Wastewater reuse

Effluent for a denim textile mill Denim textile wastewater reuse Turkey Activated sludge/ MF/NF... 

As expected for a WWTP effluent, turbidity and E. coli are higher than the specific standards for industrial wastewater reuse included in the new Spanish Regulation of Regenerated Wastewater (RD 1620/2007). Other parameters, such as conductivity or TDS may result in too much high level considering some specific industrial uses of water [11]. Therefore further treatment of the WWTP effluent is needed before reuse. 

Esteban RI, Ortega de Miguel E (2008) Present and future of wastewater reuse in Spain. Desalination 218 105-119... 

Pearce GK (2008) UF/MF pretreatment to RO in seawater and wastewater reuse applications a comparison of energy costs. Desalination 222 66-73... 

Gonzalvez-Zafiilla JM, Sanz-Escribano D, Lora-Garcia J et al (2008) Nanoflltration of secondary effluent for wastewater reuse in the textile industry. Desalination 222 271-279... 

Storage Design for Maximum Wastewater Reuse in Batch Plants... 

Majozi, T., 2006. Storage design for maximum wastewater reuse in multipurpose batch plants. Ind. Eng. Chem. Res., 45(17) 5936-5943. 

In both the above solutions a change in the length of the time horizon will affect the resulting solution. It is very possible that an increase in the length of the time horizon will allow for the production of less effluent, whilst, a decrease in the time horizon could result in an increase in the amount of effluent produced. It is impossible to say if there is a specific trend as the time horizon increases. It is assumed that the time horizon in each problem is fixed during problem specification. The impact of the time horizon on the wastewater reuse opportunities fell outside the scope of the investigation. 

Water is used in the area in product, for heating and cooling and to clean the mixers and storage vessels. In this study the only water considered is the water used for cleaning. This due to the fact that the only opportunity for wastewater reuse occurs in cleaning operations. 

Practically wastewater reuse in another cleaning cycle can only be done in steps two, three and four. The water from the first step has a very high contaminant concentration, and reuse of this water in another cleaning operation would not achieve significant wastewater reductions. The wastewater from the other three steps has relatively low concentrations of contaminants and reuse of the water is feasible. In the application of the derived methodologies to the case study, the last three steps were modelled as one processing step. 

The maximum inlet concentration of each mixer is given in Table 6.9. As can be seen the inlet concentration for the deodorant is zero for mixers 1, 3 and 4. This is due to the incompatibility of this residue with the other residues as discussed previously. Since wastewater reuse was never attempted at the facility under question, the maximum inlet concentrations were approximated. These values are conservative and still allow for the required cleanliness. 

Generally, wastewater is produced at the end of a batch and then reused for the processing of a subsequent batch of material. In general, the unit operation considered in wastewater minimisation in batch processes both consumes and produces water. Furthermore, the operations considered are generally mass transfer type processes, where mass is transferred to the water stream due to the operation occurring in a unit. In such operations wastewater reuse between the various units is governed by timing considerations and inlet and outlet concentration limitations. However, in processes where water consumption and wastewater production do not occur in the same operation, a unique opportunity arises in that the wastewater could be reused in the operations that consume water. 

The formulations presented in this section are based on the type of wastewater reuse described above, where wastewater is produced from a cleaning operation and reused in product. However, due to the fact that product integrity is a high priority a number of conditions must be ensured. Firstly, the reuse of wastewater contaminated with a certain residue can only be reused in compatible product. In most instances, this is the same product as the residue. Secondly, wastewater containing different contaminants cannot be stored at the same time in the same storage vessel. Finally, the water used for a cleaning operation has to be of the same quality as water used in product. 

The first scheduling constraints considered are binary variable constraints governing wastewater reuse. These constraints ensure the correct reuse of water, since water is only reused in distinct amounts at certain points in the time horizon. 

Scheduling constraints also have to be derived to ensure the time at which wastewater reuse occurs is correct within the time horizon. 

Two formulations were derived. The first deals with minimising the amount of effluent produced from an operation where wastewater can be reused in product formulation and the plant structure is known. The minimisation is achieved by scheduling the operation in such a manner as to maximise the opportunity for wastewater reuse. The second deals with the synthesis of a batch process operating in zero effluent mode. The formulation determines the number and size of processing and storage vessels as to minimise the cost of the equipment and the amount of effluent produced from the resulting operation, while achieving the required production. 

The first zero effluent scheduling formulation, was applied to an example, where the wastewater was reduced by 61 %. In the resulting schedule effluent was only produced at the end of the time horizon or when the required production was achieved and there were no further opportunities for wastewater reuse. 

The zero effluent synthesis formulation was applied to a second illustrative example. In the example the number of processing units and the size of the central storage vessel were not known. The resulting plant required only 3 processing units and no storage vessel. The resulting schedule produced 68% less effluent than the same operation without wastewater reuse. 

The resulting schedule is shown in Fig. 9.3. The bold numbers in Fig. 9.3 represent freshwater used and the normal numbers wastewater reused. One would notice in the figure that operation 2 sends 500 kg of wastewater to the central storage vessel. Operation 1 uses all of the 500 kg of water. Operation 4 directly reuses 500 kg of wastewater from operation 2. 

The resulting Gantt chart is shown in Fig. 9.4. The bold numbers in the figure represent freshwater used and the normal numbers represent wastewater reused. As one would notice from the figure, the unit in which operation 2 takes place serves as a wastewater storage vessel. In this unit 1000 kg of wastewater is stored, which is later used by operation 1 and operation 4. 675 kg of the stored water is used by operation 1 and 375 kg is used by operation 4. Important to note from Fig. 9.4 is... 

Jodicke, G., Fischer, U., Hungerbtihler, K., 2001. Wastewater reuse a new approach to screen for designs with minimal total costs. Comp. Chem. Eng., 25 203-215... 

Kadria E., Michel J. Effects of salinity on toxic element transfers in soils associated to agricultural wastewater reuse mobility and bioavailability of zinc and lead for ryegrass in soils irrigated with saline water. 2004. http //Kuk.uni-... 

Wastewater reuse is a good way to reduce overall pollutant loadings. However, water quality is critical in water reuse. The contaminants present must be compatible with the reuse. For example, reuse waters with high solids content are not satisfactory for crude unit desalting. Stripped foul water containing low H2S and ammonia and high concentrations of phenols has essentially no solids. It is suitable for crude unit desalter wash water if the phenols extracted by the crude are subsequently converted by hydroprocessing units into nonphenolic compounds [36]. Some other examples include ... 

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