ABSTRACT
In water or waste treatment, the streaming current detector (SCD) can estimate treatment demand or continuously control the addition of coagulation chemicals by detecting the surface charge on particles. Lowering the pH of a sample shifts its SCD reading upscale, and increasing the salt content by adding a balanced, neutral salt shifts the reading toward zero. In the usual treatment plant, the SCD may continuously control the feed of cationic chemicals. Batch samples to be taken to the SCD should be adequate to permit rinsing the apparatus several times. The SCD controller set point determination is based on downstream turbidity measurement. For continuous control, the SCD measurement signal is fed to a two-mode controller which modulates the chemical feed pump or control valve. If there is an existing flow proportioning control for the chemical feed, the SCD controller can influence its ratio set point in a cascade arrangement.
