It's dificult to narrow down the multitude of publications to a few for you to look at because of the exhaustive studies and design cases that have evolved in the wastewater jield. However, there are three books in particular that I recommend you acquire for general infomtion on the technologies of sedimentation, clarijicatiom and the overall relationship of these operations within a wastewater treatmentplantfmility. I recommend that you begin building your library with these volumes. There are plenty of design-spec.@ case studies and sample calculations, as well as equipment scale-up methodologies provided, with each volume bringing something valuable to the subject.
1. Wastewater Treatment Technology, Paul N . Cheremisinoff - editor, Published 08/01/1989, ISBN 0872012476.
SEDIMENTATION, CLARIFICATION, FLOTATION AND COALESCENCE 329
2. Water Treatment Principles and Design, James M. Montgomery, Published 08/0 1 / 1985, ISBN 047 1043842.
Municipal Water Treatment Technology: Recent Developments, USEPA, Published 03/01 / 1993, ISBN 08 15513097.
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For Web-sites, the selection process is even more challenging. A simple search on AltaVista for clarifiers and thickeners resulted in over 157,000 sites identified. The vast majoriq of these are equipment suppliers, design, engineering and consulting
$mu. In reviewing a few hundred of these sites while writing this volume, a few struck me as being quite us@l, especially for those of you that really need to nail down the basics. These sites, along with the reasons why I think you should visit them are as follows:
4. http://members.aol.com/erikschiff/primary.htm - This site is actually a review of the Lynn Regional Wastewater Treatment Facility (Lynn, Massachusetts), which is a primary and secondary treatment plant with a design purpose of the primary to remove settleable and floatable material (sludge, grease, etc.). The secondary treatment is directed principally toward the removal of biodegradable organic and suspended solids. What is very nice about this site is that it provides a reasonably good technical description of the basis for the overall design, and then focuses in on some of the key unit operations, including the primary and secondary clarifiers. There are plenty of installation and equipment photographs, and some simple but very effective animated drawings that illustrate how the equipment work. You will obtain a very good understanding of the practical aspects of clarification and sedimentation practices for a municipal water treatment facility by spending some time here.
5. http://www.baaqmd.gov/permit/handbook/sewage.htm - This is a municipal chapter titled SEWAGE TREATMENT FACILITIES (POTWs), Last adopted: July 17, 1991. This chapter covers the permitting of typical unit operations at publicly owned treament works (POTW) facilities. These plants treat wastewater from sanitary and storm sewer systems prior to discharge into surface waters or reuse as reclaimed water. Typical POTW sources may be defined as a combination of the liquid or water carried wastes removed from residences, institutions, and commercial and industrial establishments, together with groundwater, surface water, and storm water runoffs. Publicly owned treatment works are typically large land intensive facilities with numerous ponds, buildings, pump stations, etc required to handle large daily flows. I recommend you spend some time reading through this chapter, not only for the sense of overall design issues, but also to gain appreciation and understanding of air emissions issues associated with these plants.
6 . http://www.state.sd.us/denr/DES/Surfacewater/clarifie.htm - A very good
WATER AND WASTEWATER TREATMENT TECHNOLOGIES 330
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site that walks you through clarifiers, sedimentation equipment, trickling filters, aeration basins, solids thickeners, and much more. There are plenty of photographs of large-scale equipment that will give you a sense for the magnitude and complexity of these equipment, as well as a feel for the operating parameters.
http://www.Treat-Wastewater.com - This is a vendor of wastewater treatment simulation software. This is not an endorsement of the products, but I recommend you peruse the site and examine the features. You can try some sample calculations and acquire some of the products for trial periods.
I cannot vouge for the usefulness of these simulations in actual design cases, however they seem to have the features needed. The range of programs includes the following: ( I ) Process Advisor Pro [Carbon removal/nitrification/denitr@cation : Price $49.51 - A software package for real time simulation, analysis and control of the biological wastewater treatment process. Visualizes unobservable processes such as activated sludge concentration, the evolution of organic matter concentration, population dynamics, and many more! The reactor can be plug flow like most of zone- aerated treatment facilities or completely mixed. Any system of sludge and water feeding can be used. Can analyze your own data; (2) Process Advisor [Carbon removal : Price $3951 - A lesser version of Process Advisor Pro that does without nitrification and denitrification capabilities and cannot be as extensively set up to support different configurations. Otherwise supports all the features of Process Advisor Pro, including population dynamics and hydrodynamic settler model; (3) Process Advisor MBR [Carbon removal in membrane bioreactor: Price $4491 - A software package for simulation, analysis and control of the high-concentration biological wastewater treatment processes that are using membrane filter for complete separation of the sludge from treated water and partial filtration of the dissolved solids.
Supports both submerged and grossflow membrane filters; (4) SettEer Specialist [Clarifier analysis : Price $1 991 - A clarifier simulation software for 2-D analyzes of wastewater treatment processes in circular and rectangular clarifiers. Can predict processes like distribution of sludge in the settler, flow streamlines in the settler, vertical and horizontal flow velocities, and much more. Supports both turbulent and laminar flow models.
f i e following are useful references on dissolved air flotation. This bibliography contains a number of references for equipment and process scale-up, and design methods.
8. Baeyens, J., Mochtar, Y., Liers, S . , and De Wit, H. Plugflow dissolved air flotation. Water Environment Research. Vol. 67, Num. 7. 1995. pp. 1027-
1035.
Fuerstenau, M. C., ed. Flotation--A. M. Gaudin Memorial Volume. Vols. 1 and 2, AIME, New York. 1976.
Gaudin, A. M. Flotation. Second Edition, McGraw-Hill, New York, 1957.
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Grainger-Allen, T. J. N. Bubble generation in froth flotation machines.
Trans. IMM Vol79, C15-22. 1970.
Hedherg, T., Dahlqvist, J., Karlsson, D., Soerman, L.-0. Development of an air removal system for dissolved air flotation. Water science and technology. Vol. 37, No. 9, p. 81, 1998.
Haarhoff, J. and Steinbach, S. A model for the prediction of the air composition in pressure saturators. Water Research. Vol. 30, No. 12, pp.
Liers, S , Baeyens, J, Mochtar, J. Modeling dissolved air flotation. Water environment research. Vol. 68, No. 6, p. 1061, 1996.
Klassen, V. I., and Mokrousov, V. A. An lntroduction to the Theory of Flotation. English translation by J. Leja and G. W. Poling. Buttenvorths, London. 1963.
Leja J. Surface Chemistry of Froth Flotation. Plenum Press, New York.
1982.
Rykaart E. M. and Haarhoff J. Behaviour of air injection nozzles in dissolved air flotation. Water Science andTechnology. Vol. 31, No. 3-4, pp, Walter, J., Wiesmann, U. Comparison of Dispersed and Dissolved Air Flotation for the Separation of Particles from Emulsions and Suspensions Das Gas- und Wasseqach. Wasser,-Abwasser : GWF. Vol. 136, No. 2, p. 53.
1995.
Vrablik, E. R. Fundamental principles of dissolved air flotation of industrial wastes. Industrial Waste Conference Proceedings. 14th) 1959, Purdue University, Ann Arbor, USA, 743-779.
Zabel, T. The Advantages of Dissolved-air Flotation for Water Treatment.
J. Am. Water Works Assoc. Vol. 77, No. 5 , pp. 42-46. 1985.
Zlokarnic, M. Separation of activated sludge from purified waste water by induced air flotation. Water Research, Vol. 32, No. 4, pp. 1095-1 102,1998.
3074-3082, 1996.
25-35, 1995.
QUESTIONS FOR THINKING AND DISCUSSING
The following questions will challenge you and help to reinforce some of the A waste stream from a pulp mill has an average concentration of 7.2 Lbs of water/Lbs of solids. A treatment plant to be designed will have a thickening stage that concentrates the stream to 1.8 Lbs of water/Lbs of solids with the production of a relatively clear overflow. Batch settling tests were conducted on different concentration slurries to ensure that the velocity of settling exceeds the upward flow of fluid at all concentrations normally encountered in the thickening of the specified feed. Tabulated results from these tests are given below Prepare an additional column for this table showing the principles presented in this chapter.
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332 WATER AND WASTEWATER TREATMENT TECHNOLOGIES
6.3 4.3 3.4 2.5
estimated minimum area required for clear overflow in units of 1 toddaylft*
of solids feed. What is the minimum area to be used for design purposes?
4.1 4.8 1.5
3.2 3.9 1.1
2.6 3.1 0.85
1.7 2.6 0.59
Measured Rate Fluid to Solids Lbs Solids Fluid Rising of Settling
P W
I
3 z m
I IO 102 103 104 105 106 107
A R C H I M E D E S N U M B E R , Ar
Figure for Question 2. Plot of Reynolds number, and settling number (Lyashenko number) versus Archimedes number. Use this plot for question 3. It also useful for your own design problem.
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SEDIMENTATION, CLARIFICATION, FLOTATION AND COALESCENCE 333 Determine the settling velocity of spherical quartz particles in water (d = 0.9 mm) using the dimensionless plot of the Lyachshenko and Reynolds numbers versus the Archimedes number in the figure above. The Lyashenko number is the same as the dimensionless settling number. The specific weight of the quartz is 2650 kg/m3, and the temperature of the water is 20" C.
Determine the maximum size of quartz particles settling in water (t = 20' C) that can be described by Stokes' law. What is this particle's settling velocity?
The specific weight of quartz is 2650 kg/m3.
Determine the maximum diameter of spherical chalk particles entrained by an upward-moving water stream with a velocity of 0.5 d s e c . The liquid temperature is t = 10' C, and the specific weight of the chalk is 2,710 kg/lO"
C.
Determine the settling velocity in the water (t = 20" C) for lead particles having an angular shape with d, = 1 mm. The specific weight of lead particles is 7,560 kg/lO" C.
Calculate the sizes of elongated coal particles (ppl = 1,400 kg/m3) and plate-like particles of shale (pn = 2,200 kg/m3) that have the same settling velocities of 0.1 d s e c through water at 20' C.
Determine the settling velocity of solid spherical particles if the particle diameter is d = 25 pm and particle density is 2,750 kg/m3. The density of the liquid phase is 1,200 kg/m3 and its viscosity is 2.4 cp.
Determine the velocity of hindered sedimentation of the suspension considered in question 2 if the concentration of solids in the feed is x = 30%, the density of suspension is 1,440 kg/m3 , and the density of the solid phase is 2,750 kg/m3.
Determine the capacity, cross-sectional area and diameter of a continuous sedimentation tank for liquid suspension clarification in the amount of Q, = 20,000 kghr. The concentration of solids is x, = 50%, the settling velocity is u,, = 0.5 m/hr, and the density of liquid phase is 1,050 kg/m3.
During the spring, the mean temperature over the bottom 3 ft of the lagoon described above is lo" C, whereas the temperature at the surface is about 16"
C. Would you expect good separation of solids? Substantiate your conclusions.
Two primary settling basins are each 100 ft in diameter with an 8-ft side water depth. The tanks are equipped with single effluent weirs located on the peripheries. For a water flow of 10 mgd, calculate the overflow rate, gpd/ftz, detention time, hr, and weir loading, gpd/ft. The overflow rate for a clarifier
334 WATER AND WASTEWATER TREATMENT TECHNOLOGIES
is defined as the surface settling rate, Le., 90 = q/F, where q = volumetric flowrate and F = total surface area of basin.
A thickener handles 80,000 gpd of sludge, increasing the solids content from 2.0 to 8.0 wt.% with 85% solids recovery. Determine the quantity of thickened sludge generated per day.
Develop a list of air pollution issues and discuss possible permitting requirments you may have to face with a treatment plant that relies on both primary and secondary clarifiers for municipal sewerage treatment.
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