Optimised hydrodynamics for membrane bioreactors with immersed flat sheet membrane modules

Abstract

A B S T R AC TSince aeration is the largest cost factor in membrane bioreactor (MBR) operation it is clear that the biggest leap towards energy and operational costs savings can be achieved by improving the use of air. Many basics of the complex two-phase fl ow in membrane modules and in the overall MBR tank as well as their interactions, however, are still poorly understood. This work focuses both on fundamental studies on shear stress exerted by rising bubbles and on optimising the geometries of tank and module accordingly in order to obtain an improved deposition control at minimum energy input. For both, parameter studies were carried out by numerical simulations which were validated with experimental measurements. The optimum bubble size/channel width combination depended on the superimposed liquid velocity. The relationship between the liquid circulation velocity and the aeration intensity was measured for different reactor and module geometries. A modifi cation of the Chisti model for airlift loop reactors was also performed which can be used as a design rule for tank and module geometry or aeration rate. At the same gas fl ow rate, a 30-50% increase in liquid circulation velocity was achieved by a simple modifi cation of the sparger and the entry zone to the riser section.

The use of electrical resistance tomography for the characterization of gas holdup inside a bubble column bioreactor containing activated sludge

“…Because of the necessity of fluid transparency for the application of many measuring techniques and difficulties of working with real activated sludge systems, previous researchers have instead used surrogates such as water, xanthan gum solutions, yeast suspensions, and carboxylmethyl cellulose (CMC) solutions in their experiments [6,[14][15][16][17]. But the representativeness of these surrogates is questionable.…”

Membrane bioreactor technology for leachate treatment at solid waste landfills

“…The complex interaction of hydrodynamics, mass transfer, biological degradation, and existing compounds makes it difficult to isolate all the parameters that could help in predicting membrane fouling , although the most Defrance and Jaffrin 1999;Vyas et al 2002), the filtration time (short-term vs. long-term; Yang et al 2006;Zhang et al 2006), the operating conditions and cleaning procedures (Sanguanpak et al 2015a;Trussell et al 2006;Cui et al 2003), the setup configuration (external vs. submerged; Xue et al 2015) and the initial stage of the membrane (new vs. cleaned; Le Clech et al 2003). Irrespective, MBR users have resorted to several methods to control fouling such as back-pulsing or bubbling (Prieske et al 2010), the use of additives or sponge-like carriers (Ngo et al 2008), pre-settling of biomass (Ivanovic and Leiknes 2008), sludge granulation, and membrane surface change .…”

Membrane Bioreactors in Waste Water Treatment – Status and Trends

“…Thus, a smoother draft tube edge was introduced to achieve lower bend loss and thus higher circulation velocities (see Fig. 6) [71]. An additional acceleration was achieved by locating the aerators at the bottom of the tank instead of at the entrance to the draft tube where they significantly block the available cross section and slow down the flow.…”

“…Fig. 5 shows numerical results (validated experimentally in [71]) on the influence of bubble size and membrane spacing in flatsheet modules on maximum shear stress exerted on the membrane surface. Values differ by a factor of up to 10, showing the importance of optimized design.…”

“…In addition, traditional methods such as backpulsing or bubbling as well as geometric design features are being optimized systematically (e.g., [69][70][71]). Over the last four years, a significant amount of research has also begun to focus on advanced control to improve the efficiency of traditional and novel antifouling methods and to minimize energetic expenditure (e.g., [72][73][74][75]).…”