Wastewater streams, other process

Another pathway by which targeted pollutants enter the wastewater stream is through the disposal of spent batch process solutions into the sewer system. Spent solutions consist of aqueous wastes and may contain accumulated solids as well. Spent solutions are typically bled at a controlled rate into the wastewater stream. Other sources of pollutants in wastewater streams include cleanup of spills and washdown of fugitive aerosols from spray operations. 

The problem consists of determining a network of interconnections of water streams among the processes so that the expected cost is minimized while processes receive water of adequate quality, with or without change of flows. Thus, one is allowed to reuse wastewaters from other processes, diluting it with fresh water if there is a need for it... 

AH other organic waste-process and vent streams are burned in a dare, in an incinerator, or in a furnace where fuel value is recovered. Wastewater streams are handled in the plant biological treatment area. 

Processes for SS separation may fill three distinct functions in wastewater treatment, namely, pretreatment to protect subsequent processes and reduce their loadings to required levels, treatment to reduce effluent concentrations to required standards, and separation of solids to produce concentrated recycle streams required to maintain other processes. In the first two functions effluent quality is the prime consideration, but where the third function must be fulfilled along with one of the others, design attention must be given to conditions for both the separated solids (sludge) and the process effluent. 

Ammonia stripping also removes cyanide, phenols, and other VOCs typically found in cokemaking wastewater. Phenols may also be removed by conversion into nonodorous compounds or into crude phenol or sodium phenolate by either biological means (phenol concentration <25 mg/L) or by physical processes.21 However, the Koppers dephenolization process is considered to be quite effective as it lowers the phenol content by 80 to 90% in ammonia still wastes. In this process a stream stripping process followed by mixing in a solution of caustic soda results in renewal of pure phenol with the flue gas.8... 

Toxic pollutants found in the mercury cell wastewater stream include mercury and some heavy metals like chromium and others stated in Table 22.8, some of them are corrosion products of reactions between chlorine and the plant materials of construction. Virtually, most of these pollutants are generally removed by sulfide precipitation followed by settling or filtration. Prior to treatment, sodium hydrosulfide is used to precipitate mercury sulfide, which is removed through filtration process in the wastewater stream. The tail gas scrubber water is often recycled as brine make-up water. Reduction, adsorption on activated carbon, ion exchange, and some chemical treatments are some of the processes employed in the treatment of wastewater in this cell. Sodium salts such as sodium bisulfite, sodium hydrosulfite, sodium sulfide, and sodium borohydride are also employed in the treatment of the wastewater in this cell28 (Figure 22.5). 

The wastewater generated in the membrane cell and other process wastewaters in the cell are generally treated by neutralization.28 Other pollutants similar to those in mercury and diaphragm cells are treated in the same process stated above. Ion exchange and xanthate precipitation methods can be applied in this process to remove the metal pollutants, while incineration can be applied to eliminate some of the hydrocarbons. The use of modified diaphragms that resist corrosion and degradation will help in reducing the amount of lead, asbestos, and chlorinated hydrocarbon in the wastewater stream from the chlor-alkali industry.28... 

Common pollutants in a titanium dioxide plant include heavy metals, titanium dioxide, sulfur trioxide, sulfur dioxide, sodium sulfate, sulfuric acid, and unreacted iron. Most of the metals are removed by alkaline precipitation as metallic hydroxides, carbonates, and sulfides. The resulting solution is subjected to flotation, settling, filtration, and centrifugation to treat the wastewater to acceptable standards. In the sulfate process, the wastewater is sent to the treatment pond, where most of the heavy metals are precipitated. The precipitate is washed and filtered to produce pure gypsum crystals. All other streams of wastewater are treated in similar ponds with calcium sulfate before being neutralized with calcium carbonate in a reactor. The effluent from the reactor is sent to clarifiers and the solid in the underflow is filtered and concentrated. The clarifier overflow is mixed with other process wastewaters and is then neutralized before discharge. 

Other process wastewater streams would provide the needed dilution for a once-through clear solution process. The total dissolved solids content of the combined waste should be determined to ensure that all discharge requirements can be met. 

Wastewaters may be collected in separate drainage systems (for process, sanitary, and storm water) althongh industrial and stormwater systems may in some cases be combined. In addition, ballast water from bulk crude tankers may be pnmped to receiving facilities at the refinery site prior to removal of floating oil in an interceptor and treatment as for other wastewater streams. 

Control of pH is important in the wastewater stream, but it ultimately becomes a byproduct of controlling FOG and BOD. Chemical oxygen demand (COD) is a useful parameter, and it can usually be predictably estimated at 1.4 to 1.6 times BOD for the model plant discussed in this section. These ratio values can vary based on processes in-place and other unusual circumstances. Measurement of COD is more often a tool to determine whether BOD tests are being correctly conducted and are useful in that results can be obtained in a matter of hours rather than days. 

Dissolved air flotation (DAF) has been widely used over the last 40 yr for removal of oil and grease, suspended solids, and biochemical oxygen demand (BOD) from wastewater and other industrial process stream. The reliability and performance of DAF systems have been improved along with the increasing use of this technology, as shown in Table 7. 

However, in general, solvent recovery is an important step in the overall solvent extraction process. Solvent recovery from the raffinate (i.e., water phase) may be accomplished by stripping, distillation, or adsorption. The extract, or solute-laden solvent stream, may also be processed to recover solvent via removal of the solute. The solute removal and solvent recovery step may include reverse solvent extraction, distillation, or some other process. For example, an extraction with caustic extracts phenol from light oil, which was used as the solvent in dephenolizing coke plant wastewaters (4). The caustic changes the affinity of the solute (phenol) for the solvent (light oil) in comparison to water as will be explained in the equilibrium conditions section. Distillation is more common if there are no azeotropes. 

The oil and chemical industries use the adsorption process in the cleanup and purification of wastewater streams and for the dehydration of gases. The process is also used in gas purification involving the removal of sulfur dioxide from a stack gas. In addition, adsorption is employed to fractionate fluids that are difficult to separate by other separating methods. The amount of adsorbate that is collected on a unit of surface area is negligible. Therefore, porous desiccants (adsorbent) having a large internal surface area are used for industrial applications. 

Application GT-CAR is GTC s carboxylic acid recovery technology that combines liquid-liquid extraction technology with distillation to recover and concentrate carboxylic acids from wastewater. The GT-CAR process is economical for any aqueous stream generated in the production of dimethyl terephthalate (DMT), purified terephthalic acid (PTA), pulp/pa-per, furfural and other processes. 

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