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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.

which

negates

the

potential

water

quality

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

water.

When reuse water is used for

for

irrigation

water

should

be

the

on-site

pond levels.

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

Session 5B – Page 10

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