Sludge classification

Two types of sludges are produced in water treatment plants  

The secondary sludge is usually pumped from the after-sedimentation into the primary settlers, and processed together with the primary sludge as a mixed sludge. Here, the primary sludge is the prevalent material. 

Both the primary and mixed sludges are called raw sludge. 

Fresh primary sludge from municipal wastewater treatment plants is yellow-brown, brown or even grey, and it usually has a granular structure and consists of insoluble substances wich have passed through a catch-pit and rakes. It also contains a remarkable quantity of colloidal substances with the ability to bind water and to retain it — therefore, dewatering in this case is rather difficult. 

Secondary (activated) sludge has a flaky structure, it contains at least 98% water. During sedimentation the particles of sludge present are ag- 

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Figure 7-3 Schematic View of the Hydrocyclone and Elutriator Applied for Sludge Classification in Hamburg Harbour (Left). Hass Balance and Distribution of Heavy Metals (Right). After Hilligardt et al. (1986). TS = Dry Material.

There is interest in lime sludge classification in both wastewater and potable water treatment plants. If the magnesium hydroxide content of a lime sludge can be suitably reduced, the residual calcium carbonate can be recalcined to calcium oxide. Too much magnesium hydroxide will prevent the slaking of the lime. The restrictions and rising cost of disposal of spent lime makes recovery and recycling attractive. 

Finure 6.9. Graph - Recovery v Feed Rate (Pond 14 3) - Lime Sludge Classification. 

Table A.3 Lime sludge classification data used in Section 6.4.3...

The Subpart O standards apply to units that treat or destroy hazardous waste and which meet the definition of an incinerator. An incinerator is any enclosed device that uses controlled flame combustion and does not meet the criteria for classification as a boiler, sludge dryer, carbon regeneration unit, or industrial furnace. Typical incinerators1 2 3 include rotary kilns, liquid injectors, fixed hearth units, and fluidized bed incinerators (Table 23.1). The definition of an incinerator also includes units that meet the definition of an infrared incinerator or plasma arc incinerator. An infrared incinerator is any enclosed device that uses electric-powered resistance as a source of heat and which is not listed as an industrial furnace. A plasma arc incinerator is any enclosed device that uses a high-intensity electrical discharge as a source of heat and which is not listed as an industrial furnace. 

Biomass and substrate must be separately described to establish a concept for classification of wastewater directed toward a description of the microbial processes. For several reasons, e.g., to allow widespread application and to observe a basic mass balance, the organic matter expressed in terms of COD is a central parameter for wastewater quality. According to the concepts used in the active sludge models, the classification of wastewater in a sewer network can also be subdivided as outlined in Figure 3.1 (Henze et al., 1987, 1995a, 2000). A direct interaction between sewer and treatment plant processes is therefore within reach. 

The nature and sizing of equipment depends on the economic values and proportions of the phases as well as certain physical properties that influence relative movements of liquids and particles. Pressure often is the main operating variable so its effect on physical properties should be known. Table 11.1 is a broad classification of mechanical processes of solid-liquid separation. Clarification is the removal of small contents of worthless solids from a valuable liquid. Filtration is applied to the recovery of valuable solids from slurries. Expression is the removal of relatively small contents of liquids from compressible sludges by mechanical means. 

The dilution factor can be automatically computed to give absolute counts for liquids as dense as sludge. Supercount is also loaded with a special program for hydraulic fluids and phi classification. 

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