Recycled Process Water

In Table II, the compositions of surface-zone recycle water and fine tails pore water from Syncrude and Suncor are compared (2). Over time, the recycle process water is becoming more brackish (especially at Syncrude). Concentration of the major ions in the tailings ponds as a function of depth is shown in Figure 11. The concentrations of major ions in tailings water have increased with time for example, at Syncrude, from 1979 to 1993, there was a 200-300% increase in conserved ions such as Na+ and Cl. At Suncor, absolute changes were smaller (2, 3, 35, 40). However, no evidence exists of trace metal buildup over time (2). 

Wright, R. L. Let Nature Cool Your Recycle Process Water, Chem. Eng. Progr., 54(2) 99 (1958). 

ICBs to a clarifier for separation into sludge and overflow streams (Parsons, 2000e). The sludge was to be dewatered in filter presses and sent off site to a landfill. The filtrate from the filtration step was to be combined with the clarifier overflow, and the eombined stream (about 100 gallons/min) was to be sent to a brine evaporator. The distillate, about 90 percent of the feed, was to be recycled as process water. The bottoms were to be sent to an evaporator/crystallizer for additional water recovery and the crystallized salts sent off site for disposal the distillate was to be added to the recycled process-water sheam. However, EDS test results showed that (1) the clarifier is not needed, (2) the bioreactor effluent can be recycled without clarification, and (3) a slipstream can be sent to the evaporator for removal of salts and sludge. Vented air from the ICBs can be sent to the off-gas treatment system (Parsons, 2000e). 

The all-ceramic devices have material advantages for higher-temperature applications. However, many of the benefits of hot gas cleanup can be realized at the relatively mild temperatures of only 400-500°F. At these conditions, no need exists to condense water vapor out of the gas or to wet the fly ash. Chlorides and other trace components can also be removed in a dry form with the fly ash. Dry fly ash recovery significantly reduces the buildup of fixed salts in recycle process water and the cost of waste water cleanup. 

Therefore all three water sources (fresh water, recycled process water, effluent) have to be treated and clarified, mechanical treatment (filtration, sedimentation, flotation) always having first priority over chemical treatment In practice, in most cases, a combination of mechanical and chemical treatment leads to an efficient solution. 

High water usage is not sustainable and increases the cost of effluent treatment Recycle process water back through the fermentatimi... 

Secunda discharges no process water effluents. AU. water streams produced are cleaned and reused in the plant. The methane and light hydrocarbons in the product are reformed with steam to generate synthesis gas for recycle (14). Even at this large scale, the cost of producing fuels and chemicals by the Fischer-Tropsch process is dominated by the cost of synthesis gas production. Sasol has estimated that gas production accounts for 58% of total production costs (39). 

The surviving U.S. plants have embraced all types of waste treatment processes (see Wastes treatment, hazardous waste Wastes, industrial). The most desired poUution prevention processes are those which reduce the total amount of waste discharged. Treatment and disposal are less strongly emphasized options. Zero wastewater discharge faciHties and water recycling processes are becoming more common (55,56). 

The ammonolysis of phenol (61—65) is a commercial process in Japan. Aristech Chemical Corporation (formerly USS Chemical Division of USX Corporation) currently operates a plant at Ha verb ill, Ohio to convert phenol to aniline. The plant s design is based on Halcon s process (66). In this process, phenol is vapori2ed, mixed with fresh and recycled ammonia, and fed to a reactor that contains a proprietary Lewis acid catalyst. The gas leaving the reactor is fed to a distillation column to recover ammonia overhead for recycle. Aniline, water, phenol, and a small quantity of by-product dipbenylamines are recovered from the bottom of the column and sent to the drying column, where water is removed. 

Water Clarification. Process water that aeeds to be clarified comes from several differeat sources ia the recycling mill rejects from screeas and mechanical cleaners rejects from washers, thickeners, and flotation cells water that drains from the pulp as it is converted iato paper oa the paper machine (white water) and water from felt washers. These waters contain different dissolved chemicals and suspended soflds and are usually processed separately. 

Inorganic chemicals may also be used. Beatonite may be used as a flocculant ia combination with polymer treatmeat. Alum, oace a common coagulant, is less used because its concentration can build up ia recycle water. Alum oftea biads ink to fibers and iacreases the difficulty of deinking. Removal of the very small flexographic ink particles ia process water is difficult. Ultrafiltratioa (qv) has beea proposed for removing these very small dispersed ink particles (53). 

Liquids. Liquids (33) are common forming additives in plastic, paste, and slurry processing. In plastic forming operations, the Hquid aids forming and serves as the binder/plasticizer for the system. In pastes and slurries, other additives are also dissolved or dispersed in the Hquid/solvent. Water is a good, inexpensive solvent that can be recycled. Organic Hquids such as alcohols are used to process water-sensitive materials and to dissolve water-insoluble forming additives, however, at considerably more expense. 

Adhesives and resins are one of the most important raw materials in wood-based panels. Thus, each question concerning the life cycle assessment and the recycling of bonded wood panels does bring into question the adhesive resins used. This includes, for example, the impact of the resin on various environmental aspects such as waste water and effluents, emission of noxious volatile chemicals during production and from the finished boards, or the reuse for energy generation of wood panels. The type of resin has also a crucial influence on feasibility and efficiency for several material recycling processes. 

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