Karla G. Morrissey

Nutrient recovery in domestic wastewater treatment has increasingly become an important area of study as the supply of non-renewable phosphorus decreases. Recent bench-scale trials indicate that co-generation of struvite and hydrogen using electrochemical methods may offer an alternative to existing recovery options utilized by municipal wastewater treatment facilities. However, implementation has yet to be explored at plant-scale. In the development of novel nutrient recovery processes, both economic and environmental assessments are necessary to guide research and their design. The aim of this study was to conduct a prospective life cycle assessment and cost analysis of a new electrochemical struvite recovery technology that utilizes a sacrificial magnesium anode to precipitate struvite and generate hydrogen gas. This technology was modeled using process simulation software GPS-X and CapdetWorks assuming its integration in a full-scale existing wastewater treatment plant with and without anaerobic digestion. Struvite recoveries of 18–33% were achieved when anaerobic digestion was included, with a break-even price of $6.03/kg struvite and $15.58/kg of hydrogen required to offset increased costs for recovery. Struvite recovery reduced aquatic eutrophication impacts as well as terrestrial acidification impacts. Tradeoffs between benefits from struvite and burdens from electrode manufacturing were found for several impact categories.

Background: The objective of this study was to evaluate the environmental impact of the production of a range of liquid biofuels produced from the combination of fermenting sorghum stalk juice (bioethanol) and the pyrolysis/hydrotreatment of residual bagasse (renewable gasoline and diesel). Life cycle impact assessment (LCIA) was performed on a farm-to-wheels system that included: (i) sorghum farming, (ii) juice extraction, (iii) juice fermenting, (iv) bagasse pretreatment, (v) bagasse thermochemical treatment (pyrolysis, hydroprocessing, and steam reforming), and (vi) typical passenger vehicle operation. LCIA results were compared to those of petroleum fuels providing the equivalent functional unit—cumulative kilometers driven by spark ignition direct injection (SIDI) vehicles utilizing either renewable gasoline or ‘bioE85—a blend of bioethanol and renewable gasoline,’ and a compression ignition direct injection (CIDI) vehicle utilizing renewable diesel produced from 76 tons of harvested sweet sorghum (1 ha). Results: Sweet sorghum biofuels resulted in a 48% reduction climate change impact and a 52% reduction in fossil fuel depletion. Additionally, reduced impacts in ozone depletion and eutrophication were found (67% and 47%, respectively). Petroleum fuels had lower impacts for the categories of non-carcinogenic health impact, smog, respiratory effects, and ecotoxicity, showing tradeoffs between sorghum and petroleum fuels. Conclusion: Overall, sorghum biofuels provide advantages in environmental impact categories including global warming potential, fossil fuel depletion and eutrophication, showing potential for sorghum as a promising second-generation feedstock for fuel.