Hybrid Systems are being used to treat wastewater in approximately twenty locations around the state of North Carolina, with only two also implementing water reuse. (See Water Recycling in N.C. for the two reuse sites).
The following wastewater treatment sites have been designed and are being studied by researchers at North Carolina State University:
Three low marsh systems were installed for single-family homes and a furniture retail business between 1990 and 1994.
- One of these residential systems is planted with a combination of herbaceous and shrubby vegetation which constitutes a complex plant community, rather than just a few species. Thus far this site has shown greater effectiveness than most low marsh systems for the removal of phosphorus.
- Another of the residential systems has two sand hills with different carbon food sources for the microbes which treat nitrogen and different fills to treat phosphorus. Wastewater is recirculated for better nitrogen treatment.
- The Craven County furniture business compares planted and unplanted plots to show how vegetation helps remove nutrients. The plots are only one foot deep so that the plant roots are in good contact with the wastewater. Deeper plots could allow water to bypass the biologically active zone around the roots, providing for poorer treatment.
- Two different engineered environments are being compared for effectiveness at Merchants Millpond State Park. They were constructed in 1993 to treat wastewater from a ranger’s home. The first, a constructed wetland, is a low marsh with gravel fill and the second is a combined soil filter/ wetland system in which a sand hill is stacked on top of a sand-filled marsh (this saves space and improves nitrogen treatment). These two systems will test different carbon food sources for microbes that remove pollutants. The entire area is landscaped with native plants and the site is to be used as a demonstration for the public of how this alternative treatment system works and how it mimics the cleansing action of the native wetlands nearby which filter agricultural runoff.
- A high marsh/low marsh system for Buckland School treats up to 4000 gallons of wastewater daily. Wastewater from a septic tank is sprayed onto two high marsh plots, whiere it is treated further as it sinks through sand and plant roots. It flows along the bottom and is pumped either back to the septic tank (to add carbon to the microbe food supply thereby aiding in nitrogen treatment) or into the two low marsh plots. After five to seven days the water is dininfected and discharged into a nearby ditch.
- In September 1989, a residential hill/marsh plot, the first of its kind, was installed in rural Pamlico County. This system has proven itself to be low-cost, low-maintenance and effective. Wastewater is pumped into the hill (a coarse sand mound) and allowed to flow into three gravel-filled wetland plots planted on their edges with ink berry and wax myrtle. This woody vegetation often grows along the fringe between natural uplands and wetlands, where it consumes phosphorus. One wetland plot is left unplanted: the two others are planted witheither mixed vegetaion or common reeds. The combination of sand hill and low marsh provides both dry and wet environments which are able to fully treat nitrogen and remove BOD, sediment and phosphorus.
- *The above information has been excerpted with modifications from Waterwise, Winter 1995.