∆G = RT ln ƒ 2 ƒ 1 (real gas) (78) Here, ƒ 1 is the fugacity at pressure P 1 . The fugacity may be considered as an adjusted pressure. It is defined so as to coincide with the pressure at low densities: lim P→0 ƒ P = 1 (79) The ratio of fugacity to pressure is called the fugacity coefficient, φ. Thus, the previous equation may be written ϕ≡ ƒ P ⇒ lim P→0 ϕ= 1 (80) 5.4 Chemical Potential Consider a solution consisting of n species A, B, . . . . The Gibbs free energy of the solution is given by G = ∑ k=1 n N k µ k (81) where µ k is the chemical potential of species k, defined by µ k =    ∂G ∂N k    T,P,N j≠k (82) 5.5 Fugacity and Activity The chemical potential is generally a function of temperature, pressure, and composition. It is common practice to write µ A =µ˚ A (T)+RT ln a A (83) where µ˚ A (T) is the standard chemical potential and a A is the activity of species A. The activity is defined as the ratio of the fugacity ƒ A to a standard-state fugacity ƒ˚ A : a A = ƒ A ƒ˚ A (84) Activities and standard states are discussed in greater detail in many texts on chemical thermodynamics (11,12). Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. 5.6 Phase Equilibrium Consider a multicomponent system that separates into two or more phases (denoted I, II, . . .). The criteria for phase equilibrium are T I = T II = . . . (thermal equilibrium) (85) P I = P II = . . . (mechanical equilibrium) (86) (µ A ) I =(µ A ) II = . . . (equilibrium for species A) (87) (µ B ) I =(µ B ) II = . . . (equilibrium for species B) (88) . . . 5.7 Reaction Equilibrium Consider a reaction aA + bB + . . . = . . . + xX + zZ which, as before, can be expressed in the shorthand notation 0 = ∑ k=1 n ν k I k The criterion for chemical reaction equilibrium is ∆G = ∑ k=1 n ν k µ k = 0 (89) Reaction equilibrium may also be expressed in terms of the standard Gibbs free-energy change: ∆G 0 = RT ln K a (90) Here, K a is the equilibrium constant, defined by K a = ∏ k=1 n a k ν k (91) 6 ENGINEERING FLUID MECHANICS Fluid mechanics deals with the flow of liquids and gases. For most engineering applications, a macroscopic approach is usually taken. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. 6.1 Engineering Bernoulli Equation Most engineering problems in fluid mechanics can be solved using the engineer- ing Bernoulli equation, also called the mechanical energy balance. It can be derived from the macroscopic energy balance (see Ref. 13), subject to the following restrictions: (a) the system is at steady state; (b) the system has a single fluid intake and a single outlet; (c) gravity is the sole body force, with constant |g|; (d) the flow is incompressible; (e) the system may include one or more pumps or turbines. Under these conditions, the macroscopic energy balance becomes ∆    P ρ + |g|z + α 2 〈ν〉 2    = W ⋅ s m ⋅ − F ⋅ m ⋅ (92) where P = the fluid pressure 〈ν〉 = the velocity averaged over the cross section of the pipe or conduit α= average velocity correction factor (2.0 for laminar flow and 1.07 for turbulent flow) W ⋅ 2 = rate of work done by pumps or turbines (positive for pumps, negative for turbines) F ⋅ = frictional loss rate Dividing by the acceleration of gravity |g| yields the so-called head form of the Bernoulli equation: ∆    P ρ|g| + z + α 2|g| 〈ν〉 2    = W ⋅ s m ⋅ |g| − F ⋅ m ⋅ |g| (93) Each of the terms in this equation has the dimensions of length. 6.2 Fluid Friction in Pipes and Conduits The frictional loss rate F ⋅ equals the rate at which useful mechanical energy is converted to thermal energy by friction. It is usually computed from an equation of the form F ⋅ m ⋅ = 4ƒ    L D    〈ν〉 2 2 (94) where ƒ is the Fanning friction factor.* In general, the friction factor is a function *This is not the only friction factor in widespread use. Some authors prefer the Darcy-Wiessbach friction factor, ƒ DW = 4ƒ. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. of the pipe diameter D, the surface roughness ε, and the Reynolds number Re, the latter being defined as Re = ρD|ν| µ (95) where µ is the fluid viscosity. In the laminar-flow regime, ƒ = 16/Re. For turbulent flows, a number of charts, graphs, and equations are available to compute the friction factor. The Colebrook equation has traditionally been used, although it requires a trial-and- error solution to find ƒ: 1 √ƒ =−4 log    ε/D 3.7 + 1.255 Re√ƒ    (96) Wood’s approximation (Ref. 13) gives ƒ directly, without a trial-and-error procedure: ƒ = a + b Re −c (97) where a = 0.0235    ε D    0.225 + 0.1325    ε D    (98) b = 22    ε D    0.44 (99) c = 1.62    ε D    0.134 (100) The relations presented in this section were developed for cylindrical pipes or tubes; however, the same equations may be used for noncylindrical ducts if the pipe diameter D is replaced in Eqs. (94–100) by the hydraulic diameter D H : D H = 4 volume of fluid area wetted by fluid (101) 6.3 Minor Losses The relations developed in the previous section apply only to straight pipes or conduits. Most pipelines, however, include bends, valves, and other fittings which create additional frictional losses. These additional losses are often called “minor losses,” although they may actually exceed the friction caused by the pipe itself. There are two common ways to account for minor losses. One is to define an equivalent length L eq which equals the length of straight pipe that would give the same frictional loss as the valve or fitting in question. The total equivalent Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. length L total is the sum of the true length of the pipe and the individual equivalent lengths of the valves and fitting: L total = L pipe + ∑ fitting i (L eq ) i (102) The total equivalent length L total is used in Eq. (94) in place of L to compute the total frictional losses. The second common approach to computing minor losses relies on the concept of a loss coefficient K L , defined for each type of valve or fitting according to the equation F ⋅ m ⋅ = K L 〈ν〉 2 2 (103) A comprehensive listing of typical equivalent lengths and loss coefficients is published by the Crane Company (14). 6.4 Fluid Friction in Porous Media A porous medium is a solid material containing voids through which fluids may flow. The most important single parameter used to described porous media is the porosity or void fraction ε: ε= void volume bulk volume = V voids V voids + V solid (104) Fluid friction in a porous medium of thickness L is usually described by Darcy’s law: F ⋅ m ⋅ = µ ρ L k 〈ν〉 (105) where k is a material property called the permeability. REFERENCES 1. R. B. Bird, W. E. Stewart, and E. N. Lightfoot, Transport Phenomena. New York: Wiley, 1960. 2. M. M. Denn, Process Fluid Mechanics. Englewood Cliffs, NJ: Prentice-Hall, 1980. 3. R. W. Fahien, Fundamentals of Transport Phenomena. New York: McGraw-Hill, 1983. 4. W. M. Deen, Analysis of Transport Phenomena. New York: Oxford University Press, 1998. 5. E. L. Cussler, Diffusion Mass Transfer in Fluid Systems, 2nd ed. Cambridge, U.K.: Cambridge University Press, 1997. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. 6. O. Levenspiel, Chemical Reaction Engineering, 2nd ed. New York: Wiley, 1972. 7. H. S. Fogler, Elements of Chemical Reaction Engineering. Englewood Cliffs, NJ: PTR Prentice-Hall, 1992. 8. L. D. Schmidt, The Engineering of Chemical Reactions. New York: Oxford Univer- sity Press, 1998. 9. F. P. Incropera and D. P. DeWitt, Fundamentals of Heat and Mass Transfer, 3rd ed. New York: Wiley, 1990. 10. D. R. Lide (ed.), CRC Handbook of Chemistry and Physics, 80th ed. Cleveland, OH: CRC Press, 1999. 11. I. M. Klotz and R. M. Rosenberg. Chemical Thermodynamics: Basic Theory and Methods, 3rd ed. Menlo Park, CA: W. A. Benjamin, 1972. 12. K. Denbigh, The Principles of Chemical Equilibrium, 3rd ed. Cambridge, U.K.: Cambridge University Press, 1971. 13. N. De Nevers, Fluid Mechanics for Chemical Engineers, 2nd ed. New York: McGraw-Hill, 1991. 14. Flow of Fluids Through Valves, Fittings, and Pipe, Crane Technical Paper 410. Chicago: The Crane Company, 1988. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. 10 Biotechnology Principles Teresa J. Cutright The University of Akron, Akron, Ohio 1 INTRODUCTION As mentioned throughout this text, waste minimization encompasses recycling/ reuse, waste reduction (material substitution, process changes, good housekeep- ing, etc.), and waste treatment on-site (1,2). Biotechnology has a direct impact on, and applicability to, an engineer’s ability to achieve waste minimization goals. It has had demonstrated success with recycling programs via the generation of biogas as an alternative fuel. Bioremediation approaches have also been used for: point source reduction via biopolishing (3) and individual stream treatment (4); by-product utilization (5); material substitution (6); facilitation of new enzy- matic/metabolic pathways to produce “cleaner” organic substances (7); and end-of-pipe treatments (8–10). This chapter will highlight a few of the biotech- nology approaches to waste minimization. When utilizing any biotechnology, it is important to remember that the primary function of a microorganism is not to destroy man’s unwanted contami- nants. Instead, a microbe must reproduce itself and maintain its cellular functions. To that end, as shown in Figure 1, every microorganism must: (a) protect itself from the environment, (b) secure nutrients (catabolism), (c) produce energy in a usable form (catabolism), (d) convert nutrients/food into cellular material (anab- olism); (e) discard unnecessary waste products, and (f) replication genetic infor- Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. FIGURE 1 Overview of general cellular functions applicable to all living cells. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. mation. It is an added benefit to mankind that the result from the microbial metabolism of substrates (i.e., step d), that the unwanted contaminants are degraded. Once it was realized that microorganisms could degrade unwanted contaminants, engineers started to manipulate the surrounding environment to ensure that the microbes would thrive and utilize the contaminant as the substrate. Engineers currently use microorganisms to treat drinking water, municipal wastewater, and various industrial effluents. Usually the chemical and petrochem- ical industry is considered the only “real” contributor to industrial effluent (11). However, as shown in Table 1, more than just the chemical industry utilizes microorganisms for the treatment of waste on-site. Regardless of whether the microorganisms are being used for cleaning drinking water, or municipal or industrial wastewaters; for end-of-pipe treatment at contaminated sites; or for waste minimization applications, certain key aspects apply (75). The following sections will outline the key aspects applicable to any biological treatment, provide a brief description and design criteria for the common waste minimization technologies, as well as highlight a few of the TABLE 1 Some of the Industries that Utilize Biological Treatment for the Reduction of Waste Industry References Coal processing 12–14 Cosmetics 15,16 Dyes 16–20 Fertilizer plants 21,22 Food 23,24 Citric acid 23,24 Dairy 25–30 Poultry 31–34 Slaughterhouses 22,35,36 Vegetables 37,38 Heavy metals processing 13,39–45 Oil processing and refineries 46–49 Paint 50–53 Paper 6,21,22,54–57 Pesticides 13,18,58–60 Pharmaceutical 61–66 Printing 19,20,67,68 Soap 46,69 Tannery 22,70,71 Textiles 3,18,72–74 Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. innovative of bioprocesses that enable the selective removal of unwanted chem- icals in product streams. 2 KEY ELEMENTS ESSENTIAL TO ALL BIOLOGICAL TREATMENT METHODS Several basic biological requirements are essential for any biological treatment process to be successful. They are based on the principles required to support all ecosystems and include the presence of: appropriate microbes for degrading the contaminant(s), substrate for carbon and energy source, required terminal electron acceptor (TEA), inducer to facilitate enzyme synthesis, nutrients for supporting microbial growth, microbes to degrade metabolic byproducts, environmental conditions to minimize growth of competitive organisms (76–78). These factors will be discussed below. 2.1 Adequate Microbial Population The primary requirement for any successful biological treatment or waste mini- mization strategy is the presence of an adequate microbial population. Luckily for environmental engineers, Mother Nature has supplied a wide variety of microbes to select from and to cultivate. The organisms are subdivided into different categories based on their metabolic capabilities and/or requirements. Table 2 contains the classifications based on the microbial carbon source, energy source, and respiration mode. If a contaminant can only be degraded in the presence of another organic material that serves as the primary electron source, then co- metabolism is occurring. If the interaction of the two organisms is nonobligatory, then it is a synergistic relationship. Mutalism occurs if the interaction is beneficial yet obligatory. Since microbes are very versatile, it is important to remember that they may belong to more than category. The microbe’s versatility may also enable it to treat more than one par- ticular type of contaminant. As shown in Table 3, different species of Pseudo- monas have demonstrated success at reducing agricultural, heavy metal, food, and solvent wastes. In each instance, the primary requirement for successful treatment is the presence of an adequate population. Researchers have deter- mined that a microbial count of 10 3 –10 8 cfu/liter, 10 4 –10 7 cfu/g would be adequate for groundwater and soil applications, respectively (77,79–81). There- fore, to ensure a successful biological treatment for waste minimization, a minimum of 10 8 cfu/liter would be recommended. If the contaminant concen- tration or toxicity increases, the microbial population will have to increase as well. If the increase in biomass concentration does not result in the desired treatment efficiency, the microbes being utilized may have to be changed to another source. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. [...]... kd (8) The form given in Eq (8) is the operating substrate design equation used by most wastewater treatment facilities This form allows, for a fixed effluent substrate concentration and cell age, the hydraulic residence time and required biomass concentration to be determined 3.1.3 Typical Design Values and Waste Applications As stated previously, the average initial biomass concentration for activated... conventional municipal wastewater They have also been used for dairy waste, nonpesticide agricultural waste, pharmaceutical waste, and low-strength singular solvents in industrial pretreatment Activated sludge is not effective for exotic organic chemicals such as pesticides, high-strength solvents, elevated heavy metal concentrations, alkaline waters, or mixed wastes Copper, nickel, and zinc at concentrations... suspended growth process is the activated sludge system used for the majority of industrial pretreatment and municipal wastewater treatment plants The more common orientations for activated sludge include completely mixed, plug flow, oxidation ditch, contact stabilization, and sequencing batch reactors (106,107) Each configuration requires that the appropriate biomass, TEA level and source, pH, and contaminant... is sometimes needed at higher quantities and can be supplied by the contaminant for heterotrophic microorganisms There are three categories of nutrients based on the quantity and essential need for them by the microorganism: macro, micro, and trace nutrients (89,90) For example, the macronutrients carbon, nitrogen, and phosphorus are known to comprise 50%, 14%, and 3% dry weight, respectively, of a characteristic... increased and the redox potential becomes more negative For an optimal aerobic environment, the redox potential must be greater than 50 mV (78,105) If nutrient additions or deviations in pH change the redox potential the necessary TEA/ respiration mode may not be present for the desired degradation reaction 3 COMMON BIOPROCESSES USED FOR WASTE CONTROL 3.1 Suspended Growth The most widely studied and used... systems for treating most industrial pretreatment waste streams will decrease unless the waste streams are segregated and the biomass acclimated to the specific waste present (111,112) 3.2 Attached Growth Attached growth systems encompasses processes from biofilms to slime layers Biofilms are used for facilitating biooxidation reactions of contaminated gas emissions Slime layers are utilized for biofiltration... scale (for exotic chemicals) and full scale for municipal-industrial pretreatment At the pilot scale, TFs in different orientations have been effective for both inorganics and organic constituents One study demonstrated a 94% reduction of manganese, while another study degraded 97% of a 300-ppm styrene waste stream (115) TFs have been used for over 30 years as a secondary or tertiary treatment for municipal... treatment implemented for minimizing waste in the dairy, milk, and food processing industries (107) They are similar to TFs in design, operation, and use HLR, OLR, and are still the key design and operating parameters The primary difference is that biotowers use plastic media instead of the stones or rocks used in TFs By changing the media material to plastic, higher hydraulic and organic loading rates... TO WASTE MINIMIZATION 4.1 Microorganisms for Material Substitution or By-product Utilization Two of the key approaches to waste minimization are material substitution and by-product utilization (138,139) If the raw material that produces the waste can be substituted with one that either minimizes the waste or yields a viable product, then the waste minimization goal has been realized Furthermore, waste. .. to identify and employ the enzyme required for degrading the polymer (171) For instance, cellulose-based and PHA polymers are easily degraded by Hyphomicrobium sp., Rhodococcus rhidochrous, and Trichoderma reesei (172) This approach has also been used for the production and eventual degradation of other relatively new biopolymers such as polyhydroxybutyrates (173,174) 4.1.3 Conversion of a Waste Stream . metals processing 13,39–45 Oil processing and refineries 46 49 Paint 50–53 Paper 6, 21,22,54–57 Pesticides 13,18,58 60 Pharmaceutical 61 66 Printing 19,20 ,67 ,68 Soap 46, 69 Tannery 22,70,71 Textiles. may not be present for the desired degradation reaction. 3 COMMON BIOPROCESSES USED FOR WASTE CONTROL 3.1 Suspended Growth The most widely studied and used suspended growth process is the activated sludge. liquids and gases. For most engineering applications, a macroscopic approach is usually taken. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. 6. 1 Engineering Bernoulli Equation Most engineering