Apparatus for the measurement of the mobility of colloids in an electric field

A method for determining an optimum dosage of coagulant to be added to a liquid to be treated and having colloidal particles therein to achieve optimum clarification of the liquid, said method comprising:

• providing a tank having at two opposite walls thereof substantially parallelly spaced first and second electrodes and a membrane positioned within said tank and extending parallel to said electrodes, said membrane dividing said tank into first and second compartments;
• performing a plurality of density change measuring operations, each such density change measuring operation comprising:
• placing a quantity of liquid to be treated within said first and second compartments of said tank;
• adding a predetermined dosage of coagulant material to said liquid to thereby cause flocculation of colloidal particles within said liquid;
• passing a flat beam of radiation completely longitudinally through said liquid in said first compartment only at a position closely adjacent said membrane and spaced from said first electrode which is spaced across said first compartment from said membrane, while maintaining said beam of radiation parallel to said electrodes and said membrane;
• measuring the intensity of said beam of radiation after passage thereof through said first compartment to obtain a first measurement of optical density of the volume of liquid traversed by said beam of radiation;
• thereafter applying an electric field between said first and second electrodes, thereby causing unflocculated of said colloidal particles to move in a direction from said second electrode toward said first electrode;
• said membrane being formed of a material which is permeable to the passage therethrough of ions in said liquid caused by said electric field but which is impermeable to the passage therethrough of said colloidal particles, whereby during the application of said electric field unflocculated colloidal particles in said second compartment move in a direction from said second electrode toward said membrane but do not pass through said membrane and unflocculated colloidal particles in said first compartment move in a direction from said membrane toward said first electrode and out of said volume of liquid traversed by said beam of radiation;
• thereafter, after a predetermined period of time, again measuring the intensity of said beam of radiation after passage thereof through said first compartment to obtain a second measurement of optical density of said volume of liquid traversed by said beam of radiation, while maintaining said beam of radiation closely adjacent said membrane;
• and
• comparing the first and second measurements of optical density to obtain a measurement of the change in optical density of the liquid as a function of the amount of unflocculated of said colloidal particles within said liquid;
• the predetermined dosage of coagulant material added in each of said density change measuring operations being different;
• and
• comparing the measurements of change in optical density obtained from each of said density change measuring operations to determine the particular dosage representative of the least amount of change in optical density, such particular dosage representing the optimum dosage to achieve optimum clarification of the liquid to be treated.