The Orion Research ammonia monitor was investigated using the Orion specifications and environmental considerations as a guide. Laboratory tests under controlled environmental conditions showed the electronic stability (drift) to be well within + or - 10 percent of reading over the temperature range 5C to 42C. Sensor stability over the temperature range 5C to 42C was tested by applying ammonia nitrogen (standard solutions of 10 mg/l, 50 mg/l, and 100 mg/l as direct input to the monitor. The results of these tests showed that automatic restandardization maintained readings within Orion's specified tolerance of + or - 10 percent of reading. Dynamic on-stream measurements were made of a secondary sewage treatment plant effluent in a field installation. These measurements were periodically compared with those of the standard method of distillation and titration. Sixty-five percent of these comparisons were within + or - 10 percent of reading. Steady-state comparisons were made of field-collected samples with the standard method for determining ammonia nitrogen. It appeared from these tests that a 5 percent loss in ammonia concentration resulted from the required straining and filtering of the sample input to the monitor. Eight of the nine samples compared were within 10 percent of the standard method.

May 1977.