Excess phosphorus in inland Northwest lakes, rivers and streams is a concern since it contributes to algae blooms and dissolved oxygen deficits, which adversely affect fish and aquatic life. Algal blooms also can reduce drinking water quality and negatively affect recreation. To help address this challenge, a primary focus of my civil engineering research group at the University of Idaho is on phosphorus removal from wastewater.
In particular, we are advancing biological methods to more efficiently remove phosphorus while reducing the treatment process carbon/energy footprint. The purpose of this column is to provide a primer for the public on the challenges faced by and methods used by water quality professionals in reducing phosphorus loads entering natural water bodies.
As a society we use significant quantities of phosphorus, principally as fertilizer, some of which drains into bodies of water. While measuring phosphorus and identifying potential effects on water body health is relatively easy, preventing phosphorus from entering the water is more challenging. Sources are diverse - humans contribute phosphorus to wastewater, storm water, and agricultural runoff - and the quantities contributed vary.
Significant fractions of phosphorus enter surface water through "nonpoint" sources, such as storm water and agricultural runoff; the Idaho DEQ estimates that 60 percent to 70 percent of the phosphorus entering the Boise River is nonpoint. Other phosphorus comes from reclaimed water produced from municipal wastewater treatment plants (WWTPs; these are really water resource recovery facilities) - "point" sources. Currently, water quality regulations are focused on the point sources, and treatment plants are facing increasingly strict effluent limitations.
For example, plants that discharge into the Boise River are expected to reduce phosphorus from 4-6 mg/L to less than 0.1 mg/L. The cost of compliance will ultimately be hundreds of millions of dollars, ultimately borne by the users (you and me).
Wastewater phosphorus recovery can be accomplished using bacteria through an engineered process known as enhanced biological phosphorus removal (EBPR); bacteria do an excellent job removing excess phosphorus. Alternately, chemical treatment involving aluminum or iron can be used, with the phosphorus "sticking" to the chemical to form a solid. Unfortunately the chemical sludge must be landfilled, as the metal-phosphorus complex is not a good fertilizer. EBPR is much more sustainable than chemical treatment because it uses naturally occurring bacteria to recover phosphorus, and the resulting solids can be used as a natural fertilizer. At the University of Idaho we are studying enhanced biological phosphorus removal to better understand how the bacteria accumulate excess phosphorus; we are also advancing a new process configuration to achieve better overall treatment.
As we seek to reduce phosphorus discharges, it is critical to be well informed. I encourage everyone to learn more about their local treatment plants. You will find some of the most dedicated men and women operating highly complex systems, with a single focus of protecting our water environment.
Remember that we all contribute phosphorus. The more careful we are about fertilizing our landscapes and avoiding discharging water into storm drains, the better our water quality will be.