Automatic control of polymer dose using the streaming current detector

A previous phase of this study demonstrated that streaming current (SC) measurements taken from the liquid stream after dewatering can be used to adjust and optimize polymer dosages used for conditioning of wastewater solids. Consequently, use of the streaming current detector (SCD) was evaluated for continuous feedback control of polymer dosing in two full-scale dewatering facilities. Control was implemented using a slightly negative SC setpoint, and the SCD's ability to control the polymer pumps was assessed when the wastewater solids characteristics changed during routine operation and when controlled additions of ferrous chloride were made. Changes in the solids flow rate were also imposed to assess the control system's response at one facility. At the second wastewater treatment plant, an unexpected change in the polymer also occurred during SCD use, and the system's ability to adjust the polymer dose accordingly was assessed during this incident. Results indicated that the SCD adjusted the polymer feed rate appropriately during all changes in solids flow rate and characteristics and polymer concentrations. The device's success indicates that charge neutralization plays a significant role in solids conditioning and can be used as an indicator of polymer performance and for feedback control of dosage. Routine and thorough cleaning of the SCD's probe with a plastic brush may be necessary in certain applications to maintain consistent control.