This paper will highlight several process research efforts underway for some time that are converting various WWTP streams into viable products. These processes are (1) Production of commercial lipids and hydrogen gas from modified anaerobic digester operations based on ceasing digestion activity when both hydrogen levels and fatty acid production are highest with the hydrogen collected as a gaseous product and the fatty acids sent on to aerobic bioprocessing for conversion into cellular-based lipid products; (2) Conversion of microbial proteins found within both aerobic consortia from the aeration chambers and anerobic consortia found in biosolids into commercially viable adhesives; (3) Conversion of biogas into lipid products via methanotrophic bioconversion; and (4) Capture of CO2 exiting aeration basins using engineered photobioreactors cultivating green microalgae resulting in the formation of algal-based lipids and proteins that integrate back into the above-mentioned lipid/protein oriented systems. Additionally, the captured CO2 is eligible for recently passed 45Q IRS tax credits thus adding another level of profit generation.
All four R&D efforts indicate a high degree of scalable viability. The lipids produced from the three lipid-producing processes have a high degree of unsaturation fatty acid compositions making them ideal for later processing into a variety of commercial products. The proteins produced via both the microalgae and bacterial sources have been found to produce adhesives with lapped shear-strength yields in excess of 500 psi with some formulations exceeding 800 psi. Hydrogen generation was also observed with gas compositions exceeding 50% at the point of proposed digestion reorientation. Methanotrophic conversion twice as much lipids as non-amended microbial populations. Finally, concerns over heterotrophic microbial contamination overcoming the microalgal population in the photobioreactor was also evaluated with results indicating that the algae could remain as the dominant microbial population member.
The results of this presentation will show the high potential for successful conversion of a WWTP into a biorefinery with little design modification to the WWTP system and some additional process equipment needed for co-product(s) production. The results clearly illustrate both the greatly added level of sustainability to WWTP operations and a viable source of numerous commercial products from what traditionally has been viewed as a waste management problem (wastewater treatment).