Nutrient recovery from anaerobic co-digestion of
Chlorella vulgaris and waste activated sludge
Michael Gordon1, Tyler Radniecki PhD2, Curtis Lajoie PhD2
BioResource Research Interdisciplinary Program1, School of Chemical, Biological, and Environmental Engineering2
Oregon State University, Corvallis, OR 97331
Biofuels
• Renewable energy sourced from biomass
• Ideally carbon neutral
• Policy mandated
http://green.blogs.nytimes.com
• Energy Policy Act 2005, Energy Independence and Security Act 2007
• Renewable Fuel Standard- 38 billion gal by 2022
climatetechwiki.org
greenwoodresources.com
iipdigital.usembassy.gov
Algal Biofuels
• Unique advantages of algal biomass
• lipid dense: up to 70% dry wt
• High area productivity (1.25 kg m3/day)
energytrendinsider.com
• Doesn’t require arable land
• Water source flexibility
solixbiosystems.com
Algal Biofuels
Chisti et al., 2007
Algal Biofuels
• Large scale production requires substantial inputs of nutrients
• “Nutrients”= Nitrogen and Phosphorus
• 45 kg Nitrogen and 4 kg Phosphorus / 1000 kg biomass
• Nutrient inputs economically sustainable?
Rock Phosphate
mnmtraders.weebly.com
Phosphorus is non-renewable
Phosphorus
• A rise in biofuel production is
expected to increase
competition with industrial
agriculture for limited
resources
Viacarri, 2009
Anaerobic Digestion
• Proposed as a means of nutrient recovery and recycling
• Digestion releases nutrients from biomass into solution for later recovery
• Proven technology at scale
• Enhanced energy yield from CH4 production
• Provides a way to manage large quantities of
residual biomass
Stahlbush.com
Bill Chambers of Stahlbush Island Farms
Anaerobic Digestion
Backyard-scale digester
in Eugene, OR
epa.gov
Anaerobic Digestion
• Widely used in wastewater treatment plants to treat
sewage
• Produces a nutrient rich effluent
Robert Esch
Sewage
Coarse
Filter
Primary
Settling
Tank
liquid
Aerobic
Growth
primary solids
slurry
Settling
Tank
WAS
Anaerobic
Digester
grow algae
harvest
effluent: liquid
nutrient-rich
algal
debris
anaerobic
digester
effluent:
solids
biogas
drying
glycerol
lipid
extraction
lipids
MeOH +
NaOH
methyl
esters
Research Goal: Quantify recoverable nutrients in liquid phase of anaerobic digester
effluents
Questions:
1. How does the digestion of algae compare to WAS?
2. Is co-digestion necessary to maintain digester performance?
3. Does the digestion of lipid-extracted cells differ from the digestion of whole cells?
Hypothesis: digester performance and nutrient recovery will decline as the percentage of
algal substrate increases, and, the digestion of lipid-extracted cells will result in lower
digester performance and nutrient recovery when compared to whole cells
Digester Breakdown
Lab-scale batch anaerobic digesters
• Constant loading rate of 2070 mg VS L-1
• Constant inoculum to substrate ratio of 5.8:1
• Substrate composition varies
• *1 trial w/ whole cells and 1 w/ lipid-extracted algal
debris
Head space (N2)
Inoculum: Corvallis
WWTP
Total Liquid
=100 mL
Buffered H20
Digester Substrate:
Algae and or WAS
Lab-scale batch anaerobic digesters
Monitoring: pH, biogas, CH4, VS reduction
Nutrient quantification
Influent
Hach® vials
Total N
Total P
Nutrient quantification
Effluent
Centrifuge
Pellet
Hach: Total N,
Total P
Supernatant
Ion
Chromatography:
PO3 NO2
Colorimetric: NH4
Results
• Biogas production provides a
measure of digester activity
• Substrate loading standardized by
volatile solids (VS) content
• Sig. diff. in biogas yields b/w WAS
control and 100% lipid-extracted C.
vulgaris (p<0.001)
• respective cumulative biogas
yields 657 and 408 mL g-1 VS
• 85 % CH4
Results
• As the % of algae increases, a greater reductions in biogas were observed
• [1-(Treatment biogas(mL) / Control biogas (mL)]*100
• Sig. diff. in biogas yields b/w WAS control and 100% lipid-extracted C. vulgaris treatments (p<0.001)
Results
• Recoverable nutrients
are those that end up
in the supernatant
• Reductions in biogas
correlated with a
decline in recoverable
nutrients
• Nutrient recovery is
more efficient with
WAS than with C.
vulgaris
Sig. Diff: nitrogen: p<0.02, phosphorus: p<0.001
Results
• [1-(Treatment nutrients recovered (mg) / Control nutrients recovered (mg)]*100
• 100% C. vulgaris treatment sig diff than WAS control, N: p<0.02, P: p<0.001
• No sig. dif. b/w influent nitrogen in WAS control and 100% C. vulgaris treatment (p=0.8)
• Sig. dif. b/w influent phosphorus in WAS control and 100% C. vulgaris treatment (p=0.04)
Results: Co-digestion necessary?
•
Ammonia inhibition not observed
•
NH4 concentrations well below inhibitory levels (1500 ppm)
•
Future experiments: shock loading
Results: Whole cells vs lipid-extracted cell debris?
•
Whole cells produced significantly more biogas than lipid-extracted cells (p<0.001)
p<0.001
Results: Whole cells vs lipid-extracted cell debris?
• Nutrient recovery from whole cells was more efficient than lipid-extracted
p<0.001 for both N and P
Conclusions
• Increasing concentrations of C. vulgaris resulted in lower biogas production
• Decrease in biogas production correlated to a decline in recoverable nutrients
• Anaerobic digestion of algal debris as a means of nutrient recovery is possible though
not as efficient as nutrient recovery from waste activated sludge
• More data is needed to determine the relationship between % of algal substrate and
recoverable nutrients
• More precise analytical tools are needed to quantify nutrients in sludge
Acknowledgements
• Support provided through OSU’s USDA funded Bioenergy Education Project
• Collaborators: Brian Kirby and Xuwen Xiang
• City of Corvallis wastewater treatment plant
• Advisors: Dr. Radniecki and Dr. Lajoie