Direct Reuse

Formerly, water was accepted by a second user for reuse while it was still under control of the first user (5). Today, the used water is treated in such a manner that it can be used again before ultimate disposal. Furthermore, a distinction can be made between direct reuse, where the water is reclaimed without dilution or natural purification, and indirect use, where treated used water is returned to the environment for subsequent utilization as a raw water supply. 

Recychng (or reuse) refers to the use (or reuse) of materials that would otherwise be disposed of or treated as a waste product. A good example is a rechargeable battery. Wastes that cannot be directly reused may often be recovered on-site through methods such as distillation. When on-site recoveiy or reuse is not feasible due to quality specifications or the inability to perform recoveiy on-site, off-site recoveiy at a permitted commerci recoveiy facihty is often a possibility. Such management techniqiies are considered secondaiy to source reduc tion and should only oe used when pollution cannot be prevented. 

Some wastes lend themselves to direct reuse in production and may be transferred from one unit to another others require some modifications before they are suitable for reuse in a process. These reused waste streams should be quantified. 

Waste recovery and/or reuse. This comprises the identification and implementation of opportunities to recover process chemicals and materials for direct reuse or for reuse elsewhere through renovation or conversion technology. 

The resulting schedule that achieves the wastewater target is given in Fig. 6.4. Once again, the striped blocks represent each units operation, the bold numbers the amount of freshwater used and the normal case numbers represent the amount of water directly reused. The amount of water sent to storage or used from storage is given by the numbers in italics. 

The second illustrative example is a modified literature example. The example was originally presented by Kim and Smith (2004). The example involves 7 water using operations with three contaminants present in the system. The example was only solved considering a central storage vessel due to the fact that the schedule used by Kim and Smith was retained for this example and there are few direct reuse opportunities within the given schedule. Due to the schedule being known, the objective was to minimise effluent. 

The resulting schedule is shown in Fig. 7.2. The bold numbers in Fig. 7.2 show the amount of freshwater used by each process in tons, while the italic numbers the amount of water directly reused and the normal numbers the amount of water to and from each storage vessel. 

Constraint (8.1) is a raw material mass balance into a unit. The amount of raw material into a unit is the sum of the directly reused water, freshwater, water from storage and any other raw materials required for the specific final product. Constraint (8.1) is the form of the raw material balance where the contaminant mass in the reused water is negligible. Constraint (8.1) for the case where the contaminant mass is not negligible will be given at a later stage. It is important to note that only compatible water can be reused in product. The reuse streams each contain information on the contaminant present in the water through the state indices in the variables describing the reuse flows. 

The amount of water used for a cleaning operation is assumed to be fixed. The amount of water used for a cleaning operation is thus defined in constraint (8.4). The water leaving a cleaning operation can either be directly reused in a subsequent batch of compatible product, sent to storage for later reuse or discarded. This is captured in constraint (8.5). 

As with the direct reuse of wastewater, scheduling of indirect reuse of water is also necessary. 

Apart from direct reuse scheduling, constraints also have to be derived to ensure the correct scheduling of indirect reuse through inherent storage. 

Fourthly, the methodology suggests the need for storage, i.e. 37.5 t, when the processing times suggest otherwise. Processes 1 and 3 commence at 0.5 h from the beginning of the time horizon, which is actually the completion time for process 2. This provides a direct reuse opportunity with no requirement for storage. 

Figure 12.14 shows the reuse network that would result from reusing water from the B wash in the C wash. The time gap between the end of B wash and the start of C wash implies that water from B wash cannot be directly reused in the C wash... 

Figure 12.22a depicts targeting in the time interval (3 1 h). Figure 12.8 shows that only B and C reactions are active in this time interval. The A wash was completed in the previous time interval and its used water taken to storage, since there was no opportunity for its direct reuse. Figure 12.22b shows the block diagram associated with this interval. It should be noted, though, that no fresh water is needed, since the active processes started from the previous time interval. 

A further advantage of this catalytic system is that the organic cycloadducts can be easily separated from the aqueous phase, allowing the catalyst solution to be isolated and directly reused. The catalyst retains its activity for the cycloaddition through several separate uses. As illustrated for the conversion of 108 to 109, the yield of the cycloaddition remained approximately constant for five reuses of the catalyst and decreased only with the sixth use (Tab. 13.9). With alkynoate substrate 94, the experiment was repeated with rigorous deoxygenation (by freeze-pump-thaw cycles) of the catalyst solution between uses, and it was found to function cleanly after eight uses (Tab. 13.8, entry 4). 

Ionic liquids are organic salts that are liquid at or near room temperature. It has been found recently that such liquids can be useful solvents for organic reactions. Often, the organic products can be removed from the ionic liquid by extraction with, e.g., ether, without resorting to an aqueous workup. This can be particularly useful when a precious metal catalyst is used in the reaction. The catalyst often remains in the ionic liquid, so that the catalyst solution can be directly reused. 

Rozzi, A. et al.. Ozone, granular acHvated carbon, and membrane Heatment of secondary texHle effluents for direct reuse, Biol. Abwasserreinig Treatment of Wastewaters from Textile Processing), 9, 25, 1997. 

The partially demineralized water can be directly reused without furtlier polishing in some instances. This is not easy when the original condensate contains high concentrations of ammonium sulfate or nitrate, because strong acid resins are not highly selective for ammonium over hydrogen ions. To... 

A novel transition metal-catalyzed hydrosilylation process is described. The use of an ionic liquid in this process allows for the immobilization, heterogenization, and recovery of the expensive precious metal catalyst as well as its direct reuse in a subsequent hydrosilylation reaction. From an economic and ecological point of view, this process perfectly fits in the concept of "Sustainable Chemistry". Future research activities will aim at the prolongation of the catalyst life-time. For this, it is necessary to gain a deeper understanding of the catalytically active species in the catalyst/ionic liquid solution. 

Macrofiltration (MF) membrane, with pore sizes of 0.1 pm, have been used to recover surfactants in the permeate. If the salt content of oily wastewater is too high for direct reuse of the permeate in the plant, it can be treated by RO and NF (8,29). In addition, RO can selectively reject solutes of the same size order as water molecules. 

When the solvent is not miscible with water, such as hexane or ethyl acetate, water is easily removed from the solvent by decantation. In most instances, the decanted solvent can be directly reused in extraction. The decanted solvent will contain little dissolved solids, as this solvent stream would have been condensed from thermal processes. 

As all skimmers recover some water with the oil, a device to separate oil and water is usually required. The oil must be separated from the recovery mixture for disposal, recycling, or direct reuse by a refinery. Sometimes settling tanks or gravity separators are incorporated into skimmers, but separators are more often installed on recovery ships or barges. Portable storage tanks are often used as separators, with outlets installed on the bottom of the tanks so that water that has settled to the bottom of the tank can be drained off, leaving the oil in the tank. Vacuum trucks are also used in this way to separate oil and water. Screens or other devices for removing debris are also incorporated into separators. 

Spilled material is sometimes directly reused either by reprocessing in a refinery or as a heating fuel. Some power plants and even small heating plants such as those in greenhouses can use a broad spectrum of hydrocarbon fuels. Often the equipment at refineries cannot handle oils with debris, excessive amounts of water, or other contaminants and the cost of pre-treating the oils can far exceed the value that might be obtained from using them. 

X = OH) act as very efficient bases for the Heck reaction and catalyze efficiently the Henry reaction with excellent yields and selectivities. The catalyst can be used both in batch and under flow conditions and can be directly reused several times with only a minor decrease in activity. The spent polymer can be easily regenerated simply by its treatment with a basic solution [363],... 

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