Belt filter presses are continuous-feed sludge-dewatering devices that involve the application of chemical conditioning, gravity drainage, and mechanically applied pressure to dewater sludge (Tchobanoglous and Burton, 1991). In most types of belt filter presses, conditioned sludge is first introduced on a gravity drainage section where it is allowed to thicken. In this section, the majority of the free water is removed from the sludge by gravity. Following gravity drainage, pressure is applied in a low-pressure section, where the sludge is squeezed between porous cloth belts. In some units, the low-pressure section is followed by a high-pressure section, where the sludge is subjected to shearing forces as the belts pass through a series of rollers. The squeezing pressure in combination with shear forces induce the release of additional quantities of water from the sludge. The final dewatered sludge cake is removed from the belts by scraper blades.
A typical belt filter press system consists of sludge-feed pumps, polymer-feed equipment, a sludge-conditioning tank (flocculator), a belt filter press, a sludge cake conveyor, and support systems (sludge-feed pumps, washwater pumps, and compressed air).
Belt filter presses are available in metric sizes from 0.5 to 3.5 m in belt width. The most common size used for municipal sludge applications is 2.0 m. Sludge-loading rates vary from 90 to 680 kg/m-h depending on the sludge type and feed concentrations. Hydraulic throughput based on belt width ranges from 1.6 to 6.3 L/m-sec. Note that it is common to express loading rates and sizes of belt filters on the basis of filter width.
The material balances are based on the retained mass percentages in the product stream of particulate components in the sludge and the wt% of solids in cake. The retention of liquid and soluble components is based on the solids content of the cake stream. The model also adjusts the flowrate of the wash stream based on the specified composition and flow or Flow Per Unit Belt Width (in m3/m-h) for this stream. The washing is assumed to be of displacement type (embolic displacement of solutes and solvents present in the interstitial space).
In Design Mode, the belt width is calculated by dividing the solids (present in the feed) loading by the specific sludge-loading rate (in kg dry solids/m-h). If the calculated width exceeds the maximum possible (which is specified through the equipment tab), the program assumes multiple units operating in parallel with a total belt width equal to the calculated. In Rating Mode, the user specifies the number of unit and their belt width and the program calculates the sludge-loading rate.
1. Tchobanoglous G. and F.L. Burton (1991). “Wastewater Engineering: Treatment, Disposal, and Reuse”, Third edition, Metcalf & Eddy, Inc., McGraw-Hill, p. 864.
2. “Process Design Manual for Sludge Treatment and Disposal”, (1979). EPA 625/1-79-011.
The interface of this operation has the following tabs:
● Oper. Cond’s, see Belt Filtration: Oper. Conds Tab
● Labor, etc, see Operations Dialog: Labor etc. Tab
● Description, see Operations Dialog: Description Tab
● Batch Sheet, see Operations Dialog: Batch Sheet Tab
● Scheduling, see Operations Dialog: Scheduling Tab