Small particulates suspended in a solution will often have a surface charge. For example, the majority of naturally occurring particulates in surface waters are Aluminosilicates (clays) which have a negative surface charge. This means that the particulates will repel each other and therefore they will not agglomerate into particles large enough to settle out of suspension (called floccing).

To neutralize this charge a chemical called a flocculent, with particles having the opposite surface charge, can be added. The right combination of suspended particles and flocculent particles, will have no net surface charge, so they will tend to stick together, the resulting large aggregate particles will settle out.

A measurement of the charge on particles in solution can be made in two ways...

1. By using a microscope to observe the motion of particles when a voltage is applied. This method calculates the Zeta Potential.
2. By measuring the voltage produced when the particles are moved. This is called Streaming Current and is the most common method.

The AccuFloc Streaming Current Monitor uses a piston reciprocating into a closed chamber to create a high rate of flow along the chamber wall. The shearing effect of the piston strips away the charged ions in the water which normally surround the particle, leaving only the particles moving along the chamber wall. This moving charge is a current (called the streaming current) and can be measured between two probes at opposite ends of the chamber.

This signal is amplified and processed to give the output Streaming Current (SC) reading. There are no standard units of SC. The units of Zeta-Potential are seldom used in practice, as a known solution is difficult to produce. Also the correspondence between the two types of measurement depends on the precise geometry of the piston and sample chamber (this varies as the unit wears).

SC can be used to determine the flocculent dosage required to neutralise the surface charge on particles in the solution to a level that permits optimal coagulation and settling. Due to the fact that the piston invariably develops a slight surface charge of its own, there is an apparent offset between the true-zero SC (no current measured) and zero Zeta Potential. which is normally the optimal Zeta Potential for flocculation.

Unfortunately, the SC of a sample that is dosed for optimal coagulation depends on the pH of the sample. Therefore, for best use of a streaming current monitor this must be constant or controlled before flocculation.

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