Process development phase wastewater

Flocculation and sedimentation arc two processes used to separate waste streams that contain both a liquid and a solid phase. Both are well-developed, highly competitive processes, which arc oflcii used in the complete treatment of waste streams. They may also be used instead of, or in addition to, filtration. Some applications include the removal of suspended solid particles and soluble heavy metals from aqueous streams. Many industries use both processes in the rcmowal of pollutants from their wastewaters. These processes work best when the waste stream contains a low concentration of the contaminating solids. Although they are applicable to a wide variety of aqueous waste streams, these processes arc not generally used to treat nonaqueous or semisolid waste streams such as sludges and slurries. 

Recent research development of hydrodynamics and heat and mass transfer in inverse and circulating three-phase fluidized beds for waste water treatment is summarized. The three-phase (gas-liquid-solid) fluidized bed can be utilized for catalytic and photo-catalytic gas-liquid reactions such as chemical, biochemical, biofilm and electrode reactions. For the more effective treatment of wastewater, recently, new processing modes such as the inverse and circulation fluidization have been developed and adopted to circumvent the conventional three-phase fluidized bed reactors [1-6]. 

Apart from biocatalyst activity, several other parameters are important in development of a biodesulfurization process. These parameters include oil/water ratio, composition of aqueous phase used for biocatalyst suspension during desulfurization, biocatalyst loading, oil/water separation following completion of desulfurization, potential for biocatalyst recycle, recycle of aqueous phase to reduce fresh water usage and wastewater minimization, as well as secondary oil separation and purification operations. 

The 1980 s and the early 1990 s have seen the blossoming development of the biotechnology field. Three-phase fluidized bed bioreactors have become an essential element in the commercialization of processes to yield products and treat wastewater via biological mechanisms. Fluidized bed bioreactors have been applied in the areas of wastewater treatment, discussed previously, fermentation, and cell culture. The large scale application of three-phase fluidized bed or slurry bubble column fermen-tors are represented by ethanol production in a 10,000 liter fermentor (Samejima et al., 1984), penicillin production in a 200 liter fermentor (Endo et al., 1986), and the production of monoclonal antibodies in a 1,000 liter slurry bubble column bioreactor (Birch et al., 1985). Fan (1989) provides a complete review of biological applications of three-phase fluidized beds up to 1989. Part II of this chapter covers the recent developments in three-phase fluidized bed bioreactor technology. 

The most widespread biological application of three-phase fluidization at a commercial scale is in wastewater treatment. Several large scale applications exist for fermentation processes, as well, and, recently, applications in cell culture have been developed. Each of these areas have particular features that make three-phase fluidization particularly well-suited for them Wastewater Treatment. As can be seen in Tables 14a to 14d, numerous examples of the application of three-phase fluidization to waste-water treatment exist. Laboratory studies in the 1970 s were followed by large scale commercial units in the early 1980 s, with aerobic applications preceding anaerobic systems (Heijnen et al., 1989). The technique is well accepted as a viable tool for wastewater treatment for municipal sewage, food process waste streams, and other industrial effluents. Though pure cultures known to degrade a particular waste component are occasionally used (Sreekrishnan et al., 1991 Austermann-Haun et al., 1994 Lazarova et al., 1994), most applications use a mixed culture enriched from a similar waste stream or treatment facility or no inoculation at all (Sanz and Fdez-Polanco, 1990). 

Ultrafiltration (UF) is an important component in wastewater treatment and in food industry [109,110]. With increasing concerns and regulations in environment as well as in food safety, the process of ultrafiltration has become more critical, whereby new technology development to provide faster and more efficient water treatment is not only necessary but also urgent. Currently, conventional polymeric UF membranes are prepared mainly by the phase immersion process, typically generating an asymmetric porous structure with two major limitations (1) relatively low porosity and (2) fairly broad pore-size distribution [111,112],... 

The want of perfection or — to be more exact — the shortcomings of the methods that are in use now, spurred an intensive development of low-waste and no-waste technologies. Attention should be focused on including some elements of the separation process as part of the production line with the aim to separate the constituents of the wastewater produced, since this is a prerequisite to enable the technical feasibility of the two methods. The problem is significant, specifically with regard to solutions and mixtures in the liquid phase but it bas also become a question of growing importance to mixtures in the gaseous phase. 

This development is due to various factors, such as high water flow in "wet years" and the effects of the economic crisis, particularly at the end of the 1970 s. However, a significant portion of the reduction should be affected by improvement of wastewater treatment and by the partial replacement of metals in critical applications. It is indicated from these data, that the major decrease for cadmium occurred in the dissolved phases, whereas - until 1979 - the reduction of mercury concentrations mainly took place in the solid phases. This is an indication that equilibria between solid and aqueous phases have not completely established, and clearly shows the difficulties involved in the modeling such processes (see review by Honeyman Santschi, 1988). 

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