epc_fa2011_lecture_1

epc_fa2011_lecture_1 - Course Overview ‐Introductory...

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Unformatted text preview: Course Overview ‐Introductory level course in Environmental Engineering for CE major ‐Application of engineering principles and practices to one or more elements of the environment to protect human and ecosystem health. ‐Prerequisites ‐ General chemistry (CHEM 141: Principles of Chemistry) ‐ Calculus (MATH 207: Calculus I) ‐ Principles of physics (PHYS 231N: University Physics) 1 Course Overview – Component Approach Mass Balance Water Treatment Air ‐‐ Pollution ‐‐ Model ‐‐ Control Water ‐‐ Physical ‐‐ Biological ‐‐ Chemical ‐‐ Flow Model ‐‐ Flux ‐‐ Transport Wastewater Treatment Solid Waste Management Hazardous Waste Management 2 1 Environmental Engineering principles Mass and energy balances Basic chemistry Chemical kinetics and thermodynamics Basic microbiology Microbial thermodynamics and kinetics Simple hydraulics Flow models Equilibrium at environmental interfaces Mass transfer concepts Particle dynamics 3 We’ll Learn to Become familiar with the broad scopes of environmental fields and problems Understand and apply environmental engineering principles Become familiar with a quantitative, problem-solving approach Understand and design basic pollutant transport, transformation and fate in the environment (W/WW, Air, S/H Waste) Understand and design biochemical and physical processes in natural systems Investigate actions to prevent pollutant release 4 2 Environmental Engineering is Concerned with Protecting environments from the damaging effect of human activities Protecting people from the environmental danger of poor water, air and soil quality Find and design proper means of handling anthropogenic wastes into the environment "Environmental Classes“ - Atmosphere - Terrestrial (=land) - Aquatic 5 Inter-Dependency among Classes “One solution to One problem" (=Discrete event) vs. “Many solutions to Many problems" (=Parallel & Continuous events) 6 3 Environmental concerns - Why recent interests? Greater and ever-increasing population density in U.S. and around the world - Increased manufacturing, energy, resources use in past 100 years - Greater amount of wastes due to life style changes - Increases in synthetic wastes that do not break down easily Natural system's ability to assimilate wastes without degrading its baseline quality has been exceeded Politically popular -- strong "politically correct" element both in the politics and social awareness, yet real actions for environmental concerns are seldom exercised or are often over-exercised out of context 7 Local Perspectives Nutrient enrichment (=Eutrophication) - Chesapeake Bay “Dead zone” and Red tide recurrences in local waterways Heavy metals (TBT, Cu, Zn) - in waters around shipyards Resuspension of sediments by dredging Kepone (pesticide) in James River from Hopewell, VA, 1975 Elevated levels of ozone and CO (carbon monoxide) in Hampton Roads area Fly-ash and groundwater issue in Battlefield golf course in Chesapeake 8 4 Conceptualization vs. Methodology When you're dealing with an environmental problem, you need to think about the problem in two different perspectives; a forest mode and a tree mode. Any given environmental problem is normally interconnected with other environmental elements. Without clearly understanding problem's boundary conditions (=forest), you'd likely to be deal with only a specific element (=tree), which does not necessarily be the best solution in most cases. Always do the proper problem conceptualization first before jumping into existing methodologies and "just do it." If you can come up with a proper and clear conceptualization on the problem you're dealing with, you're about 80% done in solving the problem! 9 Checklist - Conceptualization for an Environmental Problem What is the problem? Why should I conceptualize it? What would be the objective(s)/deliverable(s) that I try to achieve? What is(are) best approach(s)? What kind(s) of methodology(s) is(are) currently available/feasible? Why a particular methodology(s) need to be implemented? Any alternative(s)? Who will be affected by implementing the objective(s)? Who will the recipient(s) of the benefit accomplished by the objectives? 10 5 Risk-based Approach & Design Optimum dose of chlorine for disinfecting drinking water can be determined by balancing "risk vs. benefit" relationship that maximizes the level of pathogen removal and minimizes disinfection by-product (DBP) concentration in treated drinking water. 11 Various Regulatory Approaches (applicable in design framework) Quality-based standards specifies quality of receiving body (air or water) good idea in principle hard to implement and difficult to enforce Effluent-based standards specifies quality of effluent stream not as flexible and can be over-restrictive much easier to implement and enforce Treatment-based standards specifies type of treatment required Treatment Technique (TT) in the Surface Water Treatment Rule (SWTR) is a good example. TT is a required process intended to reduce the level of a contaminant in drinking water, and often does not explicitly specify the required quality. 12 6 Key Environmental Regulatory Agencies -U.S.EPA Region 3 -Virginia Department of Environmental Quality (VDEQ) 13 7 Mass Balance Material Balance/Budget is based on the law of conservation of mass (=neither created nor destroyed). It's a quantitative description of all materials that enter, leave, and accumulate in a system with defined boundaries. What is going in [to a system] got to be coming out, at the same amount. If less came out, then the difference must be still in the system. Rate of Accumulation of mass within the system boundary = Rate of flow of mass into the system - Rate of flow of mass out of the system + Rate of mass generation within the system Accumulation = Input - Output + Generation/Reduction Accumulation = M(in) – M(out)+ Generation/Reduction Accumulation = Source - Sink + Generation/Reduction Frequently used in solving environmental engineering problems. The balance is usually made in terms of mass or mass flow rate Steady-State (SS) assumption is used often to simplify the problem = accumulation term is zero (=no variations in rate and concentration over time). ∂C A ∂t = 0 (i.e., accumulation = 0) Mass Balance Analysis Z QCA|z+Δz QCA|y Δy QCA|x QCA|x+Δx Δz X QCA|y+Δy Δx Y QCA|z Let's consider a 3-D system defined by x-,y-,z-boundaries. We can set up a mass balance for this system with sources from all three directions (QCA). Then mass rate over time for this system can be expressed in terms of the mass rates of accumulation, source, sink, and generation. ∂C A ΔV ∂t = ⎡(QC A ) x + (QC A ) y + (QC A ) z ⎤ ⎢ ⎥ ⎣ (inflow) ⎦ - ⎡(QC A ) x + Δx + (QC A ) y + Δy + (QC A ) z + Δz ⎤ ⎢ ⎥ (outflow) + (generation/reduction) ⎣ r A ΔV ⎦ where CA = mass concentration of A, [M/L3] mg/L, g/m3 Q = vA = volumetric flow rate in a single direction, [L3/T] V = volume, [L3] r = mass rate of generation/reduction, [M/L3 T] Also, flow rate for each direction can be expressed as Q x = v x ⋅ Δy Δz Q y = v y ⋅ Δx Δ z Q z = v z ⋅ ΔxΔy By taking the limit as Δx, Δy, Δz approach 0, C ⋅ v ⋅ Δy Δz C ⋅ v ⋅ Δy Δz ∂C A = A x ‐ A x ΔxΔy Δz ΔxΔy Δz ∂t x + C ⋅ v ⋅ ΔxΔy C A ⋅ v z ⋅ ΔxΔy ‐ A z ΔxΔy Δz ΔxΔy Δz z + C A ⋅ v y ⋅ ΔxΔz ΔxΔy Δz x + Δx + rA z + Δz ‐ y C A ⋅ v y ⋅ ΔxΔz ΔxΔy Δz y + Δy ΔxΔy Δz ΔxΔy Δz ∴ ∂C A ∂t = ‐ C A ⋅ v x ⋅ Δy Δ z ΔxΔy Δz ‐ x + Δx C A ⋅ v y ⋅ ΔxΔz ΔxΔy Δz ‐ y + Δy C A ⋅ v z ⋅ Δx Δ y Δx Δ y Δ z Also, if limits of Δx, Δy, Δz approach 0, they’ll become ∂x, ∂y, ∂z ∂v y ∂C A ∂v ∂v C A ‐ z C A + rA = ‐ x C A ‐ ∂t ∂x ∂y ∂z or simply expressing the rate of changes in x, y z directions, ∂v y ∂C A ∂v ∂v C A + z C A ± rA = x C A + ∂y ∂t ∂x ∂z + rA z + Δz Mass Balance Approach to Problem Solving There is no general formula for solving mass balance problems since each case you might want to calculate the mass balance at a different location [of the system] or time. Thus, the solution technique essentially involves experience, common sense, and engineering intuition. For problems that are non-trivial (a.k.a. complex systems with a lot of things going in, reacting with, and coming out), a sketch or visual representation of all the 'mass' elements over the system, i.e., a mass diagram can be extremely useful -- make a habit to draw one each time if you're in a doubt. The following are well known good steps for drawing a mass diagram and calculating a mass balance: 1. Summarize and list all flow rates, concentrations, kinetic reaction rates, coefficients, etc. -- if you clearly summarize all components, you're about 80% done! Usually the problem description (or information in that sense) is given in a narrative term, and it is quite difficult to grasp what is(are) needed to be analyzed unless you spell them out first. 2. Select a convenient unit that you'll carry out all calculations. 3. Calculate and convert all flow rates, concentrations, and so on, which can be determined from the information provided (or measurements) without actually making the balance -- not yet! 4. Now, draw/sketch a mass diagram -- define system boundaries for inflow & outflow points of interests, and draw arrows, showing all flow directions and concentrations, and most of all indicate each unknown within/outside of the system by a question mark. 5. Decide on particular solution technique; • Is the system at steady-state? • Are you going to select a particular time interval? • Are you going to derive the balance in terms of unit mass input? • Etc. 6. Identify any conservative components (=Material or Mass that does not react or decay/oxidize). 7. List all chemical and biological reactions, if there is any. 8. Now, write the mass balances -- these may include a balance on the total mass and a balance for each of the component materials involved in the problem. 9. Extract as many equations as there are unknowns -- from algebra we know that we must have as many independent equations as we have unknowns. 10. Make assumptions, if any are necessary, that make the problem simpler -- experience will be required to do this wisely. 11. Solve the resulting equations simultaneously, the "crunching" part. 12. Make a conclusion of your analysis -- always *re-state* the original problem and provide your answer correspondingly to the original problem condition(s). Just giving a number/answer does not mean anything to those who read and try to understand the significance of your analysis result. If possible, always state your conclusion in form of a future recommendation/action item. Mass Balance Example Question) A local industry, let's say 'Downtown Inc.,' discharges its liquid waste into a river that has a minimum flow rate of 10 ft3/s. The major pollutant in the waste is a non‐reactive organic material called 'X.' The waste stream has a flow rate of 0.1 m3/s, and the concentration of X in the waste stream is 300 g/m3. Hence another upstream pollution (by a similar industry, let's say 'Uptown LLC.') has caused a concentration of 20 g/m3 X in the river upstream of this industry (='Downtown Inc.') discharge under the minimum flow rate condition. The state regulatory agency, VDEQ, has set a maximum limit of 100 mg/L X allowed in the river. Assume that complete mixing occurs in the river. Will 'Downtown Inc.' industry be able to discharge its waste to the river without additional pre‐treatment? Mass Balance Problem Solving Approach 1. Summarize and list all flow rates, concentrations, kinetic reaction rates, coefficients, etc. ‐‐ if you clearly summarize all components, you're about 80% done! Usually the problem description (or information in that sense) is given in a narrative term, and it is quite difficult to grasp what is(are) needed to be analyzed unless you spell them out first. System boundary The portion of river receiving the waste stream discharge from Downtown Inc. that containing a non‐reactive organic material called 'X.' River upstream and Downtown Inc.'s waste stream discharge are sources (=inputs) to the system and the mixed river water is the sink (=output). Whatever is happening inside of the system constitutes the decay/generation term. Source term : From the river upstream Q(u) = Flow rate = 10 ft3/s C(u) = Concentration = 20 g/m3 Source term : At discharge point (Downtown Inc.) Q(X) = Flow rate = 0.1 m3/s C(X) = Concentration = 300 g/m3 Decay/Generation term: In the discharge‐receiving portion of river Noup, since the pollutant 'X' is a non‐reactive organic material and will not decay or generate in the river water R = Decay (=Reduction) = 0 G = Generation = 0 Sink term : Downstream of discharge point (Downtown Inc.) Q(d) = Flow rate = Unknown C(d) = Concentration = Unknown Will the mixed concentration at downstream be below/above the regulatory maximum limit of 100 mg/L? 2. Select a convenient unit that you'll carry out all calculations Since the regulatory agency's concentration unit is in mg/L, which you have to compare your result to at the end of the analysis, let's use mg/L in this mass balance analysis. Also, river's flow rate is given in ft3/s ‐‐ let's use ft3/s as the unit for flow rate throughout this analysis. Hence it is always a good idea to use system's unit(s) as the default unit(s) of your analysis. 3. Calculate and convert all flow rates, concentrations, and so on, which can be determined from the information provided (or measurements) without actually making the balance ‐‐ not yet! In this particular analysis, pretty much all information was provided. However we decided to use mg/L as the concentration unit and ft3/s as the unit for flow rate, let's convert them first. Concentration: (1 g/m3 = 1 mg/L) C(X in the Downtown Inc.'s waste stream) = 300 g/m3 = 300 mg/L C(X in the upstream of Downtown Inc.) = 20 g/m3 = 20 mg/L Flow rate: (1 m3/s = 35.315 ft3/s) Q(waste stream of 'X' from 'Downtown Inc.') = 0.1 m3/s = 3.532 ft3/s 4. Now, draw/sketch a mass diagram ‐‐ define system boundaries for inflow & outflow points of interests, and draw arrows, showing all flow directions and concentrations, and most of all, indicate each unknown within/outside of the system by a question mark or simply in a skeleton form, 5. Decide on a particular solution technique(s) • • • • Is the system at steady‐state? Are you going to select a particular time interval? Are you going to derive the balance in terms of unit mass input? Etc. A material balance on 'X,' 'source = sink' or 'input = output,' will be analyzed for a unit interval of 1 second (=ft3/s), and we'll consider the system as a Steady‐State, i.e., no accumulation within the system. 6. Identify any conservative components Since the pollutant 'X' is a non‐reactive organic material, we'll treat this pollutant 'X' as a conservative component ‐‐ only mixing will occur, and there will be no loss of mass due to decay. 7. List all chemical and biological reactions Again, this pollutant 'X' is a conservative component, no chemical and biological reactions within/outside of the system is considered. If you're dealing with a material that goes through any chemical and biological reactions, you should analyze for its mass rate changes within/outside of the system, respectively, and count them all at each boundaries for your mass balance. 8. Now, write the mass balances ‐‐ these may include a balance on the total mass and a balance for each of the component materials involved in the problem Input(upstream) + Input(discharge of X) + Decay/Generation(system) = Output(downstream) 9. Extract as many equations as there are unknowns ‐‐ from algebra we know that we must have as many independent equations as we have unknowns Using the mass balance we defined right above, Q(U)C(U) + Q(X)C(X) + R/G(System) = Q(d)C(d) [ 10 ft3/s * 20 mg/L ] + [ 3.532 ft3/s * 300 mg/L ] + [ 0 ] = Q(d)C(d) Thus, in this case we have only one equation for one unknown, the downstream concentration after the mixing, C(d). Because Q(d) is simply the sum of Q(u) + Q(X). 10. Make assumptions, if any are necessary, that make the problem simpler ‐‐ experience will be required to do this wisely In this case, a Steady‐State assumption, i.e., no accumulation within the system, is used since the material 'X' is non‐reactive conservative. All inputs will be completely mixed at the Downstream Inc.'s discharge point. 11. Solve the resulting equations simultaneously, the "crunch" part First, let's find a combined flow rate at the downstream of Downstream Inc.'s discharge point. Q(d) = Q(U) + Q(X) Q(d) = 10 ft3/s + 3.532 ft3/s = 13.532 ft3/s Next, calculate the completely mixed concentration of the material 'X' at the Downstream Inc.'s discharge point. [ 13.532 ft3/s ] C(d) = [ 10 ft3/s * 20 mg/L ] + [ 3.532 ft3/s * 300 mg/L ] C(d) = { [ 10 ft3/s * 20 mg/L ] + [ 3.532 ft3/s * 300 mg/L ] } / [ 13.532 ft3/s ] C(d) = [ 200 ft3/s‐mg/L + 1059.6 ft3/s‐mg/L ] / 13.532 ft3/s C(d) = 93.083 mg/L Well, not so much of crunching in this case. However if you're dealing with a number of simultaneous equations, things could be quite hairy. Imagine solving for a reactive pollutant concentration profile in the entire reach of the James River with a gazillion number of inputs along with the river, counting all its interactions with land/groundwater/air as well as any rainfall/runoff events from contributing watersheds. (Actually, this is a typical real‐world, standard situation for calculating common water quality constituents such as dissolved oxygen (DO) and biochemical oxygen demand (BOD)) Chances are that you have to solve more than 1000+ equations simultaneously for that. 12. Make a conclusion of your analysis ‐‐ always *re‐state* the original problem and provide your answer correspondingly to the original problem condition(s). Just giving a bunch of numbers/answers does not mean anything to those who read and try to understand the significance of your analysis result (i.e., "That sounds like Greek to me" situation). Also, if possible, always state your conclusion in form of a future recommendation/action item. Following illustrates a typical, standard "engineering" conclusion for this example problem. (bracketed headers are added only for illustration purpose ‐‐ normally, you don't include them in your conclusion) [Original problem statement] A local industry, Downtown Inc., discharges its liquid waste stream that containing a non‐reactive organic material 'X' into a river. [Analysis/Results] Based on a mass balance analysis, at downstream point of interest (POI), the concentration of material 'X' in the river will be 93.083 mg/L. This concentration, 93.083 mg/L, is lower than the state regulatory maximum limit of 100 mg/L, and no additional pre‐treatment is required for the discharger, Downstream, Inc. [Discussion] However, due to discharger's waste stream, the in‐water concentration of material 'X' in the river increases from 20 mg/L to 93.083 mg/L which is a substantial 73.083 mg/L jump and there's only a small margin of safety of 6.917 mg/L for the regulatory compliance. [Recommendation/Action item] Thus, the analysis further recommends that Downstream Inc. would consider a small‐ scale in‐situ pre‐treatment option to dilute its waste stream or more fundamentally, reduce the amount/concentration of waste stream as a long‐term solution and contingency. Well, in this example, we use a mass balance approach for water quality problem. However the same mass balance approach can be applied to all other situations if you know the mass and rate of the material(s) that you're dealing with. Hydrologic Cycle ‐ Movement of water in the earth's atmosphere, on the surface, and below the surface ‐‐ a process powered by the sun's energy. ‐ Hydrologic cycle becomes a single most dominant mechanism for pollutant transports in our environment. 1 2 Examples of Pollutant Transport Triggered by Hydrologic Cycle - 1 Urban environment Runoff predominates pollutant transport (little infiltration due to a high percentage of impervious surface areas) Quick rise and subsidence in runoff flow characteristic High concentrations of substances associated with automobiles (oil, gasoline, metals) and trash High concentration of nutrients from populated residential areas (lawn and garden) 3 Examples of Pollutant Transport Triggered by Hydrologic Cycle - 2 Rural/Agricultural Anvironment Runoff and infiltration are both equally important Contain nutrients, herbicides, insecticides, fungicides, animal wastes – deposition to environment and longer residual life become a major problem Erosion/Sedimentation processes are equally important 4 Examples of Pollutant Transport Triggered by Hydrologic Cycle - 3 Vicinity of Soild Waste Disposal site/Landfills 5 Water Sources and Uses - 1 Drinking Water Sources 95% of available freshwater in USA is groundwater. For 45% of USA population, main source of the drinking water comes from the groundwater. For approxmately 95% of rural population in USA, main source of the drinking water comes from the groundwater (such as wells and aquifers). 6 Water Sources and Uses - 2 Domestic Water Use A typical single family dwelling in the urban area An annual average including seasonal variations 7 Water Sources and Uses - 3 Typical Municipal Water Use Commercial or Industrial (Nondomestic) Cooling water Food Processing Public Services --public buildings, parks, street cleaning, fire protection 8 Water Sources and Uses - 4 Typical Municipal Water Use Unaccounted System Losses and Leaks -- 15% of municipal water cannot be accounted Example) 1.6 MGD (Million Gallons per Day) is lost out of 17 MGD due to meter inaccuracies, cracks and leaks (Portsmouth, VA, 2001 average water use) 9 Properties of Water - 1 What's in Water? 'Pure' water = water vapor, H2O at pH 7 Water is a polar molecule, and dissolves polar substances Real water has dissolved gases picked up from atmosphere -- CO2, O2, N2, SO2, NO2 Surface water picks up: -- traces of organics from decaying plants, animals, agricultural runoff, wastewater, hazardous waste Groundwater picks up: -- dissolved minerals such as 'salts' Ca, Mg, Na, K, sulfates (SO4-2), nitrates (NO3-), carbonates (CO3); traces of As, Cu, Pb 10 Properties of Water - 2 Most abundant chemical in biosphere! (covers 70% of planet ) Density (max = 999.975 kg/m3 at 4°C) -- only common substance that expands when it freezes Heat capacity (4.184 kJ/kg °C) -- higher than any other liquid (heats and cools slowly) -- protects life from rapid thermal fluctuations Heat of vaporization (2258 kJ/kg) -- one of highest of all liquids -- important in distributing energy through atmosphere Water as solvent -- dissolves more substances than any other common solvent -- as a result, water pollution is a common problem 11 ...
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