Evaluation of a wetland-biopower concept for nutrient removal and value recovery from the Netley-Libeau marsh at Lake Winnipeg

Nazim Cicek, Dept of Biosystems Engineering, Univ. of Manitoba

Susan Lambert, Dept of Biosystems Engineering, Univ. of ManitobaHank Venema , IISD , Winnipeg, ManitobaKen Snelgrove, Dept of Civil Engineering, Univ. of ManitobaEric Bibeau, Dept of Mechanical Engineering, Univ. of Manitoba

Lake WinnipegLake Winnipeg is the 10th largest freshwater lake in the

worldIts watershed cover 948,000 m3

Intensive agriculture – farmland & livestock productionElevated nutrient loadings – frequent algae bloomsDissolved oxygen depletion impacts fish &

invertebrates

Red River largest contributor of nutrients to Lake Winnipeg

Enters the lake through the 258 km2 Netley-Libau Marsh

The Netley-Libau Marsh58-66% of P, and about 43% of N enter Lake Winnipeg

via the Netley-Libau Marsh

58% and 28% increase P and N from 1978 to 1999

Hydropower regulation of lake discharge pattern started in 1976

Inverts natural discharge pattern with peak discharge in winter rather than summer

Results in additional retention of 200 ton of P/year

Nutrient source control difficult due to non-point sources and jurisdictional complications

The Netley-Libau Marsh

Colour Infrared Photomosaic of Netley-Libau

Marsh2001

Biomass Harvesting

End-of-pipe strategy for nutrient removal

Stimulate N and P uptake by vegetation growth

Prevent nutrient re-release from decaying marsh vegetation during fall die-back

If conservation area, harvest only possible during periods of minimal ecological impact (winter-frozen water surface)

Bio-power IntegrationUsing harvested biomass to produce carbon-

neutral energy Electrical energy by thermal processesEthanol through fermentation

Other previously suggested uses of the biomass:

Animal feed, fiber board, insulation, compost

Mitigation of GHG emission by:Displacing fossil fuels Displacing methane and NOx generation from

decaying biomass

Study ObjectivesEvaluation of integrating nutrient removal and

bio-power production at the Netley-Libeau Marsh

Determine total N and P removal capacity for a yearly biomass harvest during ice covered periods

Demonstrate the impact of varying water levels within the marsh on wetland vegetation

Evaluate a number of biomass to energy conversion processes for power and cogeneration heat production

Provide estimate for GHG emission credits

Materials and MethodsVegetation Maps for 1979 and 2001 obtained by

aerial photography, remote sensing and imaging tools, and ground verification

Emergent vegetation zones characterized by four main classes of plants: cattails (typha), Bulrushes (scirpus), river rushes, and Giant reeds (phragmites)

Samples for these classes were collected during ice covered periods and analyzed for moisture content, total N, total P, and total calorific value (per dry weight)

Main Assumptions

Once a year harvesting of emergent vegetation

60% of total emergent vegetation accessible to harvest

75% of emergent vegetation above water level

Marsh exposed to entire nutrient load from Red River due to large water exchanges

Vegetation Class

1979 2001

haha %%

Open Water 8884 34.5 13125 50.9

Bulrush (Scirpus) 3247 12.6 317 1.2

Cattail (Typha)

922 3.6 166 0.6

Giant Reed (Phragmites)

4987 19.3 4620 17.9

650 2.5 732 2.8

25774 25773total marsh area

River bulrush and Sedge

Results & Discussion

1979

2001

Hydrologic Connection

Thermal imaging of Red River flow through Marsh area

Nutrient Content

15,40016,700-20,700

17,700-18,400

15,400-19,600NA17,28517,41718,229

Heating Value, KJ/kg

0.180.270.180.210.080.10.110.32TP, % dry matter

2.571.241.221.370.640.91.321.72TN, % dry matter

----1112.812.713.2Moisture, % as fed

Giant Reeds

River RushesBulrushCattail

Giant Reeds

River RushesBulrush Cattail

Reported in Literature*Netley-Libau ResultsParameters

*Kadlec, 1996; Mitch, 1994; Reddy, 1987

Nutrient Removal Potential

227.31368.3187.81026.5Average

32.7-421.9204.8-2531.726.0-349.5144.8-1908.1Total

0.89-0.947.1-7.50.7-0.85.7-6.0Giant Reed

27.3-378-5146.7-2034.324.8-344-1133.3-1849.3Cattail

1.0-6.68.6-59.80.2-1.21.5-10.8River Rushes

3.5-35.842.4-430.20.3-3.54.1-42.0Bulrush

Total PRemoved

(ton)

Total N Removed (ton)

Total P Removed

(ton)

Total N Removed (ton)

19792001Vegetation Class

Nutrient Removal PotentialBiomass harvesting would result in reduction of 3.1-

4.2% of N and 3.8-4.7% of P loading from Red River

This is close to the total N and P removal planned by the City of Winnipeg wastewater treatment plants

To upgrade existing plants to accommodate this, an estimated capital investment of $181 million is required

Vegetation coverage and water level control play important factors in total N and P removal potential

Bio-Energy ProductionAn estimated 50,610 ton of biomass can be collected per year at

16.6% moisture and average heating value of 18.02 MJ/kg.

The total heat content of this biomass is 26.22 MW

Various harvesting strategies, which incorporate simultaneous densification and maintain low moisture content, are being investigated

On-site conversion is desirable in the Netley-Libau case due to distance to coal co-firing plants

Year-around operation with possible supplemental fuel from agricultural residues in the summer months to minimize storage space

Energy Conversion TechnologiesSmall-scale distributed power generation systems (1-5 MW):

1. Gasification System with producer gas burned in an engine

2. Small Condensing Steam System (boiler)

3. Small Steam System with co-generation heat technology

4. Air-Brayton Cycle (uses hot air as the working fluid)

5. Organic Rankine Cylce (heats and vaporizes organic fluid-butane)

6. Entropic Cycle (uses regeneration to reduce equipment size and improve overall thermal efficiency)

Vary in complexity (highest for #1 & #5), capital cost (highest for #5 & #3), and operating cost (highest for #2 & #3)

Energy Conversion Technologies-Modeling Results

0.016.40.014.515.00.0Cogeneration heat (MWth)

4.713.681.833.131.753.03Power generated (MWe)

10.57.212.115.316.515.2Cycle loss (MW)

11.05.312.37.88.08.0Heat recovery loss (MW)

Gasification1Entropic cycle

Air Brayton

cycle

Organic Rankine Cycle

Small steam with

cogeneration

Small Condensing

Steam

1Assumes Producer gas has heat value of 5.5 MJ/m3, cooled down to room temperature, and clean enough to be used in an engine

Emission Credits and GHG Implications

Due to the favorable combination of cogeneration and power production, the Entropic cycle system was used in GHG analysis

Displacement potential was base on the assumption that

1. 3.68 MW electrical power generated by the local coal power plant

2. 16.4 MW of heat was generated by natural gas in the Netley-Libau area

This yields CO2 emission credits of 55,070 ton per year.

Additional GHG credits for methane and NOX displacement could be achieved but were not included into the analysis

Conclusions

The potential benefits of the wetland-biopower concept for nutrient removal and value recovery are substantial.

Effective management of the water level within the marsh is critical for vegetation growth and nutrient removal capacity

Various technologies for small-scale conversion of biomass to energy were investigated resulting in power production from 1.75-4.71MW and usable cogeneration heat.

CO2 emission credits of 55,070 ton per year can be expected with additional GHG credits for methane and NOX displacement

The cost-benefit analysis of this concept will strongly depend on the economic and environmental circumstances for each application

On-Going/Future WorkA industrial gasification-power generation system will be tested

with marsh vegetation as feedstock this winter

Producer gas quality, N and P content of the residual ash and stack emissions will be determined

Existing biomass harvesting equipment (such as forage harvesters with cube-bailing tools) will be evaluated for their operation on ice

Energy conversion technologies will be compared with respect to nutrient re-introduction (from process emissions) via atmospheric depositions