Density and Viscosity of Water_3 potx

In addition, in the environmental engineering field, construction of water and wastewater treatment plants and the requirements of their levels ofperformance are mostly driven by governm

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Background Prerequisites

The background prerequisites for this textbook are general chemistry, mathematics

up to calculus, and fluid mechanics In very few instances, an elementary knowledge

of calculus is used, but mostly the mathematical treatment makes intensive use ofalgebra In fluid mechanics, the only sophisticated topic used is the Reynolds trans-port theorem Although this topic is covered in an undergraduate course in fluidmechanics, it was thought advantageous to review it here The other backgroundprerequisite is general chemistry Environmental engineering students and civil engi-neering students, in particular, seem to be very weak in chemistry This part willtherefore also provide a review of this topic Depending upon the state of knowledge

of the students, however, this part may or may not be discussed This state ofknowledge may be ascertained by the instructor in the very first few days of thecourse, and he or she can tailor the discussions accordingly

The contents of this “Background Prerequisites” section are not really physical–chemical treatment but just background knowledge to comfortably understand themethod of approach used in the book This book is analytical and therefore mustrequire extensive use of the pertinent chemistry, mathematics, and fluid mechanics.This section contains two chapters: “Introduction” and “Background Chemistry andFluid Mechanics.”

TX249_Frame_Intro Page 1 Friday, June 14, 2002 1:45 PM

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This book is titled Physical–Chemical Treatment of Water and Wastewater Thischapter begins by defining wastewater and physical–chemical treatment of waterand wastewater and treats briefly the coverage It also addresses the unit operationsand unit processes In addition, in the environmental engineering field, construction

of water and wastewater treatment plants and the requirements of their levels ofperformance are mostly driven by government laws and regulations For example,the Clean Water Act mandates construction of wastewater treatment facilities that,

at least, must produce the secondary level of treatment The Safe Water DrinkingWater Act also requires performance of treatment plants that produce drinking water

of quality free from harmful chemicals and pathogens For these reasons, the CleanWater Act and the Safe Drinking Water Act are discussed at length, detailing theirdevelopments and historical perspectives

WASTEWATER

Wastewater is the spent water after homes, commercial establishments, industries,public institutions, and similar entities have used their waters for various purposes

It is synonymous with sewage, although sewage is a more general term that refers

to any polluted water (including wastewater), which may contain organic and ganic substances, industrial wastes, groundwater that happens to infiltrate and tomix with the contaminated water, storm runoff, and other similar liquids A certainsewage may not be a spent water or a wastewater

inor-The keyword in the definition of wastewater is “used” or “spent.” That is, thewater has been used or spent and now it has become a waste water On the otherhand, to become a sewage, it is enough that water becomes polluted whether or not

it had been used When one uses the word wastewater, however, the meaning of thetwo words is blended such that they now often mean the same thing Wastewater

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To explore the question further, we go to the definition of chemistry Chemistry

is defined as the branch of science that deals with the composition, structure, andproperties of substances and the transformation that they undergo Now, from thisdefinition can be gleaned the distinguishing feature of chemical—the transformationthat the substance undergoes The transformation changes the original substance into

an entirely different substance after the transformation Chemical transformation can

be distinguished from physical transformation In physical transformation, althoughalso involving a change, the change is only in appearance but not in substance Forexample, FeO in the beginning is still FeO in the end; the size of the particles mayhave changed, however, during the process We now define physical treatment ofwater and wastewater as a process applied to water and wastewater in which nochemical changes occur We also define chemical treatment of water and wastewater

as a process applied to water and wastewater in which chemical changes occur.Gleaning from these definitions of physical and chemical treatments, in the overallsense, physical–chemical treatment of water and wastewater is a process applied towater and wastewater in which chemical changes may or may not occur

UNIT OPERATIONS AND UNIT PROCESSES

Figure 1 shows the schematic of a conventional wastewater treatment plant usingprimary treatment Raw wastewater is introduced either to the screen or to thecomminutor The grit channel removes the larger particles from the screened sewage,and the primary clarifier removes the larger particles of organic matter as well asinorganic matter that escapes removal by the grit channel Primary treated sewage

is then introduced to a secondary treatment process train downstream (not shown)where the colloidal and dissolved organic matter are degraded by microorganisms.The scheme involves mere physical movement of materials, no chemical orbiological changes occur In addition, the function of the various operations in thescheme, such as screening, may be applied not only to the primary treatment ofsewage as the figure indicates but to other plant operations as well For example,bagasse may be screened from sugar cane juice in the expression of sugar in a sugarmill, or the larger particles resulting from the cleaning of pineapples in a pineapplefactory may be screened from the rest of the wastewater To master the function ofscreening, it is not necessary that this be studied in a wastewater treatment plant, in

FIGURE 1 A primary treatment system.

Raw sewage Comminutor

Grit channel Screen

Primary clarifier Effluent

Sludge

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to the clarification in a water treatment plant, as well as in the clarification of tailings

in a mining operation Similar statements may be made about the operation of thegrit channel In other words, to master the function of clarification and grit removal,

it is not necessary that these be studied in a sewage treatment plant or in a watertreatment plant It can be studied in any setting where clarifiers and grit removal areused

The foregoing operations are physical; they are therefore physical treatments.These physical treatments are called unit operations and as gleaned from the previousdiscussion they may be defined as physical treatments that are identified only accord-ing to their functions without particular reference to the location of the units utilizingthe functions For example, screening may be studied without particular reference

to any sugar mills or pineapple factories The unit operations of clarification may

be studied without particular reference to any wastewater or water treatment plants

or mining operations The unit operations of grit removal may also be studied withoutparticular reference to any sewage plant but only to any setting where grit removal

is involved

The unit operations discussed previously are all physical operations In thebiological or chemical scene where materials are changed, unit operations havecounterparts called unit processes Examples of unit processes are coagulation and

biological oxidation In coagulation, a chemical called coagulant undergoes a ical reaction This chemical reaction may occur in any plant or factory or any location

chem-at all where the function of the chemical reaction in coagulchem-ation is utilized Forexample, coagulation is employed in water treatment to enhance the settling of theturbidity of raw waters Coagulation may also be used in the clarification of sugarcane juice to remove the fibers that the juice may contain

The other unit process, biological oxidation, is used in sewage treatment; it mayalso be used in biofiltration applied in water treatment The biological reaction thatoccurs in either sewage treatment or biofiltration are the same In other words, thefunction of the biological reaction is the same whether the reaction occurs in sewagetreatment or in biofiltration

Coagulation and biological oxidation are identified on the basis of the function

of their characteristic chemical or biological reactions irrespective of the plant,factory, or any other location that uses the reactions The function of a coagulationreaction is coagulation whether the reaction occurs in a water treatment plant or in

a sugar plant; and the function of a biological oxidation reaction is biologicaloxidation whether the reaction occurs in a sewage treatment plant or in a watertreatment plant The setting is immaterial; what is of concern is the function of thechemical reaction Unit processes may therefore be defined as chemical (or biolog-ical) treatments that are identified only according to the functions of the chemical(or biological) reactions irrespective of where the units utilizing the reactions areoccurring

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6 Physical–Chemical Treatment of Water and Wastewater

COVERAGE

This book is divided into four general parts and addresses important topics on thephysical–chemical treatment of water and wastewater The “first” part is titledBackground Prerequisites Its contents are not really physical–chemical treatmentbut just background knowledge to comfortably understand the method of approachused in the book This book is analytical and therefore requires the use of pertinentchemistry, mathematics, and fluid mechanics Relevant prerequisite topics are dis-cussed in this part

Part I, Characteristics of Water and Wastewater, covers the chapters on quantityand constituent physical and chemical characteristics of water and wastewater Part II,Unit Operations of Water and Wastewater Treatment, includes the chapters on flowmeasurements and flow and quality equalization; pumping; screening, sedimentation,and flotation; mixing and flocculation; conventional filtration; advanced filtration andcarbon adsorption; and aeration and stripping Part III, Unit Processes of Water andWastewater Treatment, includes the chapters on coagulation; water softening; chem-ical stabilization; removal of iron and manganese; removal of phosphorus; removal

of nitrogen by nitrification–denitrification; ion exchange; and disinfection Removal

of nitrogen by nitrification–denitrification, on the surface, is a biological process

To control the process, however, its intrinsic chemical reactions must be unraveledand totally understood The treatment (as used in this textbook) therefore turnstoward being chemical in nature The organisms only serve as mediators (i.e., theproducer of enzymes needed for the reaction) Thus, on the most fundamental level,nitrogen removal by nitrification–denitrification is a chemical process (more, accu-rately, a biochemical process), which is subsequently included as a chapter in PartIII of this book

CLEAN WATER ACT

To gain a broader perspective of the Clean Water Act, it is important to know aboutthe United States Code (USC).* This code is a consolidation and codification of the

general and permanent laws of the United States It contains several titles; in one

of these titles, the Clean Water Act is codified Because many of the general andpermanent laws required to be incorporated into the code are inconsistent, redundant,and obsolete, the Office of the Law Revision Counsel of the House of Representativesrevises for enactment into law each title of the code This process is called positive law codification Positive law codification is the process of preparing a bill andenacting it into law, one title at a time, a revision and restatement of the general andpermanent laws of the United States This codification does not change the meaning

or legal effect of the statute but removes ambiguities, contradictions, and otherimperfections from the law Certain titles of the code have now been enacted intopositive law, and pursuant to Section 204 of Title 1 of the code, the text of thesetitles is legal evidence of the law The other titles of the code that have not been

* The United States Code itself is public domain Portions of the code can be used and redistributed without permission from the U.S Government Printing Office.

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is the codification of the Clean Water Act.

Each title of the USC is divided into several sections Title 33, of course, starts withSection 1, which is under Chapter 1, Navigable Waters Generally Chapter 26 starts atSection 1251 and ends at Section 1387 A portion of the USC is cited by specifyingthe title number before the USC and the section or the range of sections after the USC.For example, 33 USC 1251-1387 is the codification of the Clean Water Act

Environmental pollution is global Both developed and developing countries allexperience this problem These countries therefore enact laws and regulations to

TABLE 1

The United States Code

Title 4 Flag and Seal, Seat of

Government, and the States

Title 29 Labor Title 30 Mineral Lands and Mining Title 5 Government Organization and

Employees

Title 31 Money and Finance Title 32 National Guard

Services Title 11 Bankruptcy

Title 18 Crimes and Criminal Procedure Title 44 Public Printing and Documents

Radiotelegraphs Title 22 Foreign Relations and

Title 25 Indians

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control the continuing pollution of the environment In the United States, the passage

of the Rivers and Harbors Act of 1899 may be considered as the first law controlling

water pollution Subsequently, the Federal Water Pollution Control Act, codified as

33 U.S.C 1251-1387, was passed in 1948 The Federal Water Pollution Control Act

is the full name of the Clean Water Act mentioned in the previous paragraphs This

Act is the principal law governing pollution of surface waters of this country The

following years show various amendments to this act: 1956, 1961, 1965, 1966, and

1970; but it was in 1972 that the act was totally revised by amendments to have

taken practically its current shape The 1972 legislation spelled out ambitious

programs for water quality improvement that have since been expanded by various

additional amendments Congress made certain fine-tuning amendments in 1977,

revised portions of the law in 1981, and enacted further amendments in 1987, the

last year that the act was amended Table 2 traces the dates of the major amendments

to the Clean Water Act and Table 3 summarizes the major sections of the Act

(indicated in the second column) as codified in the corresponding sections of the

USC (first column)

The following events were common before 1972: Lake Erie was dying; the

Chesapeake Bay was deteriorating rapidly; and the Potomac River was clogged with

blue-green algae blooms Many of the rivers were like open sewers, and sewage

frequently washed up on shores Fish kills were a common sight Wetlands were

disappearing The Cuyahoga River in Cleveland, Ohio, was burned because of gross

pollution due to a discharge of oil To stop this widespread water pollution, in 1972,

Congress enacted the first comprehensive national clean water legislation—the

The Clean Water Act focuses on improving the water quality of the nation It

provides for establishment of standards, development of technical tools, and financial

assistance to address the causes of pollution and poor water quality, including

municipal and industrial wastewater discharges, nonpoint source runoff pollution

TABLE 2

Clean Water Act (Chapter 26) and Major Amendments

1972 Federal Water Pollution Control Act Amendments P.L 92-500

1981 Municipal Wastewater Treatment Construction Grants

Amendments

P.L 97-117

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Introduction 9

TABLE 3

Major U.S Code Sections of the Clean Water Act

Code Section Subchapter

Subchapter I—Research and Related Programs

1251 Congressional declaration of goals and policy, Sec 101

1252 Comprehensive programs for water pollution control, Sec 102

1253 Interstate cooperation and uniform laws, Sec 103

1254 Research, investigations, training and information, Sec 104

1256 Grants for pollution control programs, Sec 106

1258 Pollution control in the Great Lakes, Sec 108

1260 Applications for training grants and contracts, allocations, Sec 110

1266 Hudson River reclamation demonstration project, Sec 116

Subchapter II—Grants for Construction of Treatment Works

1283 Plans, specifications, estimates, and payments, Sec 203

1294 Wastewater recycling and reuse information and education, Sec 214

1297 Guidelines for cost effective analysis, Sec 217

1299 State certification of projects, Sec 219

(continued)

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Subchapter III—Standards and Enforcement

1312 Water quality-related effluent limitations, Sec 302

1313 Water quality standards and implementation plans, Sec 303

1317 Toxic and pretreatment effluent standards, Sec 307

1321 Oil and hazardous substance liability, Sec 311

1323 Federal facility pollution control, Sec 313

Subchapter IV—Permits and Licenses

1342 National pollutant discharge elimination system, Sec 402

1344 Permits for dredge and fill materials, Sec 404

Subchapter V—General Provisions

1369 Administrative procedure and judicial review, Sec 509

1371 Authority under other laws and regulations, Sec 511

1374 Effluent standards and water quality information advisory committee, Sec 515

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mainte-Aside from research and related programs provision, essentially, the Clean WaterAct consists of three major parts:

1 Regulatory requirements under the title of Subchapter III

2 Provisions that authorize federal financial assistance for municipal sewagetreatment plant construction under the titles of Subchapters II and VI

3 Permits and enforcement under the titles of Subchapters IV and III,respectively

In terms of historical perspective, these parts are discussed in sequence next

Subchapter VI—State Water Pollution Control Revolving Funds

1381 Grants to states for establishment of revolving funds, Sec 601

1383 Water pollution control revolving loan funds, Sec 603

1386 Audits, reports, fiscal controls, intended use plan, Sec 606

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As mentioned previously, the act requires each state and tribe to establish waterquality standards for all bodies of water in their jurisdictions (Section 303) The CleanWater Act utilizes both water-quality- and technology-based effluent limitations tomeet these standards (Sections 301 and 302) Technology-based effluent limitationsare normally specified in discharge permits for industries, while water-quality-basedeffluent limitations are normally specified in discharge permits for publicly ownedtreatment works (POTWs), although the requirement of secondary treatment inpublicly owned treatment works is also technology-based Water-quality-based effluentlimitations are derived by a water quality modeling which, for simple discharges,uses the Streeter–Phelps equation

Because of strict demands imposed on those who are regulated to achieve higherand higher levels of pollution abatement, the act is a technology-forcing statute Forexample, the act started with only requiring the implementation of the secondaryand best practicable treatment (BPT) levels of treatment The requirements, however,gradually increased to requiring the use of the best available technology (BAT)economically achievable, control of toxics, and control of nonpoint pollution sources The following scenario depicts the technology-forcing nature of the Clean WaterAct Publicly owned treatment works were once required to meet the secondarytreatment level of treatment by July 1, 1977 By this date, industries were alsorequired the equivalent BPT level of treatment Municipalities that were unable toachieve the secondary treatment by the deadline were allowed to apply for extensions

on a case-by-case basis up to July 1, 1988 According to an estimate by the EPA,86% of all cities met the 1988 deadline with the remainder being put under judicial

or administrative schedules requiring compliance as soon as possible

By no later than March 31, 1989, the act required greater pollutant removal thanBPT, generally forcing that industry use BAT technology Toxic pollutants are generallythe target of BAT levels of control For industrial sources utilizing innovative oralternative technology, compliance extensions of as long as two years were available Control of toxic pollutant discharges has now become a key focus in waterpollution abatement programs For waters expected to remain polluted by toxicchemicals even after industrial dischargers have installed the best available cleanuptechnologies required under the law, the states are required to implement controlstrategies, in addition to the BAT national standards In the 1987 Clean Water Actamendments, development of management programs for these post-BAT pollutantproblems was a prominent element This would likely be a key continuing aspect

of any Clean Water Act amendments

It should be realized that all these extensions for compliance are in the nature

of forcing the development of technology to achieve compliance Thus, it is nolonger sufficient that the rule of thumb that has been traditionally used in environ-mental engineering be used in an effort to meet requirements Instead, the design

of unit operations and processes to achieve compliance should be instituted in amore rational and analytical approach

The original attention of the Clean Water Act prior to the 1987 amendmentswas primarily directed at point source pollution, which includes wastes discharged

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