The laboratory staff at the wastewater treatment plant in Loveland, Colo., wanted an easier way to analyze and report influent and effluent ammonia levels.

The 10 mgd plant’s process reduces influent ammonia of 25-30 mg/L to below 0.1 mg/L in effluent. At those low levels, the staff found it challenging to use the U.S. EPA-approved SM4500-NH3D Ion Selective Electrode (ISE) method for ammonia measurement and compliance reporting.

The staff successfully switched to Hach Method 10205 using TNTplus vial chemistry. “We have saved a significant amount of time in our daily samples and quality control checks,” reports analyst Nick Marusin. “We can now run a day’s worth of ammonia samples in about 30 minutes, where before it took over an hour and a half, even without electrode calibration problems.”

Looking to improve

The ISE method has a wide measuring range that makes it attractive to many wastewater and environmental laboratories. However, the Loveland lab analysts experienced various issues in using it, including:

• Daily preparation of calibration standards, including a low-level standard of 0.05 mg/L ammonia, taking up to 30 minutes per calibration
• Frequent failures of calibrations or electrode membranes, occurring without obvious cause after several months of routine analysis
• Hours spent troubleshooting and subsequent concerns with sample holding times
• Time and cost required to replace electrode membranes

Validating a new method

After learning about Hach Method 10205, the lab team investigated the procedure as an alternative to ISE. The TNTplus ammonia method is classified as an EPA Equivalent method, as it uses a slightly modified version of the approved indophenol/phenate chemistry. It can be run in less than 20 minutes, as all required reagents are included in the test vial.

In the process, ammonium ions react at pH 12.6 with hypochlorite ions and salicylate ions in the presence of sodium nitroprusside as a catalyst to form indophenol. The amount of color formed by the reaction is directly proportional to ammonia concentration in the sample. The sample vial with barcode communicates with a Hach DR 5000, which reads the results at a wavelength of 690 nm and displays the ammonia concentration at the end of the test.

Many states have approved the method without further validation studies. Some states may require a simple validation study before the method is used for compliance reporting. This process is outlined by the EPA and Federal Register in 40CFR Part 136.6, Method Modifications and Analytical Requirements.

Because facilities in Colorado had not yet used the new method for compliance reporting, Marusin took on the task of validation. It included standard quality control samples and procedures typically followed in a laboratory Initial Demonstration of Capability. He ran method comparison studies including the Method Detection Limit, Initial Precision and Recovery, Matrix Spike, and Matrix Spike Duplicate.

“The study was easy to conduct and was a painless process,” Marusin says. “We ran about 10 effluent samples, and the study report we sent to the state authority only took about four hours to compile.” The accompanying tables show the results of the side-by-side method validation.

Consistent results

The side-by-side validation study showed that the TNTplus method performed significantly better than the ISE method. Most notably, recoveries of standard additions (“spikes”) in both reagent water and effluent matrix were significantly better. Method precision and consistency also improved significantly. The team attributed the greater accuracy and precision to features built into the vial chemistry and spectrophotometers:

• Barcode recognition of the test vial, ensuring that the correct method settings are always used
• Automatic updating of built-in calibration factors
• Automatic 10-time measurement while the vial is rotated, eliminating errors from dirty spots or cracks in vials
• Precise, consistent and convenient delivery of reagents sealed in the vial cap and tube

Going forward

Based on the validation study results, the lab staff petitioned the state regulatory authority and gained quick approval to use Method 10205. The facility now uses the new method for daily process control and for discharge monitoring reporting. Marusin reports, “Overall, the TNTplus method is awesome and has solved a number of headaches for us.”

About the authors

Ruth A. Hecker is water quality laboratory coordinator for the City of Loveland, Colo. Derek Walker is an applications development manager for Hach Company.