Use of Algae Reactors to Remediate Eutrophication
in the Mississippi River Delta
Brendan ScottJoseph Vassios
BZ 572November 9, 2010
Mississippi River Basin 1.5 Million Square Miles
Ecology of Hypoxia
Introduction – Mississippi River Increased fertilization and leaching of top soil
has increased nitrogen concentrations in the Mississippi River and consequently the Gulf of
Mexico Increased concentrations of nitrogen has led to
seasonal eutrophication of the Gulf of Mexico
Nitrogen Nitrogen is used by plants for:
Nucleic acid (DNA & RNA) Amino acids Pigments
Eutrophication as a result of increased nitrogen can lead to: Detrimental algae blooms Reduced dissolved oxygen (hypoxia) Fish kills
http://toxipedia.org/display/toxipedia/Algal+Bloom
Nitrogen’s Role in Eutrophication
http://www.physicalgeography.net/fundamentals/9s.html
Current Regulation of Nitrogen EPA limits for nitrogen in drinking water:
Nitrate – 10 ppm Nitrite – 1 ppm Ammonia – Varies Total N – 11 ppm Leaching from agricultural soils is currently
unregulated
USGS, 2010
Nitrogen Levels Directly Proportional to Amount of Tile Farming
USGS, 2010
Current Remediation Strategies
Current strategies incorporate mitigation by altering farming processes Reduce nitrogen inputs
Crop rotation Modified cultural practices
Previous research using algae for wastewater remediation (phytoaccumulation): Algae turf scrubber Algae biofilm
Algae Turf Scrubber
Algae Biofilm
Qun et al., 2008
Algae Biofilm
~80% Reduction in Total N
Qun et al., 2008
Potential Algae SpeciesAnabaena cylindrica Spirogyra sp.
http://plantphys.info/plant_biology/labaids/cyanobacteriaslides.shtml
http://www.uwsp.edu/biology/courses/botlab/Lab20a.htm
Algae is also intentionally cultivated, supporting a multimillion dollar international industry
Design Criteria For Algae Reactor
Simple Passive Relatively efficient Movable Exploit a natural ecosystem Turn a waste stream into energy
Palate sized for ease of transport with a footprint of 11 square feet
Ergonomically accessible for reach with a height of 5 feet
Effective surface area of 1320 square feet created by 120 trays spaced one ½ inch apart
Cheap durable construction materials
Plexi glass for reactor housing
Removable screens as scaffolding for algae
Hybridization of Existing Technologies
Wastewater Treatment Calculations
Monod Growth KineticsWith variables of
Influent Nitrogen ConcentrationReactor Effluent Substrate Concentration
Specific Growth RateHydraulic Retention Time
S=K[(1+bθ)/(θ(Yq-b)-1)]
Yielded reactor surface areas smaller than “Dead Zone”
Optimal Residence Time of 8 Days
Calculation Based on Equal Areas
Area of “Dead Zone”
8000 square miles at peak
Effective surface area of reactor
1320 Square feet
Number of units required for total removal 169 million, Equivalent to 67 square miles of reactors 0.004% of farm land in Mississippi River basin
Moving Forward
Create working prototype Trials with various algae species, light conditions,
residence times Test influent and effluent conditions over long
time span Test reactor algae as fertilizer or product stream Determine economic viability of reactors Conduct risk assessment and feasibility studies
Questions?
References Size-Dependent Nitrogen Uptake in Micro and Macroalgae, M.
Hein, Marine Ecology Press Series Vol. 118, 1995 Sources and Transportation of Nitrogen in the Mississippi River
Basin, D. Goolsby, USGS Phytoremediation as a Management Option for Contaminated
Sediments in Tidal Marshes, V. Bert, Environmental Science Vol. 16, 2009
Nutrient Uptake in Streams Draining Agricultural Catchments of the Midwestern United States, M. Bernot, Fresh Water Biology Vol. 51, 2006
Nutrient Removal Potential of Selected Aquatic Macrophytes, K. Reddy, Journal of Environmental Quality Vol. 14, 1985
Nitrogen and Phosphorus Removal from Urban Wastewater by the Microalga Scendesmus obliquus, M. Martinez, Bioresource Technology, Vol. 73, 2000
Nitrogen and Phosphorus in the Upper Mississippi River: Transport, Processing, and effects on the river ecosystem, J. Houser, Hydrobilogia Vol. 640, 2010
Nutrient Content of Seagrass and Epiphytes in the Northern Gulf of Mexico: Evidence of Phosphorus and Nitrogen Limitation, M. Johnson, Aquatic Botany Vol. 85, 2006
Reducing Hypoxia in the Gulf of Mexico: Advise from Three Models, D. Scavia, Estuaries Vol. 27, 2004
Limnology, Third Edition, R. Wetzel, Academic Press
Ecological Stoichiometery in Freshwater Benthic Systems: Recent Progress and Perspectives, W. Cross, Freshwater Biology Vol. 50, 2009
Postaudit of Upper Mississippi River BOD/DO Model, W. Lung, ASCE
Environmental Biotechnology: Principals and Applications, P. McCarty, McGraw-Hill, 2001
An economic assessment of algal turf scrubber technology for treatment of dairy manure effluent, C. Pizarro, Biological Engineering Vol. 26, pg. 321-326, 2006
Removing nitrogen and phosphorus from simulated wastewater using algal biofilm technique, W.E.I. Qun, Front. Environ. Sci. Engin. Vol. 2, pg. 446-451, 2008
Nutrients in the Nation’s Streams and Groundwater, 1992-2004, Circular 1350, N. Dubrovsky, USGS, 2010. Accessed at: http://pubs.usgs.gov/circ/1350/