Nutrient Regulations are Coming - Got Carbon? Carbon Deficit and Master Planning Analysis for Enhanced Biological Nutrient Removal: A Case Study

This paper discusses a planning approach for assessing biological nutrient removal (BNR) carbon needs and a unique approach to satisfying anticipated carbon demands using a combination of traditional and alternative carbon sources. The goal is to demonstrate a repeatable planning approach that municipalities, utilities, and industries can use to explore sustainable, cost effective, and practical alternate carbon sources for carbon deficient biological nutrient removal (BNR) processes.The J D Phillips Water Reclamation Facility (JDPWRF) is a 20 MGD capacity plant operated by Colorado Springs Utilities (Utilities) that utilizes a 3-stage A2O process for biological nutrient removal (BNR). The plant is currently carbon limited with respect to effectively meeting its BNR goals.A carbon deficit analysis was performed for JDPWRF at current and future flow and load conditions with assumed corresponding nutrient discharge limits. This included an analysis of both traditional and alternative supplemental carbon sources, including a local dairy waste product (acidic whey), primary sludge and commercially available chemicals to fill the deficit through time with a focus on using the lowest cost and most sustainable carbon sources first. The fermentation of acidic whey was identified as the lowest cost, most sustainable source. However, based on the flow and load projections and supplemental carbon required to meet the future nutrient limits, it was determined that whey alone cannot meet the carbon demands for JDPWRF at build out conditions.To augment the fermented whey, it was determined that primary sludge fermentation from the plant's primary sedimentation tanks (PSTs) provides the next most favorable supplemental carbon source. This additional supplemental carbon source readily available on-site, can easily be integrated into the overall supplemental carbon supply plan for JDPWRF.Since the fermented whey is more potent than fermented primary sludge and has the potential to yield larger quantities of volatile fatty acids (VFAs), it is the preferred supplemental carbon source. When the carbon demand at JDPWRF outstrips the carbon available from whey (either due to lowering of the nutrient discharge limits or increasing demand due to higher flows and loads), or if the whey supply is disrupted for some reason, the plant can utilize the supplemental carbon available from fermentation of primary sludge.The carbon deficit analysis indicated that there is enough carbon available between whey and primary sludge to fulfill the carbon demands for JDPWRF and to yield an effluent with low N and P concentrations up to the rated plant flows of 20 MGD. Further, the carbon available from whey is more than adequate to meet the carbon demands for current flow conditions and the anticipated first phase of nutrient limits for the facility of 10 mg/L TIN and 1 mg/L TP that will be implemented in the next permit cycle. In addition, the infrastructure for whey/primary sludge fermentation can be designed such that commercially available carbon sources such as methanol, acetic acid, or other proprietary products can be interchangeably used on an interim basis if and when whey and/or primary sludge is unavailable. The infrastructure will be completely modular in nature so that additional facilities can be added to the process as supplemental carbon demands and/or sources change through time.