Evaluation of a Subsurface Flow Wetland Processing Sewage from the Sevilleta LTER Field Station

A wetland was constructed in the fall, 1991 to evaluate the performance of a three-cell subsurface-flow constructed wetland containing various species of emergent aquatic plants for treating domestic wastewater. These were: 1) a multiculture, 2) a reed monoculture, and 3) a bulrush monoculture. Wetland cells were fed by two septic tanks of the Sevilleta Long Term Ecological Research Field Station near Socorro, New Mexico. Biochemical oxygen demand, total and fecal coliform bacteria, total Kjeldahl Nitrogen, NH3, and NO3- were measured. Wastewater from the septic tank and from the wetland cells was discharged to the ground through a conventional absorption field divided in half. The wetland cell system was constructed to allow sample collection from septic tank wastewater entering, midway, and at the end of each cell. Water samples also were collected from the septic and wetland drainfields. Water quality from the wetlands was substantially better than in the drainfield receiving water from the septic tank directly. In May 1992 and 1993 the field station population increased from three or four people to 25 for summer research. Following startup of the wetland, effluent water quality rapidly improved. However, at the beginning of each research season effluent quality dropped, then subsequently improved as each cell acclimated to the increased hydraulic and organic loadings. Based on ranked data, the multiculture performed best of the three cells, which may be the result of a variety of plant-microbial associations in this channel opposed to a more limited plant-microbial association in the two monocultures.