From The Editor | November 2, 2015

Nutrient Reduction Improvements Made Easy (And Cheap): Inside The EPA's Guide

Peter Chawaga - editor

By Peter Chawaga, Associate Editor, Water Online

Nutrient Reduction Improvements Made Easy (And Cheap): Inside The EPA’s Guide

Concerned about potential nutrient discharge from non-advanced treatment plants and the lack of information available to help them combat it, the U.S. EPA has taken matters into their own hands. In August it released “Case Studies on Implementing Low-Cost Modifications to Improve Nutrient Reduction at Wastewater Treatment Plants” to demonstrate affordable methods of nutrient removal at facilities that weren’t designed for it.

“EPA developed this draft report to help fill existing gaps in information about relatively low-cost techniques for reducing nutrient pollution at plants with basic treatment processes,” an agency spokesperson told Water Online. “Cost is often seen as a barrier to enhancing nutrient removal at publicly-owned community wastewater treatment plants. EPA Regions and States asked the office of water for case studies they could use in dialogue with communities about opportunities to make low-cost plant modifications to incrementally reduce nutrient discharges.”

The report aims to be the foremost empirical data resource for non-advanced plants (read: ones that were not designed for nutrient removal) to make improvements without costly infrastructure upgrades. The EPA spokesperson elaborated on the “gaps in information” mentioned above, explaining that most published literature on the topic focuses on optimizing existing nutrient removal systems, not improving facilities without them. In fact, the agency had their own difficulties drumming up the data necessary for a comprehensive report.

“In spite of extensive efforts to identify and develop relevant case studies, relatively few met the qualification criteria established by EPA, typically due to insufficient monitoring or cost data, difficulty identifying prospective case study plants, and limited responses from plant contacts during the time available for data collection for this study,” the agency said.

Even with the trouble, its contributors were able to review 80 case studies that qualified. Of those, a total of 12 cases were summarized for this project. They were selected based on their ability to improve nitrogen and phosphorous reduction using low-cost techniques and the availability data, while being representative of a range of scenarios and nutrient optimization approaches. The plants are found in Florida, Montana, and lands in between. The capital costs for modification reached as high as $2.2 million in one case, but in several cases was zero.  

“Their value lies in their number, which includes examples from various sizes, locations, and site-specific factors,” said the agency. “No one case is more instructive [than another]. Each may provide a different piece of information that could be useful for another similar community.”

The report includes five modifications the EPA recommends considering for improving nutrient removal:

  1. Aeration modifications: Physical changes to a plant’s aeration equipment, controls, operation, function, or aerated areas are typically used to optimize anoxic conditions and support denitrification or biological nitrogen removal. Consider installing energy efficient blowers, variable frequency drives, diffusers with improved distribution and oxygen transfer efficiency, airflow meters, and airflow control valves.
  2. Process modifications: Consider adjusting process control characteristics like solids retention time, food-to-microorganism ratio, and recycle/return rate. You can improve physical processes by adding return activated sludge pumps for internal recycling, adding online monitoring equipment for process control and optimization, or installing new screens or grit removal equipment to improve performance.
  3. Configuration modifications: Tweaking flowstreams within the process or changing the process configuration by changing channels, manipulating gates, or adding pipes can enhance environments for denitrification.
  4. Chemical modifications: Adding or changing the supplemental alkalinity and organic carbon feed can support nitrogen removal.
  5. Discharge modifications: Utilizing a soil-based treatment system or wetland assimilation discharge at the end of treatment can reduce nutrients before they are delivered to surface waters.

Each of the 12 case studies took place at activated sludge plants with capacity that can be leveraged to facilitate nitrification and denitrification without requiring physical infrastructure modifications.

“Activated sludge plants typically have reactor volumes and aeration capabilities that exceed their current operational demands,” the spokesperson said. “Accordingly, this excess capacity can be used to promote conditions that increase nutrient removal, primarily by increasing anoxic treatment conditions.”

Other types of systems, like trickling filters and lagoons, may also have excess capacities, but the EPA found it more difficult to manipulate these systems to affect nutrient removal.

Image credit: "Wastewater treatment plant, Richmond, California," Michael Layefsky © 2014, used under an Attribution 2.0 Generic license: https://creativecommons.org/licenses/by/2.0/