Filter-press sludge

These may be either fresh or dried. The former are prepared for analysis by reducing them to a pulp by means of the machines used for the non-exhausted slices the latter are ground to a fine powder. As a rule only the sugar in these products is determined, but in some cases also the water. 

With dry slices, the half-normal weight is introduced with basic lead acetate into a 200 c.c. flask and the volume made up to 206 c.c. or 12 64 grams of substance are made up to 200 Mohr c.c. or 12 62 grams up to 200 true c.c. The polarisation in a 20 cm. tube, multiplied by 4, gives the percentage of sugar. 

—This is determined by drying at 105 110° as with beet ( )  

Sugar is detected in these waters by treating 2 c.c. of the liquid with 5 drops of 20% alcoholic a-naphthol solution and then carefully adding 10 c.c. of concentrated sulphuric acid (absolutely free from nitric acid) so that the two liquids do not mix. In presence of sugar, a violet ring forms at the surface of separation. A few comparative tests will indicate if the quantity of sugar is estimable the reaction is very sensitive and detects even o ooi% of sugar. 

When quantitative determination is necessary, the procedure is as with diffusion juice. With very small amounts of sugar, extra long polarimefcer tubes are used, or the liquid is rendered faintly alkaline with a few drops of milk of lime and evaporated, the residue being neutralised with dilute acetic add, clarified, made up to one-half or one quarter of the original volume and polarised. 

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A pressure filter is a plate-and-frame press which operates on an intermittent time cycle. Drier cakes are generally attainable from a filter press. Sludge drying beds are usually used for smaller sludge volumes, which drain and dry rapidly. Thein appHcation is usually restricted to the more arid climates. 

Belt filter presses are made up to a width of 2.5 m and produce a final soHds concentration of the discharge sludge in the range of 35 to 60%. 

Screw presses (Fig. 2) do not produce a clear liquid product. Frequendy, the product is further filtered in a filter press to give a clear Hquid product. Press aids are added to feed materials containing fine particles or particles that can deform and plug the slots in the edge of a screw press. Typical press aids include sawdust, rice hulls, perlite, and diatomaceous earth (see Diatomite). A vertical screw press is a continuous press that has been used for dewatering sewage sludge (2). 

Comparisons are available on the relative performance and costs for dewatering municipal sludges (2). The relative performance of different filters and conditioners on waste sludges is shown in Table 3. The same sludge was treated on two belt-filter presses, two different centrifuges, and rotary vacuum filter (75). In another study, a variable chamber filter press, fixed-volume filter press, continuous belt-filter press, and rotary vacuum filter were compared for performance, capacity, and capital and operating costs (69). 

Fig. 7. Sohds content of sludges dewatered by C, soHd bowl centrifuge VF, vacuum filter BP, belt press FP, filter press, and DFP, diaphragm filter press...

Tyj)e of dryer Applicable with dry-product recirculation True and colloidal solutions emulsions. Examples inorganic salt solutions, extracts, milk, blood, waste liquors, rubber latex, etc. Pumpable suspensions. Examples pigment slurries, soap and detergents, calcium carbonate, bentonite, clay sbp, lead concentrates, etc. does not dust. Recirculation of product may prevent sticking Examples filter-press cakes, sedimentation sludges, centrifuged sobds, starch, etc. 

Fiberglass manufacturing scrubber sludge Secondary and synthetic fiber Chemicals Variable-volume filter press 3 37... 

Metal ore concentrates Fine coal refuse Metal tailings Refinery sludges Wastewater treatment plant sludges Potable water treatment sludges Variable-volume filter press 46-55 81-93"... 

Corrective Action Application An acidic groundwater at a Florida site (pH 2.5-3) required treatment. The groundwater was collected by extraction wells, pumped to an above-ground reactor, and neutralized with lime. In the course of neutralizing the waste stream, precipitates were formed which were removed by clarification and filtration prior to discharge. Sludges produced from the clarification and filtration steps were dewatered by a filter press. 

After thickening, a variety of sludge handling and disposal options are available. For example, the thickened sludge can be applied directly to land. If liquid disposal is not applicable to a specific project, the thickened sludge can be dewatered by centrifugation, vacuum filtration, or filter pressing. The dewatered residue can then be land fill or incinerated. These options are discussed further on. 

Sludge treatment (filter press and final disposal)... 

Concentrated metal hydroxide sludge is pumped from the clarifier to a polypropylene plate filter press [T-102], The plate filter press56 is of sufficient capacity without any buildup in the lamellar portion of the unit. This also prevents any overflow of precipitate to the sewer system. The metal hydroxides form a dense sludge cake suitable for disposal in an approved landfill. The liquid effluent from the plate filter is returned to the surge tank [T-99],... 

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