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Table 3 summarizes the mean effluent pollutant concentrations and percentage removal in each of the experimental reactors with different substrates. In terms of pH attenuation, peat exhibited the highest capability for pH attenuation over one HRT cycle and maintained this pH level throughout the experimental period. Only gravel and topsoil demonstrated positive percentage removal of COD, while the organic substrates, peat and organic mulch, showed a tendency to increase the COD concentration in the reactors. Only organic mulch exhibited the potential to exceed the wastewater effluent COD concentration guidelines of 25 mg/L, which would be above the regulatory discharge guidelines set by Environment Canada (Environment Canada 2012). In terms of nutrient removal, although the influent synthetic wastewater had relatively low nutrient concentrations (TN = 1.49 mg/L, TP = 0.41 mg/L), the substrates are able to contribute to further treatment; the only exception was the effluent TN concentration of peat.

Table 3

Mean pollutant removal performance across the wetland reactors. (Standard deviation of pollutant concentration is indicated in brackets)

ParametersUnitINFGravel
Peat
Topsoil
Organic mulch
EFFRFEFFRFEFFRFEFFRF
pH N/A 10.37 (0.20) 9.21 (0.11) N/A 7.76 (0.11) N/A 9.27 (0.17) N/A 9.12 (0.21) N/A 
Eh mv 91.4 (5.9) 123.9 (10.1) N/A 143.1 (23.9) N/A 125.1 (15.3) N/A 121.9 (10.5) N/A 
Alkalinity mg/L 128.0 (50.0) 47.5 (5.0) 62.9 52.2 (10.0) 56.9 102.3 (33.6) 20.1 105.1 (35.9) 17.9 
COD mg/L 17.38 (7.47) 10.50 (1.98) 39.6 19.00 (1.85) NEG 13.63 (4.27) 21.6 28.00 (11.22) NEG 
Ammonium mg/L 0.17 (0.08) 0.07 (0.03) 58.8 0.13 (0.04) 23.5 0.05 (0.01) 70.6 0.04 (0.01) 76.5 
Nitrate mg/L 3.02 (0.78) 2.53 (0.69) 16.2 4.13 (1.03) NEG 2.02 (0.84) 33.1 4.00 (2.45) NEG 
Nitrite mg/L 0.009 (0.003) 0.004 (0.002) 55.6 0.014 (0.010) NEG 0.027 (0.022) NEG 0.044 (0.015) NEG 
TN mg/L 1.49 (0.27) 1.30 (0.48) 12.8 1.64 (0.21) NEG 1.00 (0.15) 32.9 1.00 (0.24) 32.9 
TP mg/L 0.41 (0.19) 0.11 (0.02) 73.1 0.19 (0.05) 53.7 0.15 (0.05) 63.4 0.20 (0.03) 51.2 
ParametersUnitINFGravel
Peat
Topsoil
Organic mulch
EFFRFEFFRFEFFRFEFFRF
pH N/A 10.37 (0.20) 9.21 (0.11) N/A 7.76 (0.11) N/A 9.27 (0.17) N/A 9.12 (0.21) N/A 
Eh mv 91.4 (5.9) 123.9 (10.1) N/A 143.1 (23.9) N/A 125.1 (15.3) N/A 121.9 (10.5) N/A 
Alkalinity mg/L 128.0 (50.0) 47.5 (5.0) 62.9 52.2 (10.0) 56.9 102.3 (33.6) 20.1 105.1 (35.9) 17.9 
COD mg/L 17.38 (7.47) 10.50 (1.98) 39.6 19.00 (1.85) NEG 13.63 (4.27) 21.6 28.00 (11.22) NEG 
Ammonium mg/L 0.17 (0.08) 0.07 (0.03) 58.8 0.13 (0.04) 23.5 0.05 (0.01) 70.6 0.04 (0.01) 76.5 
Nitrate mg/L 3.02 (0.78) 2.53 (0.69) 16.2 4.13 (1.03) NEG 2.02 (0.84) 33.1 4.00 (2.45) NEG 
Nitrite mg/L 0.009 (0.003) 0.004 (0.002) 55.6 0.014 (0.010) NEG 0.027 (0.022) NEG 0.044 (0.015) NEG 
TN mg/L 1.49 (0.27) 1.30 (0.48) 12.8 1.64 (0.21) NEG 1.00 (0.15) 32.9 1.00 (0.24) 32.9 
TP mg/L 0.41 (0.19) 0.11 (0.02) 73.1 0.19 (0.05) 53.7 0.15 (0.05) 63.4 0.20 (0.03) 51.2 

INF, influent concentration; EFF, effluent concentration; RF, removal efficiency; N/A, not applicable; NEG, negative removal efficiency.

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