Nutrient recovery from wastewater by a consortium of algae species
Current energy sources are predominantly petroleum-based and their use increases greenhouse gas (GHG) emissions. As the global population grows, and along with it the demand for energy, there is a need to further develop renewable energy sources to avoid the effects of increasing atmospheric CO2 concentrations on the climate. Biofuels, a renewable energy source, have gained significant interest as a replacement for petroleum-based fuels due to their environmental benefits and carbon neutrality. Biofuels are expected to make up 9.0% of the total fuel consumption in the U.S. by 2040, up from 7.3% in 2019 . Currently, terrestrial crop-based biofuels are the most widely used. However, their production competes for land, fertilizer, and water resources with food production. Cultivation of microalgae-based biofuels can avoid this competition through higher productivity that leads to lower land requirements and their ability to use wastewater as a water and nutrient source for cultivation. We designed and tested a large-scale and semi-continuous operating algal polyculture cultivation system to determine the utility of using undiluted agricultural wastewater as the sole nutrient and water source for algal production. Algal biomass was evaluated for both biofuel production and water treatment (i.e., nutrient sequestration). Algal biomass was converted to a bio-oil by hydrothermal liquefaction (HTL). We also asked if algal production could be maximized by recycling nutrients recovered from HTL processing into a secondary bench-scale algal cultivation system (i.e., in a closed nutrient-loop system). Semi-continuous operations resulted in increased biomass yields, with projections estimated at 4,000 kg biomass/year in PHAE. Recycling HTL(aq) did not present additional benefits in sustaining or increasing algal productivity. Based on our estimations, the highest economic return will result from coupling nitrogen (N) water quality trading (WQT) with biomass conversion to bio-crude.
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