From Wastewater to Gasoline - Aqueous Biorefining of Polyhydroxybutyrate (PHB)-Enriched Biosolids

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Increasing population and rising living standards are driving the demand for more clean water and inexpensive energy, materials, and food. At the same time, this demand produces growing volumes of solid and liquid wastes that public utilities must manage. Current approaches to wastewater treatment expend large amounts of energy to remove organic carbon, nutrients, and pathogens from the water. However, these same "waste" constituents can potentially be recovered as energy or other valuable products during the wastewater treatment process. Recent research demonstrates that wastewater treatment can be accomplished using microorganisms that funnel waste organic carbon into their cells to form polyhydroxybutyrate (PHB) granules. The PHBs can then be separated from the resulting waste and converted to high-value products such as renewable gasoline, industrial chemicals, and bioplastics. Through integration of biological and catalytic technologies, the wastewater treatment processe can be reinvented as a "bio-refinery" that yields clean water as just one product of many. This re-invention of water infrastructure will also allow the diffusion of sustainable waste treatment and resource management concepts to a broader audience of students at all levels. Ultimately, such research and educational efforts are needed to support the Nation's shift towards more sustainable infrastructure.Motivated by developments in nascent biorefinery technologies, this project aims to realize and optimize the conversion of waste organic carbon streams to valuable industrial chemicals and gasoline-grade hydrocarbon fuels through the processing of PHB-enriched biomass. Experiments will be conducted to: (1) develop effective strategies for separating PHB from microbial biomass and promoting PHB depolymerization in an aqueous environment; (2) identify reaction conditions and catalysts for optimal dehydration and decarboxylation of the resultant PHB-derived monomers; and (3) demonstrate integrated conversion of waste organic carbon to gasoline-grade fuels and establish a techno-economic analysis (TEA) framework for the system. PHB separation from biomass and subsequent depolymerization will focus on aqueous-only strategies to minimize chemical inputs and byproduct wastes. Catalyst development will focus on low-cost solid acid catalysts (SACs) such as zeolites. The most promising catalysts will be evaluated in continuous flow reactors, and both preventative and regenerative strategies for maintaining catalyst activity will be tested. This research will support a path forward towards increased valorization of organic carbon-rich waste streams in municipal, agricultural, and industrial sectors, potentially flipping the energy balance and cost model for wastewater utilities. In addition, this project supports the career development of graduate and undergraduate student participants, and educational and outreach activities designed for K-12 students and teachers will support the diffusion of sustainable waste treatment and renewable energy production methods to a larger audience.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.