The top five things that life cycle assessment can teach us about algae-to-energy technology

Size: px

Start display at page:

Download "The top five things that life cycle assessment can teach us about algae-to-energy technology"

Tiffany Skinner
7 years ago
Views:

1 The top five things that life cycle assessment can teach us about algae-to-energy technology A Presentation to Nov. 3, 2010 Andres Clarens University of Virginia Civil and Environmental Engineering

2 overview Background The impetus for algae bioenergy What has been learned in the past decades Methods Stochastic life cycle model Modeling assumptions Results Algae have much higher burden than expected - may not be silver bullet Alternative nutrient sources are a must Regional differences less important Discussion Top 5 things LCA can tell us about algae system Conclusions

3 background. algae biofuels concept is not new Efficient photosynthesis = accelerated growth Accelerated growth = accelerated element cycling Engineered element cycling = sequestration Bioresource Technology, (2008)99:6494.

4 motivation. no example of a process level LCA exists ethanol boom suggests that LCA should be used to drive decision making up front a lot of information floating in the literature suggesting yields that seemed too good to be true, e.g., times other forms of biomass Goal: to produce a cradle to gate analysis of algae production and compare it to conventional sources of next generation biofuel: corn silage and switchgrass.

5 method. stochastic LCA model 30-years region-specific climatological data photosynthetic efficiency data from the literature separations, mixing, etc from first principles process level impacts from ecoinvent database nutrient impacts from literature/stoichiometry Energy Use (MJ) Greenhouse gas emissions (kg CO2-eq) Eutrophication potential (kg PO4 - -eq) Land use (m 2 ) Water use (m 3 )

6 method. modeling assumptions Cradle-to-gate model: Functional unit: 317 GJ/year - primary energy used by 1 American, 2 Japanese, 3 Polish Citizens for 1 year (2008) Compare biomass production process with three benchmark crops Switchgrass Corn silage Canola Assumptions: Algae are grown in open ponds Wild-type, mixed communities of algae species Fresh water species Start-up environmental impacts (e.g., liners) small compared to use phase Separation of algae by flocculation, centrifugation Final product is wet biomass that could be: Reacted to make liquid fuels Burned to make bio-electricity

7 method. algae productivity

8 method. algae productivity 35! Productivity, dry (g/m2/day)! 30! 25! 20! 15! 10! 5! 0! Jan! Feb! Mar! Apr! May! Jun! Jul! Aug! Sep! Oct! Nov! Dec! Kadam, 2001! Benemann, 1997! Weissman & Tillett, 1990! Current Work!

9 results. base case not very rosy Base case analysis suggests many algae claims missing the full story land (ha) energy (MJ) x 10 4 GHG (kg CO2 eq) water (m 3 ) x 10 4 x 10 4 eutrophication (kg PO4 - eq) algae corn canola switchgrass But land use is important... the rest can be optimized algae: corn silage: switchgrass: canola:

10 top 5 things LCA can tell us about algae system 1. seemingly unfavorable LC impacts of algae compared to other biofuel stocks unfavorable v. infeasible? Algae is not a silver bullet, but it is an opportunity to do biofuels better

11 interlude. the trouble with blogs This work was published online in January (Environ. Sci. Technol. 2010, 44, )

12 interlude. the abstract Algae are an attractive source of biomass energy since they do not compete with food crops and they have higher energy yields per area than terrestrial crops. In spite of these advantages, algae cultivation has not yet been compared with conventional crops from a life cycle perspective. In this work, the impacts associated with algae production were determined using a stochastic life cycle model and compared with switchgrass, canola, and corn farming. The results indicate that these conventional crops have lower environmental impacts than algae in energy use, greenhouse gas emissions, and water regardless of cultivation location. Only in total land use and eutrophication potential does algae perform favorably. The large environmental footprint of algae cultivation is driven predominantly by upstream impacts, such as the demand for CO2 and fertilizer. To reduce these impacts, flue gas and, to a greater extent, wastewater could be used to offset most of the environmental burdens associated with algae. To demonstrate the benefits of algae production coupled with wastewater treatment, the model was expanded to include three different municipal wastewater effluents as sources of nitrogen and phosphorus. Each provided a significant reduction in the burdens of algae cultivation and the use of source-separated urine was found to make algae more environmental beneficial than the terrestrial crops.

13 results. mass balance check algae = C106H181O45N15P CAS = x 10 6 MGD BNR = x 10 6 MGD 1.5% of US population (supplemented)

14 results. sensitivity analysis Studied to understand the rate limiting steps

15 top 5 things LCA can tell us about algae system 1. seemingly unfavorable LC impacts of algae compared to other biofuel stocks unfavorable v. infeasible? Algae is not a silver bullet, but it is an opportunity to do biofuels better 2. quantification of burdens using LCA facilitates optimization use of wastewater to grow algae, energy efficient dewatering processes, etc.

16 results. what is the source of these impacts?

17 results. wastewater as a nutrient source?

18 top 5 things LCA can tell us about algae system 1. seemingly unfavorable LC impacts of algae compared to other biofuel stocks unfavorable v. infeasible? Algae is not a silver bullet, but it is an opportunity to do biofuels better 2. quantification of burdens using LCA facilitates optimization use of wastewater to grow algae, energy efficient dewatering processes, etc. 3. projected dual benefits for combined system approach algae from agricultural not engineering perspective, WWT mindset and margins at best

19 discussion. boom in algae LCA follows interest

20 discussion. comparative LCA Study FU Data Sources Co-products Uncertainty Stephenson et al. 1 tonne biodiesel NREL US LCI Digestion/ electricity no Campbell et al. 1 tonne km diesel truck Australian LCI Digestion/ electricity no Jorquera et al. 1 tonne dry solids Literature review None no Clarens et al. 317 GJ Ecoinvent and others None yes Lardon et al. 1 MJ fuel Ecoinvent Glycerin no

21 discussion. comparative LCA Study Algae type Culture Lipid content Yield Stephenson et al. Chlorella vulgaris Raceways + tubular airlift 40% 40 Mg TAG/ha-yr Campbell et al. Not specified Raceway ponds Not specified g/m2/d Jorquera et al. Nannochloropsis Raceway, plate PBR, tubular PBR 29.60% kg/m2-d Clarens et al. Wild type Raceway Not specified 43 Mg Ds/ha/yr Lardon et al. Chlorella vulgaris Raceway 38.50% g Ds/m2-d

22 discussion. system boundaries

23 discussion. system boundaries Sander and Murthy, 2010

24 discussion. system boundaries. biodiesel + bioelectricity

25 discussion. allocation a. multiple inputs b. multiple outputs c. open-loop recycling

26 discussion. differences in modeling endpoints Study Stephenson et al. Campbell et al. Jorquera et al. Clarens et al. Lardon et al. Impacts GWP, energy use, water use GWP, energy use, land use energy use GWP, land use, eutrophication, water use, energy use abiotic depletion, acidification, eutrophication, GWP, ODP, human toxicity, marine toxicity, land use, ionizing radiation, and photochemical oxidation

27 top 5 things LCA can tell us about algae system 1. seemingly unfavorable LC impacts of algae compared to other biofuel stocks unfavorable v. infeasible? Algae is not a silver bullet, but it is an opportunity to do biofuels better 2. quantification of burdens using LCA facilitates optimization use of wastewater to grow algae, energy efficient dewatering processes, etc. 3. projected dual benefits for combined system approach algae from agricultural not engineering perspective, WWT mindset and margins at best 4. normative methodologies must be established to enable comparison differences in functional units, boundaries, and allocation confusing to non-lca experts

29 results. incorporate conversions

30 top 5 things LCA can tell us about algae system 1. seemingly unfavorable LC impacts of algae compared to other biofuel stocks unfavorable v. infeasible? Algae is not a silver bullet, but it is an opportunity to do biofuels better 2. quantification of burdens using LCA facilitates optimization use of wastewater to grow algae, energy efficient dewatering processes, etc. 3. projected dual benefits for combined system approach algae from agricultural not engineering perspective, WWT mindset and margins at best 4. normative methodologies must be established to enable comparison differences in functional units, boundaries, and allocation confusing to non-lca experts 5. we need development on many fronts and to validate outcomes with LCA without compromising IP companies should seek to publish independent results of their processes

31 acknowledgments Co-authors: Funding: Lisa Colosi Shane Resurreccion Mark White

32 thank you for more information:

COMPARISON OF FIXED & VARIABLE RATES (25 YEARS) CHARTERED BANK ADMINISTERED INTEREST RATES - PRIME BUSINESS*

COMPARISON OF FIXED & VARIABLE RATES (25 YEARS) 2 Fixed Rates Variable Rates FIXED RATES OF THE PAST 25 YEARS AVERAGE RESIDENTIAL MORTGAGE LENDING RATE - 5 YEAR* (Per cent) Year Jan Feb Mar Apr May Jun