The U.S. EPA is studying nutrient discharges from POTWs in an effort entitled the National Study of Nutrient Removal and Secondary Treatment. The study will first involve requesting data from all POTWs in the U.S. to develop a baseline of nutrient loadings from the POTW sector as a whole, and second focus on conventional secondary treatment facilities to develop information on optimization, operation, and management to identify low cost techniques for increasing nutrient removal.
This study arose from an expressed need for information by multiple entities attempting to address significant issues regarding nutrient discharges and energy savings at POTWs. Insome areas of the country, states, EPA, consultants, and academic institutions have been working with POTWs to demonstrate that nutrient reduction improvements do not always require major capital investments, but rather can be obtained by optimization of operation and maintenance (O&M) practices. For example, collaborative efforts have been underway in EPA’s Region 4 to optimize performance at POTWs to reduce energy usage, which coincidentally achieve significant nutrient reductions. However, despite individual successes, identification of candidate facilities is impeded due to a lack of basic information about facilities in general such as plant capacity, types of biological treatment, process control methods, aeration method, etc. Additionally, EPA looked at more than 80 different case studies of POTWS that were identified as having optimized their operations to compile a report on low cost modifications to improve nutrient reduction .From these 80 case studies, EPA was able to use the information from only 12 facilities to document the ability to optimize secondary treatment to improve nutrient reduction. The remainder of the projects were not selected because they lacked monitoring or cost data, or involved advanced wastewater treatment facilities. Therefore, these studies emphasize the need for baseline information on nutrient removal across varying geographic regions and varying secondary treatment trains, with and without optimized O&M, in order to provide the POTW community and states with enough information to investigate adoption of optimization practices at secondary treatment on a national scale.
The Need to Update Information on Nutrient Removal Performance at POTW Facilities
The second main need for this survey is to update information on nutrient removal performance at POTW facilities. Estimates on nutrient discharges from POTWs are outdated – up to 50 years old – and do not incorporate the process controls that many use today. Moreover, these estimates do not reflect variable attributes such as differential plant loadings or temperature effects. Regulatory entities, such as states, rely on estimates of POTW nutrient removal capabilities when developing waterbody and watershed plans, Total Maximum Daily Loads, or estimates of nutrient contributions from the POTW sector. Discharge data for nutrients are only reported by facilities if they have nutrient effluent limits or monitoring requirements, and influent data are rarely reported, if collected at all. Presently, only a small percentage of POTWs have these requirements to report nutrient concentrations. Thus, the estimates of nutrient loading, not to mention removal efficiency, coming from POTWs remain a very rough estimate. As states proceed with plans to address nutrient loadings, it will be helpful for them to have the data on the nutrient contribution from the POTW sector at the local watershed, regional, and national levels. Whether or not facilities decide to incorporate optimization processes observed in the study, this nutrient loading information will provide states and POTWs with necessary information to set realistic, achievable nutrient reduction targets.
The Study will consist of multiple phases of data collection. EPA is preparing the first phase which involves taking a census of POTWs to collect basic information on location, size, and technology in place. Subsequent phases will involve collecting more detailed data from a representative sample of secondary treatment POTWs on technology operation and maintenance, and sampling data from a representative population of all POTWs.
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