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June 5, 2017
Dr. Thomas H. Johengen, ACT Chief Scientist
University of Michigan CILER
4840 South State Rd
Ann Arbor, MI 48108
Re: Nutrient Challenge Company Response Letter
Dear Dr. Johengen,
Real Tech Inc. would like to thank you and the Alliance for Coastal Technologies (ACT) team for the
opportunity to participate in the Nutrient Challenge competition and comment on the performance of the
Real Nitrate Analyzer GL series.
We are very pleased that ACT has organized this challenge and shined a spotlight on the benefits of real-
time sensors for environmental nutrient monitoring. Real Tech’s analyzers utilize spectrophotometry to
detect nitrate nitrogen in water without the use of reagents, are highly modifiable based on clients’ needs,
and can generate data at a frequency of every minute. Below we expand on some of the most important
aspects of Real Tech’s experiences in this challenge.
1) Design Application
Real Tech’s nitrate monitoring systems are designed for and most commonly used at well water blending
stations, and municipal and industrial water/wastewater treatment facilities. Due to the current regulations
and the typical nitrate concentrations encountered in these environments, two of the field tests
(Chesapeake Bay, MD and Kaneohe Bay, HI) were not within the design specifications of our analyzer.
Both of these field test sites had high salinity and very low nitrate concentrations (less than 0.04 mgN/L
compared to 10 mgN/L maximum allowable concentration in drinking water).
2) Custom Calibration
Real Tech’s preferred method of deployment for its analyzers involves an initial in-house calibration
followed by an on-site audit of the calibration after installation. This allows for an adjustment of the
calibration for background water interferences. However, as deployment prior to the actual testing days was
not a possibility and collecting audit data during the testing period would interfere with the testing, we were
not able to implement a correction based on on-site data. We strongly believe that spectrophotometric
measurement techniques work best when a custom calibration is built on-site. For instance, in the Maumee
River field test, Real-NO3 measurements appear to have tracked the actual nitrate concentrations well,
however, it is evident that a slight offset was present. This offset could have been corrected for with an on-
site correction factor on the first day of installation, had on-site data auditing been allowed. Furthermore,
continued collaboration between the client and the manufacturer will provide superior data as our analyzers
are capable of building a site-specific library which improves performance over time.
3) Range
Real Tech’s analyzers come with adjustable flow cell components. This allows for a customized approach to
concentration range. A longer path length flow cell increases sensitivity and accuracy at low concentrations
while a shorter path length flow cell provides the widest range, but has reduced sensitivity at low
concentrations. During the laboratory testing part of the nutrient challenge, we were asked to provide an
analyzer that would measure a range of 0.01-50 mgN/L NO
3
. We provide analyzers that can measure up to
hundreds of mgN/L. However, as explained above, a wider range comes with a trade-off of losing the
required sensitivity at low concentrations. For this reason, Real Tech participated in the laboratory testing
with an 8-mm flow cell that aimed to maintain a reasonable level of accuracy at low concentrations (0.01-0.1