This study focuses on sustainability impacts as wastewater treatment plants implement treatment technologies to meet increasingly stringent nutrient limits. The objective is to determine if a point of “diminishing returns” is reached where the sustainability impacts of increased levels of nutrient removal outweigh the benefits of better water quality.
Five different hypothetical treatment trains at a nominal 10 mgd flow were developed to meet treatment targets that ranged from cBOD mode (Level 1) to four different nutrient removal targets. The nutrient removal targets ranged from 8 mg N/L; 1 mg P/L (Level 2) to the most stringent at <2 mg N/L; <0.02 mg P/L (Level 5). Given that sustainability is a broad term, the industry-accepted three pillars of sustainability were evaluated and discussed, and particular emphasis was placed on the environmental and economic pillars. The following variables received the most attention: greenhouse gas (GHG) emissions, a water quality surrogate that reflects potential algal growth, capital and operational costs, energy demand, and consumables such as chemicals, gas, diesel, etc. The results from the GHG emissions metric are shown below. Note that biogas cogeneration is represented by negative values as biogas production can be used to offset energy demands. The nitrous oxide (N2O) emissions values are based on the average biological nutrient removal (BNR) and non-BNR plants evaluated in the United States national survey
Chapter
LIST OF SYMBOLS AND ABBREVIATIONS
ES.1 Background and Goals
ES.2 Five Levels of Treatment
1.2 Role of Wastewater Treatment Plants in Sustainability
1.3 Measuring Sustainability
1.4 Energy Demand at Wastewater Treatment Plants
1.6 Previous GHG Emissions Studies
1.9 Impact of Nutrient Removal on GHG Emissions at WWTPs
1.9.1.1 Benefits of Longer Solids Retention Time
1.9.2 Role of Dissolved Organic Nitrogen on Permits
1.9.3 Role of Phosphorus Species on Permits
1.9.4 Greenhouse Gas Emissions at Wastewater Treatment Plants
1.9.4.1 Energy Demand at Wastewater Treatment Plants
1.9.4.2 Methane Production in Wastewater Processes
1.9.4.3 Nitrous Oxide Production in Wastewater Processes
1.9.4.4 External Carbon Sources
1.9.4.6 Brine Reject Management
1.10 Example of GHG Emissions Inventory Performed on WWTP
1.10.1 Accounting and GHG Emissions Boundary Conditions for a 15 mgd WWTP
1.10.2 Emission Calculations
1.10.2.2 Basis of Calculation
1.10.3 Base Year and Future Years Used for GHG Emissions
2.2 U.S. EPA Numeric Nutrient Standards
2.3 Stakeholder Input to the Nutrient Impact Discussion – NRDC and Others
2.4 The Ecoregion Concept and Nutrient Criteria
2.5 Effluent Technology Limits Do Not Guarantee Water Quality
3.1.1 Level 1 (30 mg/L BOD; 30 mg/L TSS; no nutrient requirements)
3.1.2 Level 2 (8 mg N/L; 1 mg P/L)
3.1.3 Level 3 (4-8 mg N/L; 0.1-0.3 mg P/L)
3.1.4 Level 4 (3 mg N/L; 0.1 mg P/L)
3.1.5 Level 5 (2 mg N/L; <0.02 mg P/L)
3.3 Greenhouse Gas Calculation Assumptions
3.4 Incremental Increase in GHG Emissions per Additional Pound Nutrient Removed
3.5 Economic Variables Assumptions
4.1.1 Steady State Mass Balance Results
4.1.2 GHG Emissions Distribution per Treatment Level
4.1.3 Incremental GHG Emissions with Increased Treatment
4.1.4 Algal Production Potential in Receiving Waterbodies
4.1.5 Transportation Impacts on Sustainability for Chemicals
4.1.6 Costs per Treatment Level
4.2.1 Environmental Pillar
4.2.1.1 Which Parameter is Governing GHG Emissions?
4.2.1.2 Plant Configurations
4.2.1.3 Ancillary Benefits of a Longer SRT
4.2.1.4 Methane Emissions
4.2.1.5 Nitrous Oxide Emissions
4.2.1.6 Incremental GHG Emissions Increase per Treatment Level
4.2.1.7 Dissolved Organic Nitrogen
4.2.1.8 Dissolved Organic Phosphorus Removal
4.2.4 Point versus Non-Point Loadings
Impact of Different Levels of Enhanced Biological Phosphorus Removal on N2O Emissions
Striking the Balance between Nutrient Removal in Wastewater Treatment and Sustainability
( WERF Research Report Series )
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