OMEGA is a system for cultivating microalgae using wastewater contained in floating photobioreactors (PBRs) deployed in marine environments and thereby eliminating competition with agriculture for water, fertilizer, and land. The offshore placement in protected bays near coastal cities co-locates OMEGA with wastewater outfalls and sources of CO 2 -rich flue gas on shore. To evaluate the feasibility of OMEGA, microalgae were grown on secondary-treated wastewater supplemented with simulated flue gas (8.5% CO 2 V/V) in a 110-liter prototype system tested using a seawater tank. The flow-through system consisted of tubular PBRs made of transparent linear low-density polyethylene, a gas exchange and harvesting column (GEHC), two pumps, and an instrumentation and control (I&C) system. The PBRs contained regularly spaced swirl vanes to create helical flow and mixing for the circulating culture. About 5% of the culture volume was continuously diverted through the GEHC to manage dissolved oxygen concentrations, provide supplemental CO 2 , harvest microalgae from a settling chamber, and add fresh wastewater to replenish nutrients. The I&C system controlled CO 2 injection and recorded dissolved oxygen levels, totalized CO 2 flow, temperature, circulation rates, photosynthetic active radiation (PAR), and the photosynthetic efficiency as determined by fast repetition rate fluorometry. In two experimental trials, totaling 23 days in April and May 2012, microalgae productivity averaged 14.1 ± 1.3 grams of dry biomass per square meter of PBR surface area per day (n = 16), supplemental CO 2 was converted to biomass with >50% efficiency, and >90% of the ammonia-nitrogen was recovered from secondary effluent. If OMEGA can be optimized for energy efficiency and scaled up economically, it has the potential to contribute significantly to biofuels production and wastewater treatment.
KeywordsBiofuelsWastewater TreatmentMicroalgaePhotobioreactorCO<sub>2</sub>Mass Transfer
T. Mata, A. Martins and N. Caetano, “Microalgae for Biodiesel Production and Other Applications: A Review,” Renewable and Sustainable Energy Reviews, Vol. 14, No. 1, 2010, pp. 217-232. doi:10.1016/j.rser.2009.07.020
G. C. Dismukes, et al., “Aquatic Phototrophs: Efficient Alternatives to Land-Based Crops for Biofuels,” Current Opinion in Biotechnology, Vol. 19, No. 3, 2008, pp. 235240. doi:10.1016/j.copbio.2008.05.007
Y. Chisti, “Biodiesel from Microalgae,” Biotechnology Advances, Vol. 25, No. 3, 2007, pp. 294-306. doi:10.1016/j.biotechadv.2007.02.001
M. Johnson and Z. Wen, “Production of Biodiesel Fuel from the Microalga Schizochytrium limacinum by Direct Transesterification of Algal Biomass,” Energy & Fuels, Vol. 23, No. 10, 2009, pp. 294-306. doi:10.1021/ef900704h
Y. Shen, et al., “Microalgae Mass Production Methods,” Transactions of the ASABE, Vol. 52, No. 4, 2009, pp. 12751287.
C. M. Beal, et al., “Energy Return on Investment for Algal Biofuel Production Coupled with Wastewater Treatment,” Water Environment Research, Vol. 89, No. 9, 2012, pp. 692-710. doi:10.2175/106143012X13378023685718
A. Clarens, et al., “Environmental Life Cycle Comparison of Algae to Other Bioenergy Feedstocks,” Environmental Science & Technology, Vol. 44, No. 5, 2010, pp. 1813-1819. doi:10.1021/es902838n
A. F. Clarens, et al., “Environmental Impacts of AlgaeDerived Biodiesel and Bioelectricity for Transportation,” Environmental Science & Technology, Vol. 45, No. 17, 2011, pp. 7554-7560. doi:10.1021/es200760n
T. Lundquist, et al., “A Realistic Technology and Engineering Assessment of Algae Biofuel Production,” Energy Biosciences Institute, Univeristy of California, Berkeley, 2010, p. 178.
J. Park, R. Craggs and A. Shilton, “Wastewater Treatment High Rate Algal Ponds for Biofuel Production,” Bioresource Technology, Vol. 102, No. 1, 2011, pp. 35-42. doi:10.1016/j.biortech.2010.06.158
M. O. P. Fortier and B. S. M. S. Sturm, “A Geographic Analysis of the Feasibility of Collocating Algal Biomass Production with Wastewater Treatment Plants,” Environmental Science & Technology, Vol. 46, No. 20, 2012, pp. 11426-11434. doi:10.1021/es302127f
J. Trent, et al., “Research Spotlight: The Future of Biofuels: Is It in the Bag?” Biofuels, Vol. 3, No. 5, 2012, pp. 521-524. doi:10.4155/bfs.12.53
J. Trent, “Wind Sea Algae,” International Workshop on Offshore Algae Cultivation, Lolland, 20-22 April 2009.
Fast Repetition Rate Fluorometry
Instrumentation and Control
P. E. Wiley, J. E. Campbell and B. McKuin, “Production of Biodiesel and Biogas from Algae: A Review of Process Train Options,” Water Environment Research, Vol. 83, No. 4, 2011, pp. 326-338. doi:10.2175/106143010X12780288628615
L. Harris, et al., “Potential Impact of Biofouling on the Proposed Offshore Membrane Enclosures for Growing Algae (OMEGA),” Biofouling, 2012, under Review.
J. H. Bailey-Brock, “Fouling Community Development on an Artificial Reef in Hawaiian Waters,” Bulletin of Marine Science, Vol. 44, No. 2, 1989, pp. 580-591.
K. A. Dafforn, T. M. Glasby and E. L. Johnston, “Comparing the Invasibility of Experimental ‘Reefs’ with Field Observations of Natural Reefs and Artificial Structures,” PLoS One, Vol. 7, No. 5, 2012, Article ID: e38124. doi:10.1371/journal.pone.0038124
W. Mulbry, P. Kangas and S. Kondrad, “Toward scrubbing the Bay: Nutrient Removal Using Small Algal Turf Scrubbers on Chesapeake Bay Tributaries,” Ecological Engineering, Vol. 36, No. 4, 2010, pp. 536-541. doi:10.1016/j.ecoleng.2009.11.026
M. C. Barnhart, “An Improved Gas-Stripping Column for Deoxygenating Water,” Journal of the North American Benthological Society, Vol. 14, No. 2, 1995, pp. 347-350. doi:10.2307/1467786
F. Ka?tánek, et al., “In-Field Experimental Verification of Cultivation of Microalgae Chlorella sp. Using the Flue Gas from a Cogeneration Unit as a Source of Carbon Dioxide,” Waste Management & Research, Vol. 28, No. 11, 2010, pp. 961-966. doi:10.1177/0734242X10375866
R. Putt, et al., “An Efficient System for Carbonation of High-Rate Algae Pond Water to Enhance CO2 Mass Transfer,” Bioresource Technology, Vol. 102, No. 3, 2011, pp. 3240-3245. doi:10.1016/j.biortech.2010.11.029
A. Carvalho, L. Meireles and F. Malcata, “Microalgal Reactors: A Review of Enclosed System Designs and Performances,” Biotechnology Progress, Vol. 22, No. 6, 2006, pp. 1490-1506.
J. Doucha, F. Straka and K. Lívansky, “Utilization of Flue Gas for Cultivation of Microalgae Chlorella sp.) in an Outdoor Open Thin-Layer Photobioreactor,” Journal of Applied Phycology, Vol. 17, No. 5, 2005, pp. 403-412. doi:10.1007/s10811-005-8701-7
T. Sobczuk, et al., “Carbon Dioxide Uptake Efficiency by Outdoor Microalgal Cultures in Tubular Airlift Photobioreactors,” Biotechnology and Bioengineering, Vol. 67, No. 4, 2000, pp. 465-475. doi:10.1002/(SICI)1097-0290(20000220)67:4 3.0.CO;2-9
American Public Heath Association, “Standard Methods for the Examination of Water and Wastewater,” Water Environment Federation, Alexandria, 1998.
Z. S. Kolber, O. Prá?il and P. G. Falkowski, “Measurements of Variable Chlorophyll Fluorescence Using Fast Repetition Rate Techniques: Defining Methodology and Experimental Protocols,” Biochimica et Biophysica Acta (BBA)-Bioenergetics, Vol. 1367, No. 1, 1998, pp. 88-106. doi:10.1016/S0005-2728(98)00135-2
A. Richmond, “Handbook of Microalgal Culture: Biotechnology and Applied Phycology,” Wiley-Blackwell, Hoboken, 2004.
H. Quiang, H. Guterman and A. Richmond, “Physiological Characteristics of Spirulina platensis Cultured at Ultra-High Cell Densities,” Journal of Phycology, Vol. 32, No. 6, 1996, pp. 1066-1073. doi:10.1111/j.0022-3646.1996.01066.x
J. Doucha and K. Livansky, “Productivity, CO2/O2 Exchange and Hydraulics in Outdoor Open High Density Microalgal (Chlorella sp.) Photobioreactors Operated in a Middle and Southern European Climate,” Journal of Applied Phycology, Vol. 18, No. 6, 2006, pp. 811-826. doi:10.1007/s10811-006-9100-4
P. Carlozzi and G. Torzillo, “Productivity of Spirulina in a Strongly Curved Outdoor Tubular Photobioreactor,” Applied Microbiology and Biotechnology, Vol. 45, No. 1, 1996, pp. 18-23. doi:10.1007/s002530050642
F. Rubio, et al., “Prediction of Dissolved Oxygen and Carbon Dioxide Concentration Profiles in Tubular Photobioreactors for Microalgal Culture,” Biotechnology and Bioengineering, Vol. 62, No. 1, 1999, pp. 71-86. doi:10.1002/(SICI)1097-0290(19990105)62:1 3.0.CO;2-T
M. Berenguel, et al., “Model Predictive Control of pH in Tubular Photobioreactors,” Journal of Process Control, Vol. 14, No. 4, 2004, pp. 377-387. doi:10.1016/j.jprocont.2003.07.001
B. S. Ferreira, et al., “Microporous Hollow Fibres for Carbon Dioxide Absorption: Mass Transfer Model Fitting and the Supplying of Carbon Dioxide to Microalgal Cultures,” Journal of Chemical Technology & Biotechnology, Vol. 71, No. 1, 1998, pp. 61-70. doi:10.1002/(SICI)1097-4660(199801)71:1 3.0.CO;2-R
E. Grima, et al., “Gas-Liquid Transfer of Atmospheric CO2 in Microalgal Cultures,” Journal of Chemical Technology and Biotechnology, Vol. 56, No. 4, 1993, pp. 329-337. doi:10.1002/jctb.280560402
P. Talbot, et al., “Absorption of CO2 in Algal Mass Culture Systems: A Different Characterization Approach,” Biotechnology and Bioengineering, Vol. 37, No. 9, 1991, pp. 834-842. doi:10.1002/bit.260370907
C. M. Beal, et al., “The Energy Return on Investment for Algal Biocrude: Results for a Research Production Facility,” BioEnergy Research, Vol. 5, No. 2, 2012, pp. 341-362. doi:10.1007/s12155-011-9128-4
C. M. Beal, et al., “Comprehensive Evaluation of Algal Biofuel Production: Experimental and Target Results,” Energies, Vol. 5, No. 6, 2012, pp. 1943-1981. doi:10.3390/en5061943
E. W. Becker, “Microalgae: Biotechnology and Microbiology,” Cambridge University Press, Cambridge, 1994.
A. Carvalho and F. Malcata, “Transfer of Carbon Dioxide within Cultures of Microalgae: Plain Bubbling versus Hollow-Fiber Modules,” Biotechnology Progress, Vol. 17, No. 2, 2001, pp. 265-272. doi:10.1021/bp000157v
A. Kumar, et al., “A Hollow Fiber Membrane PhotoBioreactor for CO2 Sequestration from Combustion Gas Coupled with Wastewater Treatment: A Process Engineering Approach,” Journal of Chemical Technology & Biotechnology, Vol. 85, No. 3, 2010, pp. 387-394. doi:10.1002/jctb.2332
S. Gao, et al., “Electro-Coagulation-Flotation Process for Algae Removal,” Journal of Hazardous Materials, Vol. 177, No. 1-3, 2009, pp. 336-343. doi:10.1016/j.jhazmat.2009.12.037
P. Holt, G. Barton and C. Mitchell, “The Future for Electrocoagulation as a Localised Water Treatment Technology,” Chemosphere, Vol. 59, No. 3, 2005, pp. 355-367. doi:10.1016/j.chemosphere.2004.10.023
G. Mouedhen, et al., “Behavior of Aluminum Electrodes in Electrocoagulation Process,” Journal of Hazardous Materials, Vol. 150, No. 1, 2008, pp. 124-135. doi:10.1016/j.jhazmat.2007.04.090
G. Azarian, et al., “Algae Removal by Electro-Coagulation Process, Application for Treatment of the Effluent from an Industrial Wastewater Treatment Plant,” Iranian Journal of Public Health, Vol. 36, No. 4, 2007, pp. 57-64.
P. Chen, et al., “Review of the Biological and Engineering Aspects of Algae to Fuels Approach,” International Journal of Agricultural and Biological Engineering, Vol. 2, No. 4, 2009, pp. 1-30.
O. Pulz, “Photobioreactors: Production Systems for Phototrophic Microorganisms,” Applied Microbiology and Biotechnology, Vol. 57, No. 3, 2001, pp. 287-293. doi:10.1007/s002530100702
Y. Lee, “Microalgal Mass Culture Systems and Methods: Their Limitation and Potential,” Journal of Applied Phycology, Vol. 13, No. 4, 2001, pp. 307-315. doi:10.1023/A:1017560006941
L. Downing, et al., “Nitrogen Removal from Wastewater Using a Hybrid Membrane-Biofilm Process: Pilot-Scale Studies,” Water Environment Research, Vol. 82, No. 3, 2010, pp. 195-201. doi:10.2175/106143009X426103
Y. S. Yun, et al., “Carbon Dioxide Fixation by Algal Cultivation Using Wastewater Nutrients,” Journal of Chemical Technology and Biotechnology, Vol. 69, No. 4, 1997, pp. 451-455. doi:10.1002/(SICI)1097-4660(199708)69:4 3.0.CO;2-M
D. Aitken and B. Antizar-Ladislao, “Achieving a Green Solution: Limitations and Focus Points for Sustainable Algal Fuels,” Energies, Vol. 5, No. 5, 2012, pp. 16131647. doi:10.3390/en5051613
L. Christenson and R. Sims, “Production and Harvesting of Microalgae for Wastewater Treatment, Biofuels, and Bioproducts,” Biotechnology Advances, Vol. 29, No. 6, 2011, pp. 686-702. doi:10.1016/j.biotechadv.2011.05.015
L. B. Christenson and R. C. Sims, “Rotating Algal Biofilm Reactor and Spool Harvester for Wastewater Treatment with Biofuels by Products,” Biotechnology and Bioengineering, Vol. 109, No. 7, 2012, pp. 1674-1884. doi:10.1002/bit.24451
L. E. de-Bashan and Y. Bashan, “Immobilized Microalgae for Removing Pollutants: Review of Practical Aspects,” Bioresource Technology, Vol. 101, No. 6, 2010, pp. 1611-1627. doi:10.1016/j.biortech.2009.09.043
H. V. Perales-Vela, J. M. Pena-Castro and R. O. CanizaresVillanueva, “Heavy Metal Detoxification in Eukaryotic Microalgae,” Chemosphere, Vol. 64, No. 1, 2006, pp. 1-10. doi:10.1016/j.chemosphere.2005.11.024
Q. Gao, Y. Wong and N. Tam, “Removal and Biodegradation of Nonylphenol by Different Chlorella Species,” Marine Pollution Bulletin, Vol. 63, No. 5, 2011, pp. 445451. doi:10.1016/j.marpolbul.2011.03.030
Y. Ghasemi, S. Rasoul-Amini and E. Fotooh-Abadi, “The Biotransformation, Biodegradation and Bioremediation of Organic Compounds by Microalgae,” Journal of Phycology, Vol. 47, No. 5, 2011, pp. 969-980. doi:10.1111/j.1529-8817.2011.01051.x
R. Munoz and B. Guieysse, “Algal-Bacterial Processes for the Treatment of Hazardous Contaminants: A Review,” Water Research, Vol. 40, No. 15, 2006, pp. 2799-2815. doi:10.1016/j.watres.2006.06.011
E. P. Kolodziej, et al., “Muncipal Wastewater Treatment Using an OMEGA Photobioreactor,” Water Research, Under Review.
US DOE, “National Algal Biofuels Technology Roadmap,” US Department of Energy, Office of Energy Efficiency and Renewable Energy, Biomass Program, 2010. http://biomass.energy.gov