Evaluation of Ecological Nitrogen Removal Mechanisms

From Freshwater Tributaries Feeding Bournes, Green and

Great Ponds

By

 

Harvesting Wetlands Plants and Microbial Denitrification in

Constructed Plant/Rock Filters

 

April 17, 2002

 

Prepared by

 

David Del Porto, Principle Investigator

Sustainable Strategies

50 Beharrell Street

Concord, Massachusetts 01742

 

Prepared for

 

Ashumet Plume Citizens committee

The Town of Falmouth, Massachusetts

59 Town Hall Square

Falmouth, Massachusetts, 02540

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table of Contents

Table of Contents. 1

1.      INTRODUCTION. 2

Findings. 2

Removal Rates and Area requirements. 3

2.      Mechanisms for Nitrogen Removal 3

2.1.        Plant Nitrogen Uptake. 3

2.2.        Microbial Nitrification and Denitrification. 5

2.3        Aquaculture. 8

3.      Hypothesis for plant/rock filters (p/rf) 8

3.1.        Nitrogen Uptake by Plants. 8

3.2.        Nitrification. 8

3.3.        Heterotrophic Denitrification. 9

3.3.1.         Passive Carbon Production from Natural Self-Organization. 9

3.4.        Autotrophic Denitrification. 9

3.5.        Sulfate Attenuation. 9

3.6.        Re-Oxygenation. 9

4.      Detailed system proposal 10

4.1.        System Design. 10

Option 1:  Self Organizing. 10

Option 2: Self Organizing with Alkalinity Addition. 10

Option 3: Addition of Mineral Carbon. 11

Option 4: All Mineral Nutrients Provided. 11

4.2.        Full-Scale Site Identification Issues: 11

4.2.1          Size constraints. 11

4.2.2          Consideration of site hydrology – flooding, etc. 11

4.2.3          Consideration of Existing and Proposed Land Use. 11

4.2.4          Construction Constraints – Diverting the River During Construction. 12

5.0        Evaluation of proposed system. 12

5.1.        System Performance. 12

5.2.        Reliability Considerations (drawbacks) 13

5.3.        Maintenance. 13

5.4.        Economic Analysis. 14

5.4.1. Sale of Harvested Plants to Offset the Cost of Harvesting. 14

5.4.2.         Initial Cost Estimates for Full-scale Design Implementation. 14

5.4.3.         Cost of Maintenance for each P/RF(not including material replacement) 15

5.4.4.         Cost/Benefit Analysis of Proposed System. 15

5.5.        Non-Economic Factors. 15

5.5.1.         Permitting. 15

5.5.2.         Aesthetic impacts. 15

5.5.3.         Fish passages. 16

5.5.4.         Multi-functional uses. 16

6.0        References. 16

Plants. 16

System Design and Bio-Chemistry. 17