UF-membrane bioreactor

UF-Membrane Bioreactors for Kinetics Characterization of Nitrile Hydratase-Amidase-catalyzed Reactions a Short Survey... 

Figure 173 (a) Time course of reaction rate in UF-membrane bioreactor at different temperature. Appropriate substrate feed solution (benzonitrile or benzamide) lOmM, resting cell load 2mgocw, flow-rate 12mlh. Filled symbols for nitrile hydratase activity ... 

Figure 17.4 (a) Time course of product concentration in UF-membrane bioreactor at various substrate concentration (benzonitrile in 50mM sodium phosphate buffer, pFI 7.0). Cell load lOrngocw, temperature 10°C, flow-rate 12mlh. ... 

Figure 17.5 Scheme of the reaction runs performed in UF-membrane bioreactor in the presence of high substrate concentration inactivating the nitrile hydratase activity (for... 

X-Mean residence time (h) Figure 17.6 UF-membrane bioreactor ioaded with lOmgDcw, and run at 10 C. The reactor was fed with benzonitriie buffered (50 mM sodium phosphate buffer, pH 7.0) soiution. (a) % Conversion at steady state ( ) and reactor capacity (o) as a function of... 

Table 13.1 Equations used to calculate reaction-rate in batch and continuous stirred UF-membrane bioreactors.

Poly(vinylidene fluoride) (PVDF) is one of the promising polymeric materials that has prominently emerged in membrane research and development (R D) due to its excellent chemical and physical properties such as highly hydrophobic nature, robust mechanical strength, good thermal stability, and superior chemical resistance. To date, PVDF hollow-fiber membranes have dominated the production of modem microfiltration (MF) ultrafiltration (UF) membrane bioreactor (MBR) membranes for municipal water and wastewater treatment and separation in food, beverage, dairy, and wine industries. In the last two decades, increasing effort has been made in the development of PVDF hollow fibers in other separation applications such as membrane contractors [6,7], membrane distillation (MD) [8-11], and pervaporation [12,13]. 

Generally, a distinction can be made between membrane bioreactors based on cells performing a desired conversion and processes based on enzymes. In ceU-based processes, bacteria, plant and mammalian cells are used for the production of (fine) chemicals, pharmaceuticals and food additives or for the treatment of waste streams. Enzyme-based membrane bioreactors are typically used for the degradation of natural polymeric materials Hke starch, cellulose or proteins or for the resolution of optically active components in the pharmaceutical, agrochemical, food and chemical industry [50, 51]. In general, only ultrafiltration (UF) or microfiltration (MF)-based processes have been reported and little is known on the application of reverse osmosis (RO) or nanofiltration (NF) in membrane bioreactors. Additionally, membrane contactor systems have been developed, based on micro-porous polyolefin or teflon membranes [52-55]. 

The chapter focuses on membrane bioreactors where a UF or MF membrane is employed for biomass retention and filtration. However, membrane bioreactors where the membrane provides a support for biofilms are an alternative form of membrane bioreactor for wastewater treatment application. Two processes, in particular, the membrane-aerated biofilm reactor (MABR) and the extractive membrane bioreactor (EMB), have seen significant interest in recent years. Figure 36.4 shows these two technologies schematically. The application of biofilms reactors for wastewater treatment systems is advantageous in view of... 

The concept of coupling reaction with membrane separation has been applied to biological processes since the seventies. Membrane bioreactors (MBR) have been extensively studied, and today many are in industrial use worldwide. MBR development was a natural outcome of the extensive utilization membranes had found in the food and pharmaceutical industries. The dairy industry, in particular, has been a pioneer in the use of microfiltra-tion (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) membranes. Applications include the processing of various natural fluids (milk, blood, fruit juices, etc.), the concentration of proteins from milk, and the separation of whey fractions, including lactose, proteins, minerals, and fats. These processes are typically performed at low temperature and pressure conditions making use of commercial membranes. 

The Lyonnaise des Eaux in France [4.116] has developed a process for the denitrification of underground waters in order to produce drinking water. This process combines a bioreactor with adsorption by powdered activated carbon, together with a hollow-fiber UF unit. This process allows the elimination of nitrates, nitrites, pesticides, and herbicides (atrazine, diethylatrazine, simazine, metabenzthiazuron, and urea derivatives, etc.) as well as taste and odor compounds. These molecules are frequently present in underground waters in Europe, as a result of past intensive agricultural practices. The UF membrane unit also disinfects the water by removing protozoa, bacteria, and viruses. 

A membrane bioreactor (MBR) combines membrane filtration with a biological active sludge system. The membrane can either be positioned outside (= external) or in the biological basin (= internal). Both MF and UF membranes can be used for MBR. hi external systems a continuous cross-flow is circulating along the membranes. In internal systems the effluent is extracted from the active sludge using under-pressure. 

The effect of the wetting characteristics of membrane bioreactors on the operation of organic-aqueous two-liquid phase systems was discussed by Vaidya and co-workers [127, 157, 184]. A similar discussion, but considering the use of membranes for separation of liquid/liquid mixtures downstream of a bioreactor, was carried out by Schroen and Woodley [126]. Some trends for the use of membranes in organic-aqueous two-liquid phase systems can be summarized from these works. The use of UF hydrophilic or amphiphilic membranes was usually advised for two-phase bioreactors [127], although fluo-ropolymer-based membranes could present an exception [126]. PTFE membranes, on the other hand, led to low breakthrough pressures, and therefore their use was limited. 

The effect of detoxification of the medium by removal of toxic compounds with UF membranes was demonstrated by Boyaval et al. [36] in the fermentation of propionic acid. UF runs led to an eightfold increase in volumetric productivity relative to fed batch experiments. The effectiveness of membrane bioreactors in the lowering of toxicity of the compounds involved in the bioconversion system was demonstrated by Edwards and co-workers [159]. An eightfold increase in the removal of phenoHc compounds from effluents was observed when polyphenoloxidase was immobilized in a capillary poly(ether)sulfone membrane as compared to the use of the free enzyme. Butanol recovery from the fermentation medium with organic solvent extraction or membrane solvent extraction led to similar results, both processes leading to decreased product inhibition. Due to the low toxicity of the extractive solvent used (isopropyl myristate) on Clostridium beyerinckii cells, no protective effect of the membrane was observed. However, precipitates observed in two-Hquid phase extraction were not observed... 

Molecular separation along with simultaneous chemical transformation has been made possible with membrane reactors [17]. The selective removal of reaction products increases conversion of product-inhibited or thermodynamically unfavourable reactions for example, in the production of ethanol from com [31]. Enzyme-based membrane reactors were first conceived 25 years ago by UF pioneer Alan Michaels [49]. Membrane biocatalytic reactors are used for hydrolytic conversion of natural polymeric materials such as starch, cellulose, proteins and for the resolution of optically active components in the pharmaceutical, agrochemical, food and chemical industries. Membrane bioreactors for water treatment were introduced earher in this chapter and are discussed in detail in Chapters 2 and 3. 

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.

Membrane processes for this analysis include SWRO, BWRO, low-pressure RO (LPRO), brine recovery RO (BRO), pressurised MF/UF (pMF/UF), immersed membrane bioreactor (iMBR), cross-flow membrane filtration (XMF) and electrodeionisation (EDI). Membrane process characteristics for water treatment are detailed in Table 5.1. Typical process flow schematics of RO membrane plants are shown in Figures 5.1 and 5.2. RO/NF systems are typically multi-stage and single-pass or multi-stage and double-pass, as shown in Figures 2.21-2.23. 

The UF membrane flux was automatically calculated daily by the control system. The results indicate the flux was typically in the 3-15 L/m. h range. Because of the siphon design, the TMP was constant at 0.11 bar (11 kPa). Periodic cleaning of the membranes was performed as required. Hypochlorite cleaning proved to be more effective than citric acid cleaning. This is as expected considering the low operating pH of the bioreactor. 

Consequently, membrane bioreactors are an example of the combination of two unit operations in one step for example, membrane filtration with the chemical reaction. In a typical membrane bioreactor, as weU as acting as a support for the biocatalyst, the membrane can be a very effective separation system for undesirable reactions or products. The removal of a reaction product from the reaction environment can be easily achieved thanks to the membrane selective permeability, and this is of great advantage in thermodynamically unfavourable conditions, such as reversible reactions or product-inhibited enzyme reactions. A very interesting example of a membrane bioreactor is the combination of a membrane process, such as microfiltration or ultrafiltration (UF), with a suspended growth bioreactor. Such a set up is now widely used for municipal and industrial wastewater treatment, with some plants capable of treating waste from populations of up to 80 000 people (Judd, 2006). 

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