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Phosphorus (1st of 2 articles)

Why be concerned about phosphorus?

Tim Loftus

Eutrophication is when a body of water becomes rich in dissolved nutrients. This leads to one of two conditions. The nutrient-rich water continually contributes to the production of plant biomass, eventually turning water bodies into marshes; and if left to continue, into meadows and then forests. The second condition happens when there are enough nutrients to support massive algal blooms in the water body. This often leads to periods of low dissolved oxygen, which can result in die-offs of fish and other organisms.

It takes many nutrients like nitrogen and carbon, as well as micronutrients like copper and zinc, to support biological growth during eutrophication. However, if you take any one of these nutrients or micronutrients away, eutrophication will not happen. In many natural settings, most of these nutrients and micronutrients are present in excess amounts to support plant life. However, the limiting factor in most cases that keeps excessive eutrophication from happening is the lack of readily available phosphorus.

Much of the available phosphorus found in our waterways can be traced directly to human sources. Phosphorus is used in many detergents, boiler treatments, fertilizers, and in some water supply treatments. When this phosphorus reaches the environment through runoff or through wastewater discharges, accelerated eutrophication can, and often does, happen. That is why many treatment facilities must now remove phosphorus from the wastewater prior to discharge.

This can also lead to certain challenges. In a biological (secondary) treatment process, a significant amount of phosphorus is needed to support cell growth. Then the phosphorus must be reduced to a much lower level prior to effluent discharge. The success of a phosphorus removal process at a treatment facility depends a large part on knowing what forms of phosphorus you need to monitor, and on the accuracy of the analyses.

In the environmental field, we are concerned with a few forms of phosphorus: organically bonded phosphorus, orthophosphate (a simple inorganic compound of phosphorus and oxygen), and condensed phosphorus (a chemical chain of phosphorus and oxygen similar to a number of orthophosphate molecules bonded together). However, orthophosphate is the only form that can be easily determined in a wastewater laboratory. If you want to determine the total phosphorus content of primary effluent, for example, you must convert all the phosphorus forms in that sample into orthophosphate.

An overview of converting phosphorus into orthophosphate for NPDES purposes will be covered in the next article. Sample collection for phosphorus, avoiding common interferences, and how phosphorus results are to be reported will also be addressed.

The information in this article is very general. As usual, check your federal, state, and local regulations. You may have additional regulations or requirements that you must meet.

If you have any questions, suggestions, or comments, contact NEWEA Lab Practices Committee Chair Tim Loftus at (508) 949-3865 timloftus@msn.com. For more information on the NEWEA Laboratory Practices Committee, please contact Tim Loftus or Elizabeth Cutone, NEWEA Executive Director, 100 Tower Office Park, Woburn, MA 01801, (781) 939-0908, ecutone@newea.org.