Clarification quality assessment

In order to verify that the products or services meet the specified requirements you will need to carry out tests, inspections, assessments, etc. and these need to be performed against unambiguous standards of acceptability. You need to establish for each requirement that there are adequate criteria forjudging compliance. You need to establish how reliable is reliable , how safe is safe , how clean is clean , how good is good quality . Specifications often contain subjective statements such as good commercial quality, smooth finish, etc., and require further clarification in order that an acceptable standard can be attained. The secret is to read the statement then ask yourself if you can verify it. If not, select a standard that is attainable, unambiguous, and acceptable to both customer and supplier. 

One factor in assessing the quality of surface waters is the amount of suspended solids or, "how muddy is it " For example the standard for many rivers and streams is 100 mg/L. If more than this occurs that segment of the stream is declared "impaired." Much of this solid material is colloidal and cannot be filtered under ordinary means. In water treatment plants, aluminum hydroxide is used to surface adsorb or simply trap the solids, and this floe then either settles out or is filtered by a gravel bed. It has been found that cationic surfactants will surface adsorb to most of the solids suspended in water, and this coating will attach to air bubbles passing th ough the system. Some surfactants proven effective are cetyldimethylethylammonium chloride, cetyldimethylbenzylammonium chloride, cetylpyridinium chloride, and ethylhexadecyldimethyl ammonium bromide. These are all antiseptics as well and are used in many mouthwashes. Only a few ppm are necessary (10 to 60) to provide clarification, and the LDjq s are in the range of 500 mg/kg. 

Table 11.8 shows an example of industrial filtration, assessing the quality of clarification and, consequently, making it possible to select the filter sheets best adapted to this process. The results show that it is indispensable to use sufficiently fine filters to achieve perfect clarification just before bottling. The resulting loss of polysaccharides, a negative effect of filtration on quality, is negligible. 

Once a set of data has been obtained which correlates, the flocculant consumption, if used, needs to be optimised. Alternative polymers might be examined if centrate quality had been difficult to maintain or if the quantity needed was considered excessive. The relative flow rates of polymer solution, and feed, would be assessed to see whether the polymer concentration needs to be adjusted to make it minimum strength, without causing it to be a large fraction of the total flow. This should not be more than, say, 10 or 15%. Polymer tends to be most efficient when it is most dilute. Moreover it is easier to get a uniform mix of two liquids when they are both of comparable size. However the larger the volume the flocculant is, then the greater is the clarification capacity lost unnecessarily to the clean flocculant. The location for admitting the polymer may be questioned, and considered for introduction further upstream, if flocculation in the centrate has been observed, or if extra dryness is required at the expense of extra polymer in dry solids work. 

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