Response to the following in 2 PAGES :
While Bahadori (2014) spends considerable time discussing solid waste treatment strategies (related to sludge and scum generated from the influent waste stream), it may be easy for us to forget exactly what it is that we are intending to do in this part of the process. Let's look at this phase of the treatment process from a macro-scaled perspective first, and then dive into the micro-scaled perspectives of the physical and chemical activities related to this phase.
First, we must remember that all we have done to this point in the entire treatment process is received the influent waste streams from industry, physically removed some (not all) of the oil and other easily-accessed contaminants, tied up some (not all) contaminants with chemical binding, digested and broken down other contaminants with biological organisms, and then removed as many solids as possible from the system that resulted from those activities (Texas Water Utilities Association [TWUA], 1991).
As such, we are now left with a system that is still too heavily loaded with remaining solids that are presently in suspension. These are the solids that did not get physically removed during the physical treatment phase, precipitated out during the chemical treatment phase, digested during the biological treatment phase, or settled out during the secondary settling phase. Consequently, we must find a way to remove these suspended solids that represent a wide cross-section of oils, metals, salts, biological organisms, and general debris from the treatment system (TWUA, 1991; Haas & Vamos, 1995).
One of the better demonstrated successful strategies at this point is to intentionally form more sludge (some of which was already removed during the earlier stages of treatment) by forcing these suspended solids to bind with something more, thereby increasing the particle size, specific gravity, and subsequent physical attainability of the solids in the remaining solution. Once this is achieved, the solid particles can then be filtered or pressed out of the suspension, dewatering the solids for ultimate solid waste disposal (TWUA 1991).
Understanding this, we can now consider the micro-scaled perspective of this phase of treatment, focusing specifically on dewatering. It is now understandable that, given the earlier stages of treatment (chemical and biological), a larger proportion of dissolved solids (from solution) have been removed, relative to the smaller
Reference: Designing Solid Waste Management Systems for Industrial and Hazardous Waste