Solid removals

EPA Process Design Manualfor Suspended Solids Removal, U.S. Environmental Protection Agency Technology Transfer, Washington, D.C., 1975, pp. 5-6. 

Suspended Solids Removal. Depending on the concentration and characteristics of the suspended soflds, they can be removed by filtration, flotation, or sedimentation. Coarse soflds are removed by screening. Settleable suspended soflds are removed in a clarifier, which may be circular or rectangular. The efficiency of soflds removal is a function of the overflow rate (m /-d (gal/ft -d) as shown in Figure 5. 

Tank settling as a means of contaminant removal is not very efficient with fuels having the viscosity of kerosene. It is common practice to design tanks with cone-down drains and floating suctions to facilitate water and solids removal. 

To reduce the quantity of ash in the extracts even further, steps were implemented using a sequential solids removal scheme that entailed a combination of centrifugation and filtration. Following extraction of the coal... 

For wet ESPs, consideration must be given to handling wastewaters. For simple systems with innocuous dusts, water with particles collected by the ESP may be discharged from the ESP system to a solids-removing clarifier (either dedicated to the ESP or part of the plant wastewater treatment system) and then to final disposal. More complicated systems may require skimming and sludge removal, clarification in dedicated equipment, pH adjustment, and/or treatment to remove dissolved solids. Spray water from an ESP preconditioner may be treated separately from the water used to wash the ESP collecting pipes so that the cleaner of the two treated water streams may be returned to the ESP. Recirculation of treated water to the ESP may approach 100 percent (AWMA, 1992). 

Aluminum based chemicals have been used for many years in wastewater treatment applications for suspended solids removal. These include dry and liquid alum, with sodium aluminate used in activated sludge plants for phosphorus removal. 

Cake Filters - These are filters that are used to remove large amounts of solids from a slurry solution. They would normally be seen in biotechnology in the primary clarification of fermentation batches and in a variety of solids removal steps seen in the production of drugs via organic synthesis. 

The water is then pumped through series operated sand filters, which provide the final stage of suspended solids removal and protect the garnualr activated carbon (GAC) filters from particulate contamination. Series operated GAC filters are then used to remove the dissolved creosote and pesticides from the water. To achieve compliance with specifications levels, water should be sampled and analyzed after leaving the first GAC filter. The second GAC filter normally serves as a guard bed. 

We will address some of these issues later on in this chapter. But for now, simply recognize the fact that the most basic part of waste water treatment is solids removal. Solids are removed in primary and secondary treatment tanks, but without such effective removal there is no treatment process efficiency. 

Solvent Action. Materials that tend to respond well to extraction by pressing will be more effective in solids removal when solvents are used. The complication is that it becomes necessary to separate not only the solids and the containing liquid from the finished process, but the solvent as well. 

In the case of gravitational settling, the unit design depends on the method of solid removal after settling. The methods in use are... 

The activated sludge process usually must be preceded by neutralization and some metal removal, and possibly by solids removal. The process is normally followed up by a separation step, usually sedimentation, to remove the biological sludge from the waste liquid stream. 

Figure 4-52A. Liquid-solids removal cyclones. Feed enters tangentially along sidewall. By permission, Krebs Engineers.

Also, the higher degree of shear thinning provides for lower bit viscosities. This enables more effective use of hydraulic horsepower and faster penetration rates. In addition, shear thinning promotes more efficient operation of the solids removal equipment. 

The system can be weighted to a maximum of 11 Ib/gal provided the ratio of drill solids to clay solids is maintained at less than 2 1, by correct use of the solids removal equipment and careful dilution and makeup with bentonite from a premix tank. 

The surface mud system is designed to restore the mud to the required properties before it is pumped downhole. Most of the equipment is used for solids removal only a small part of the surface mud system is designed to treat chemical contamination of the mud. There are three basic means of removing drilled solids from the mud dilution-discard, chemical treatment, and mechanical removal. 

The chemical treatment methods reduce dispersability property, of drilling fluids through the increase of size of cuttings which improves separation and prevents the buildup of colloidal solids in the mud. These methods include ionic inhibition, cuttings encapsulation, oil phase inhibition (with oil-base muds), and flocculation. The mechanical solids removal methods are based on the principles presented in Table 4-55. 

A solution of 5-acctyl-5//-dibcnz[ft,/]azcpine (39, R1 = R2 = H R3 = Me 23.5 g, 0.1 mol) in EtOH (70 mL) and KOH (14 g) was heated under reflux for 18 h. The mixture was cooled and the orange-yellow solid removed by filtration. The residue was washed with cold EtOH and then thoroughly with cold H20 until neutral washings were obtained. The crude product was crystallized (first EtOH then benzene) yield 17.3 g (90%) mp 204 206 C. 

The effluent obtained after solids removal and microbiological disinfection could be reused as cooling water, cleaning water or industrial process water in many industrial uses. A final polishing step may be necessary if higher quality requirements are needed in some specific industrial uses, e.g., cooling and boiler feed-water. Membrane processes such as NF or RO eliminate inorganic ions and reduce parameters like conductivity, alkalinity or salinity, etc. 

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