The Iowa Nutrient Reduction Strategy is a pragmatic approach for reducing nutrient discharges from the state’s largest wastewater treatment plants together with targeted best management practices designed to reduce contributions from nonpoint sources.
The point source portion of the nutrient reduction strategy established a process to achieve significant reductions in the amounts of nitrogen and phosphorus discharged to Iowa’s rivers and streams by the largest industrial and municipal wastewater treatment plants. Major point sources will be required to assess the feasibility and reasonableness of reducing the amounts of nitrogen and phosphorus discharged to Iowa surface waters. Practices determined to be feasible and affordable will be required to be implemented.
A total of 102 major municipal facilities serve the wastewater treatment needs of 55-60 percent of Iowa’s population and treat more than 80 percent of the volume of all wastewater handled by Iowa cities. Twenty-nine major and seventeen minor industries also have the potential to discharge significant amounts of nitrogen and phosphorus into Iowa waters.
For the first time, discharge permits issued to these 148 facilities will require implementation of technically and economically feasible process changes, primarily additional biological treatment to remove nutrients. These changes are designed to achieve at least a two-thirds reduction in the amount of nitrogen and a three-fourths reduction in the amount of phosphorus from levels currently discharged by these facilities.
The process is unique and innovative. In the traditional approach limits are established in a permit and treatment facilities are constructed to meet those limits. In this approach, nutrient reduction facilities are constructed, sampling is performed and technology-based limits are developed using actual treatment plant performance data.
This strategy has the potential to reduce by at least 11,000 tons per year the amount of nitrogen and 2,170 tons per year the amount of phosphorus discharged by municipal facilities alone. These figures represent a 4% reduction in nitrogen and a 16% reduction in phosphorus from the estimated statewide amounts of nitrogen and phosphorus entering Iowa waters from both point and nonpoint sources.
This approach is estimated to have a total present worth cost (includes capital costs and operation and maintenance cost over a 20-year period) of approximately $1.5 billion with an annual cost of $114 million.
Results to Date:
Iowa’s Nutrient Reduction Strategy was recently finalized in May 2013 after nearly two years of development. National Pollutant Discharge Elimination System permits are already being developed with requirements to implement the strategy. Several treatment plants that were already under construction while the strategy was being developed voluntarily included nutrient removal processes in their design.
NPDES Program Supervisor
Iowa Department of Natural Resources