Constructed wetlands: Combination wastewater treatment systems design and operation

Two constructed wetland systems, a horizontal subsurface configuration serving a single family home and a combination vertical flow/horizontal flow configuration serving a school, were evaluated for their wastewater treatment effectiveness. Treatment of nitrogen, phosphorus, biological oxygen demand and total suspended solids were evaluated within the horizontal subsurface system from 1992--1994 and within the combination system from 1992--1999. Influent NH3-N from the septic tank (59.30 mg/L) was significantly lowered (p < .001) to an average of 14.73 mg/L or 75% by the one foot deep cell and to 10.66 mg/L (p < .001) or 82% by the two foot deep cell. Influent TP concentration from the septic tank (6.70 mg/L) was significantly lowered (p < .001) to an average of 1.34 mg/L or 80% by the one foot deep cell and to .63 mg/L (p < .001) or 91% by the two foot deep cell. Influent TSS concentration from the septic tank (60.87 mg/L) was significantly lowered (p < .001) to an average of 11.31 mg/L or 81% by the one foot deep cell and to 12.92 mg/L (p = .001) or 79% by the two foot deep cell. Influent BOD concentration within liquid samples from the septic tank (271.97 mg/L) was significantly lowered (p < .001) to an average. of 51.80 mg/L or 81% by the 1 foot deep cell and to 24.40 mg/L (p < .001) or 91% by the 2 foot cell. Another research system evaluated, the VF/HF combined constructed wetland system has provided effective wastewater treatment during the six year study. The system effectively lowered TN to a six year average value of 11.1 mg/L, an estimated 80.4% decrease; NH3-N concentrations to a six year average value of 1.11 mg/L, an estimated 917.2%; TP was lowered to a six year average of 3.8 mg/L or 53%; TSS concentration to an average of 15.59 mg/L, or 61.5% during the six years evaluated; and effectively lowered BOD to an average six year concentration of 4.9 mg/L or 97%. Design and treatment performance information gained from these two installations was used to design and install a combination vegetated sand filter/constructed wetland to treat and recycle domestic wastewater for toilet flush and landscape irrigation.