Digested sludge thickening

Thus a good way of correlating digested sludge thickening results from a decanter is to plot solids recovery, and cake solids, separately, against the empirical thickening factor (N/ Qf. r 

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Fifjiire 6.21. Grap/i - Cake Dryness v Factor Psi - Digested Sludge Thickening. 

Table A.6 Digested sludge thickening data used in Sections 6.4,6 and 7.1...

Water treatment Clarification of potable water, industrial effluents, municipal waste water thickening and dewatering of sludge filtration of primary sludge, digested sludge food processing... 

The above-cited studies demonstrate the performance of a particular unit system for the treatment of specific type of waste stream. A particular unit system alone may not be able to treat the wastewater to a level of effluent standard prescribed for its safe disposal. Hence a number of pretreatments, such as screening, sedimentation, equalization, and neutralization, and post-treatment units such as secondary sedimentation, sludge thickening, digestion and disposal, disinfection, and so on, are extremely important for complete treatment. The effluent treatment and disposal facilities adopted by various types of pharmaceutical industries are described in the following sections. 

Plant 000012 produces 3.9 x 10" kkg/year (8.7 x lO lb/year) of emulsion crumb rubber, primarily neoprene. The contact wastewater flow rate is approximately 8.45 m /day (2.25 X 10 gpd) and includes all air pollution control equipment, sanitary waste, maintenance and equipment cleanup, and direct contact wastewater. The treatment process consists of activated sludge, secondary clarification, sludge thickening, and aerobic sludge digestion. Noncontact wastewater, with a flow rate of approximately 1.31 x 10 m /day (3.46 x 10 gpd), is used on a once-through basis and is remrned directly to the river source. Contact wastewater is also returned to the surface stream after treatment. 

Fig. 3. Typical thickening curve for digested sludge = 5.2 % solids with different additives. All experiments were carried out after hydrotransport sludge - D = 250 mm, 1 = 6615 m...

Following digestion, sludge is generally conditioned and thickened to concentrate and stabilize it and make it more dewaterable. Relatively inexpensive processes, such as gravity thickening, may be employed to get the moisture content down to about 95%. Sludge can be further conditioned chemically by the addition of iron or aluminum salts, lime, or polymers. 

An anaerobic digester is a no-recycle complete mix reactor. Thus, its performance is independent of organic loading but is controlled by hydraulic retention time (HRT). Based on kinetic theoiy and values of the pseudo constants for methane bac teria, a minimum HRT of 3 to 4 days is required. To provide a safety factor and compensate for load variation as indicated earlier, HRT is kept in the range 10 to 30 days. Thickening of feed sludge is used to reduce the tank volume required... 

Both thickening, digestion and sludge dewatering very often cause odour problems. 

This Is the proceedings from the WEF 1992 conference. Topics include aerobic and anaerobic sludge digestion, thickening, dewatering, beneficial reuse, thermal processing, ultimate use. and composting. 

Even after anaerobic digestion the voluminous sludge contains a lot of water. It is thus necessary to decrease the amount of water in it and hence also its volume so that its transport and eventual further processing would become more economical. For this purpose various methods can be used, especially thickening, dehydration and drying, or eventually incineration (for details see Section 3.11). 

Experimental data obtained with primary thickened sewage sludge in laboratory digesters under standard high-rate conditions. Sludge obtained from Metropolitan Sanitary District of Greater Chicago. 

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