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The Ozark Villas in Shell Knob, MO are a senior center and residential housing complex. The subdivision is a collection of 32 duplex units and 32 single-family homes. Discharge of the 12,000 gpd system is to the Lake and because of very real concerns with phosphorus the Missouri DNR required a phosphorus limit of 0.5 mg/L. Reaching these low levels in Missouri had never been achieved in small wastewater treatment systems.

NSI was asked to design a demonstration facility that would be inexpensive to build and operate. Treatment elements consist of interceptor tanks with biofilters for every two units, a small diameter collection system (2 inch sewer lines, no manholes), constructed wetlands with a gravel trickling filter (recycle mound), a recirculating sand filter, and a alum polymer for the phosphorus. Essentially the system operates by itself with an operator visiting once every two weeks. The construction cost was $125,000.