UMD ENCE 310 - Lecture One: Introduction to Environmental Engineering

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Lecture One: Introduction to Environmental EngineeringRoots of environmental engineering are from sanitation and public healthJohn Snow’s Theory – cholera infected baby diaper was being washed upstream of the broad street well. This is the first proof the water is a vehicle for diseaseMIT – first college for joint education in engineering, chemistry, and biologySilent Spring – credited with launching the environmental awareness movementRelationship: Public Health -------> (waste) ----> Environmental Health -----> (resources) ----> back to public healthEnvironmental Engineering: application of science and technology to: protect human health from effects of environment, protect human health from human activities, protect environmental health from human activitiesHuman population is growing exponentially and the amount of resources needed to sustain life exceeds what is available on earth.Grand Challenges for Engineering: making solar energy economical, obtaining energy through nuclear fusion, carbon sequestration, restoring urban infrastructure, access to clean water, secure cyberspace1/3 of earths population is in water-stressed regions.Aging water and wastewater infrastructure = water main breaks, Emerging contaminants, High Energy Consumption (wasting)Trace contaminants in water cycle: surface water and drinking water ---> wastewater -----> back to surface and drinking waterSuperfund Sites: highly contaminated (and abandoned) sitesLove Canal – hooker chemical buried toxic waste, then neighborhood was built, kids born in area had birth defectsHydrofacking – injection of high pressure water, chemicals, gases down into earth and then horizontally drilled which causes rock layers to crack and release natural gas up the well.Desalination – necessary for much of our water accessLecture Two: Risk Assessment and Chemistry ReviewEnviromental risks deal with incremental risksRisk Assessment:1. Hazard Identification: gather site specific data, preliminary assessment of potential human and ecosystem exposureidentify possible contaminants, contaminant concentrations, site characteristics2a. Dose-Response Assessment: Carcinogens versus non-carcinogens (causes cancer versus doesn’t cause cancer)2b. Exposure Assessment: Direct and indirect exposure of contaminants (drainage and runoff, bioaccumulation, leaching, ingestion, inhalation)3. Risk Characterization: using data to determine likelihood of humans experiencing forms of toxicityAspects including socioeconomic, political, and economic pressures and concerns4. Risk Management: balancing human and environmental health risks with costs of controlChemistry Concept Review:Stoichiometry – balancing chemical reactions to determine and predict mass of products and reactants and equilibrium statesEquilibrium – reaction is not favored to left or right side at that moment k = [C]^c [D]^d / [A]^a [B]^b [x] = mol / LSolubility, Acid Base reactions, Solubility of gases in water (oxygen and CO2) involves Henrys Law (C = K’P) – BOD levels need to be monitored for organisms in water (biological oxygen demand)Kinetics – how fast a reaction occursRegulations on Environmental Health => Safe Drinking Water Act, Clean Water Act, Clean Air Act, Resource Conservation and Recovery ActLecture Three: Mass and Energy BalanceConservation of matter – materials and mass balances is used to show that matter is not created or destroyedWater Mass Balance: hydrologic budgeting = amount water extracted from aquifers is usually much higher than the amount going in ( irrigation >>> percolation or recharge)Density = mass / volume; Concentration = grams / liter; flow rate = mass per timeACCUMULATED = RATE IN – RATE OUT + PRODUCED – CONSUMEDBlack Box -> 1. No Reaction and no accumulation: influents going in, effluents going out must be equal (this means its at steady state)2. No Reaction with Accumulation – mass flow rate in not equal to mass flow rate out (unsteady state)3. Reaction with No Accumulation – fluid flow is at steady state, but mass flow has a produced / consumedEnergy Conservation – energy is not created or destroyed, but can be changed into unusable energyEfficiency = useful energy out / energy inNonrenewable energy sources = coal, natural gas, oil, nuclear; Renewable = hydropower, solar, waste, biomass, wind, geothermLecture Four: ReactionsReaction Rate = how fast a reaction is happening determined by how fast concentrations are changingHomogeneous solution – reaction takes place in a single phase, but heterogeneous solutions, reaction takes place at surfaces b/w phasesZero Order Reactions – reaction rate does not depend on concentrations of reactants ( k = mass or mol / (volume x time) )First Order Reactions – reaction rate is dependent on concentration of one of the reactants ( k = inverse time)Second Order Reactions – reaction rate is depending on concentration of the reactants ( k = inverse concentration * inv. Time)Linear Plots: 0th order – time versus concentration, 1st order – time vs. ln(concentration), 2nd order – time vs. 1/concentrationLecture Five: ReactorsCompletely mixed system – every drop of fluid is homogeneous with all other dropsBatch Reactors: material added to tank, stirring causes reaction to occur, then reactor is drainedPlug flow reactor: fluid flows through reactor is sequence, no lateral mixing, composition / concentrations vary throughout length of reactorContinuous Flow Stirred Tank Reactor / Completely Mixed Flow Reactors: materials flow into tank, mixed, then flow out continuously. Composition of effluent is the same concentration as everywhere in the tank (if influent is consistent, then effluent is consistent)Hydraulic retention time – time that any fluid will remain in a reactor ( t = V/Q )Ideal reactor – all fluid particles have same retention timeBatch Reactors – inexpensive, easy to operate (especially with small volumes of wastewater)Conservative substance – concentration is linear (conservative implies that nothing is produced or consumed)Non conservative substance – concentration is exponential, doesn’t follow any “pattern”Plug Flow Reactors – pipes and long narrow riversConservative substance addition will lead to step increase in concentrationPulse of conservative substance will flow through and flow out of the reactorLn(concentration) will be linearCompletely Mixed Flow Reactors – best for flow rates too large for batch

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