In situ flow-injection monitoring of ammonia in landfill leachate

摘要

A portable, 12 V battery-powered, automated spectrophotometric field monitor has been developed that permits the continuous long-term recording of the total ammonia concentration in the surrounding aquatic environment. The flow-injection (FI)–based monitor incorporates a gas diffusion unit and an acceptor stream containing an acid-base indicator. The detection system utilizes a red solid-state light-emitting diode source and photodiode detector. Remote control and data processing are achieved by an in-house–designed microcomputer system. The instrumentation was fully evaluated in the laboratory and was shown to operate unattended for periods of up to 1 week (analyzing every hour) before battery charging and reagent replacement were required. The precision and accuracy 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 minute intervals over a 7 day period (n = 170). The calculated mean concentration was 79.0 mg L−1 (using 50 and 150 mg L−1 standards) with an RSD of 5.2%. The detection limit (3σ) was determined as 2.5 mg L−1. The feasibility of using the system in situ was demonstrated by a 2 week field trial in which the automated field monitor was successfully deployed at a landfill leachate lagoon. Data from the trial are presented, and the potential applications of the system in environmental management are discussed. © 1997 John Wiley & Sons, Inc. Lab Robotics and Automation 9: 175–183, 1997.