Abstract
This work presented a Spatially-Explicit-High-Resolution Life Cycle Assessment (SEHR-LCA) model for wastewater-based algal biofuel production, by integrating life cycle assessment, GIS analysis, and site-specific Wastewater Treatment Plants (WWTPs) data analysis. Wastewater resources, land availability, and meteorological variation were analyzed for algae cultivation. Three pathways, Microwave Pyrolysis, hydrothermal liquefaction, and lipid extraction were modeled for bio-oil conversion. This model enables the assessment of seasonal and site-specific variations in productivity and environmental impacts of wastewater-based algal bio-oil across the whole U.S. Model results indicate that wastewater-based algal bio-oil can provide an opportunity to increase national biofuel output. The potential production of algal bio-oil can reach to 0.98billiongallon/yr, nearly 20% of advanced biofuel projection as outlined in the U.S. Energy Independence and Security Act (EISA) of 2007. LCA results shows significant variations among different locations, WWTPs, and operational seasons. Although not competitive to conventional fossil fuel in energy efficiency, wastewater-based algal biofuel could offer significant benefit in controlling GHG emissions. However, spatial analysis shows that only 61% of the total wastewater could be used, based on current land use efficiency for algae cultivation and land availability around each WWTP in a radius where algal biofuel production is energy positive (energy output>energy input). These results indicate that land availability could be a significant challenge for wastewater-based algal biofuels that have not been considered in previous studies. They also suggest that improvement should be made in technological development and system design to increase energy and land use efficiency for full potential of wastewater as a promising resource for algal biofuel production. Although focusing on the U.S. as the case study, the developed methodology could be used for spatially explicit analysis of algal biofuel integrated with wastewater on macro-scale in other regions as well.
Highlights
Algae have unique and desirable characteristics as a source for biofuel, including rapid growth and capability of growing in poor quality water, but there remain a number of challenges before the technology can be deployed at large-scale [1,2]
The functional unit (FU) was defined as 50,700 MJ/yr, the average energy embodied in gasoline required for driving a compact car by an American for a year (13,476 miles driving per year) [48,49]
Environmental impacts associated with nitrogen and phosphorous removal by algae were considered as credits, as algae cultivation replaced the corresponding N and P treatment from Wastewater Treatment Plants (WWTPs)
Summary
Algae have unique and desirable characteristics as a source for biofuel, including rapid growth and capability of growing in poor quality water, but there remain a number of challenges before the technology can be deployed at large-scale [1,2]. A number of studies have been conducted to investigate the potential of the synergies of algae biofuels and wastewater, from empirical selection of algal strains to pilot-scale algae cultivation systems and energy conversion pathways [8,9,10,11]. Despite such progress and promise, there has been no large-scale algae-wastewater facilities emerging yet. LCA has become an actively researched area and has been increasingly applied in academic and industrial fields for environmental impact assessments
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