Membrane bioreactors techniques

Intensive technologies are derived from the processes used for the treatment of potable water. Chemical methods include chlorination, peracetic acid, ozonation. Ultra-violet irradiation is becoming a popular photo-biochemical process. Membrane filtration processes, particularly the combination microfiltration/ultrafiltra-tion are rapidly developing (Fig. 3). Membrane bioreactors, a relatively new technology, look very promising as they combine the oxidation of the organic matter with microbial decontamination. Each intensive technique is used alone or in combination with another intensive technique or an extensive one. Extensive... 

Recent scattered reports on use of immobilized bioreactors [38,197,302,303], membrane separation techniques [271] provide initial results and possible ways to employ these techniques to achieve product separation however, the limitations posed by each of these such as reduced rates due to immobilization, or limited yield using membranes are issues which have not been completely addressed. 

Membrane bioreactors can be easily integrated with other systems, for example, with delivery of drugs or genes to individual cells achieved on the nanoscale using electroporation techniques. In one method developed in a recent patent, a flowthrough bioreactor having an inlet and an outlet connected by a flow chamber and a nanoporous membrane positioned in the flow chamber was used [28]. 

The OHLM systems, integrating reaction, separation, and concentration functions in one equipment (bioreactor), find a great interest of researchers in the last few years. A bioreactor combines the use of specific biocatalyst for the desired chemical reactions, and repeatedly or continuously application of it under very specific conditions. Such techniques were termed as hybrid membrane reactors. In biotechnology and pharmacology, these applications are termed as hybrid membrane bioreactors or simply bioreactors (see Table 13.11). Experimental setup of the bioreactor system is shown schematically in Figure 13.17. 

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. 

Membrane bioreactors have been tested for the treatment of foul condensates at various temperatures. The temperature of the foul condensates originating from kraft evaporators and digesters is around 50°C-70°C and an interesting option is to treat this stream using MBRs at thermophilic conditions without cooling the stream [98]. Dias et al. [99] used an MBR technique (0.03 pm hollow fiber membrane) to purify foul condensates from a Brazilian kraft mill (Eucalyptus) at different temperatures. They achieved a very high COD removal as shown in Table 35.3. 

Desalination of seawater is one of the important applications of membrane processes. There are various ways to produce fresh water such as distillation, electrodialysis, membrane distillation, freezing, membrane bioreactor, and reverse osmosis. Among them, distillation is the most used technique, but RO is becoming more popular in the desalination industry. A flow diagram of a single-stage RO system is shown in Fig. 4. 

Among several techniques used, the advantages offered by membrane bioreactor (MBR) technology have been recognized for some time. An MBR comprises a conventional activated sludge process coupled with membrane separation to retain the biomass. Since the effective pore size is generally below 0.1 pm, the MBR effectively produces a clarified and substantially disinfected effluent. In addition, it concentrates up the biomass and, in doing so, reduces the necessary tank size and also increases the efficiency of the biotreatment process [1]. 

The basic principles of bioconversion, bioreactors and biocatalysis are introduced, together with a description of the most important biocatalyst immobilization techniques. The mass transfer phenomena involved in membrane systems are discussed along with some representative configurations of membrane bioreactors, whose behaviour can be described using a simple mathematical approach. For all the aforementioned systems the most significant parameters have been defined to estimate the system performance. 

Ethanol production from biomass using membrane bioreactors (MBRs) is considered a plausible option for the production of alternative Uquid fuels. It is therefore interesting to consider the application of the MD technique to ethanol productivity, coupled with a fermentation MBR. 

Combination of bioreactor and various membrane separation techniques... 

Recently, membrane separation techniques have been applied to a variety of fields, as shown in Table 22.2. The combination of bioreactor and membrane separation techniques such as microflltration (MF), ultraflltration (UF), electrodialysis (ED) and reverse osmosis (RO) can result in a multifunctional membrane reactor as shown in Fig. 22.4. 

Two-dimensional fluorescence can be also applied for the monitoring of membrane bioreactors, due to the ability of this technique to perceive fluorescence differences between feedwater streams, bioreactor media and treated water permeates (Figure 12.8). 

Figure 12.9 Spectra deconvolution by using the subtraction technique to elicit the response of membrane bioreactor when exposed to different concentrations of pollutant (3-chloro-4-methylaniline). Fluorescence spectra acquired (a) in the presence of 500mg/L of pollutant, (b) in the presence of 250mg/L of pollutant and (c) subtraction fluorescence spectrum.

The use of 2D fluorescence techniques for the monitoring of membrane processes, namely the ones involving water treatment and biological systems such cell culture/membrane bioreactors, may be adopted soon. The applications envisaged (some of them under study for which results were not shown) involve ... 

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