TABLE 4-6 Energy Return on Investment (EROI) Values for Open-Pond Systems


Source Nutrients Harvesting Extraction/ Processing Products and Coproducts EROI

Brentner et al. (2011)

Flue gas

Centrifuge, drying,

Hexane/

BDb

0.13

reference case Brentner et al. (2011) reference case with coproducts

Flue gas

press
Centrifuge, drying,
press

esterification
Hexane/
esterification

BDb, electricity, nutrients

0.28

Brentner (2011) best case swap raceways

Flue gas

Chitosan-flocculation

Supercritical methanol

BDb, electricity, nutrients

0.96

Clarens et al. (2010)

Industrial CO2

Alum flocculation, centrifuge

-

Algal biomass

1.06

Clarens et al. (2011) C-2

CCa coal plant

Auto-flocculation,
gravity,
homogenization

Hexane/ esterification

BDb, electricity, nutrients

1.36

Clarens et al. (2011) C-3

Flue gas

Auto-flocculation,
gravity,
homogenization

Hexane/ esterification

BDb, electricity, nutrients

1.99

Clarens et al. (2011) C-4

WWc, flue gas

Auto-flocculation,
gravity,
homogenization

Hexane/ esterification

BDb, electricity, nutrients

2.32

GREET baseline pathway

Flue gas

Bio-flocculation, flotation, centrifuge, homogenization

Hexane/ esterification

BDb, electricity, nutrients

0.39

Jorquera et al. (2010)

N/A

N/A

N/A

Algal biomass

7.01

Sander and Murthy (2010) filter press

N/A

Filter press, drying

Hexane/ esterification

BDb, fermentation stock

3.33

Sander and Murthy (2010) centrifuge

N/A

Centrifuge, drying

Hexane/ esterification

BDb, fermentation stock

1.77

Stephenson et al. (2010)

Flue gas

Alum flocculation,
centrifuge,
homogenization

Hexane/ esterification

BDb, electricity, nutrients

1.60

Vasudevan et al. (2012) dry extraction, nominal

Flue gas

Dissolved air flotation, centrifuge

Belt dryer

BD, electricity

0.3

Vasudevan et al. (2012) wet extraction, nominal

Flue gas

Dissolved air flotation centrifuge

Stream lysing, centrifuge, wash

BD, electricity

2.51


aCC = carbon capture.

bBD = biodiesel.

cWW = wastewater.

Notes: The GREET (Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation) model is a spreadsheet model developed at the Argonne National Laboratory for evaluating energy and emission impacts of advanced vehicle technologies and new transportation fuels.

Results in EROI show tremendous variation. The values at the low end suggest that the technology in its current form is not feasible for net energy return. In contrast, values at the high end suggest algal biofuel could have EROI considerably higher than corn-grain ethanol (EROI = 1.2; see Farrell et al., 2006). One source of variation in EROI is differences in choices of processes and inputs in the supply chain. Table 4-6 summarizes some results from comparison of technology systems. The three scenarios from Clarens et al. (2011) show changes as a function of carbon source and use of wastewater as replacement of nutrient input. Brentner et al. (2011) and Sander and Murthy (2010) highlighted how changing harvesting (and extraction) technologies have major effects on energy use.



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