What is Flocculation?
Flocculation is the process of bringing the small particles together into a larger floc to enable them to be either seperated out in some clarification process or more commonly nowadays in a Dissolved Air Flotation unit (DAF).
In order to avoid the flocs being sheared the flocculant needs to added in a low shear area and certainly after transfer pumps such as those of centrifugal design. Full flocculation can take a few minutes to occur. The particle weight has to produce settlement to overcome the upflow velocity in the clarifier otherwise solids carryover will occur.
Modern flocculants are organic long chain polymers typically based on polyacrylamide. They come in various chain length and ionicity, i.e cationic,anionic ,non-ionic. They are produced in powder, emulsion, dispersion and solution forms.
Due to the removal of the colloidal particles there will be the additional benefit of the reduction of Chemical Oxidation Demand (COD) of the effluent. Typically for a 90% solids removal a 50-60% reduction in the COD will be achieved.