CH221 Intro to Environmental Engineering

Prof. Benito C. Shea, MSc Mgt. Engg.

Reference

Introduction to Environmental Engineering and Science, International Edition, 2nd Ed., Gilbert M. Masters, 1998, Prentice-Hall International Inc.

Course Description

Introduction to Environmental Science and Engineering

•An introduction to the array of major scientific and engineering issues related to environmental quality on a local, regional, and global scale. •Fundamental aspects of major environmental problems will be addressed with an overall focus on the dynamic interplay among the atmosphere, biosphere, geosphere, and hydrosphere. •Underlying scientific principles based on biology, chemistry, and physics. •Engineering solutions to major environmental problems.

Course Objectives

At the end of the course, the students are expected to know the basic on:

1. Mass and Energy Transfera. Unit of measurementb. law of conservation of mass and energyc. Materials Balanced. Energy Fundamentals

2. Environmental Chemistrya. Stoichiometryb. Enthalpy of chemical systemc. Chemical equiliria

3. Mathematics for Growtha. Risk Assessment

4. Global Atmospheric Change5. Water Pollution6. Air Pollution7. Solid Waste and Resource Recovery

Main Topics

1. Water Pollution - Surface and Groundwater Quality

2. Hazardous Substances and Risk Analysis

3. Introduction to Engineered Systems for Water and

4. Wastewater Treatment and Solid Waste Disposal

5. Air Pollution

6. Global Changes

7. Sustainable Technologies

Mass and Energy Transfer

While it focuses on specific environmental problems, such as pollution in surface waters or degradation of air quality, other important concepts that find application throughout the study of environmental engineering and science.

Units of measurement

In the study of environmental engineering, it is quite common to encounter both extremely large quantities or extremely small ones, such as toxic substance maybe expressed in parts per billion (ppb), or the rate of energy use maybe measured in thousands of billions of watts (terawatts)

Quite often, it is the concentration of some substance/s in air or water that is of interest.

In either medium, concentration maybe based on mass, volume or a combination of both.

Concentration of Substances

For liquids, the concentrations of substances dissolved in water are usually expressed in terms of mass of substance per unit volume of mixture, such as, milligrams (mg) or micrograms (ug) of substance per liter of mixture.For Gases (air pollution work), it is customary expressed in gas pollutant concentrations in volumetric terms, such as volume of pollutant per volume of the air mixture (ppmv).

Materials Balance

“ Everything has to go somewhere” is a simple way to express one of the most fundamental engineering principles.

Materials Balance Diagram

Law of Conservation of Mass

When chemical reactions take place, matter is either created nor destroyed (though in nuclear reactions, mass is converted to energy).

What this concept allows us to do is track materials (pollutants) from one place to another with mass balance equation.

Input Rate

Output Rate

DecayRate

AccumulationRate

First Step in a Mass balance Analysis

Define a particular region in space that is to be analyzed. A “region” maybe a simple mixing tank to entire coal-fired power plant, a lake, air basin or the globe itself. By picturing an imaginary around

Identify the flow of materials across the boundary as well as the accumulation of the materials within the region.

Conservative Substances

Under steady-state conservative systems, there is no radioactive decay, bacterial decomposition, or chemical reaction occurring, thus, the “decay rate” is “zero”. Pollutants enter and leave the region at the same rate.

Conservative substances are –Dissolved solid in a body of water.–Heavy metals in soils.–Carbon dioxide in air.

InputRate

OutputRate

Nonconservative Substances

Nonconservative substances, such as organic wastes in a river.

Under steady-state systems with nonconservative substances, contaminants undergo chemical, biological, or nuclear reactions at a rate sufficient to necessitate treating them as nonconservative substances, the decay is modeled as first-order reaction, that is, it is assumed that the rate of loss of the substance is proportional to the amount of the substance that is present.

InputRate

DecayRate

OutputRate

Sample of Nonconservative Pollutant

Energy Fundamentals

Energy, the capacity of doing work, where work can be described by the product of force and the displacement of an object caused by that force.

Power, is the rate of doing work.

The use of law of conservation of mass to write mass balance equation that are fundamental to understand and analyzing the flow of materials.

First Law of Thermodynamics

The use of the First Law of Thermodynamics to write energy balance equations that will help us analyze energy flows.

Energy can be neither created nor destroyed.

Energy can change forms in any given process.

To apply the first law, it is necessary to define the system being studied, much as was done in the analysis of mass flows.

Systems in which both energy and matter can flow across the boundary are referred to as open systems, while, those in which energy is allowed to flow but not of the matter, are called closed systems.

Energy Balance Equation System

In many applications of the energy balance equation system, the net energy added to the system will cause an increase in temperature.

Example, the waste heat from the power plant will increase the temperature of cooling water drawn into its condenser.

Units of energy:1. BTU, the energy required to raise 1 lb. of water by

1oF2. Kilocalorie, the energy required to raise 1 kg. of

water by 1oC

Second Law of Thermodynamics

Waste heat (Qc) is in any kinds of reaction.

When work is done there is always be some inefficiency; that is, some portion of the energy put into the process will end up as waste heat.

Note: It is impossible to device a machine that can convert heat to work with 100% efficiency (page 23).

Conductive, Convective and Radiation of Heat Transfer

When two objects are at different temperatures, heat will be transferred from the hotter object to the colder one.The heat transfer can be conductive when there is direct physical contact between the objects; by convection when there is a liquid or gas between or by radiation, which can take place even in the absence of any physical medium between the object.

Conductive heat transfer is usually associated with solids, the rate of heat transfer in a solid is proportion to the thermal conductivity of the material.

Convective heat transfer occurs when a fluid at one temperature comes in contact with a substance at another temperature.

Radiation is transported by electromagnetic waves and does not require a medium to carry the energy.

Example, radio waves, X-rays and gamma rays.

Environmental Chemistry

Every pollution problem has a chemical basis. such as, greenhouse effect, ozone depletion, toxic wastes, groundwater contamination, air pollution, and acid rain requires at least a rudimentary understanding of some basic chemical concepts.

Basic Requirements for an Environment Engineer

An environmental engineer who must design an emission control system or a waste treatment plant must be grounded in chemical principles and the techniques of chemical engineering.

An essential chemical principles required to understand the nature of the pollution problems and the engineering approaches to their solutions.

StoichiometryStoichiometry is the branch of chemistry and chemical engineering that deals with the quantities of substances that enter into, and are produced by, chemical reactions. 

Every chemical reaction has it's characteristic proportions.  The method of obtaining these from chemical formulas, equations, atomic and molecular weights, and determination of what and how much is used and produced in chemical processes, is the major concern of Stoichiometry

Stoichiometry provides the quantitative relationship between reactants and products in a chemical reaction.

example, when methane unites with oxygen in complete combustion….. 16g of methane require 64g of oxygen.  At the same time 44g of carbon dioxide and 36g of water are formed as reaction productions.

Enthalpy in Chemical Systems

The use of conservation of mass to balance chemical equations, we can use conservation of energy to learn about heat absorbed or released during chemical reactions.

Since energy must be conserved, we should be able to track it from the beginning to end.

The change of enthalpy during a constant pressure reaction is equal to the heat absorbed by the system.

The first law of thermodynamic, the energy in the reactants on the left side of the equation, plus any heat added to the system, should be equal to the energy contained in the reaction products on the right side plus any work done during the reaction.

U1 + Q = U2 + W

where: U1 = internal energy of the chemical system at the beginning

U2 = internal energy at the end

Q = heat absorbed during the reaction

W = work done by the system during the reaction

Chemical Equilibrium – reaction where, the rates of reaction are the same (that is, products are being formed on the right at the same rate as they are being formed on the left).

Example: aA + bB cC + dD

H2O H+ + OH—

Endothermic reaction– heat is absorbed

Exothermic reaction – heat is liberated