The Practical Application of Fine Time Increment, Diurnal, Nitrate Analyses Using Portable In Situ UV Spectrometers in an Effluent Dominated Urban Stream

Many wastewater facilities use a nitrifying biological process to eliminate or reduce ammonia concentrations which are toxic to fauna in their receiving water. One byproduct of this process is nitrate. Nitrate is generally non-toxic to fauna in receiving streams at levels produced by a nitrification process. However, chronic exposures of 10mg/L NO3-N, or greater, may produce toxic responses in human infants. As a result, nitrate concentrations are regulated in waters that may impact drinking water sources. Some wastewater facilities are now being required to add an additional biological process to de-nitrify effluent. While there are a number of traditional methods for measuring nitrate in water, they are not suitable for on-going, rapid analysis of wastewater or environmental waters. Because nitrate (and nitrite) in water absorbs UV light at a specific wavelength that has little interference, it can be used to estimate nitrate concentrations. I will discuss the principles of nitrate measurement using UV spectroscopy and the various instruments that are available in the market. I will also discuss the selection, modification and application of a small portable UV spectrometer. This instrument can be placed inconspicuously in any water body, without connection to the shore. The instrument typically measures nitrate every five minutes and can save a week's worth of data for later analysis. Vital information is currently being collected on daily nitrate variation and patterns downstream from a wastewater plant; this information will be used to measure changes from baseline conditions when a major de-nitrification facility begins operation and can also provide an assessment of natural de-nitrification in a river system. The instrument(s) can also be used by a wastewater treatment facility to evaluate the de-nitrification process at various stages.