Sequestration and Transformation in Chemically Enhanced Treatment Wetlands: DOC, DBPPs, and Nutrients
Abstract
Introduction
Methods
Wetland Design and Treatments
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Water Monitoring, Sampling, and Analyses
Water and Mass Budgets, Calculations and Statistical Analyses
Kinetic Model
Results
DOC and DBPP Concentrations, Loads and Concentration Ratios
Analyte | Trt | N | Concentrations and loads | Load removal | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Inflow (In) | Postdosing (PD) | Seepage | Outflow (Out) | Coagulation | Wetland | Total system | |||||||||
Concentration | Load () | Concentration | Load () | Load () | Concentration | Load () | Mean () | % inflow | Mean () | % inflow | Mean () | % inflow | |||
DOC () | Co | 161 | 643a | 643b | 89b | 605c | 0a | 0 | b | a | |||||
Al | 165 | 601a | 176a | 37a | 215a | 424b | 71 | b | 349c | 58 | |||||
Fe | 162 | 600a | 167a | 39a | 316b | 433b | 72 | a | 245b | 41 | |||||
HAA () | Co | 8 | 49a | 49b | 7a | 48c | 0a | 0 | a | a | |||||
Al | 9 | 46a | 10a | 2a | 10a | 36b | 79 | a | 33b | 73 | |||||
Fe | 8 | 49a | 9a | 2a | 21b | 39b | 81 | a | 25b | 52 | |||||
THM () | Co | 8 | 67a | 67b | 9a | 62b | 0a | 0 | b | a | |||||
Al | 9 | 63a | 21a | 4a | 20a | 42b | 66 | b | 39b | 61 | |||||
Fe | 8 | 66a | 21a | 4a | 35ab | 46b | 69 | a | 27b | 41 | |||||
DAl () | Co | 20 | 4.5a | 4.5b | 0.6ab | 2.9b | 0a | 0 | 1.0ab | 23 | 1.0a | 23 | |||
Al | 21 | 3.9a | 2.9b | 0.3b | 0.4a | 1.1b | 27 | 2.1b | 54 | 3.2a | 81 | ||||
Fe | 20 | 4.1a | 1.1a | 0.1a | 1.0ab | 2.9b | 72 | 0.0a | 0 | 2.9a | 72 | ||||
DFe () | Co | 41 | 89.0a | 89.0c | 16.5c | 69.7c | 0a | 0 | 2.9ab | 3 | 2.9a | 3 | |||
Al | 45 | 84.5a | 6.8a | 1.5a | 4.5a | 77.8b | 92 | 0.8b | 1 | 78.5b | 93 | ||||
Fe | 43 | 84.2a | 17.2b | 5.7b | 27.6b | 67.0b | 80 | a | 50.9b | 60 | |||||
DIN () | Co | 20 | 37.0a | 37.0a | 3.7a | 10.7a | 0.0a | 0 | 22.6a | 61 | 22.6a | 61 | |||
Al | 21 | 34.8a | 35.7a | 4.1a | 15.5a | b | 16.1a | 46 | 15.1a | 43 | |||||
Fe | 20 | 35.9a | 37.0a | 3.2a | 17.0a | b | 16.9a | 47 | 15.8a | 44 | |||||
DON () | Co | 20 | 46.8a | 46.8b | 7.1a | 34.0b | 0.0a | 0 | 5.7a | 12 | 5.7a | 12 | |||
Al | 21 | 44.1a | 20.6a | 3.6a | 14.5a | 23.5b | 53 | 2.5a | 6 | 26b | 59 | ||||
Fe | 20 | 45.5a | 20.5a | 3.9a | 22.7ab | 25.0b | 55 | a | 18.9ab | 42 | |||||
TDN () | Co | 20 | 83.9a | 83.9a | 10.8a | 44.7a | 0.0a | 0 | 28.3a | 34 | 28.3a | 34 | |||
Al | 21 | 78.9a | 56.3a | 7.7a | 30.1a | 22.5b | 29 | 18.6a | 24 | 41.1a | 52 | ||||
Fe | 20 | 81.4a | 57.5a | 7.1a | 39.7a | 23.9b | 29 | 10.7a | 13 | 34.7a | 43 | ||||
() | Co | 41 | 4.9a | 4.9b | 0.9b | 3.8b | 0.0a | 0 | 0.2a | 4 | 0.2a | 4 | |||
Al | 45 | 4.6a | 1.1a | 0.2a | 0.9a | 3.5b | 75 | 0.0a | 3.4b | 75 | |||||
Fe | 43 | 4.6a | 1.0a | 0.2a | 1.0a | 3.6b | 78 | a | 3.4b | 74 | |||||
DO () | Co | 155 | 172.3a | 172.3a | 23.3a | 135.1a | 0.0a | 0 | 13.9b | 8 | 13.9b | 8 | |||
Al | 159 | 165.3a | 160.4a | 32.5b | 148.6a | 4.9b | 3 | a | −15.8a | ||||||
Fe | 157 | 165.7a | 167.6a | 26.9ab | 159.6a | b | a | −20.8a | |||||||
pH | Co | 158 | — | — | — | — | — | — | — | — | — | — | |||
Al | 162 | — | — | — | — | — | — | — | — | — | — | ||||
Fe | 159 | — | — | — | — | — | — | — | — | — | — |
Note: DOC = dissolved organic carbon; HAA = haloacetic acid; THM = trihalomethane; DAl = dissolved Al; DFe = dissolved Fe; DIN = dissolved inorganic nitrogen; DON = dissolved organic nitrogen; TDN = total dissolved nitrogen; = phosphate; DO = dissolved oxygen. Trt = treatments: Al = polyaluminum chloride, Fe = ferric sulfate; Co = control; N = sample size; and STD = standard deviation. Seepage loads at inflow, postdosing, and outflow locations take into account evapotranspiration and precipitation. Post-hoc letters indicate significant differences between treatments and control for each constituent and process type.
Analyte | Treatment | Coagulation | Wetland | Total system |
---|---|---|---|---|
DOC | Co | N/A | 1.19a | 1.19c |
Al | 0.27a | 1.78b | 0.47a | |
Fe | 0.27a | 3.03c | 0.76b | |
HAA | Co | N/A | 1.24a | 1.24c |
Al | 0.21a | 1.34a | 0.28a | |
Fe | 0.16a | 4.56b | 0.61b | |
THM | Co | N/A | 1.17a | 1.17c |
Al | 0.31a | 1.21a | 0.37a | |
Fe | 0.26a | 2.83b | 0.68b |
Note: DOC = dissolved organic carbon; HAA = haloacetic acid (HAA); and THM = trihalomethane. Constituent concentrations (, , ) at inflow (In), postdosing (PD), and outflow (Out) locations were used to calculate ratios. Ratios indicate net removal of constituent; ratios indicate release of constituent. Post-hoc letters indicate significant differences between treatments and control for each constituent and process type.
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Ancillary Parameters, Nutrients and Metals Concentrations and Loads
Kinetic Models
Step | Equation | Wetland(s) | Constant | Mean | SE | p-value | |
---|---|---|---|---|---|---|---|
1 | Eq. (1) | Co | 0.0036 | 0.00 | 0.78 | ||
2 | Eq. (2) | Co | 0.0038 | 0.00 | 0.82 | ||
Co | 1.2336 | 0.1155 | 0.00 | — | |||
3 | Eq. (1) | Co, Al, Fe | 0.0036 | 0.00 | 0.57 | ||
4 | Eq. (2) | Co, Al, Fe | 0.0035 | 0.00 | 0.58 | ||
Co, Al, Fe | 1.0845 | 0.0365 | 0.00 | — | |||
5 | Eq. (4) | Co, Al, Fe | 0.0038 | 0.00 | 0.83a | ||
Co, Al, Fe | 1.2336 | 0.1155 | 0.00 | — | |||
Fe | 0.7578 | 0.0331 | 0.00 | — | |||
Fe | 1.1507 | 0.0122 | 0.00 | — | |||
Al | 0.2447 | 0.0332 | 0.00 | — | |||
Al | 1.0533 | 0.0235 | 0.00 | — |
Note: = rate constants; = rate constants at 20°C; = temperature dependency of the rate; = temperature dependency of release in Al treatments; = temperature dependency of release in Fe treatments; = coagulant-dependent release coefficients at 20°C in Al treatments; and = coagulant-dependent release coefficients at 20°C in Fe treatments. Calculated constants are presented in means with standard errors (SE), along with coefficients of determination () for model fit and probability value (p-value). Negative values represent net ecosystem production; positive values represent net ecosystem uptake. Larger (where Me is Fe or Al) represents larger constituent release from wetlands. Larger indicates larger temperature dependency of constituent processes.
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Discussion
Coagulation, Wetland, and Total System Performance
Coagulation
Control Wetlands
Coagulation Wetlands
Total System
Kinetic Models
Model Predictions and Insights
Practical Implications and Further Considerations
Conclusions
Supplemental Data
Notation
- inflow concentration;
- outflow concentration;
- concentration at inflow postdosing;
- concentration change due to desorption;
- rate constant;
- rate constant at 20°C;
- concentration change due to coagulation;
- temperature dependency of the rate;
- temperature dependency of release at 20°C, where Me indicates treatment (Fe or Al); and
- floc release coefficient, the percentage of removal that is reversible, where Me indicates treatment (Fe or Al).
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