Field Verification of On-Line Instrumentation at a Municipal Wastewater Treatment Plant

As part of a full-scale project to demonstrate the advantages of using automated process control in wastewater treatment plants, on-line sensors used in various control loops were calibrated and/or verified during control system commissioning and startup. The on-line measurements included liquid flow rates, air flow rates, suspended solids concentrations, and dissolved oxygen concentrations. The methods used to confirm instrument performance are presented along with results that show that several instruments were found to operate outside the manufacturers' written specifications. In addition, on-line methods which can help determine when recalibrations are required, and thereby help to reduce maintenance costs and ensure reliability, are also presented.