Nutrient Study

As regulatory limits on nutrients and algae become an increasing reality in Texas, it is imperative that a reliable and site-specific approach be developed for establishing Texas Pollutant Discharge Elimination System (TPDES) permit effluent quality limits for nutrients. Nowhere is this more important than in the Upper Trinity River watershed. The Upper Trinity Basin Water Quality Compact (Compact) includes utilities operating every major wastewater treatment facility in the Dallas-Fort Worth Metroplex – which totals up to 767 MGD in permitted flow.

To prepare for potential future regulatory requirements and to address limitations in the existing tools for predicting nutrient impacts, the Compact embarked on a multi-phase study to accomplish four objectives:

1. Improve the understanding of nutrient impacts on algal growth in the Upper Trinity River in the Dallas-Fort Worth area.
2. Adapt existing modeling data to a new model platform that predicts the effects of nutrients on in-stream algal growth.
3. Use the nutrient impact model to assess the benefits of applying increasingly more stringent nutrient limits (in this case, phosphorus) in the Upper Trinity River with respect to decreasing in-stream concentrations of algae.
4. Analyze costs associated with process intensification to remove nutrients from the effluents of the major wastewater treatment plants (WWTPs) that discharge to the Trinity River in the Dallas-Fort Worth Metropolitan Area.

Plummer developed a model for the Compact to simulate the impacts of nutrients on the Upper Trinity River system. The goal of the modelling exercise is to evaluate the effectiveness of implementing total phosphorus (TP) effluent limits in permits for the major wastewater treatment plants (WWTPs) in the Dallas-Fort Worth Metroplex in controlling algal levels in the Upper Trinity River. Based on the results, a cost-benefit analysis of implementing nutrient removal processes at the major wastewater treatment facilities was performed. The Compact nutrient model is a powerful tool that can help the Compact respond to future proposed nutrient regulations in the Trinity Basin.