Originally posted September 02, 2002
The best reference I have concerning gray- or black water treatment with constructed wetlands is published by the TVA (see below). It has detailed recommendations for designing a constructed wetland for secondary treatment of sewage effluent for individual residences, either gray- or black water (i.e. which contains toilet waste). The system they recommend consists of primary treatment with a traditional two-cell septic tank which allows capture of sludge and scum. The tank effluent then flows to secondary treatment, a wetland cell constructed of a 12-18 inch deep layer of gravel, in which is planted native plants such as cattail, through which the water slowly flows for purification. Experiments have shown an astounding capacity of these systems to remove nitrogen, biological oxygen demand, etc. Surprisingly, the systems function in the dormant growing season as well as in summer. Apparently the oxidizing purification activity resides in the root network itself and is not a function of removal of nutrient by the growing plants. The systems are very compact: typically, one square foot of cell is required for each gallon of daily flow. We have reliable measurements for our household: sixty gallons per day for all our needs. Hence, a cell less approximately 10 x 10 feet using this technology would be sufficient!
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Here's the reference mentioned above: Technical Report Series: General Design, Construction, and Operation Guidelines: Constructed Wetlands Wastewater Treatment Systems for Small Users Including Individual Residences, 2nd edition. TVA/WM 93/10, May 1993, Water Management Resources Group, Tennessee Valley Authority. Prepared by Gerald R. Steiner, P.E. and James T Watson, P.E. Copies available by calling 423/751-3164. The authors may be reached at: Tennessee Valley Authority, Water Management, Haney Building 2C, 1101 Market Street, Chattanooga, Tennessee 37402-2801 USA. I regret I do not have email and fax numbers.