Performance of Surface-Flow Domestic Wastewater Treatment Wetlands

Abstract

Treatment wetlands can be a viable alternative for rural wastewater treatment where conventional centralized methods of treatment may not be feasible. The seasonal treatment performance associated with two surface-flow domestic wastewater treatment wetlands located at the Bio-Environmental Engineering Centre in Truro, Nova Scotia was investigated between October 2007 and April 2009. Each wetland had a surface area of ≈ 100 m², was loaded with ≈ 1,400 L of domestic septic tank effluent d⁻¹, and had a theoretical hydraulic retention time (HRT) of ≈ 25 d. The wetlands achieved average% reductions on a concentration basis of 95% E. coli, 69% BOD₅, 78% TSS, 46% TKN, 42% NH₃, 39% TP, and 34% SRP. Average% mass reductions based on monthly flows were 92% E. coli, 59% BOD₅, 65% of TSS, 23% TKN, 21% NH₃, 8% TP, and 2% SRP. First order removal rate constants averaged 0.19 d⁻¹ for E. coli, 0.08 d⁻¹ TSS, 0.07 d⁻¹ BOD₅, 0.03 d⁻¹ TKN, 0.04 d⁻¹ NH₃, and 0.03 d^-1 for both TP and SRP. Treatment performance was highly variable and appeared to decrease over time. Seasonal variability, hydrologic loading, and long term performance must be considered during the design stage to ensure adequate treatment capacity.