EPA OKs Use of RDO Methods for DO Analyses

In-Situ® Inc. of Fort Collins, Colo., announced recently that the U.S. Environmental Protection Agency has granted nationwide approval to three In-Situ RDO® optical dissolved oxygen (DO) methods under the Alternate Test Procedure, or ATP, process.

The In-Situ RDO methods are the only optical- or luminescence-based DO methods to pass the ATP approval process for measuring biochemical oxygen demand (BOD), carbonaceous biochemical oxygen demand (CBOD) and DO under the Clean Water Act.

The ATP process validated three methods using the optical (luminescent) DO sensor as the determinative technique. Results from the validation establish the methods as the most widely tested and applicable optical DO methods available for compliance monitoring.

Ten federal- or state-certified laboratories performed testing in nine water and wastewater sample matrices. Over 1,300 samples were tested in municipal wastewater (influent and effluent), industrial wastewater from significant and categorical dischargers, ambient surface water, drinking water and other categories. No significant matrix interferences were observed in any of the 1,300 samples tested.

Entities holding National Pollution Discharge and Elimination System (NPDES) permits must use EPA-approved methodologies for BOD, CBOD and DO testing.

The EPA Office of Science and Technology will recommend the In-Situ RDO methods for inclusion at 40 CFR Part 136.3. In the interim, NPDES permit holders can begin monitoring with the In-Situ RDO methods after seeking approval from their regional EPA authority.

The sensors measure DO using the principle of “dynamic luminescence quenching.” Unlike other optical sensors, these sensors do not require hydration. In addition, they exhibit minimal sensor drift over extended periods of use and are not subject to matrix interferences that plague electrochemical sensors (e.g., sulfides, oils, greases, ammonia).

Complete and accurate names of the In-Situ methods are:

  • In-Situ Inc. Method 1003-8-2009 Biochemical Oxygen Demand (BOD) Measurement by Optical Probe (ATP Case No. N09-0020)
  • In-Situ Inc. Method 1004-8-2009 Carbonaceous Biochemical Oxygen Demand (CBOD) Measurement by Optical Probe (ATP Case No. N09-0021)
  • In-Situ Inc. Method 1002-8-2009 Dissolved Oxygen Measurement by Optical Probe (ATP Case No. N05-0014)

The In-Situ RDO sensor and sensing foil are manufactured entirely by In-Situ Inc. in Fort Collins and Boulder, Colo. RDO sensors are available for process, laboratory and field applications.

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