Pollutants can occur in water in various forms, e.g. colloidal, suspended and dissolved. This type of pollution cannot be removed as such by DAF/DGF or by settling. A physical-chemical pre-treatment is needed to render them into a separable form. This can be achieved by means of coagulation and/or flocculation.
In conventional water treatment plants flocculation is commonly achieved in one or more continuously stirred tank reactors or in long channels fitted with stirring devices. In those flocculator types disturbing short-circuiting and back mixing effects occur. As a consequence a portion of water leaving the flocculator has been treated for an unnecessary long time. In addition, the turbulent flow patterns in this reactor cause a great variety of velocity gradients, e.g. eddy turbulence at the stirrer tips.
This combination of varying residence times and uncontrolled G-values is a major factor contributing to a disturbed floc growth. Floc structure, shape and size will differ widely, impeding subsequent separation by DAF/DGF or settling. To compensate for these poor characteristics, the retention time in conventional type flocculators is three to five times longer than those indicated by the jar test.
How it Works
How T-Floc™ Works
T-Floc™ is a combination of pipe flocculators and plate flocculators, which are both based on the principle of the “tube-plug flow reactor”. The pipe flocculator consists of a calculated length of pipe which is expanded in diameter along its length in order to facilitate the slower ortho-kinetic floc building up. The pipe is divided into certain lengths that are connected by 180° elbows. The result is a “coiled” pipe flocculator that can be suspended on a steel support frame. The flocculator pipe length and diameters can be exactly determined on the basis of jar test results. Chemicals can be injected into the flocculator precisely at those points where they are most effective. The energy required for the flocculation process is not derived from stirring devices but by well-defined factors such as fluid velocity and pipe friction under plug flow conditions.
The plate flocculator consists of a number of vertical corrugated plates arranged in two or more compartments. Part of the plates is fixed, while the other plates can be moved in a vertical direction. The water flows between the plates from compartment to compartment in an alternately upward and downward direction. The first flocculator compartment is the smallest one with each successive compartment being larger. This means that the flow velocity of the water decreases in each compartment, resulting in the so-called tapered velocity flocculation.
By raising or lowering the adjustable plates a corrugation phase shift can be affected. The phase shift causes a higher flow resistance between the plates, thus creating increased G-values. The advantage of the plate flocculator is that G-values can be adjusted so that the flocculation process can be optimised to the maximum possible extent. The plate flocculators are mainly used in combination with our plate settlers in process or drinking water plants.