemicals for use by society. This (a) prevent those wastes from being released and (b) offset the need to produce more of the chemical for societal uses from non-renewable resources. Reactive nitrogen (ammonia, nitrates, and organic nitrogen) currently operates as a once-through process, rather than a circular process, requiring energy intense synthesis using the Haber-Bosch process and is released as valueless N₂ in wastewater treatment. A biochemical process that can effectively concentrate and homogenize reactive nitrogen species from wastewater could create clean water, while making a nitrogen co-product.

Here, we describe a biochemical process that converts reactive nitrogen species into a nitrogen storage polymer cyanophycin. Cyanophycin granules accumulate in the cytoplasm, are composed of aspartate and arginine (22% wt% N), and can be processed into high performance or water absorbent polymers. We have focused on two approaches: recombinant Acinetobacter baylyi ADP1 and microbial consortia currently used to convert reactive nitrogen into N₂. ADP1 can concentrate nitrogen 1000-fold and in mock wastewater reduce reactive nitrogen to below the Environmental Protection Agency (EPA) limit. Deletion of a cyanophycinase (cphB) increased the intracellular cyanophycin accumulation by four-fold. In denitrifying microbial consortia, we have identified previously overlooked cyanophycin synthase genes in several species. These data strongly suggest organisms commonly found in wastewater treatment have the capacity and to some degree may already accumulate cyanophycin. This work demonstrates a new approach to denitrification that produces a valuable co-product and enhances the circular economy by recycling waste nitrogen from point sources.