Irrigation With Recycled Wastewater - Good Intentions Gone Awry?

Harvey H. Harper


The use of recycled wastewater for irrigation is an increasingly popular practice. Many new developments are required to use recycled wastewater, if available, and demand for this water has exceeded capacity in many areas of the U.S. 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 5-10 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 wastewater reuse irrigation at a single-family home site may exceed the loading from the septic tank system. The environmental impacts of the reuse water are further increased as a result of direct runoff of the irrigation water onto impervious surfaces and waterways. Nitrogen concentrations in reuse water are commonly in the range of 5-15 mg/l, which also exceeds raw untreated runoff by a factor of 2-5. Recent water quality improvement projects have implicated reuse water as a significant source of nutrient loadings to surface waters which My negate the potential water quality improvements from nonpoint source reduction projects. A recent study conducted by ERD indicated a 100-fold increase in phosphorus loadings through a golf course area irrigated with reuse water. The additional loadings from reuse water need to be included in TMDL evaluations.

Reduction of the negative environmental impacts from reuse irrigation is essential to prevent reuse water from becoming an environmental catastrophe. 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. First, the existing elevated nutrient concentrations must be reduced. One method of accomplishing this objective is to provide advanced wastewater treatment (AWT) for reuse water. Next, when reuse water is used for subdivisions and golf courses, the primary source for irrigation water should be the on-site stormwater ponds with reuse used to supplement the pond levels. This will allow dilution of the reuse water with the pond water as well as provide an opportunity for additional nutrient removal within the pond. Storage ponds should be constructed to allow the use of reclaimed water “as needed” rather than at a constant rate. Irrigation with reuse water should be carefully controlled to prevent direct discharges into waterways or stormsewer systems.

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