Microfiltration membrane bioreactors

Lee, K. S., Lin, P. J., Fangchiang, K., Chang, J. S. (2007). Continuous hydrogen production by anaerobic mixed microflora using a hoUow-fiber microfiltration membrane bioreactor. International Journal of Hydrogen Energy, 32, 950—957. 

Microbial contamination is mainly caused by the presence of the microorganisms used in the biological process and can be eliminated by using ultra/microfiltration membrane bioreactors. The membrane effectively retains the microbial culture inside the reactor so that it may be operated under low hydraulic residence time. It has been previously demonstrated that the membrane bioreactor ensures a high nitrate removal rate (up to 7.7 Kg NO /m reactor-day) and a residual concentration of nitrate and nitrite, in the treated water, below the maximum admissible values (Barreiros et al., 1998). 

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... 

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]. 

Figure 7.17 Experiments showing the rate of fouling of 0.22-p.m microfiltration membranes used to treat dilute biomass solutions. The membranes were operated at the fluxes shown, by increasing transmembrane pressure over time to maintain this flux as the membranes fouled [12]. Reprinted from J. Membr. Sci. 209, B.D. Cho and A.G. Fane, Fouling Transients in Nominally Sub-critical Flux Operation of a Membrane Bioreactor, p. 391, Copyright 2002, with permission from Elsevier...

Xing, C.-H., Wena, X.-H. and Tardieub, E. (2001) Microfiltration-membrane-coupled bioreactor for urban wastewater reclamation. Desalination, 141, 63-73. 

One of the first cases of the application of membrane bioreactors in food processes was the production of milk with low lactose content. (3-galactosidase was entrapped into cellulose acetate fibers to carry out the hydrolysis of milk and whey lactose [2] recently the system was improved by the use of microfiltration and by UV irradiation of the enzyme solution to avoid growth of micro-organisms [45]. 

Microfiltration plants are also being installed in membrane bioreactors to treat municipal and industrial sewage water. Two types of systems that can be used are illustrated in Fig. 7.6. The design shown in Fig. 7.6(a), using a crossflow filtration module, was developed as early as 1966 by Okey and Stavenger at Dorr-Oliver [17]. The process was not commercialized for another 30 years for lack of suitable membrane technology. In the 1990s, workers at Zenon [15,16] in Canada and... 

Deng, H.-T., Xu, Z.-K., Dai, Z.-W., Wu, J. and Seta, P. 2005. Immobilization of Candida rugosa lipase on polypropylene microfiltration membrane modified by glycopolymer Hydrolysis of olive oil in biphasic 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). 

The driving force in membrane bioreactors with conventional biomass separation is the transmembrane pressure, which also affects the flux rate through the membrane. Microfiltration membranes with pore sizes between 0.1 and 5 xm can be used to confine cells in the reactor (Salmon and Robertson, 1995). The selection of the pore size depends on... 

Microfiltration and Ultrafiltration are the best available technology for water reuse. Two options are available conventional activated sludge followed by tertiary filtration and an integrated membrane bioreactor. Both provide effluent of high quality suitable for treatment by reverse osmosis. The cost of tertiary filtration can be lower than a membrane bioieactor if the water reclamation plant is designed for constant flow and is located at a different site. 

Membrane bioreactors combine the activated sludge process for wastewater treatment with biomass separation from the mixed liquor by ultra- or microfiltration membranes. Advantages are the superior effluent quality characterized by complete solids removal and disinfection, the small footprint of the plant resulting from more compact aeration tanks, the absence of a secondary sedimentation tank, and the modular construction. 

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]. 

Fig. 7.6 Schematic flow diagram of microfiltration bioreactors operated with (a) crossflow membranes and (b) submerged...

Figure 3.26 Processing of cheese whey using multiple membrane systems and a membrane recycle bioreactor. Source Cheryan, Copyright 1998 from Ultrafiltration and Microfiltration Handbook by M. Cheryan. Reproduced by permission of Routledge/Taylor Francis Group, LLC.

---