Sequestration and Transformation in Chemically Enhanced Treatment Wetlands: DOC, DBPPs, and Nutrients
Abstract
Introduction
Methods
Wetland Design and Treatments
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.
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.
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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