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/