Final Report: Electrodialytic Nutrient Recovery From Wastewater

EPA Contract Number: 68HERC20C0028
Title: Electrodialytic Nutrient Recovery From Wastewater
Investigators: Forbis-Stokes, Aaron
Small Business: Triangle Environmental Health Initiative
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2020 through August 31, 2020
Project Amount: $100,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2020) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Clean and Safe Water

Description:

Nutrient pollution contributes to global water quality issues in the form of eutrophication, which leads to algal blooms and dead zones due to oxygen depletion, as well as public health issues such as methemoglobinemia. A major source of that nutrient pollution is inadequately treated sewage, in particular, from onsite wastewater treatment systems (OWTSs) which are not designed to remove nutrients before discharge into the environment. The USA and global populations reliant on OWTSs are large and growing, and the EPA estimates that over 2.6 million existing OWTSs may require technical treatment improvements for nitrogen removal due to their location in nitrogen-sensitive watersheds [2]. The forms of nitrogen and phosphorus exiting from these systems is almost entirely as ammonium (NH4+) and phosphate (PO43-), respectively.

Triangle Environmental (TE) developed a concept to solve this challenge - a plug-in technology that could remove nutrients from existing OWTS technology as a retrofit to systems currently in the ground or as an integration for new installations. TE's innovation is Electrodialytic Nutrient Recovery (ENR) which selectively removes nutrient ions from wastewater streams, creating separate nutrient-free and nutrient-rich steams. The nutrient-free stream is safe for environmental release, and the nutrient-rich stream can be reuse as a fertilizer or returned to the primary treatment tank of the OWTS.

The purpose of our EPA Phase I SBIR research was to demonstrate that the core technical approach of ENR would be effective and suitable with residential onsite wastewater. Electrodialysis has previously been demonstrated in industrial waste streams, but not in the challenging environment presented by onsite wastewater due to the high potential of organic and biological fouling as well as necessity of minimal operating requirements and low power usage.

Summary/Accomplishments (Outputs/Outcomes):

A lab-scale ENR prototype (605 mL) was operated to remove nutrients first from a nutrient-salt simulant solution and then from effluent collected for an Advanced OWTS in Wake County, North Carolina. Varied flow rates (10-30 mL/min) and inlet concentrations (6-65 mg N/L) were tested to project nutrient mass flux rates for the final system, and long-duration tests were performed to understand performance change over time. The prototype demonstrated that effluent could quickly (less than 15 minutes) be reduced to concentrations less than 12 mg N/L and typically had nitrogen reduction values ranging from 60-75%. Our longest test to date (170 hours continuous), showed that high removal rates could be sustained for long periods and that our fouling reduction strategies can prolong performance. Additionally, power consumption over long trials did not significantly change and remained near or less than 0.6 W throughout. Based on mass removal rates, the final product should be less than 15 gallons in volume, allowing for easy bolt-on to existing OWTS.

Conclusions:

ENR shows promise as a plug-in nutrient removal technology for existing OWTSs. Results indicate that it can produce a final effluent with less than 12 mg N/L, operate with low power consumption, and be packaged as a compact unit. The COVID-19 pandemic reduced our team's access to laboratory facilities, but these results are encouraging through the shortened performance period. TE will continue operations to further explore performance characteristics over time. Beyond initial testing, we expect optimization studies to yield improved results.

Triangle Environmental will operate in a business-to-business model. TE's end goal will be to license the ENR technology to other waste treatment companies with marketing and distribution capabilities. The initial target scale is individual households, but the technology can easily be scaled to cluster systems for multiple homes, parks, schools, shopping centers, or other public facilities. Additionally, TE envisions this technology having a broader application and exploring additional industries such as agriculture waste treatment. During Phase I, TE created meaningful relationships with local OWTS companies that specialize in installation and operation as well as state-wide regulators. By utilizing industry relevant input from these partnerships, we aim to develop a technology that is a simple plug-in to existing systems, meets direct needs of product manufacturers, and is a streamlined solution to nutrient removal. Based on the positive data gathered from Phase I, TE plans to file for intellectual property (most likely in the form of a utility patent) to strengthen licensing options with industry partners in Phase II and beyond.

SBIR Phase II:

Electrodialytic Nutrient Recovery for traditional and advanced OWTS effluent