Guilford County School District, NC Living Machine
The Guilford Hybrid Wetland Living Machine® system uses plant-based strategies to cleanse 30,600 gallons of wastewater per day from the middle and high school buildings and produces enough clean water to irrigate three athletic fields. This part of the water saving strategy saves an additional 5 million gallons per year by using the water twice. This environmentally sound, onsite treatment strategy costs less than other secondary treatment strategies and helps to reduce the amount of nitrogen entering the watershed. The Living Machine system was incorporated because there are no central sewer lines within miles of the site. The cost of extending the city waste lines to the site would have been significantly more expensive to the school system.
Septic tank effluent passes through two buried 25,000 gallon primary tanks before it is treated by the Hybrid Living Machine system. Settled and equalized flow enters the Horizontal Subsurface Flow Wetland (HSSFW), which reduces wastewater strength and removes suspended solids. The wastewater then undergoes thorough nitrification in the Tidal Flow Wetland (TFW).
An effluent collection chamber lifts the HSSFW effluent to the TFW which consists of three watertight basins containing subsurface plumbing, gravel-like media, and an assortment of wetland plantings. The Living Machine tidal wetland cells go through “fill and drain” cycles. The draining process oxygenates thin films of beneficial microorganisms that grow on the surface of the treatment media which provide ample nitrification of the wastewater. The TFW effluent is recycled to the front end of the HSSFW to dilute the high strength raw wastewater.
The processed wastewater is pumped to a buried 25,000 gallon effluent tank equipped with ultraviolet disinfection. Treated and disinfected wastewater is then stored in a second 25,000 gallon buried fiberglass tank, used for groundwater recharge via the subsurface distribution of high quality effluent.
The Living Machine system at Guilford allowed the schools to avoid the cost of extending city waste lines to the site, reuse the water and add beauty to the site. The Living Machine system not only returns high quality effluent to the aquifer but uses some of the clean water for irrigation of athletic fields, showcasing an important strategy for a water-short area. In addition, the Living Machine system is strongly linked to the science curriculum and gives students unique opportunities to learn through first-hand experience.