Contained microfiltration systems

According to the TCLP Method 1311 (EPA SW 846) (40), for a liquid waste containing less than 0.5% solids, the liquid portion of the waste after filtration is defined as the TCLP extract. For a microfiltration system operated at a 2.5 mg Fe(III)/L dose, 2.8 gpm flow rate (1.4 gpm/m ), and 29-min backwash interval, and assuming that all the solids are removed from the filter upon backwash, the backwash water (assuming a backwash volume of 1.8 gal/m ) will have a solids content (calculated) of 0.01% (by wt). Arsenic concentration in such a filtered backwash water (average of 20 filtered samples) was determined to be 2.6 2.4 ug/L. The backwash water can thus be directly disposed as a nonhazardous waste assuming that the arsenic TCLP limit stays at its current value of 5000 fig/L. 

A microfiltration system contains modules with 200 capillaries with an internal diameter of 1.5 mm and a length of 0.5 m. These membranes are used to concentrate a cell suspension. The diameter of the cells is 5 jim and the flow rate is 2 m /h. Calculate the membrane surface area, the Reynolds number and the mass transfer coefficient. 

Phase Separation. Microporous polymer systems consisting of essentially spherical, intercoimected voids, with a narrow range of pore and ceU-size distribution have been produced from a variety of thermoplastic resins by the phase-separation technique (127). If a polyolefin or polystyrene is insoluble in a solvent at low temperature but soluble at high temperatures, the solvent can be used to prepare a microporous polymer. When the solutions, containing 10—70% polymer, are cooled to ambient temperatures, the polymer separates as a second phase. The remaining nonsolvent can then be extracted from the solid material with common organic solvents. These microporous polymers may be useful in microfiltrations or as controlled-release carriers for a variety of chemicals. 

In the early 1960s and 1970s, the in-line plate-and-frame module was the only available microfiltration module. These units contained between 1 and 20 separate membrane envelopes sealed by gaskets. In most operations all the membrane envelopes were changed after each use the labor involved in disassembly and reassembly of the module was a significant drawback. Nonetheless these systems are still widely used to process small volumes of solution. A typical plate-and-frame filtration system is shown in Figure 7.10. 

In this chapter, the impact of other membrane technologies on the operation of RO systems is discussed. Technologies considered include microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) as pretreatment to RO, and continuous electrodeionization (CEDI) as post-treatment to RO. This chapter also describes the HERO (high efficiency RO—Debasish Mukhopadhyay patent holder, 1999) process used to generate high purity water from water that is difficult to treat, such as water containing high concentrations of silica. 

Yeast rests in fermenting cellars in beer breweries typically have a composition of 90% beer and 10% solids, mainly yeast. The amount of this waste material is 2-3% of the annual output. It can be sold as cattle feed or discharged. In a system with 4 m 0.4 pm ceramic microfiltration membranes, beer recovery amoimts to 42-62% the concentrate contains 23% solid matter [51]. Fluxes in... 

Microfiltration membranes are typically periodically cleaned by backpulsing these membranes. This can be accomplished through a variety of ways, some incorporating air and some using just product water or water containing a small amount of hypochlorite. Some immersed-membrane systems also use diffused air to agitate the membranes and prevent solids from caking on the membrane surface. 

At the end of Section 7.2.1, the process of rotary vacuum filtration is described. Here the membrane containing the particulate cake/deposit (see Figure 6.3.25(a)) is moved perpendicular to the pressure induced crossflow causing filtration through the filter. If we imagine the coordinate system to be fixed to the membrane, then the system configuration is similar to the crossflow microfiltration briefly considered earlier (Figure 6.3.25(b)) where the liquid slurry/suspension moves parallel to the membrane but perpendicular to the direction of the force. 

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