There is an ever increasing need to remove solids from liquid streams which can contain solids. Many waste streams from industrial, manufacturing or other processes often contain solids which are undesirable or which can pollute natural waterways if such waste streams are directed into such waterways without complete solids separation.
For example, the separation of precipitated metal hydroxides from effluent water is a most cumbersome and expensive part of the prior art metal finishing waste treatment. Precipitated metal hydroxides, such as nickel, chromium, zinc, copper, iron, and the like, are bound with water in the effluent from plating plants, and the like, and the floc formed has nearly the same specific gravity as the water. This factor tends to keep the flocculent precipitate in suspension, and it has proven most difficult and time consuming to attempt to settle the precipitated particles in the prior art settling tanks. It has been found that the more dilute the waste, the harder it is to settle the precipitated hydroxides. In general, the prior art settling tanks require an inordinate amount of time to perform their settling function to any material extent, and are incapable of removing the precipitates in sufficient quantities to satisfy present and proposed government standards with respect to effluent purity. Additives, such as aluminum sulfate, ferric salts, or polyelectrolytes are used in the prior art settling processes in an effort to promote the precipitation and settling of the precipitates.