Streaming Current Monitor Pilot Study 'The Detection Of A Coagulant Feed Failure'

An Accufloc streaming current monitor (SCM), now known as the Hach AF7000, was placed at a local surface water treatment plant for field testing. The facility was considering the evaluation of streaming current technology for the monitoring and confirmation of coagulant feed.

This drinking water facility practices conventional treatment for surface water with a production capacity of between 15 (winter) and 35 (summer) MGD. Treatment includes chemical injection to adjust pH and the addition of ferric chloride as the primary coagulant. After sedimentation, the water is filtered through dual media anthracite filtration and then followed by post disinfection. The source water originates in the central Rocky Mountains and is primarily from snowmelt. This surface water flows approximately 60 miles before being captured in an impoundment of approximately 1,000 surface acres that is located in an urban area, approximately three miles from the plant. The reservoir is considered to be a very stable raw water source, but is susceptible to flashing from the rare strong thunderstorm.

An SCM was installed in the plant to continuously sample the flash mixer effluent. The SCM signals were logged directly into the plant SCADA system, but were not wired to any alarms. The trends were displayed and updated every minute. At a glance, the operators could determine if the SCM readings were stable and in their expected range. The displayed value was expected to remain close to zero after setting it at the assumed optimal coagulation conditions, due to the typical stability of the raw water. If the readings have a strong negative deviation, it is a potential signal that the coagulant feed is lower than the previous optimum. If the deviation is positive, the coagulant feed could be higher than optimum. Similarly, changes in the raw water quality or pH control may be interpreted by the direction and magnitude of the SCM reading deviations.