Advanced Septic System Nitrogen Sensor Challenge

By Best Plumbers On Aug 26, 2024

background

Conventional septic systems are often not designed to remove nitrogen to a level that protects local water quality, which can lead to problems such as excessive nitrogen pollution of waterways. This issue is especially important for coastal communities, where excess nitrogen can lead to eutrophication, hypoxia, and toxic algal blooms, which in turn can lead to beach closures and other problems that negatively impact coastal communities. The EPA estimates that over 2.6 million existing systems are suitable for upgrading to modern septic systems that treat the nitrogen because of their location in nitrogen-sensitive watersheds. By adding nitrogen sensors to these modern septic systems, manufacturers, homeowners, and local and state agencies can be assured that these systems are working as designed and protecting valuable coastal resources.

The Challenge – Phase I

In January 2017, EPA, in collaboration with The Nature Conservancy, USGS, and others, launched the first phase of the Advanced Septic System Nitrogen Sensor Challenge. Phase I asked participants to develop a nitrogen sensor for use in advanced on-site nitrogen removal wastewater treatment systems (also known as advanced septic tanks) to monitor their long-term performance. Phase I ran through mid-March 2017, and written proposals were judged by an external panel of experts. EPA hosted a Sensor Showcase Day and awarded prizes on June 29, 2017.

Prototype testing – PRabbit II

EPA began prototype testing in December 2017. Prototype testing was open to any sensor technology developer who had a nitrogen sensor for advanced septic systems. EPA contracted Battelle Memorial Institute to support the prototype testing program by developing a Test/Quality Assurance Plan (T/QAP) and a Verification Plan and to oversee testing of the sensors. The T/QAP is based on the International Organization for Standardization (ISO) standard for Environmental Technology Verification (ETV) – ISO 14034. Funding for the testing program is provided by EPA's Office of Research and Development and EPA's Office of Water and Wastewater Management.

Sensor testing was conducted from 2018 to 2019 at the Massachusetts Alternative Septic System Test Center, a National Sanitation Foundation-certified testing facility in Barnstable, Massachusetts. The final challenge test was held August 21-27, 2019. The EPA offered a cash prize of up to $50,000 to the sensor that performed best during the August test.

Dr. Qingzhi Zhu from Stony Brook University and the New York State Center for Clean Water Technology in Stony Brook, NY

On May 5, 2020, EPA announced that Dr. Qingzhi Zhu of Stony Brook University and the New York State Center for Clean Water Technology in Stony Brook, NY, was awarded the $50,000 Challenge Prize, the opportunity for commercialization support, and eligibility to participate in the six-month ISO ETV 14034 field verification test scheduled to begin in fall 2020. If the sensor package successfully completes the ISO ETV 14034 field test and meets the minimum performance targets listed in the table below, a verification report and statement will be posted on the VerifiGlobal website in summer 2021.

Advanced Nitrogen Sensor for Septic Tanks ISO 14034 ETV 6-month Field Test Performance Objectives

attribute	Attribute Description	Performance objectives
attribute	Attribute Description	minimum	Almost ideal	Ideal
Parameters1	What is measured	NO3-, NH4+	NO3-, NH4+, TOC	Total nitrogen (TN)2
Installation price	Price for the homeowner to install	1,500 US dollars	$1,250	1,000 US dollars
Data management	Ability to record and transmit data (e.g. telemetry) for real-time access by practitioners, regulators and interested stakeholders	Record data and automatically transfer it to the specified server or cloud	Record data and automatically transfer it to the specified server or cloud	Record data and automatically transfer it to the specified server or cloud. Includes the ability to remotely program variable sampling frequencies.
Applicability and accessibility	Applicability of the sensor(s) to various innovative/alternative system designs and easy access to OWTS for installation and maintenance	Installed on site to provide performance information on the OWTS; must be accessible for maintenance	Mounted on site to provide performance information on the OWTS; must be accessible for maintenance	Mounted on site to provide performance information on the OWTS; must be accessible for maintenance
Frequency of sensor system maintenance	How often the sensor(s) need to be serviced	Not more often than quarterly	At most every six months	Not more often than annually
accuracy	Accuracy of sensor measurements compared to actual measurement	Within 20% of the true value3	Within 20% of the true value3	Within 20% of the true value3
precision	Repeatability of sensor measurements	≤ 30% RDS	≤20-30% RDS	≤20% RDS
Area4	Range of detection	2-60 mg N/L	2-60 mg N/L 2-60 mg/L TOC	2-60 mg N/L
Frequency of sensor measurements5	Ability of the sensor to measure parameter concentrations at time frequencies of:	Hourly5	Hourly5	Hourly5
Operating temperature range of the sensor	Temperature range in which the sensor can operate	4°C to 35°C	4°C to 35°C	4°C to 35°C
Mission	Duration of use	Continuously	Continuously	Continuously
System lifetime	Expected sensor lifetime	5 years	5 to 10 years	10 years

1 For information on the sources of nitrate (NO3-), ammonia (NH4+) and total organic carbon (TOC), see Section B1.4.

2 Total nitrogen (TN) is defined as the sum of total Kjeldahl nitrogen (ammonia, organic and reduced nitrogen) and nitrate-nitrite.

3 The true value is defined as the certified laboratory result for the parameter using accepted test methods.

4 The sensors must be able to give an alarm or otherwise indicate when the range is exceeded.

5 The frequency of sensor measurements during the pre-tests and the 6-month tests is listed in Section B1.2. For use in an actual application, the frequency of sensor measurements depends on the end user requirements and can vary from hourly to daily or more frequently than hourly. Sensors should provide the flexibility for different measurement frequencies.

Market stimulation opportunity 2021

Following the release of the verification report and statement in summer 2021, an external technical panel and The Nature Conservancy (TNC) will review the results. TNC and others are seeking funding for an order of 200 deployable septic tank sensor units, with a total cost not to exceed $300,000. The order would be awarded in fall 2021 to the best performing sensor that passes the 6-month on-site performance test and meets or exceeds performance goals.