Recovery of nutrients from biomass for nutrient recycling John Hewson, Ryan Davis, Todd Lane, Nicholas Wyatt Sandia National Laboratories Anthony Siccardi, Zachary Fuqua Texas A&M University 2013 Algae Biomass Summit October 1, 2013 Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy s National Nuclear Security Administration under contract DE-AC04-94AL85000.
Background: Biomass at energyconsumption relevant scales exceeds current nutrient production Pate, Klise, Wu, Resource demand implications for US algae biofuels production scale-up, Applied Energy, 88:3377-3388 (2011). To meet 10% of liquid fuel needs (roughly 30 BGY) Algal biomass: 200 500 Mt/yr. Nitrogen: 18 45 Mt/yr Compare 14 Mt/yr in 2006 Haber-Bosch process requires energy. Phosphorous: 2.4 6 Mt/yr Compare 4.1 Mt/yr in 2006 P is mined resource. Recent concerns over peak phosphate: The Achilles Heel of Algae Biofuels: Peak Phosphate, Forbes, Feb. 2012. base 10% 20% base 10% 20% Food vs fuel: Nutrient use for algae should not compete with food production Nutrient run-off has detrimental environmental consequences (algal blooms).
Need to recycle nutrients Cannot afford to pass through once only Nutrients are needed for biological productivity, not fuel. N: amino acids (incl. chlorophyll) P: nucleic acids, phospholipids, ATP. Our work: Develop and evaluate processes for nutrient recycling. Two steps: Convert organic N and P to inorganic forms. Separate nutrients from energy products & return to culture. Target struvite (MgNH 4 PO 4 ) as transportable, fungible nutrient. http://wastemgmt.ag.utk.edu/researchprograms/struvi te_2.htm Recovers 1:1 N:P Precipitates at accessible concentrations. Experience in waste water treatment industry. Involves Mg readily available in seawater (and inexpensive otherwise). Alternates include Ca and Mg phosphates.
Hypothetical process Cultivation Harvest and dewater (>90% water) Initial lipid extraction Lipids Remineralize phosphate Secondary lipid extraction Protein fermentation Butanol Lipids Mg, Struvite PO NH 4 precipitation 3 4 MgNH 4 PO 4
Remineralize phosphorous Remineralize P from organic phosphates (nucleic acids, ATP, phospholipids, luxury phosphate storage). Approaches Dilute acid hydrolysis Endogenous enzymes. Supplemental enzymes. See Todd Lane s Wednesday afternoon talk. mm PO 4 released from 2% solids TX biomass Results in PO4 availability in mm concentrations. 5
Remineralize N through protein fermentation Amino acid fermentation yields ammonium and higher alcohols. Huo et al., Nature Biotechnology, 29(4):346-351, 2011. Proteins recalcitrant to dilute acid hydrolysis. Adding enzymemix more than doubles amino acid availability. Resulting ammonium available at moderate concentrations. 6
Hypothetical process Cultivation Harvest and dewater (>90% water) Initial lipid extraction Lipids Remineralize phosphate Secondary lipid extraction Protein fermentation Butanol Lipids Mg, Struvite PO NH 4 precipitation 3 7 MgNH 4 PO 4
Recover nutrients through precipitation Struvite (MgNH 4 PO 4 ) is useful mineral form of nutrients. Alternates include Ca and Mg phosphates. Looking at designing system to maximize recovery need to measure precipitation kinetics. At concentrations available in nutrient recovery, potential to recover >90% PO 4-3. Outstanding issues with effect of organics on kinetics. 8
Volume Fraction Experiment Details: Struvite precipitated in situ in a Malvern Mastersizer Particle size distributions measured via laser diffraction ph range 8.7 8.85 Equimolar concentrations Mg, NH 4, and PO 4 Salts used MgCl 2 6H 2 O, KH 2 PO 4, NH 4 Cl Total solution volume is 120 ml ph adjusted using 1.0 M NaOH Time started when ph rises above 8.0 Most results at 3000 rpm. Notes on the data: D[4,3] = Volume weighted mean D[3,2] = Surface weighted mean All diameters are in microns Times are in minutes 10 9 8 7 6 5 4 3 2 1 0 0.1 1 10 100 1000 Particle Diameter (µm)
Struvite size distribution (high mixing rates) Volume Fraction Crystal size distribution is measured ph is controlled within 8.5 < ph < 9 Greater supersaturation yields greater mass precipitated. Size distributions are similar even with very different total mass precipitated. Supersaturation affecting nucleation more than size for this configuration 10 9 8 7 6 5 Particle size distribution Time since ph > 8 0.52 0.80 1.10 1.70 1.98 2.58 12.05 4 3 D[4,3] = Volume weighted mean D[3,2] = Surface weighted mean 2 1 0 0.1 1 10 100 1000 Particle Diameter (µm)
Precipitation rates derived from measurements Obscuration Rate (%/min) 25 20 15 10 5 0 0 1 2 3 4 5 6 Salt Concentrations (mm) Rate at which crystals form is strongly dependent on the salt concentration (supersaturation) Low initial salt concentrations result in very slow crystal growth while higher concentrations result in greatly increased rates of precipitation
Precipitation rates derived from measurements Predictions of reactant depletion using different reaction rate models (with lines) are compared with measurements (symbols) from (Kofina and Koutsoukos, 2005). (Nominally the two sets of symbols should follow the same trend: their spread is indicative of experimental uncertainty)
Mixing rates affect final size distribution Volume Fraction 16 14 12 10 Time since ph > 8 11.63 12.38 11.67 30 30 Precipitation in a beaker using magnetic stir bar (much lower shear rate) 8 6 4 2 0 0.1 1 10 100 1000 Particle Diameter (µm) Need a good estimation for the actual shear rate in the geometries used to determine effects of shear on precipitation kinetics
Hypothetical process Cultivation Harvest and dewater (>90% water) Initial lipid extraction Lipids Remineralize phosphate Secondary lipid extraction Protein fermentation Butanol Lipids Mg, Struvite PO NH 4 precipitation 3 14 MgNH 4 PO 4
Grams Ash Free Dry Weight/m 2 /day Outdoor N. salina cultivation with struvite Nannochloropsis salina (CCMP 1776) Control: seawater supplemented with ODI nutrients at a 16:1 N:P ratio Struvite: commercial struvite to replace 33, 67 and 100% of the P. Initial stocking density of ~0.15 g/l afdw at 5 cm depth Water depth in each raceway was gradually increased to a final depth of 20 cm providing a total working volume of 550 L 16 Daily biomass productivity (g AFDW/m 2 /day) cultivated with P replacement (% of control) using commercial struvite 14 12 10 8 6 4 2 0 Control 100 67 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Day of Culture 15
Cultivation with struvite (reagent grade and dairy-waste byproduct) Replace phosphate with struvite (reagent grade or dairy waste effluent product). With dairy waste effluent: remove trace metals and nutrients? 16
Cultivation with excess struvite Use enough struvite to provide recommended N, excess P (16x). 2/3 struvite does not initially dissolve (noisy absorption signal). Multicultivator, sinusoidal diurnal cycle, peak 1000 E, 21 to 24 C 17
Summary Production of algal biofuels at petroleum-replacement levels will involve substantial nutrients, impacting supplies unless recycling is implemented. Enhance biomass utilization Remineralize P via acid hydrolysis or enzymatic processes. Remineralize N in conjunction with protein fermentation. Recover nutrients through mineral precipitation, other separations. Struvite is promising approach to recovery of P and fraction of N. Measurements of size distribution evolution as function of reactant concentrations and mixing rates will guide process development. Cultivation using struvite is equivalent to that with original nutrients. 18
Acknowledgments DOE EERE BioEnergy Technology Office Sandia National Labs Texas Agrilife Ryan Davis Anthony Siccardi Todd Lane Pamela Lane Nicholas Wyatt Deanna Curtis Open Algae Peter Kipp Hoyt Thomas
THANK YOU JCHEWSO@SANDIA.GOV 20
Induction time affects struvite size distribution Induction Time (sec) 700 600 500 400 300 200 100 0 0 1 2 3 4 5 6 Salt Concentrations (mm) Induction time shows a strong dependence on initial salt concentration (supersaturation) at low values and becomes relatively independent at high salt concentrations]
Algae cultivation and N:P ratios Traditionally: Redfield ratio (16:1 to 13:1) adopted for N:P ratio. Recent evidence suggests productive growth under range of N:P ratios Geider, R. J. and J. L. Roche (2002). "Redfield revisited: variability of C:N:P in marine microalgae and its biochemical basis." European J. Phycology 37: 1-17. Li, X., et al. (2010). "Effects of different nitrogen and phosphourous concentrations on the growth, nutrient uptake and lipid accumulation of a freshwater microalga Scenedesmus sp." Bioresource Technology 101: 5494-5500. 22
Nutrient costs are substantial Recent paper suggests nutrient costs (even with partial recycle) are substantial. Liu, et al., "Pilot-scale data provide enhanced estimates of the life cycle energy and emissions profile of algae biofuels produced via hydrothermal liquefaction " Bioresource Technology, 148:163-171, 2013. 23