Membrane bioreactors effluents treatment

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. 

Stahl N, Tenenbaum A, and Galil NI. Advanced treatment by anaerobic process foUowed by aerobic membrane bioreactor for effluent reuse in paper mill industry. Wat. Sci. Techn. 2004 50(3, Eorest Industry Wastewaters VE) 245-252. 

Van Kempen, R., Draaijer, H., Postma, H., A membrane bioreactor for industrial effluents Compact, versatile and proven. Proceedings of the First International Meeting on Membrane Bioreactors for Wastewater Treatment, Cranfield, U.K., 1997. 

W.G. Scholz, P. Rouge, A. Bodalo, U. Leitz, Desalination of mixed tannery effluent with membrane bioreactor and reverse osmosis treatment, Env. Sci. Tech. 39 (21) (2005) 8505—8511. 

Gander M A, Jefferson B and Judd S J (2000), Membrane bioreactors for use in small wastewater treatment plants membrane materials and effluent quality . Water Sci Technol, 41,205-211. 

Effluent treatment may be carried out using ceramic membrane bioreactors. However, equipment remains expensive compared to conventional activated sludge treatment methods. However, where tubular membranes are used, the performance can be improved by using tube inserts, which are effective turbulence promoters. It was found (Xu et al., 2002) that the permeate flux was increased by a factor of 2.5 without any detrimental effect on the effluent quality. Other formats for membrane bioreactors include fully stirred tanks, packed-bed columns and jet loop columns. 

Figure 7.1 shows the two major treatment options to obtain RO-quality water from sewage and seawater. The key in water reclamation is to first treat the sewage biologically and use MF/UF membrane filtration to remove suspended solids. Two membrane filtration alternatives are available for water reclamation tertiary filtration (TF) of the effluent from a conventional activated sludge (CAS) process and an integrated membrane bioreactor (MBR). For seawater desalination, pretreatment must be provided if the source is open seawater. The current practice involves multimedia filtration, but membrane filtration has also been considered. 

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 are an option for municipal wastewater treatment when high effluent water quality is required, for example, bathing water quality, or when the receiving water body is very sensitive or when the water is to be treated for reuse. As mentioned before (see Section 9.2.5.1), the effluent quality is superior to that of secondary sedimentation. To attain a similar effluent quality by conventional treatment, effluent filtration and disinfection would be required in addition. This needs to be taken into account when comparing the cost of MBR and conventional activated sludge treatment. 

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. 

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