Drying Beds

Drying beds are the most widely used method of municipal wastewater sludge dewatering in the United States. They have been used for more than 100 years. Although the use of drying beds might be expected in small plants and in warmer, sunny regions, they are also used in several large facilities and in northern climates. In the United States, a majority of wastewater treatment plants with less than 5-mgd capacity use drying beds for biosolids dewatering. In Russia and other Eastern European countries, more than 80% of the plants use drying beds.

The main advantages of sludge drying beds are low capital cost, low energy consumption, low to no chemical consumption, low operator skill and attention required, less sensitivity to sludge variability, and higher cake solids content than that of most mechanical methods. Disadvantages include large space requirements, the need for prior sludge stabilization, consideration of climatic effects, odor potential, and the fact that sludge removal is usually labor intensive. Sludge drying beds may be classified as: (1) conventional sand, (2) paved, (3) artificial media, and (4) vacuum assisted.

Conventional Sand Drying Beds Conventional sand drying beds are the oldest and most commonly used type of drying bed. They are generally used for communities with populations of fewer than 20,000. Many design variations are possible, including the layout of drainage piping, the thickness and type of gravel and sand layers, and construction materials.

Figure 3.23 shows a typical sand drying bed construction. Current practice is to divide the bed into multiple rectangular cells, each with dimensions of 4.5 to 18 m (15 to 60 ft) wide by 15 to 47 m (50 to 150 ft) long. The cells are sized such that one or two beds will be filled in a normal loading cycle. The outer walls may be earth embankments or vertical walls constructed of concrete blocks or reinforced concrete. The interior partitions may be constructed of concrete blocks, reinforced concrete, or planks stretching between slots in concrete posts. The planks can be wood, but the preferable material is precast

Drying Bed With Laterals
(a) Plan
Sand Drying Bed

Figure 3.23 Conventional sand drying bed. (Plan from Metcalf & Eddy, 2003.)

(b) Typical Section

Figure 3.23 Conventional sand drying bed. (Plan from Metcalf & Eddy, 2003.)

concrete. If mechanical equipment such as a wheeled front-end loader is used for cake removal, at least one solid vertical wall in each cell against which the loader can push will speed bed cleaning.

Usually, 230 to 380 mm (9 to 15 in.) of sand is placed over 200 to 460 mm (8 to 18 in.) of graded gravel. A thicker sand layer secures a good filtrate and reduces the frequency of sand replacement caused by losses from cleaning operations. However, a deeper sand layer generally retards the draining process. The sand is usually 0.3 to 0.75 mm (0.01 to 0.03 in.) in effective diameter and has a uniformity coefficient of less than 4.0. Gravel is normally graded from 3 to 25 mm (0.1 to 1.0 in.) in effective diameter.

Underdrain piping is perforated plastic or vitrified clay pipe laid with open joints (without gaskets) and should take into account the type of sludge removal vehicles to be used to avoid damage to the pipes. The lateral underd-rains pipes feeding into the main underdrain pipe should be spaced 2.4 to 6 m (8 to 20 ft) apart. The pipes should not be less than 100 mm (4 in.) in diameter and should have a minimum slope of 1%.

Sludge is applied to the cells of the sand drying bed through a pressurized pipe with a valved outlet to each cell or with a shear gate at the end of the outlet to each cell. Provisions should be made to flush the piping and, if necessary, to prevent it from freezing in cold climates. Sludge can also be applied through an open channel with an inlet to each cell controlled by a slide gate. With either type, a concrete splash block should be provided to receive the falling sludge and to prevent erosion of sand surface.

Sludge drying beds with greenhouse-type enclosures allow dewatering sludge throughout the year, regardless of the weather. They may also eliminate potential odor or insect problems. Sometimes a roof is placed over the top of the drying bed, leaving the sides open. Such a cover protects the bed from precipitation but provides little temperature control. Because of better temperature control, completely covered beds, require about 25 to 30% less area than open beds.

Sludge drying bed sizing criteria are given in unit area of bed required for dewatering on a per capita basis. These criteria are only valid for the characteristics of a particular wastewater and have no rational design basis. A better criterion for sizing the bed is the unit loading of kilograms of dry solids per square meter per year (pounds of dry solids per square foot per year) for a particular type of sludge. Table 3.20 shows the criteria for various types of biosolids. The criteria selected should take into consideration climatic conditions such as temperature, wind velocity, and precipitation; biosolids characteristics such as grit, grease, and biological content; and solids concentration.

The depths of application range from 200 to 400 mm (8 to 16 i n.). The applied depth should result in an optimum solids loading of 10 to 15 kg/m2 (2 to 3 lb/ft2). The total drying time required depends on the desired cake dryness. In addition to the water draining through the sand bed, moisture is removed by evaporation also. The time require for evaporation of moisture

TABLE 3.20 Sand Drying Bed Design Criteria for Digested Sludge

Uncovered Beds

. Area Dry Solids Loading Covered Beds Area Type of _ ____ _

Biosolid m2/capita ft2/capita kg/m2 • yr lb/ft2-yr m2/capita ft2/capita

. Area Dry Solids Loading Covered Beds Area Type of _ ____ _

Biosolid m2/capita ft2/capita kg/m2 • yr lb/ft2-yr m2/capita ft2/capita

TABLE 3.20 Sand Drying Bed Design Criteria for Digested Sludge

Uncovered Beds

Primary

0.09-

-0.12

1.0

1.3

120

150

25

30

0.07-

0.09

0.8

-1.0

Primary +

0.18-

-0.23

1.9

-2.5

100

160

20

33

0.09-

0.17

1.0

1.8

chemical

Primary +

0.12-

-0.17

1.3

1.8

90

120

18

25

0.09-

-0.14

1.0

1.5

trickling

filter

Primary +

0.16-

-0.23

1.7

2.5

60

100

12

20

0.12-

0.16

1.3

1.7

WAS

Source: Adapted from U.S. EPA, 1979.

Source: Adapted from U.S. EPA, 1979.

Minimum 1.5% Slope

Concrete Sludge Drying Beds

- Drainage

Figure 3.24 Cross section of a paved drying bed.

Asphalt or Concrete Lining

- Drainage

Figure 3.24 Cross section of a paved drying bed.

is considerably longer than that require for drainage. Therefore, the time the sludge must remain on the bed is determined by the amount of water that must be removed by evaporation. The drying time is shorter in regions that experience low rainfall and humidity and greater sunshine. Under favorable conditions, sludge may be dried to a solids content of about 40% after 10 to 15 days. As discussed previously, natural freezing and thawing in northern climates have been reported to improve dewaterability of sludge. Dried sludge has a coarse, cracked surface and is dark brown. At small treatment plants, sludge is usually removed by manual shoveling into wheelbarrows or trucks. At larger plants, a scraper or front-end loader, or special mechanical cake removal equipment, is used.

Paved Drying Beds Paved drying beds use concrete or asphalt lining. Normally, the lining rests on a 200- to 300-mm (8- to 12-in.)-thick built-up sand or gravel base. Figure 3.24 shows typical paved drying bed construction. The beds are normally rectangular in shape and are 6 to 15 m wide (20 to 50 ft)

by 20 to 45 m (70 to 150 ft) long with vertical sidewalls. The lining should have a minimum 1.5% slope to a center drainage area that is not paved. The drainage area is 0.6 to 1 m (2 to 3 ft) wide. A minimum 100-mm (4-in.)-diameter perforated pipe would convey the drainage away. The main advantages of paved drying beds are that front-end loaders can be used for easy removal of sludge cake, augur mixing vehicles can speed up drying, and bed maintenance is reduced. However, for a given amount of sludge, paved drying beds require more area than do conventional sand drying beds.

Artificial Media Drying Beds Two types of artificial media can be used for drying beds: stainless steel wedgewire or high-density polyurethane panels. Wedgewire drying beds have been used successfully in England for about 50 years and in the United States for about 30 years. Figure 3-25 shows a typical cross section of a wedgewire bed. The bed consists of a shallow rectangular watertight basin fitted with a false floor of wedgewire panels. The slotted openings in the panels are 0.25 mm (0.1 in.) wide. An outlet valve to control the rate of drainage is located underneath the false floor.

The procedure used for dewatering sludge begins by introducing water, usually plant effluent, onto the surface of the bed to fill the septum and the wedgewire to a depth of approximately 25 mm (1 in.). This water serves as a cushion that permits the added sludge to float without causing upward or downward pressure across the wedgewire surface. When the bed is filled with sludge, the water permits the sludge to settle and initially compact against the screen so that the settled sludge acts as the filtration media. Next, the water is allowed to percolate at a controlled rate by controlling the outlet valve. After the free water has been drained, the sludge further concentrates by drainage and evaporation until it is ready for removal. In a high-density polyurethane media system, 300 mm (12-in.)-square panels with a built-in underdrain system are paved over a sloped slab. Each panel has an 8% perforated area for dewatering.

Controlled differential head in vent by restricting rate of drainage

Controlled differential head in vent by restricting rate of drainage

Sludge Drying Bed Plan Figure
Figure 3.25 Cross section of a wedgewire drying bed.

Advantages of artificial media drying beds include (1) no clogging of the media, (2) constant and rapid drainage, (3) higher throughput rate than with sand beds, (4) easy bed maintenance, and (5) difficult-to-dewater sludges such as aerobically digested waste activated sludge can be dried. Drying beds with polyurethane panels have the added advantage of (1) dewatering dilute sludge, (2) low suspended solids in filtrate, and (3) easy removal of sludge cake possible with a front-end loader.

Artificial media beds can typically dewater 2.5 to 5.0 kg of solids per square meter (0.5 to 1.0 lb/ft2) per each application. Most types of sludge dry to a concentration of 8 to 12% within 24 hours. However, such a sludge cake is still relatively wet and thus may complicate disposal.

Vacuum-Assisted Drying Beds Vacuum-assisted drying beds (see Figure 3.26) accelerate dewatering and drying from the application of vacuum to the underside of the porous filter plates. The bed is usually rectangular and has a reinforced concrete slab at the bottom. A layer of aggregate several millimeters thick is placed on top of the slab, which in turn supports a rigid multimedia porous filter top. The aggregate layer is also the vacuum chamber and is connected to a vacuum pump. The operating sequence is as follows:

• The sludge is preconditioned with a polymer.

• Sludge is introduced onto the drying bed by gravity flow at a rate of 9.4 L/s (9150 gpm) and to a depth of 300 to 750 mm (12 to 30 in.).

Hawaii Sludge Drying Bed
Figure 3.26 Vacuum-assisted drying bed. (Reprinted with permission from WEF, 1998.)

TABLE 3.21 Typical Performance Data for Vacuum-Assisted Sludge Drying Beds

Type of Sludge

Dry Solids Loading lb/ft2

Cycle Time (h)

Polymer Dosage g/kg

TABLE 3.21 Typical Performance Data for Vacuum-Assisted Sludge Drying Beds

Type of Sludge

Dry Solids Loading lb/ft2

Cycle Time (h)

Polymer Dosage g/kg

Anaerobically digested

Primary

1-

-7

10-

-20

2

4

8-

24

2

20

4

40

12

26

Primary + WAS

1-

-4

5-

-20

1

4

18-

24

15

20

30

40

15

20

Primary + TF

3-

-10

15-

-30

3

-6

18-

24

20

26

40

52

20

26

Aerobically digested

Conventional WAS

1-

-4

5-

-15

1

3

8-

24

1

17

2

34

10

23

Oxidation ditch WAS

1-

-2

5-

-10

1

2

8-

24

2

7

4

14

10

20

Source: Adapted from WEF, 1998.

Source: Adapted from WEF, 1998.

• After the sludge is applied, it is allowed to drain by gravity for about 1 hour.

• At the end of the gravity drainage period, the vacuum system is started and it maintains a vacuum at 34 to 84 kPa (910 to 25 in.Hg).

• When the cake cracks and the vacuum is lost, the vacuum pump is shut off.

• The sludge is allowed to air dry for 1 to 2 days.

• The cake is removed from the bed using a front-end loader.

• The surfaces of the media plates are washed with a high-pressure hose.

Table 3.21 lists performance data for vacuum-assisted drying beds for various types of sludges. The principal advantages of this system are: the cycle time for sludge dewatering is short, thereby reducing the effects of weather on sludge drying; a smaller area is required; and the sludge cake is easily removable using a small front-end loader. Because of their small area requirements, these beds can be covered more easily for use in colder or wetter climates. The principal disadvantage is that polymer conditioning of sludge is required for successful operation.

3.4.5 Other Dewatering Methods

Vacuum Filters Since its first introduction in the United States in the mid-1920s, thousands of vacuum filters have been installed in municipal wastewater treatment plants for dewatering sludge. In vacuum filtration, a vacuum applied downstream of the media is the driving force on the liquid phase that moves it through the porous media. The medium can be natural or synthetic fiber cloth, woven stainless steel mesh, or coil springs. Figure 3.27 is a cross-sectional view of a rotary vacuum filter with a coil-spring filter. The unit consists of a horizontal drum that rotates, partially submerged, in a vat of conditioned sludge. The drum surface is divided into sections around its cir-

Process Control For Rotary Drum Filters

(a) Cross section rotary vacuum filter with coil spring media

Cake discharge

(a) Cross section rotary vacuum filter with coil spring media

(b) Operation zones Figure 3.27 Vacuum filter.

cumference. Each section is sealed from its adjacent section and the ends of the drum. A separate drain line connects each section to a rotary valve at the axis of the drum. As the drum rotates, the valve allows each segment to function in sequence as one of the three distinct zones: for cake forming, cake drying, and cake discharging. A vacuum is applied to each of the drum sections through drain lines. As the drum rotates, each section is carried successively through the cake-forming zone to the cake-drying zone. In the final zone, cake is removed from the coil-spring media. After cake discharge, the coils are washed.

Optimum performance is dependent on the type of sludge, solids concentration, type and quality of conditioning, and how the filter is operated. Ferric

TABLE 3.22 Typical Dewatering Performance Data for Vacuum Filters

Type of Sludge

Feed

Cake

Solids

Raw sludge

Primary + trickling filter 4-8 15-30 3-6 20-28

Primary + WAS 3-7 12-30 2.5-6.0 18-25 Digested sludge

Primary 4-8 15-34 3-7 25-32

Primary + trickling filter 5-8 20-34 4-7 20-28

Source: Adapted from U.S. EPA, 1979.

chloride/lime conditioning is the most common type of conditioning used. The selection of vacuum level, degree of drum submergence, type of media, and cycle time are all critical to optimum performance. Table 3.22 shows typical dewatering performance data for vacuum filters.

Vacuum filters consume the largest amount of energy per unit of sludge dewatered in most applications, and they require continuous operator attention. Because of the improvements to other dewatering devices and the development of new dewatering devices with lower operation and maintenance costs, the use of vacuum filter is declining.

Screw Presses A screw press is a dewatering device that employs a dewater-ing and conveying screw inside a screen. Figure 3.28 shows two types of screw presses, one with an inclined screw arrangement, the other with a horizontal installation with the added steam feed capability for additional drying of the cake.

In the inclined arrangement, the screw press consists of a wedge section basket with a 0.25-mm (0.01-in.) spacing. The slowly rotating screw, at variable speed, conveys the polymer-conditioned sludge upward through the inclined basket. The lower section of the basket serves as a predewatering zone, where free water drains by gravity. The upper section of the basket serves as the pressure zone. Here the sludge is compressed between narrowing flights of the screw (or progressively enlarging flights of the screw, as shown in Figure 3.28). The pressure in the pressure zone is controlled by the position of a cone at the discharge end of the basket. The dewatered sludge cake is driven through the gap between the cone and the basket and drops onto a conveyor or directly into a dumpster. The screw flights are provided with brushes for continuous internal cleaning of the wedge section basket. Spray nozzles are also provided for periodic cleaning of the basket from the outside with spray water. The basket is provided with a cover for housekeeping and odor containment.

Steam Inlet

Condensate Outlet

Steam Inlet

Condensate Outlet

Table Screen Draining
Filtrate

(a) Horizontal Press

(a) Horizontal Press

(b) Inclined Press

Figure 3.28 Screw presses. [Part (a) from FKC Co., Port Angles, WA; part (b) from Huber Technology Inc., Huntersville, NC.]

(b) Inclined Press

Figure 3.28 Screw presses. [Part (a) from FKC Co., Port Angles, WA; part (b) from Huber Technology Inc., Huntersville, NC.]

Advantages of screw presses include fewer space requirements and relatively low capital cost and power consumption. It is typically used in small wastewater treatment plants. The hydraulic capacity is about 10 m3/h (45 gpm), and the solids capacity is about 275 kg/h (600 lb/hr). Cake solids concentration of 20 to 25% can be obtained with a polymer dosage of 4 to 6 g/kg (8 to 12 lb/ton) of dry solids. Solids capture rates of better than 95% have been reported.

Reed Beds The reed bed system for municipal sludge dewatering combines the action of conventional drying beds that have the effects of aquatic plants on water-bearing substrates. The system is constructed similar to drying beds with rectangular basins that have concrete sidewalls. The bottom of beds are provided with a 250-mm (10-in.) -thick layer of 20-mm (0.8-in.) washed gravel and perforated underdrain piping for filtrate removal. This bottom layer is topped with another 250-mm (10-in.) layer of 4 to 6 mm (0.16 to 0.25 i n.) washed gravel, and a layer of filter sand of 100 to 150 mm (4 to 6 i n.). A

minimum freeboard of 1 m (3.3 ft) is provided above the sand. Reeds of the genus Phragmites communis are planted in the middle gravel layer on 300mm (12-in.) centers. The plants provide a pathway for continuous drainage of water from the applied sludge. Additionally, the root system of the plants establishes a rich microflora that feeds on the organic content of the sludge. Degradation by the microflora is so effective that up to 97% of the organic content is converted to carbon dioxide and water, with a corresponding reduction in volume. The reeds are harvested once every year in the fall when they have become dormant.

The design solids loading rate is 30 to 60 kg/m2-yr (6 to 12 lb/ft2-yr). The basin is loaded over a 24-hour period, and a 1-week resting period is provided before the cycle is repeated. A bed can be operated for up to 10 years before the accumulated residues have to be removed. To remove the residues, the beds are first taken out of service for 6 months. This allows the uppermost layer to become mineralized and disinfected. When the solids are removed for disposal, the top gravel and sand layers are also removed and must be replaced. The use of reed beds is practical for wastewater treatment plants of capacities of less than 0.2 m3/s (5 mgd).

Drying Lagoons Sludge drying lagoons are another method of dewatering stabilized sludge when sufficient land is available. They are similar to drying beds; however, the sludge is placed at depths three to four times greater than it would be in a drying bed. Dewatering occurs by evaporation and transpiration, of which evaporation is the most important dewatering factor. Sludge should be stabilized prior to discharging to the lagoons to minimize odor problems. The advantages and disadvantages of drying lagoons are listed in Table 3.13.

Drying lagoons are normally rectangular in shape, enclosed by earthen dikes 0.6 to 1.2 m (2 to 4 ft) high. Appurtenant equipment includes sludge feed lines, supernatant decant lines, and some type of mechanical sludge removal equipment. The removal equipment can be a bulldozer, dragline, or front-end loader. Stabilized sludge is pumped into the lagoon over a period of several months until a lagoon depth of 0.6 to 1.2 m (2 to 4 ft) is achieved. Supernatant is decanted, either continuously or intermittently, from the lagoon surface and returned to the treatment plant. Depending on the climate and the depth of the sludge, the time required for dewatering to a final solids content of 20 to 40% may be 3 to 12 months. After the sludge cake is removed, the cycle is repeated.

Proper design of sludge drying lagoons requires consideration of several factors, such as precipitation, evaporation, sludge characteristics, and volume. Solids loading criterion is 35 to 38 kg/m3-yr (2.2 to 2.4 lb/ft3-yr) of lagoon capacity. Per capita design criteria vary from 0.1 m2/capita (1 ft2/capita) with primary digested sludge in an arid climate to 0.3 to 0.4 m2/capita (3 to 4 ft2/ capita) for activated sludge plants in areas where 900 mm (36 in.) of annual rainfall occurs.

REFERENCES

Albertson, O. E., and Walz, T. (1997), Optimizing Primary Clarification and Thickening, Water Environment and Technology, Vol. 9, No. 12.

Albertson, O. E., et al. (1991), Dewatering Municipal Wastewater Sludges, Noyes Data Corporation, Park Ridge, NJ, p. 189.

Agranonic, R. Y. (1985), Technology of Wastewater Sludge Treatment with Centrifuges and Belt Filter Presses, Stroyizdat, Moscow.

ASCE (1988), Belt Filter Press Dewatering of Wastewater Sludge, ASCE Task Force on Belt Press Filters, ASCE Journal of the Environmental Engineering Division, Vol. 115, No. 5, pp. 991-1006.

Ashbrook Corporation (1992), Aquabelt Operation and Maintenance Manual, Houston, TX.

Carmen, P. C. (1933, 1934), A Study of the Mechanism of Filtration, Journal of the Society Chemical Industry London, Vol. 52, p. 280 T; Vol. 53, pp. 159 T, 301 T.

Chang, L. W., Furst, A., and Nordberg, G. (1995), Toxicology of Metals, Vol. 1, July, p. 480.

Cheremisinoff, P. N. (1995), Solids/Liquids Separation, Technomic Publishing Co., Lancaster, PA.

Christensen, G. L., and Dick, R. I. (1985), Specific Resistance Measurements: Methods and Procedure, ASCE Journal of the Environmental Engineering Division, Vol. 111, No. 3, p. 258.

Citton, F. W., Jr., Adams, T. E., and Dohoney, R. W. (1991), Managing Sludge Through In-Vessel Composting, Water Engineering and Management, December, p. 21.

Coacley, P., Swenwic, V. D., Gabe, R. S., and Bascerville, R. C. (1956), Water Pollution Research and Proceedings of the Institute for Sewage Purification, Vol. 2.

Coker, C. S., et al. (1991), Dewatering Municipal Wastewater Sludge for Incineration, Water Environment and Technology, March.

Davis, J. (1986), Sludge Disposal Thinking Seminar in U.K. and U.S.A., Water Engineering and Management, Vol. 12, pp. 25-28.

Diaz, L. F., et al. (1993), Composting and Recycling Municipal Solid Waste, Water Environment Federation, Alexandria, VA, p. 320.

Dicht, N. (1986), Zweistufige Ferfahren der Shlämmstabkizierung, Korrespondenza Abwasser, Vol. 11, pp. 1055-1056.

Dick, R. I., and Ewing, B. B. (1967), Evaluation of Activated Sludge Thickening Theories, ASCE Journal of the Environmental Engineering Division, Vol. 93, No. 4, p. 9.

D. R. Sperry Co., Prospect, A vision for Tomorrow, North Aurora, IL.

Dvinskich, E. V., et al. (1991), Drying Beds, VNIPIE Lesprom, Moscow, p. 65.

Eckenfelder, W. W., and Santhanam, C. J. (1980), Sludge Treatment, Marcel Dekker, New York.

EPA Design Information Report (1987), The Original Vacuum Sludge Dewatering Bed, Journal of the Water Pollution Control Federation, Vol. 59, No. 4, pp. 228-234.

Epstein, E. (1997), The Science of Composting, Technomic Publishing Co., Lancaster, PA.

FDEP (1994), Domestic Wastewater Residuals, Chapter 62-640, Florida Department of Environmental Protection, Tallahassee, FL.

Foess, G. M., and Singer, R. B. (1993), Pathogen/Vector Attraction Reduction Requirement of the Sludge Rules, Water Engineering and Management, June, p. 25.

Frontier Technologies, Inc., Prospect, FT1 Belt Filter Press, Allegan, MI.

Garvey, D., Guairo, C., and Davis, R. (1993), Sludge Disposal Trends Around the Globe, Water Engineering and Management, December, p. 17.

Ghosh, S. (1987), Improved Sludge Classification by Two-Phase Anaerobic Digestion, Environmental Engineer, Vol. 6, pp. 1265-1284.

Goldfarb, L., Turovskiy, I., and Belaeva, S. (1983), The Practice of Sludge Utilization, Stroyizdat, Moscow.

Gulas, V., Benefield, L., and Randall, C. (1978), Factors Affecting the Design of Dissolved Air Flotation Systems, Journal of the Water Pollution Control Federation, Vol. 50, p. 1835.

Hallulen (1989), Thickening of the Activated Sludge, Symposium, Warsaw, Poland, April 24-29.

Hammer, M. J. (1975), Water and Wastewater Technology, New York.

Infilco Degremont, Inc. (1979), Water Treatment Handbook, 5th ed., Richmond, VA.

Jordan, V. J., and Scherer, C. H. (1970), Gravity Thickening Techniques at a Water Reclamation Plant, Journal of the Water Pollution Control Federation, Vol. 42, p. 180.

Karr, P. R., and Keinath, T. M. (1978), Influence of Particle Size on Sludge Dewater-ability, Journal of the Water Pollution Control Federation, Vol. 50, p. 1911.

Komline-Sanderson, Inc., Prospect, GRS Series III Kompress, Peapack, NJ.

Lawler, D. F., and Chung, V. J. (1986), Anaerobic Digestion: Effect on Particle Size and Dewaterability, Journal of the Water Pollution Control Federation, Vol. 12, p. 1107.

Metcalf & Eddy, Inc. (2003), Wastewater Engineering: Treatment and Reuse, 4th ed., Tchobanoglous, G., Burton, F. L., and Stensel, H. D. (Eds.), McGraw-Hill, New York.

Ohara, G. T., Raksit, S. K., and Olson, D. R. (1978), Sludge Dewatering Studies at Hyperion Treatment Plant, Journal of the Water Pollution Control Federation, Vol. 50, p. 912.

Olson, R., Gendreau, A., and Cyr, S. (1999), Biosolids Technical Bulletin, MarchApril, pp. 5-9.

Parkin, G. F. (1986), Fundamentals of Anaerobic Digestion of Wastewater Sludges. Environmental Engineer, Vol. 5, pp. 867-920.

Popel, F. (1967), Sludge Digestion and Disposal, Stuttgart, Germany.

Randall, C. W. (1969), Are Paved Drying Beds Effective for Dewatering Digested Sludge? Water and Sewage Works, Vol. 116, p. 373.

Roberts, K., and Olsson, O. (1975), Influence of Collodial Particles on Dewatering of Activated Sludge with Polyelectrolyte, Environmental Science and Technology, Vol. 9, p. 945.

Schroeder, W. (1960), What Is Better—Raw or Digested Sludge? Das Gas-und Wasserfach, Vol. 101, No. 50, pp. 1298-1301.

Seabright Products, Inc., Prospect, Dewatering Solutions, Hopkins, MI.

Serna Technologies, Inc., Prospect, Belt Filter Press, Jasper, AL.

Siger, R. B. (1993), Practical Guide to the New Sludge Standards, Water Engineering and Management, November, p. 26.

-, and Hermann, G. (1993), Land Application Requirements of the New Sludge

Rules, Water Engineering and Management, August, p. 26.

Sludge Treatment and Disposal, Vol. 1, Sludge Treatment, and Vol. 2, Sludge Disposal (1985), Stroyizdat, Moscow.

Spellman, F. R. (1996), Wastewater Biosolids to Compost, Technomic Publishing Co., Lancaster, PA.

-(1997) Dewatering Biosolids, Technomic Publishing Co., Lancaster, PA.

Tchernova, N. M. (1966), Zoological Characteristics of Compost, Nauka, Moscow.

The Wave (1998), U.S. Filter magazine, Municipal Water and Wastewater, February, Vol. 2, No. 1.

The Wave (2000), U.S. Filter magazine, Municipal Water and Wastewater, March, Vol. 4, No. 1.

Turovskiy, I. S. (1986), Design Handbook of Wastewater Systems, Methods of Wastewater Sludge Treatment, Vol. 2, Sec. 10, Allerton Press, New York, pp. 531-610.

-(1988), Wastewater Sludge Treatment, Stroyizdat, Moscow.

-(1992), Endickung, Ehtwasserung und Enseuhung von Abwasserschlämmen,

-(2000), Dewatering of Wastewater Sludge, Proceedings 75th Annual Florida

Water Resources Conference, Tampa, FL.

Turovskiy, I. S., et al. (1970), Thermal Treatment of Sludges, Gos INTI, Moscow.

-(1971), Sludge Incineration, Gos INTI, Moscow.

-(1988), Sludge Dewatering by Belt Filter Presses, Water Supply and Sanitary

-(1989a), Biothermal Treatment of Sludge, ZBTI Minvodchoz, Moscow.

-(1989b), Systems with Press Filters, ZINTICHIMNEFTE Mash, Moscow.

-(1991), Technology of Sludge Composting, VNIPIEI Lesprom, Moscow.

U.S. EPA (1978), Effects of Thermal Treatment of Sludge on Municipal Wastewater Treatment Cost, EPA 600/2-78/073.

——— (1979), Process Design Manual for Sludge Treatment and Disposal, EPA 625/1-79/011.

——— (1987a), Design Manual: Dewatering Municipal Wastewater Sludge, EPA 625/1-87/014.

——— (1987b), Innovation in Sludge Drying Beds: A Practical Technology.

——— (1989), Summary Report: In-Vessel Composting of Municipal Wastewater Sludge, EPA 625/8-89/016.

U.S. Filter, Prospect, Belt Filter Presses, U.S. Filter, Dewatering Systems Group, Holland, MI.

Vesilind, P. A. (1979), Treatment and Disposal of Wastewater Sludges, Ann Arbor Science, Ann Arbor, MI.

-(1996), Sludge Dewatering: Why Water Wins, Industrial Wastewater, Vol. 4

Wech, F. (1986), Untersuchungen zur Optimiesierung der zweistufigen anaeroben Klarschlammstabilisierung, GWF, Wasser-Abwasser, Vol. 3, pp. 109-117.

WEF (1980), Sludge Conditioning, Manual of Practice FD-1, Water Environment Federation, Alexandria, VA.

- (1983), Sludge Dewatering, Manual of Practice 20, Water Environment

Federation, Alexandria, VA.

-(1987), Operation and Maintenance of Sludge Dewatering Systems, Manual of Practice OM-8, Water Environment Federation, Alexandria, VA.

-(1988), Sludge Conditioning, Manual of Practice FD-14, Water Environment

Federation, Alexandria, VA.

-(1996), Operation of Municipal Wastewater Treatment Plants, 5th ed., Manual of Practice 11, Water Environment Federation, Alexandria, VA.

-(1998), Design of Municipal Wastewater Treatment Plants, 4th ed., Manual of

Practice 8 (ASCE 76), Water Environment Federation, Alexandria, VA.

Yakovlev, S. V. (1994), Utilities in Building and Structures, Stroyizdat, Moscow.

Organic Gardeners Composting

Organic Gardeners Composting

Have you always wanted to grow your own vegetables but didn't know what to do? Here are the best tips on how to become a true and envied organic gardner.

Get My Free Ebook


Responses

  • iago
    What optimum depth sludge over waste water drying bed?
    2 years ago
  • juliane
    How does a sludge drying bed functions?
    2 years ago
  • regina
    How thick should sludge be applied on a sand drying bed?
    2 years ago
  • Wilimar
    What are the methods of sludge drying using unpaved drying beds?
    2 years ago
  • JASKA
    What is cycle in sludge drying beds?
    11 months ago
  • christian
    What is function of sludge drying bed?
    10 months ago
  • ralph
    What controls odor for partially digested sludge in drying bed?
    10 months ago
  • tanta
    How to size up drying bed for sludge?
    9 months ago
  • Kate
    Is there suppose to be vegetation in wastewater drying beds?
    8 months ago
  • luana trentino
    When would a drying bed be considered a tank?
    8 months ago
  • kerttu
    How to design a sand drying bed?
    7 months ago
  • destiny
    How to design paved drying bed?
    7 months ago
  • fethawit zula
    What sewage plan can u use for a sewage system?
    6 months ago
  • rudi
    How to get rid of sludge odors in drying beds?
    6 months ago
  • nadine
    What is a residual drying bed?
    5 months ago
  • MATHIAS
    How many times can you reapply to a drying bed?
    5 months ago
  • Luca
    How paved sludge drying bed works?
    4 months ago
  • Marko
    How build a sludge drying bed?
    4 months ago
  • Arsi Koskela
    Do drying beds work the same as dewatering?
    4 months ago
  • mya
    What happens when sludge drying beds near capacity?
    3 months ago
  • Chloe Russell
    What is the advantage of drying bed?
    2 months ago
  • bucca
    What kind of odor comes from dry sludge bed?
    2 months ago
  • joel
    What are some ways to thicken up wet sludge from drying beds?
    21 days ago
  • fallon
    What is a drying bed refinery waste water?
    15 days ago
  • peter
    How long doer sludge take to dry in normal atmospheric pressure?
    7 days ago

Post a comment