IN-SITU FLOW-INJECTION MONITORING OF AMMONIA IN LANDFILL LEACHATE

A portable, 12 V battery-powered, automated spectrophotometric field m onitor has been developed that permits the continuous long-term record ing of the total ammonia concentration in the surrounding aquatic envi ronment. The flow-injection (FI)-based monitor incorporates a gas diff usion unit and an acceptor stream containing an acid-base indicator. T he detection system utilizes a red solid-state light-emitting diode so urce and photodiode detector. Remote control and data processing are a chieved by an inhouse-designed microcomputer system. The instrumentati on was fully evaluated in the laboratory and was shown to operate unat tended for periods of up to 2 week (analyzing every hour) before batte ry charging and reagent replacement were required. The precision and a ccuracy of the chemical monitor was examined by continuously analyzing a sample of a known ammonia concentration (80.0 mg L-1 NH3-N) at 60 m inute intervals over a 7 day period (n = 170). The calculated mean con centration was 79.0 mg L-I (using 50 and 150 mg L-1 standards) with an RSD of 5.2%. The detection limit (3 sigma) was determined as 2.5 mg L -1. The feasibility of using the system in situ was demonstrated by a 1 week field trial in which the automated field monitor was successful ly deployed at a landfill leachate lagoon. Data from the trial are pre sented, and the potential applications of the system in environmental management are discussed. (C) 1997 John Wiley & Sons, Inc.