Conference Agenda

Clean Water Services (CWS) operates three water resource recovery facilities (WRRFs) that are subject to thermal load and daily maximum 1-hour average effluent temperature limits under their watershed-based NPDES permit. Current compliance strategies include water quality trading, flow augmentation, wetlands treatment, and riparian shade and recycled water programs. The recent discovery of the invasive emerald ash borer is expected to decimate the population of Oregon ash trees, a major riparian shade species. To expand their temperature management portfolio and compliment these “outside the fence” strategies, CWS is conducting studies to better understand temperature dynamics in WRRFs and explore potential “inside the fence” mitigation strategies.

Several models have been published that account for the major heat gains and losses from the activated sludge process. These models were reviewed and adapted into a spreadsheet that allows the temperature dynamics of each unit process in the WRRF to be modeled. The model was calibrated to three months of data collected at the Durham WRRF.

The calibrated Durham temperature model shed light on the relative contribution of each unit process to the overall thermal balance of the WRRF and was used to identify the most significant heat sources and losses in each. The aeration basins were the largest contributors to increased effluent temperature. The secondary and tertiary clarifiers gained heat during the day and lost it overnight. In contrast, the covered primary clarifiers largely followed the influent temperature with less extreme daily temperatures.

Basin shading was explored as a potential peak hour effluent temperature mitigation strategy. First, solar radiation was reduced by 90% in the model, which suggested peak hour temperature reductions > 0.5°C were possible. Second, a two-month pilot study was conducted at the Rock Creek WRRF. Two basins were evaluated side-by-side. One was left uncovered while the other was covered with a shade cloth with a 90% UV reduction rating. The peak effluent temperature from the shaded basin was lower than the unshaded basin by 0.2°C on average.

This presentation highlights the insight gained from temperature modeling in WRRFs and highlights basin shading as a promising low-capital, low-energy temperature mitigation strategy.

Clean water agencies, regulatory agencies, and watershed stakeholders are searching for innovative approaches and best practices to address water quality challenges due to nutrient enrichment and a changing climate. Through a series of interactive workshops in three different geographic regions, this Water Research Foundation project developed a framework to advance nutrient management that fosters innovation and new opportunities. The project goal is to focus on approaches that may be applied nationally and tailored to address unique water quality improvement needs and varying watershed contributions from point and nonpoint sources.

The culmination of Water Research Foundation Project No. 4974 is a new framework to improve holistic watershed nutrient management through Practices, Policies, and Partnerships. "Practices" refers to the technical considerations related to nutrient removal wastewater treatment, best management practices for nonpoint sources such as stormwater and agricultural land uses, and nutrient processing and impacts on receiving water environments and the atmosphere. "Policies" refers to the regulatory, institutional, and administrative aspects that govern nutrient management. This includes nutrient discharge permitting and compliance with receiving water quality standards, as well as watershed management requirements. "Partnerships" refers to the potential for collaboration, building relationships and trust, and leadership in nutrient watershed management. This includes consideration of diverse stakeholders with varied interests that may, or may not, be aligned.

This nutrient management framework provides a structured process with key success factors that can be tailored to develop holistic watershed-based nutrient reduction plans. Balanced nutrient reduction plans that integrate practices, policies, and partnerships should yield more effective and efficient implementation focused on consensus-based outcomes that provide greater net environmental benefits. The framework also provides a diagnostic lens to identify missing elements of existing nutrient reduction efforts that have not achieved planned outcomes.

Impacts of climate change and environmental justice (EJ) challenges were overarching themes that are addressed through this framework and within each element. Climate change complicates water resources management in multiple ways, from extreme weather events to potentially more significant responses to waterbody nutrient inputs (e.g., harmful algal blooms). The overarching issue of EJ spans all three nutrient management factors (practices, policies, and partnerships).