Clarification stages

Decanters are frequently used in conjunction with disc-stack-type centrifuges in the pre-preparation of clear juices and juice concentrates, where the initial decanter treatment results in a partially clarified juice with a low level of suspended solids. This is followed by a clarification stage using a disc-stack whereby the solids are thrown outwards from the through-flow juice stream into a solids-holding space and automatically discharged therefrom as and when an optimum level of solids is reached (see Figure 3.6). 

Physical impurities consist mainly of the cells, cell debris, and insoluble medium components, most of which will be removed by the initial clarification stages. This process may be facilitated by preliminary broth conditioning for example, the addition of flocculating agents, pH adjustment, or heat treatment. Such operations may have the added advantage of promoting the release of intracellular products to the liquid phase, thereby removing the need for wholecell extraction. Cell lysis will, of course, also increase the biochemical impurity load (11). 

An advantage of the lime treatment process is that it can precipitate dissolved metals (see section 28.3.3) and remove them at the clarification stage. Increasingly, however, industry is required to treat its waste-water before discharge to sewer and this includes the removal of heavy metals. 

The plant required for the above operations is relatively simple digestion is carried out in a stainless-steel vessel, steam jacketed, fitted with a stirrer, reflux condenser, conical base and bottom outlet. Special provision is made for passing a slow stream of hydrogen into the vessel via a pipe at the base. Filtration is on a Nutsche vacuum filter, a suitable filter medium being paper between two layers of terylene cloth. An additional clarification stage is also used to remove fine suspended particles of iron oxide. A bed of firmly packed paper pulp is satisfactory for this purpose. 

In one arrangement, shown schematically in Figure 6.18 as an example, the thickener is in the first stage, followed by one (or more) clarification stage. 

In practice, the most frequently applied method for the treatment of iron-rich waters is oxidation of ferrous iron to ferric iron and simultaneous pH adjustment and hydroxide precipitation. Typical process configurations for hydroxide precipitation comprise a neutralization-precipitation stage, and a settling or clarification stage. 

Fig. 1. An amplified outline scheme of the making of various wiaes, alternative products, by-products, and associated wastes (23). Ovals = raw materials, sources rectangles = wines hexagon = alternative products (decreasing wine yield) diamond = wastes. To avoid some complexities, eg, all the wine vinegar and all carbonic maceration are indicated as red. This is usual, but not necessarily tme. Similarly, malolactic fermentation is desired in some white wines. FW = finished wine and always involves clarification and stabilization, as in 8, 11, 12, 13, 14, 15, 33, 34, followed by 39, 41, 42. It may or may not include maturation (38) or botde age (40), as indicated for usual styles. Stillage and lees may be treated to recover potassium bitartrate as a by-product. Pomace may also yield red pigment, seed oil, seed tannin, and wine spidts as by-products. Sweet wines are the result of either arresting fermentation at an incomplete stage (by fortification, refrigeration, or other means of yeast inactivation) or addition of juice or concentrate.

Likewise, it may happen that a scheme on the grid u> cannot provide local approximations in t, but at the final stage the approximation will be achieved once we bring together the residuals over several time layers. The notion of summarized approximation needs certain clarification. It seems worthwhile giving simple examples. 

The initial processing steps are determined to a large extent by the location of the product species, and they generally consist of cell/broth separation and/or cell debris removal. For products retained within the biomass during production, it is first necessary to concentrate the cell suspension before homogenization or chemical treatment to release the product. Clarification to remove the suspended solids is the process goal at this stage. 

Controlled single-stage carbometallation reactions of alkenes and alkynes with group 4—7 metals are discussed with emphasis on regio-, stereo-, and chemoselectivity including clarification and understanding of factors governing these synthetically important aspects. 

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