Nutrient recovery from anaerobic co-digestion of Chlorella vulgaris and waste activated sludge Michael Gordon 1, Tyler Radniecki PhD 2, Curtis Lajoie PhD 2 BioResource Research Interdisciplinary Program 1, School of Chemical, Biological, and Environmental Engineering 2 Oregon State University, Corvallis, OR 97331

Biofuels Renewable energy sourced from biomass Ideally carbon neutral Policy mandated Energy Policy Act 2005, Energy Independence and Security Act 2007 Renewable Fuel Standard- 38 billion gal by climatetechwiki.org iipdigital.usembassy.gov greenwoodresources.com

Algal Biofuels Unique advantages of algal biomass lipid dense: up to 70% dry wt High area productivity (1.25 kg m 3 /day) Doesn’t require arable land Water source flexibility energytrendinsider.com 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? mnmtraders.weebly.com Rock Phosphate

Phosphorus is non-renewable

Viacarri, 2009 Phosphorus A rise in biofuel production is expected to increase competition with industrial agriculture for limited resources

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 CH 4 production Provides a way to manage large quantities of residual biomass Bill Chambers of Stahlbush Island Farms Stahlbush.com

Anaerobic Digestion epa.gov Backyard-scale digester in Eugene, OR

Sewage Coarse Filter Primary Settling Tank liquid Aerobic Growth primary solids WAS Anaerobic Digester Robert Esch Anaerobic Digestion Widely used in wastewater treatment plants to treat sewage Produces a nutrient rich effluent Settling Tank slurry

grow algae harvest drying lipid extraction algal debris lipids glycerol methyl esters MeOH + NaOH anaerobic digester biogas effluent: liquid nutrient-rich effluent: solids

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

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 Inoculum: Corvallis WWTP Buffered H20 Digester Substrate: Algae and or WAS Head space (N 2 ) Digester Breakdown Total Liquid =100 mL

Lab-scale batch anaerobic digesters

Monitoring: pH, biogas, CH 4, VS reduction

Nutrient quantification Influent Hach® vials Total NTotal P

Nutrient quantification Effluent CentrifugePellet Supernatant Hach: Total N, Total P Ion Chromatography: PO 3 NO 2 Colorimetric: NH 4

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 % CH 4 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)]* % 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 NH 4 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