Membrane bioreactors separation processes, water

For membrane separation processes, two types of membrane modular units are generally employed hollow fiber and spiral wound. The hollow fiber-based modules comprise bundles of hollow fibers encapsulated at hoth ends with the feed stream separated from the permeate stream hy the hollow fibers. For spiral wound units, alternate layers of membrane and spacers (to allow gas flow across the membrane on both the feed side and the permeate side of the membrane) are employed. Gas separation processes generally use hollow fibers, whereas desalination and water filtration processes generally employ spiral wound constructions. For membrane bioreactors for sewage water treatment, hollow fiber constructions are common. 

It is expected that in the very near future, the application of closed water loops will show an intensive growth, strongly supported by the further development of separate treatment technologies such as anaerobic treatment, membrane bioreactors, advanced biofilm processes, membrane separation processes, advanced precipitation processes for recovery of nutrients, selective separation processes for recovery of heavy metals, advanced oxidation processes, selective adsorption processes, advanced processes for demineralisation, and physical/chemical processes which can be applied at elevated temperature. 

Membrane technology may become essential if zero-discharge mills become a requirement or legislation on water use becomes very restrictive. The type of membrane fractionation required varies according to the use that is to be made of the treated water. This issue is addressed in Chapter 35, which describes the apphcation of membrane processes in the pulp and paper industry for treatment of the effluent generated. Chapter 36 focuses on the apphcation of membrane bioreactors in wastewater treatment. Chapter 37 describes the apphcations of hollow fiber contactors in membrane-assisted solvent extraction for the recovery of metallic pollutants. The apphcations of membrane contactors in the treatment of gaseous waste streams are presented in Chapter 38. Chapter 39 deals with an important development in the strip dispersion technique for actinide recovery/metal separation. Chapter 40 focuses on electrically enhanced membrane separation and catalysis. Chapter 41 contains important case studies on the treatment of effluent in the leather industry. The case studies cover the work carried out at pilot plant level with membrane bioreactors and reverse osmosis. Development in nanofiltration and a case study on the recovery of impurity-free sodium thiocyanate in the acrylic industry are described in Chapter 42. 

In some technological and medical applications protein adsorption and/or cell adhesion is advantageous, but in others it is detrimental. In bioreactors it is stimulated to obtain favourable production conditions. In contrast, biofilm formation may cause contamination problems in water purification systems, in food processing equipment and on kitchen tools. Similarly, bacterial adhesion on synthetic materials used for e.g. artificial organs and prostheses, catheters, blood bags, etc., may cause severe infections. Furthermore, biofilms on heat exchangers, filters, separation membranes, and also on ship hulls oppose heat and mass transfer and increase frictional resistance. These consequences clearly result in decreased production rates and increased costs. 

Figure 3.53 Membrane bloreactor (MBR) system process flow schematic. MBR combines biological degradation with membrane separation. Raw municipal water flows to an aerated bioreactor where the organic components are oxidised by the activated sludge. The aqueous sludge then passes through a MF or UF membrane filtration unit, separating water from the sludge. The sludge flows back to the bioreactor while the membrane permeate is discharged or reused. Source USFilter.

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