Florida Lake Management Society Annual Conference, Naples, Florida, June 4 – 7, 2007
IRRIGATION WITH RECYCLED WASTEWATER – GOOD ITENTIONS GONE AWRY?
Harvey H. Harper, III, Ph.D., P.E. Environmental Research & Design, Inc. Orlando, FL
The use of recycled wastewater for irrigation is an increasingly popular practice within the State of Florida. Many new developments are required to use recycled wastewater, if available, and demand for this water has exceeded capacity in many areas of the State. Thousands of miles of pipelines have been installed to support this use. One of the largest users of reuse water is golf courses which provide a large open area where large volumes of reuse can be deposited. Irrigation with reuse water is an excellent water conservation technique, which has converted, treated wastewater from a liability into a coveted resource.
Although wastewater reuse has many conservation benefits, an increasing amount of evidence is pointing to reuse as a significant pollutant source to surface waters. Reuse water commonly has total phosphorus concentrations in excess of 1 mg/l and may exceed 5 mg/l, depending on the level of treatment. Phosphorus concentrations in this range are similar to concentrations in septic tank drain fields and are 5-25 times higher than commonly observed in untreated urban runoff. As a result, the phosphorus loading from reuse irrigation at a single- family home site may exceed the loading from the septic tank system. For example, a single- family irrigation system with four zones operating at 50 gpm for 30 minutes per zone twice each
week would generate 125 gpd/capita and
12,000 gallons/week. A four residents, would
septic tank system, assuming generate 3500 gal/week.
a generation rate of Assuming similar
concentrations in the reuse water phosphorus loading which is 3.4 impacts of the reuse water would water onto impervious surfaces
and septic system leachate, the reuse water would have a total times greater than the septic tank system. The environmental be further increased as a result of direct runoff of the irrigation and waterways. Nitrogen concentrations in reuse water are
commonly in Recent water
the range of 5-10 mg/l, which also exceeds raw untreated runoff by a factor of quality improvement projects conducted by ERD have implicated reuse water
2-5. as a
significant source of nutrient loadings to surface waters improvements from nonpoint source reduction projects.
Reduction of the negative environmental impacts from reuse irrigation is essential to prevent reuse water from becoming an environmental catastrophe. First, it must be universally recognized that, although reuse water is an excellent conservation measure, steps must be taken to reduce or eliminate the potential environmental impacts. Next, the existing elevated nutrient concentrations must be reduced. One method of accomplishing this objective is to provide
advanced wastewater subdivisions and golf stormwater ponds with
treatment (AWT) for reuse courses, the primary source reuse used to supplement the
When reuse water is used for
This will allow dilution of the
reuse water with the pond water as removal within the pond. The overall
well as provide any opportunity for objective of this program should be to
additional nutrient minimize release of