chapter 22 - water and wastewater treatment plant hydraulics

7/27/2019 Chapter 22 - Water and Wastewater Treatment Plant Hydraulics

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22.1 INTRODUCTION

Designers of water treatment plants and wastewater treatment plants are faced with thenee to esign treatment processes which must meet the following general hy raulicrequirements:

Water treatment p ants. Provide the head required to allow the water to flow throughthe treatment processes an to e elivere to the transmission/ istri ution system inthe flow rates and at the pressures required for delivery to the users.

W s ewa er reatment p ants. Provi e the hea require to raise the flow of wast water

from the sewer system to a level which allows the flow to procee through the treat-ment processes and be delivered to the receiving body of water.

The above requires knowledge of open-channel, closed-conduit, and hydraulicmachine flow principles. It also requires an un erstan ing of the interaction etween theseelements an their impact on the overall plant (site) hy raulics. Hea is either availa lethrough the difference in elevation (gravity) or it has to be converted from mechanicalenergy using hy raulic machinery. Distri ution of flows using open channels or closecon uit is critical for proper hy raulic loa ing an process performance.

This chapter rings together information on commonly use hy raulic elements anspecific applications to water treatment plants an wastewater treatment plants. The evel-

opment of hydraulic profiles through the entire treatment process with examples for watertreatment plants an wastewater treatment is also presente .

Many processes and flow control devices are similar in both water treatment plants andwastewater treatment plants. Both types of plants require flow istri ution evices, gatesan valves, an flowmeters. These evices are iscusse in Section 22.2. The evelopmentof water treatment plant hy raulics, inclu ing examples from in-place facilities, are pre-sente in Section 22.3. Wastewater treatment plant hy raulics are iscusse in Section22.4, and Section. 22.5 is devoted to non-Newtonian flow principles.

CHAPTER 22

WATER AND WASTEWATERTREATMENT PLANT

HYDRAULICS

e er co . a scSharon L. Cole

av . o sran . antone

am . u yGree ey an Hansen

Ric mon , VA

22.1

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)Copyright 2004 The McGraw-Hill Companies. All rights reserved.

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Source: HYDRAULIC DESIGN HANDBOOK


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an possi ly a higher water surface at each ensuing weir. Chao an Trussell (1980), Campand Graber (1968), and Yao (1972) have presented comprehensive approaches for thedesign of distribution channels and manifolds and should be reviewed for details of

esign.As in istri ution oxes, the most important consi eration to achieving equalize flow

istri ution is to minimize the effects of unequal hy raulic con itions relative to eachpoint of istri ution. In channels this can e accomplishe y tapering the channel crosssection, varying weir elevations, making the channel large enough to cause velocity headchanges to e insignificant or a com ination of these. Similar consi erations may eapplied to manifolds with submerged orifice outlets. A reliable approach here is to pro-vi e a large enough manifol , resulting in a total hea loss along the length of the istri -ution of less than one tenth the loss through any in ivi ual orifice. This approach essen-tially results in the orifices ecoming the only hy raulic control an the accuracy of the

flow istri ution is then epen ent on the uniformity of the orifices themselves.

22.2.3 Gates and Valves

Gates an va ves generally serve to either control the rate of flow or to start/stop flow.Gates and valves in treatment plants are typically subjected to much lower pressuresthan those in water istri ution systems or sewage force mains an can e of lighterconstruction.

22.2.3.1 ates. Gates are typically use in channels or in structures to start an stop flowor to provi e a hy raulic control point which is sel om a juste . Because of the time aneffort require to operate gates, they are not suite for controlling flow when rapiresponse, frequent variation, or delicate adjustments are needed. Primary design consid-erations when using gates are the type of gate fa rication an the installation con itionsduring construction.

There are many fa rication etails inclu ing materials use , ottom arrangement, anstem arrangement. For instance, for soli s earing flows, a flush ottom, rising stem gatecan e use to avoi creating a point of soli s eposition an to minimize soli s contactwith the threa e stem. Gate manufacturers are a goo source of information for gate fa -rication details and can assist with advice regarding specific applications.

Most commonly use gates are esigne to stop flow in a single irection. They mayuse upstream water pressure to assist in achieving a seal (seating ea ), but typically alsomust e esigne to resist static water pressure from ownstream (unseating ea ). Bothseating an unseating hea s must e evaluate in esign of a gate application. For mostmanufacturers, the seating or unseating hea is expresse as the pressure relative to thecenter line of the gate.

22.2.3.2 Valves. Ta le 22.1 provi es a summary of several types of valves an theirapplications. Valves are used to either throttle (control) flow or start/stop flow.Start/stop valves are inten e to e fully open or fully close an nonthrottling. Theyshoul present minimum resistance to flow when fully open an shoul e inten e forinfrequent operation.

Gate va ves, plug valves, cone valves, all valves, an utterfly valves are the mostcommon start/stop valve selections.Butterf y va ves have a center stem, are most commonin clean water applications an shoul not e use in applications inclu ing materials thatcould hang-up on the stem. Therefore, they are seldom used at wastewater plants prior toachieving a filter effluent water quality.

Water and Wastewater Treatment Plant Hydraulics 22 3



WATER AND WASTEWATER TREATMENT PLANT HYDRAULICS


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C ec va ves are a special case of a start/stop valve application. Check valves offer

quick, automatic reaction to flow changes an are inten e to stop flow irection rever-

sal. Typical configurations inclu e swing check, lift check, all check an spring loa e .

These valves are typically use on pump ischarge piping an are opene y the pressure

of the flowing liquid and close automatically if pressure drops and flow attempts to

reverse irection. The rapi closure of these valves can result in unaccepta le water-

hammer pressures with the potential to amage the system. A etaile surge analysis may

e require for many check valve applications (see Chapter. 12). At times, mechanicallyoperating check valves should be avoided in favor of electrically or pneumatically operat-

ed valves (typically plug, ball, or cone valves) to provide a mechanism to control time of

closing and reduce surge pressure peaks.

T rott ing va ves are use to control rate of flow an are esigne for frequent or near-

ly continuous operation epen ing on whether they are manually operate or electroni-

cally controlle . Typical throttling valve types inclu e glo e valves, nee le valves, an

angle valves in smaller sizes, an all, plug, cone, utterfly, an pinch/ iaphragm valves

in larger sizes. Throttling valves are typically most effective in the mi -range of loose line

open/close travel an for est flow control shoul not e routinely operate nearly fully

closed or nearly fully open.

22.2.4 Flow meters

The most common types of flow meters used in water and wastewater treatment plants aresummarize in Ta le 22.2 an fall into the following categories:

22.4 Chapter Twenty-Two

TABLE 22.1 Typical Valves and Their Application*

Type Open/C ose T rott ing Water Wastewater

S u ce gate X X

Slide gate X X X

Gate valve X X X

Plug valve X X X X

Cone va ve X X X

Ball valve X X X X

Butterfly valve X X X

Swing check X X X

L t c ec X

Ball check X X X

Spring check X X X

Globe valve X X

Needle valve X X

Ang e va ve X

Pinch/diaphragm X X X X

*Typical applicationsexceptions are possible, but consultation with valve manufacturers is recommended.





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Pressure ifferential/pressure measuring meters (e.g., Venturi, orifice plate, pitot tu e,an Parshall flume meters)

Magnetic meters

Doppler (ultrasonic) meters

Mechanical meters (e.g., propeller an tur ine meters)

Accurate flow measurements require uniform flow patterns. Most meters are

significantly impacted by adjacent piping configurations. Typically a specific number of

straight pipe iameters is require oth upstream an ownstream of a meter to o tain

reliable measurements. In some cases, 15 straight pipe diameters upstream and 5 straight

pipe diameters downstream are recommended. However, different types of meters have

varying levels of susceptibility to the uniformity of the flow pattern. Meter manufacturers

shoul e consulte .

22.2.4.1 Pressure ifferentia /pressure measuring meters. Pressure ifferential/pressure

measuring flow meters include Venturi meters, orifice p ates, averaging pitot meters, andPars a f umes. These meters measure the change in pressure through a known flow cross

sectionor in the case of the pitot meter, measure the ifference in pressure at a point in

the flow versus static pressure just ownstream in a uniform section of pipe.

Venturi meters and orifice plates are commonly used in water and wastewater. Solids

in wastewater coul plug the openings of a pitot tu e meter-limiting their use to relative-

ly clean liqui s. The Venturi meter an orifice plate meter use pressure taps at the wall of

the evice an can e arrange to minimize potential for e ris from clogging the taps.

The Parshall flume can be arranged with a side stilling well and level measuring float sys-

tem or an ultrasonic level sensing evice to measure water level.

22.2.4.2 Magnetic meters. In a magnetic f owmeter, a magnetic fiel is generate aroun

a section of pipe. Water passing through the fiel in uces a small electric current propor-

tional to the velocity of flow. Because a magnetic meter imposes no o struction to the

flow, it is well suited to measuring solids bearing liquids as well as clean liquids and pro-

duces no headloss in addition to the normal pipe loss. Magnetic meters are among the least

suscepti le to the uniformity of the stream lines in the approaching flow.


TABLE 22.2 Common Types of Flow Meters

Type Typica Accuracy Size Range Hea oss Cost W WW

Venturi 0.7 % of rate 1120 in Low Medium X X

Orifice plate 2% of scale Any size Medium Low X X

P tot tu e 0. % of scale 1/296 in Low Low

Parshall flume % of rate Wide range Low Medium X X

Magnetic 0. % of rate 1/10120 in None High X X

Doppler 12. % of rate 1/8120 in None High X X

Propeller 2% of rate Up to 24 in High High X

Tur ne 0. 2% of rate Up to 24 in High High X





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Walski(1992)

CraneCo.(

1987)

Ten-State

Standards(1978)

BulletinN

o.2552,UniversityoWisconsin

Daugherty(1977)

CameronHydraulicData

Simon(19

86)

Sanks(1989)

CommitteeonPipelinePlanning(1975)

TypicallyUsedValue

TABLE 22.3 Typical Factors for Computing Local Losses

Va ve an Fitting Types

Gate valve

100% open 0.39 0.19 0.19 0.10.3 0.2 0.2

75% open 1.1 1.15 1.2 1.2

50% open 4.8 5.6 5.6 5.6

25% open 27 24 24 25

Globe valveopen 10 10 10 4.06.0 10 10

Angle valveopen 4.3 5 2.13.1 5 1.82.9 2.5 5

Check valveball 4.5 6570 5

Swing check 0.62.3 062.2 0.62.5 2.5

Butterfly valveopen 1.2 0.160.35 0.5

Foot valvehinged 2.2 1.01.4 2.2

Foot valvepoppet 12.5 5.014.0 14

Elbows

45 regular 0.300.42 0.42 0.42

45 long radius 0.180.20 0.18 0.5 0.2

90 regular 0.210.3 0.25 0.7 0.25

90 long radius 0.140.23 0.18 0.6 0.19

180 regular 0.38 0.38

180 long radius (flanged) 0.25 0.25

Tees

Std. teeeflowthrough run 0.6 0.6 0.6 0.3 1.8 0.6Std. teeeflow-through branch1.8 1.8 1.8 1.8 0.75 1.8

Return bend 1.5 2.2 2.2 0.4 2.2

Mitre bend

90 1.8 1.1291.265 0.8 1.3

60 0.75 0.4710.684 0.35 0.6

30 0.25 0.1300.165 0.1 0.16

Expansion

d/D = 0.75 0.18 0.19 0.2 0.2

d/D = 0.5 0.55 0.56 0.6 0.6

d/D = 0.25 0.88 0.92 0.9 0.9

Contraction

d/D = 0.75 0.18 0.19 0.2 0.2d/D = 0.5 0.33 0.33 0.3 0.33

d/D = 0.25 0.43 0.42 0.4 0.43

Entranceeprojecting 0.78 0.78 0.83 0.8 0.8 0.78 0.8

Entranceesharp 0.5 0.5 0.5 0.5 0.5 0.5 0.5

Entranceewell rounded 0.04 0.04 0.04 0.04 0.25 0.04 0.04

Exit 1.0 1.0 1.0 1.0 1.0





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population an the per capita use of water y the population serve . The per capita use ofwater can e o taine from literature sources as an initial approximation. However, theseinitial estimations must be corroborated with actual site specific population counts and

water usage. For nonmunicipal treatment facilities, treate water nee s of the service areamust e in ivi ually evaluate .

22.3.1.1 Sources of supply. Natural sources of supply inclu e groun water an surfacewater supplies. Groun water supplies typically are smaller in aily elivery ut servemore systems than surface water supplies. Groun water supplies normally come fromwells, springs, or infiltration galleries.

Wells constitute the largest source of groundwater. Except in rare circumstances ofartesian wells (wells under the influence of a confined aquifer) and springs, groundwatercollection involves pumping facilities. Hy raulics of groun water treatment plants are fre-

quently ase on hy raulics of con uits un er pressure, such as pipelines, pressurefilters, an pressure tanks. Raw water characteristics of groun waters are uniform inquality compare with surface supplies.

Surface water supplies are normally larger in daily delivery. Surface supplies are usedto service larger population centers an in ustrial centers. In areas where groun watersupplies are limited in yield or where groundwater supplies contain undesirable chemicalcharacteristics, smaller surface water treatment plants may e utilize . Surface watersources of supply inclu e rivers, lakes, impoun ments, streams, an pon s. The treatmentprocesses chosen in plants treating surface water favor nonpressurize systems such asgravity se imentation. The larger flow volumes characteristic of surface water suppliesalso favor open channel hydraulic structures for conveying water through the treatment

process. Raw water characteristics of surface supplies can vary rapi ly over short perio sof time an also experience seasonal variation.

22.3.1.2 Treatment requirements. Treatment requirements for municipal water treat-ment plants are normally defined by regulatory agencies having authority over the plants

service area. In the Unite States, regulatory agencies inclu e national government regu-

lations promulgate through the Environmental Protection Agency an state government

regulations. Water treatment plants are esigne to meet these regulations. Treatment reg-

ulations change through improved knowledge of health effects of water constituents and

through i entification of possi le new water- orne threats. The esigner therefore shoul

attempt to select treatment processes which will also meet treatment requirements whichare expected to be promulgated over the next few years. To the extent possible, treatment

plant process esign shoul provi e flexi ility for future plant expansions or for possi le

additional treatment processes. Because hydraulic design of plants must go hand-in-hand

with the process selection, plant hy raulic esign shoul provi e for the flexi ility to a

future plant facilities.Treatment requirements for industrial water treatment plants are dictated by process

nee s of the in ustry an less y regulatory agency requirements. In ustrial water treat-ment plants that result in contact etween or ingestion of the treate water y humansmust conform to the local regulatory requirements.

22.3.1.3 Genera esign p i osop y. Effective esign of water treatment plant hy raulicsrequires that the hy raulic esigner have a thorough knowle ge of all aspects of the watersystem. The overall treatment system hydraulic design must be integrated and coordinat-e inclu ing the treatment plant, the raw water intake an pumping facilities, the treatewater storage, an treate water pressure/hea requirements. The esign within the watertreatment plant must also e integrate etween the various treatment processes.






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Water and Wastewater Treatment Plant Hydraulics 22.11

FIGURE

22.

Hydraulicprofile.





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From stu ies of projecte population an per capita eman , planne esign flows forthe water treatment facilities may e evelope . These eman s inclu e the following:

Annua average eman . The average aily water consumption for the water serviceareas, generally compute y multiplying the average aily consumption (gallons percapita) y the projecte population of the service area.

Maximum eman . Maximum eman experience y the water plant throughout itsservice life. The maximum hour eman is generally 200 to 300 percent of the aver-age eman ut numerous factors affect the peak eman experience y water treat-ment plants. These factors inclu e seasonal eman s (particularly for plants where ser-vice areas are located in extremes of hot and cold temperatures), normal daily flowvariations, the community size, in ustrial usage, an system storage. Normally systemstorage is provided to service peak hour demands, allowing the treatment facilities to

be designed on peak day demands. Peak day demands generally range between 125an 200 percent of the average eman .

Minimum f ow. As the name suggests, the minimum flow expecte to e processethrough the treatment facilities. Minimum flow depends upon system operations. Ingeneral, minimum flows for municipal plants may be estimated as 50 percent of theaverage demand, but range between 25 and 75 percent of the average demand.

22.3.5.2 Rated treatment capacity. The rate treatment capacity of a plant is that capac-ity for which each of the unit processes are esigne . For municipal treatment plants witha equate system storage, the rate treatment capacity is the systems maximum ay

demand. Where storage is limited, the rated treatment capacity may be greater, for exam-ple, the system maximum hour eman or greater. Smaller systems may e esigne toproduce the rated treatment capacity in one or two 8-h shifts rather than over the entire24-h ay.

22.3.5.3 Hydraulic treatment capacity. Treatment plants are normally esigne for ahy raulic capacity greater than the rate treatment capacity.Hy rau ic treatment capaci-ties are normally equal to 125 to 150 percent of the rated treatment capacity. The hydraulictreatment capacity provides flexibility for future process changes or alternative flow rout-ings through the plant. Hy raulic capacities in excess of the rate treatment capacity pro-vide some margin of safety for operations which may not be optimal (e.g., control gates

ina vertently left partially open).

22.3.5.4 Treatment process bases for design. The evelopment of the water treatmentplants Bases for Design is a key step in esta lishing the criteria to which the plant wille esigne . This ocument must e reviewe carefully with the water treatment plant

owner representatives and understood and agreed to by all before the final design pro-cee s. The Bases for Design presents a summary of each treatment process inclu ingdesign flows (minimum, average, rated capacity), specification of dimension of major ele-ments (e.g., tanks, pumps), oth hy raulic an process loa ing characteristics, requireperformance, an esign ata for the chemical storage an fee system. Ta le 22.4 pre-sents an example of the ases for esign for se imentation asins (one of the many unit

processes in a water treatment plant).

22.3.6 Plant Hydraulic Design

As note a ove, a water treatment plant consists of a series of treatment processesconnected by free surface flow channels and pipelines. During development of the plants






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TABLE 22.4 Treatment Process Bases for DesignSedimentation Basins

Item Stage I Stage II StageIII

Maxi Maxi Maxi-

Annua mum Annua mum Annua mum

verage Day verage Day verage Day

Number of basins 4 4 8 8 12 12

Basin characteristics

Plan7 ft 2306 in

Nominal side water

depth12 ft (SWD)

Sur ace area/ as n17,288 t

o ume as n ,

Channels/basin2

L:W ratio6.1:1

Displacement time (h) 3.17 1.99 3.17 1.99 3.17 1.99

Surface loading [(gal m)/ft2] 0.47 0.7 0.47 0.7 0.47 0.7

Flowthrough velocity (ft/min) 1.21 1.93 1.21 1.93 1.21 1.93

Sludge collectors

Long tu na co ectors

Type: c a n g t

Number per basin 8 8 8 8 8 8

Cross collectors

Type: chain flight

Number per basin 1 1 1 1 1 1

Settled sludge pumps

Type: progressive cavityNum er:

100 gal/min capacity 4 4 4 4 4 4

400 gal/min capacity 4 4 4 4 4 4

200 gal/min capacity 8 8 16 16

Capacity (gal/min)

Installed 2000 2000 3600 3600 200 200

Firm 1600 1600 3200 3200 4800 4800

Bases for Design, the esigner etermines the rate treatment capacity, average flow,minimum flow an hy raulic capacity of the plant.

Following evelopment of the Bases for Design, the esigner must evaluate plantoperating modes to develop a detailed plant flow diagram and hydraulic profilethrough the plant.





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22.3.6.1 P ant operating mo es. Operating mo es escri e the sequence of treatmentprocesses the water goes through to achieve the require level of purification. Operationalmodes are normally presented in the form of simplified block diagrams which illustrate

the flow path through the plant from one process to the next. These operationa mo eoc iagrams are useful in visualizing stages uring construction, future planne plant

expansions or simply alternative operating mo es.Figures 22.4 through 22.9 show an example of a sequence of plant operating mo es for

a surface water treatment plant which illustrate three stages of a plant expansion programwith alternatives for the flocculation an se imentation asins to work in series or in par-allel. Plant processes proposed include raw water control chambers, rapid mix chambers,flocculation/se imentation asins, ozone contact cham ers, an filters. In this example,the raw water control cham ers are use to split flow etween plant process groups analso as a rapi mix cham er for chemical a ition.


FIGURE 22.4 Stage Ioperational mode diagram.

FIGURE 22.5 Stage IIparallel operational mode diagram.





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The Stage I facilities inclu ing raw water control cham er, flocculation/se imentationasins an filters are epicte in Fig. 22.4. Operational mo es for a propose plant expan-

sion to double the plant capacity (Stage II) are shown in Figs. 22.5 through 22.7 and oper-

ating mo es for a secon plant expansion to triple the plant capacity (Stage III) are shownin Figs. 22.8 an 22.9. Settle water ozone contact cham ers were a e to the expan eplant, which illustrates treatment upgra es.

Operational mo es for the Stage II treatment plant inclu e parallel an series floc-culation/sedimentation. When the plant is operated in the parallel mode, influent rawwater for each set of se imentation asins flows y gravity from the raw water controlchamber serving the basin set. Raw water flow is divided between each sedimentation

asin in service at the raw water control cham er. Settle water from each set of asinsis route to an ozone contact cham er. Ozonate settle water is then com ine prior toflowing to the filters.


FIGURE 22. Stage IIseries flocculation/sedimentation basinoperational mode diagram.

FIGURE 22.7 Stage IIsplit parallel operational mode diagram.





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Hy raulic profiles are evelope for each of the esign flows. In the case of watertreatment plants, the esign flows may inclu e rate treatment capacity, hy raulic capac-ity, average flow, and minimum flow. Hydraulic profiles should also take into considera-

tion unit processes or con uits which may e taken out of service. Hy raulic profiles arevalua le esign an operational tools to assist in sche uling routine maintenance activi-ties an for evaluating the impact to the treatment plant capacity uring outages of processunits or con uits.

Computations of hydraulic profiles begin at control points where there is a definiterelationship etween the plant flow an water surface epth. For gravity flow plants, themost common forms of control points are weirs and tank water surface elevations (e.g.,clear well water surface elevations), ut other types of control points may e use . Fromeach control point, hea losses associate with local losses, plant piping, an open chan-nel flow are a e to the control water surface. Since flows in water treatment plants are

mostly in the su critical regime (Frou e num er 1), most hy raulic esigners will workupstream from the control point. For pressure plants, control points are typically pressureregulating or pressure control points, frequently in the service area istri ution system.From these control points and knowledge of the flow velocity, both the EGL and HGLmay e compute ack to the treatment facilities.

Hy raulic profiles are valua le esign tools to i entify overall losses through the plant.Profiles are also valua le to i entify units with excessive losses. Since total hea availa leis normally limite , units with excessive losses shoul e consi ere for re esign toreduce local loss coefficients or to reduce velocities.

Figure 22.3 is an example hy raulic profile for a gravity surface water treatment plantwith conventional treatment processes. The metho of computing hea losses is presentein Section 22.3.7.

22.3.7 Water Treatment Plant Process Hydraulics

In this section calculations require to esta lish the WSEL through a me ium-size watertreatment plant will e presente . A schematic of the water treatment plant is shown inFig. 22.10. Notice that future growth has been considered in the initial design. Threeexamples are inclu e which illustrate typical hy raulic calculations. The first examplecalculates the WSEL from the sedimentation basin effluent chamber back through the

flocculation/se imentation asins to the Raw Water Control Cham er. The secon followsthe flow from the clear well ack through the filters. Filter hy raulics are illustrate in thethir example. All examples are presente in a sprea sheet format which is esigne tofacilitate calculating the EGL, HGL, an WSEL at various points through the treatmentprocess and for multiple flow rates (i.e., minimum, daily average, peak hour, futurecon itions).

22.3.7.1 Coagu ation. Process criteria an ey y rau ic esign parameters. The -u ation process, use to re uce particulates an tur i ity, is carrie out in three steps: mix-ing (often referre to as rapi or flash mixing), flocculation, an se imentation. Each ofthese steps is riefly iscusse elow.

Rapi mixing. The mixing process imparts energy to increase contact etween

existing soli s an a e coagulants. Possi le mixer types inclu e tur ine, propeller,

pneumatic, and hydraulic. Headloss that occurs in mixing chambers depends on the cho-

sen mixing evice. Most mechanical mixers o not create significant hea losses. The

hea loss coefficient (K) associate with a specific mixer can e o taine from the manu-

facturer. Pneumat c m x ng, which is not common, has associate losses similar to those






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TABLE 22.5 (Continue )

Initia Operation Design Operation

Parameter Min. Day. Avg. Day Avg. Day Max. Hour

Velocity flow/area (m/s) 0.02 0.02 0.03 0.03

r A/P

(P w 2 ) (m) 1.41 1.41 1.41 1.41

Conduit loss [(V n)/(r2/3

)]2 L (m)

where n 0.014 and L 21.95 m 0.00 0.00 0.00 0.00

WSEL at Point 4 (m) 109.73 109.73 109.74 109.74

6. Point 4 to Point 5

Flow Q/32 (m3/s) 0.07 0.10 0.10 0.14

Port area 0.30 m deep 0.76 m wide (m2) 0.23 0.23 0.23 0.23


Submerged entrance loss .8 /2 (m) 0.00 0.01 0.01 0.01

WSEL at Point 5 (in Sedimentation Tank) (m) 109.73 109.74 109.74 109.76


Width of sedimentation basin (W) (m) 23.16 23.16 23.16 23.16

Flow (Q/4) (m3/s) 0.55 0.77 0.82 1.09

Invert elevation of sedimentation baffles (m) 105.97 105.97 105.97 105.97

Flow depth (H) (WSEL at Point 5baffle invert) (m) 3.76 3.77 3.77 3.79

Area downstreams of baffle (WH (m2) 87.21 87.36 87.41 87.68

Horizontal openings in baffle, 2.54 cm wide

spaced every 22.86 cm. Area of

openings A W .0254 H/.2286 (m ) 9.69 9.71 9.71 9.74

Velocity of downstream baffle (V ownstream) 0.01 0.01 0.01 0.01

(Q/A) (m/s)

Velocity of 2.54 cm opening section (V1) (Q/ ) (m/s) 0.06 0.08 0.08 0.11

Local losses sudden expansion (1.0 (Vdownstream)2/2 )

sudden contraction (0.36 (VI)

2/ 2 ) (m) 0.00 0.00 0.00 0.00

WSEL at Point 6 (Upstream of sedimentation baffles) (m) 109.73 109.74 109.74 109.76


Loss per stage (provided by flocculator manufacturer) (m) 0.01 0.01 0.03 0.05

Total loss (three stages) (m) 0.04 0.04 0.09 0.15

WSEL at Point 7 (m) 109.77 109.78 109.83 109.91

9. Point 7 to Point 8Flow Q/24 (m3/s) 0.09 0.13 0.14 0.18

Port area 0.30 m deep 0.46 m wide (m2) 0.14 0.14 0.14 0.14

Velocity flow / area (m/s) 0.65 0.92 0.98 1.31

Entrance loss 1.25 V

/2 (m) 0.03 0.05 0.06 0.11

WSEL at Point 8 (inlet port) (m) 109.80 109.83 109.89 110.02

Note: For Points 8 through 14, see Fig. 22.13


Average flow Q/24 (m /s) 0.09 0.13 0.14 0.18

Flow depth WSEL @ 8 invert (109.12 m) (m) 0.68 0.72 0.77 0.90

Flow area 0.91 m width depth (m ) 0.62 0.65 0.71 0.82


r A/P (P w 2d (m) 0.27 0.28 0.29 0.30

Conduit loss [(V )/(r2/3

)] L (m)

where n 0.014 andL 3.86 m 0.00 0.00 0.00 0.00

WSEL at Point 9 (m) 109.80 109.83 109.89 110.02


Average flow Q/12 (m3/s) 0.18 0.26 0.27 0.36





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Flow area 0.91 m width depth (m2) 0.62 0.65 0.71 0.82


r=A/P (P w 2 ) (m) 0.27 0.28 0.29 0.30

Conduit loss [(V )/( 2/3)]2 L (m)

where 0.014 andL 3.86 m 0.00 0.00 0.00 0.00

WSEL at Point 10 (m) 109.80 109.84 109.89 110.02


Flow Q/8, m3/s 0.27 0.38 0.41 0.55


Flow area 0.91 width depth (m2) 89.01 89.04 89.09 89.21


Loss at two 45 bends 2 .2 V2/2g (m) 0.00 0.00 0.00 0.00

WSEL at Point 11 (m) 109.80 109.84 109.89 110.02


Flow Q/4 (m3/s) 0.55 0.77 0.82 1.09


Flow area 1.52 m width depth (m2) 1.04 1.09 1.18 1.37


Loss at two 45 bends 2 .2 V2/2 (m) 0.00 0.00 0.00 0.00

r=A/P (P w 2d) (m) 0.36 0.37 0.38 0.41

Conduit loss [(V )/(r2/3)]2 L (m)

where 0.014 andL 9.75 m 0.00 0.00 0.00 0.00

WSEL at Point 12 (m) 109.81 109.84 109.90 110.03


Flow Q/4, (m3/s) 0.55 0.77 0.82 1.09


Inlet area 1.52 m width depth (m2) 1.05 1.10 1.19 1.38


Inlet loss 1 2/2 (m) 0.01 0.02 0.02 0.03

WSEL at Point 13 (Mixing Chamber No. 2 outlet) (m) 109.82 109.87 109.92 110.06


Note: Mixers provide negligible head loss

Flow Q/4 (m3/s) 0.55 0.77 0.82 1.09

Chamber area 1.83 m 1.83 m (m2) 3.34 3.34 3.34 3.34


Losses Mixer (1 V2/2g) Sharp bend (1.8 V2/2g) (m) 0.00 0.01 0.01 0.02

WSEL at Point 14 (Mixing Chamber No. 2 inlet) (m) 109.82 109.87 109.93 110.07

Note: For Points 14 through 21, see Fig. 22.14


Flow Q/2 (m /s) 1.09 1.53 1.64 2.19

Conduit area 2.29 m wide 1.22 m deep (m ) 2.79 2.79 2.79 2.79Velocity flow/area ( m/s) 0.39 0.55 0.59 0.78

R A/P (P 2 2 ) (m) 0.40 0.40 0.40 0.40

Conduit losses L [V(0.849 CR0.63)] 1/0.54 (m)

whereL 47.24 m and Hazen-Williams C 120 0.00 0.01 0.01 0.02

Local losses flow split (0.6 V2/2g) contraction

(0.07 /2 0.67 /2 (m) 0.01 0.01 0.01 0.02

WSEL at Point 15 (at Mixing Chamber No. 1) (m) 109.83 109.89 109.95 110.11






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17. The above calculations (for Points 1 through 15) have

been for flow routed through Tank No. 4. When the

flow is routed through Tank No. 1. the WSEL (m) is: 109.82 109.88 109.94 110.08

In reality, the headloss through each basin is equal.

The flow through the basin naturally adusts to

equalize headlosses, i. e. flow through Tank

No. 1 is greater than Q/4 and flow through Tank

No. 4 is less than Q/4. The actual headloss through

each basin can be estimated as the average of: Losses

through Tank Nos. 1 and 4

and the WSEL (m) at Point 15 is: 109.83 109.89 109.95 110.10


Flow Q (m3/s) 2.19 3.06 3.28 4.38

Conduit area 2.29 m wide 1.22 m deep (m2 2.79 2.79 2.79 2.79


R A/P (P 2 2 ) (m) 0.40 0.40 0.40 0.40

Conduit losses L V(0.849 CR0.63)]

1/0.54 (m) whereL 125.58 m and

Hazen-Williams C 120 0.04 0.08 0.10 0.16

WSEL at Point 16 (m) 109.87 109.97 110.04 110.26


Flow Q (m3/s) 2.19 3.06 3.28 4.38

Conduit area @ 16 2.29 m wide 1.22 m deep (m2) 2.79 2.79 2.79 2.79

Conduit area @ 17 1.68 m wide 1.68 m deep (m2) 2.81 2.81 2.81 2.81

Average area (m2) 2.80 2.80 2.80 2.80

Velocity flow / Area (m/s) 0.78 1.09 1.17 1.56

R @ 16 A16/ (2 (2.29 m 1.22 m)) (m) 0.40 0.40 0.40 0.40

R @ 17 A17/ (2 (1.68 m 1.68 m)) (m) 0.42 0.42 0.42 0.42

AverageR, (m) 0.41 0.41 0.41 0.41

Conduit losses L V(0.849 C

R0.63)]1/0.54 (m) whereL .14 m

and Hazen-Williams C 120 0.00 0.01 0.01 0.01

WSEL at Point 17 (m) 109.88 109.98 110.05 110.27


Flow Q (m3/s) 2.19 3.06 3.28 4.38

Conduit area @ 17 1.68 m wide 1.68 m

deep (m2) 2.81 2.81 2.81 2.81

Velocity 17 flow/area 17 (m/s) 0.78 1.09 1.17 1.56

Pipe area @ 18 (D4)

2 (m) where D 1.68 m 2.21 2.21 2.21 2.21

Velocity 18 flow/area 18 (m) 0.99 1.39 1.49 1.98

Exit osses V182/2g V172/2g (m/s) 0.02 0.04 0.04 0.8

WSEL at Point 18 (m) 109.90 110.01 110.09 110.3521. Point 18 to Point 19

R =A/P (P ) (m) 0.42 0.42 0.42 0.42

Local losses 3 elbows (3 0.25 /2

entrance (0.5 V2/2 ) 1.25 V2/2g (m) 0.06 0.12 0.14 0.25

Conduit losses L V(0.849 C

R0.63)]1/0.54 (m) whereL 138.68 m

and Hazen-Williams C 120 0.07 0.13 0.15 0.26

WSEL at Point 19 (exit of Control Chamber) (m) 110.03 110.27 110.39 110.86






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Weir elevation (m) 109.73 109.73 109.73 109.73

Depth of flow over weir (WSEL @

19 weir elevation), (m) 0.30 0.54 0.66 1.13

Length of weir,L, (m) 2.74 2.74 2.74 2.74

Flow over weir q 1.71 /2 [ 1 ( /n3/2

]0.385

L

Note: Rather than solve for , find an by trial

and error that gives a q equal to the flow

for the given flow scenarios (given in Item 1)

assume h (m) 0.60 0.90 0.95 1.35

then (m3/s) 1.84 3.14 3.12 4.21

assume h (m) 0.66 0.89 0.97 1.37

then (m3/s) 2.18 3.07 3.27 4.42

Note: These qs equal the flows for the given

scerios (Item 1)

h (m) 0.66 0.89 0.97 1.37

WSEL at Point 20 ( WSEL @ Point 19) (m) 110.39 110.62 110.70 111.10


Flow Q (m /s) 2.19 3.06 3.28 4.38

Sluice gate area 1.37 m 1.37 m (m2 1.88 1.88 1.88 1.88

Velocity Flow/Area (m/s) 1.16 1.63 1.74 2.33

Gate Losses 1.5 V2/2g (m) 0.10 0.20 0.23 0.41

WSEL at Point 21 (Raw Water Control

Chamber) (m) 110.49 110.82 110.93 111.51

The overflow weir in the Raw Water Control

Chamber is 3.05 m long and is sharp crested

Q = 1.82 /2 so (Q/1.82 )2/3 (m) 0.54 0.67 0.70 0.85

The water surface must not rise above elevation 112.78 m

The overflow weir elevation may be safely set at 111.86 m


hy raulic reaches analyze in the example. The circle num ers in icate points at whichthe WSEL is calculate . Hy raulic calculations start ownstream of the se imentationasins (Fig. 22.12) an procee upstream through the mixing cham er (Fig. 22.13) an

the Raw Water Control Chamber (Fig. 22.14). Mechanical mixers and mechanical floccu-lators are use . Con uit losses etween the rapi mix cham ers an the Raw WaterControl Chamber are also calculated in the example. Three different flow rates (i.e., min-imum ay, average ay, an , maximum hour) are use in the calculations. This is a rangeof esign flow con itions that a esign engineer woul typically take into consi eration.

The longest path through the flocculation an se imentation processes, through BasinNo. 4, is followed (Points 1 through 15). Although not shown, losses along the shortestpath have also been calculated. As would be expected, the calculated head loss is smallerfor the shorter path. The actual losses are equal for each path. The flows through each pathnaturally adjust to equalize losses. The flow through the longest path is slightly smallerthan the flow through the shortest path. In the example, the WSEL at Point 15 is adjusteto reflect the average losses through the asins. The WSEL calculations upstream of Point





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FIGURE 22.13 Mixing chamber

FIGURE 22.14 Raw water control chamber





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Parameter Min Day Avg Day Avg Day Max Hour

WSEL at Point 23 (m) 105.16 105.17 105.17 105.18


Flow Q/2 (m3/s) 1.09 1.53 1.64 2.19

1.68 (m) diameter pipe

Flow area 2/4 (m2 2.21 2.21 2.21 2.21


Exit loss @ clearwell 2/2 (m) 0.01 0.02 0.03 0.05

Loss @ 2 - 90obends (0.25 V2/2g 2 (m) 0.01 0.01 0.01 0.03

Entrance loss @ Filter Building 0.5 V/2g (m) 0.01 0.01 0.01 0.03

Pipe loss (3.022 V1.85 L)/

(C 1.85 D 1.165) where C 120 and

L 57.91 m (m) 0.00 0.00 0.00 0.00

WSEL at Point 24 (m) 105.19 105.22 105.23 105.28


Flow Q/4 (m3/s) 0.55 0.77 0.82 1.09

Flow area 1.52 m 1.52 m 2.32 2.32 2.32 2.32

Velocity Q/A (m/s) 0.24 0.33 0.35 0.47

Loss as flows merge 1.0 V2/2g (m) 0.00 0.01 0.01 0.01

Conduit loss [(V n)/(R2/3)]2 L (m)

where 0.013, 16.76 m and A/

(P 6.10 m) 0.00 0.00 0.00 0.00

WSEL at Point 25 (m)


Sluice Gate No. 1 flow area 1.22 m .91 m (m2) 1.11 1.11 1.11 1.11

Velocity Q/A

(m/s) 0.49 0.69 0.74 0.98

Loss 0.5 /2 (m) 0.01 0.01 0.01 0.02

WSEL at Point 26 (m) 105.20 105.24 105.24 105.32


Sluice Gate No. 2 Loss 0.8 V2/2g (m) 0.01 0.02 0.02 0.04

WSEL at Point 27 (m) 105.21 105.25 105.27 105.36

7. Point 27 to Point 28Port to Filter Clearwell: Calculate losses through port

as if were a weir when depth of flow is below top

of port. Port dimmensions 2.74 m wide

by 0.813 m deep. Flow Q/4 (m s) 0.55 0.77 0.82 1.09

Weir (bottom of port) elevation (m) 104.85 104.85 104.85 104.85

Depth of flow over weir

(WSEL @ 27 weir elevation) (m) 0.36 0.40 0.42 0.51

Flow over submergedweir q 1.71 h /2

[1 - ( /

/2]0.385 L

Note: Rather than solve for h, find an h, by trial

and error, that gives a equal to the flow for thegiven flow scenario

assume (m) 0.40 0.45 0.50 0.60

then q (m3/s) 0.59 0.69 0.95 1.23

assume (m) 0.39 0.46 0.48 0.58

then q (m3/s) 0.52 0.76 0.82 1.09

Note: These qs equal the flows for the given

scenarios

h (m) 0.39 0.46 0.48 0.58





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FIGURE 22.15 Clearwell to filter effluent

FIGURE 22.1 Filter effluent





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TABLE 22.7 Example Hydraulic Calculation of a Typical Filter


Parameter Min. Day Avg. Day. Avg. Day. Max. Hour.

Plant flow (m3/s) 2.19 3.06 3.28 4.38

Filter loading, [(m3 m)/m2] 0.083 0.167 0.250 0.334

Filter area per filterseven (7) out of eight (8) 115 115 115 115

filters in operation (m )

Flow loading area (m3/s) 0.16 0.32 0.48 0.64

Losses through filter effluent piping (Fig. 22.17)

0.51 m piping (Q :

Pipe velocity Q/A

(m/s) 0.79 1.58 2.37 3.16

Local losses Exit (0.5) butterfly

valves (2 0.25) 0o

elbows (2 .4)

tee (1.8) 3.6 V2/2g (m) 0.11 0.46 1.03 1.83

R A/P

( 2/4 p /( p) /4 (m) 0.13 0.13 0.13 0.13

Conduit losses L [V

(0.849 CR0.63)]

1/0.54 whereL 6.10 m and Hazen-

Williams C 120 (m) 0.01 0.03 0.06 0.11

0.51 m piping (Q/2):

Pipe velocity Q/A (m/s) 0.40 0.79 1.19 1.58

Local Losses Butterfly Valve (0.25) (m) 0.00 0.01 0.02 0.03

R A/P

( /4 )/( /4 (m) 0.13 0.13 0.13 0.13

Conduit losses L [V

(0.849 CR0.63)]

1/0.54 whereL 3.05 m and Hazen-

Williams C 120 (m) 0.00 0.00 0.01 0.02

0.61 m piping (Q/2):

Pipe velocity Q/A

(m/s) 0.27 0.55 0.82 1.10

Local losses entrance (1.0) tee (1.8)

2.8 V2/2 (m) 0.01 0.04 0.10 0.17

Filter (clean) and underdrain losses (obtain from

manufacturer) (m) 0.09 0.15 0.23 0.34

Total losses (effluent pipe and clean filters) (m) 0.23 0.70 1.45 2.50Assume that headloss will be allowed to increase 2.44 m before the filters are backwashed. A rate controller

will be used to maintain a constant flow through the filters. Determine the ranges of available head over

which the rate controller will operate.

Static Head (Fig. 22.18)

WSEL above filters (m) 109.73 109.73 109.73 109.73

WSEL in filter effluent conduit, Point 29

(see Example 22.2) break Maximum (m) 105.61 105.61 105.61 105.61

Minimum (m) 105.16 105.16 105.16 105.16

Static head WSEL above filtersWSEL at

Point 29 (Filter effluent conduit-2)Maximum (m) 4.57 4.57 4.57 4.57

Minimum (m) 4.11 4.11 4.11 4.11

Available head static head 2.44 m

Maximum (m) 2.13 2.13 2.13 2.13

Minimum (m) 1.68 1.68 1.68 1.68





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metal ions in the fee stream an preventing precipitation. Equili rium constants for theseantiscalants are not available which prohibits direct calculation. However, some manufac-turers provi e computer programs for estimating the require antiscalant ose for a givenrecovery, water quality, an mem rane.

Bio ogica fou ing is controlle with some mem ranes such, as cellulose acetate, ymaintaining a free chlorine resi ual of not more than 1 mg/L. Other mem ranes, such as

the thin-film composites, are not chlorine tolerant an must rely on upstream isinfectiony, for example, ultraviolet isinfection or chlorination- echlorination. The extent of foul-

ing for a specific application and its influence in the design of nanofiltration and RO mem-rane systems is est etermine y pilot stu ies.

It has een suggeste that some uil up on the mem rane may e eneficial to treat-ment y provi ing an a itional filtering layer. At facilities operate y the MetropolitanWater District of Southern California (MWD), removal rates of 1.72.9 logs were


FIGURE 22.19 Membrane configurations. (a) Spiral wound, (b) hollow fiber, ( ) tubular, (d) plateand frame.





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o serve for see e virus MS2 acteriophage through microfilters that ha a pore size anor er of magnitu e larger than the nominal size of MS2 (1).

The microfiltration system used by MWD utilizes an air backwash procedure where-

y compresse air at 90100 psig is intro uce into the filtrate si e of the hollow fi ermem ranes. Accumulate particulates islo ge y the compresse air are swept away

y raw water intro uce to the fee si e of the mem ranes. The ackwash sequence iscarrie out automatically at preset time intervals. MWD foun the est interval to eevery 18 minutes. The total volume of backwash represents approximately 57 percentof influent flow.

The difference between influent and effluent pressure across the membrane is termedthe transmem rane pressure (TMP). Despite the frequent air an water ackwashes, theTMP gra ually increases over time. Generally, when the TMP reaches approximately15 psig, chemical cleaning of the membranes is carried out. If the TMP is allowed

to increase beyond 15 psig, particulates can become deeply lodged within the lattice struc-ture of the membranes and will not be removed, even by chemical cleaning. Chemicalcleaning typically lasts 23 hours an involves circulating a solution of so ium hy roxi eand a surfactant through the membranes, and soaking them in the solution.

The membranes at the MWD microfilter plants have a surface loading rate of 4067ft . The lower flux rate of 40 ft has the a vantage that the rate of increase of TMP isre uce an the interval etween chemical cleanings is increase . A possi le explanationfor this is that particulates are not force as eeply into the lattice structure of the mem-branes, thereby allowing the air-water backwash to clean the membranes more effective-ly. By reducing the flux rate from 6740 ft , the interval etween chemical cleanings wasincrease from 2 to 3 weeks to almost 20 weeks. However, MWD has institute a maxi-mum run time of 3 months etween chemical cleanings to ensure the long-term integrityof the mem ranes.

Nanofiltration is widely used for softening groundwaters in Florida. A typical nanofil-tration plant woul inclu e antiscalant for scale control a e to the raw water. Cartri gefilters, usually rated at 5 microns, remove particles that may foul the membrane system.Fee water pumps oost the pretreate water pressure to a out 90130 poun s per squareinch (psi) efore entering the mem rane system. The mem ranes typically are spiralwoun nanofiltration mem ranes generally with molecular weight cutoff values in the200500 dalton range.

22.4 WASTEWATER TREATMENT

Many factors and considerations influence the hydraulic design of a wastewater treatmentplant. This section escri es typical phases of wastewater treatment planning require fordesign of new plants or additions to existing plants, and then presents typical unit processhy raulic computations.

22.4.1 Wastewater Treatment Planning

Hy raulic ecision making for a new wastewater treatment plant or expansion of an exist-ing plant involves several planning phases. Typical planning phases are presente elowin their common order of consideration.

22.4.1.1 Service area and flows. More than 15,000 municipal wastewater treatment plantsare in operation in the Unite States to ay. The plants are esigne to treat a total of a out






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Peak flow is use for hy raulic esign, whereas average flow is use for treatmentprocess esign. Pea f ow is efine as the maximum hour flow experience y the waste-water treatment plant throughout its service life. The maximum hour flow is generally two

to five times the average aily flow. Plants serving com ine collection systems can expe-rience even greater flow variations. Treatment plant unit processes must convey the max-imum flow unless this flow woul cause a hy raulic washout of the treatment plant. In thissituation, the esigner shoul consi er the use of equalization asins to minimize negativeimpact on the treatment process. In addition, the plant must also be able to fully processminimum flow without un esira le settling of soli s throughout the treatment train. Plantsnormally encounter diurnal fluctuation of pollutant loadings, as well as flow loadings.Fluctuation in pollutant loa ings may impact treatment process selection an consequent-ly impact process hy raulics.

22.4.1.5 Flow diagram. A flow iagram shoul e prepare to epict the results ofprocess selection an hy raulic ases of esign. Details in a flow iagram shoul inclu ethe type of unit processes, num er of asins for process re un ancy, flow istri ution anjunction chambers, piping, and conduits for interconnecting the unit processes and majorrecycle streams such as return-activate s u ge (RAS). Figure 22.20, which was men-tioned above, shows a typical flow diagram.

22.4.1.6 Plant siting. Several factors affect the plant site selection process, including siteelevation, topography, geology, an hy rology; site access; utility availa ility; seismicactivity; surroun ing lan use an future availa ility; noise, o or an air quality require-ments at an near the site; existing collection system an receiving water proximity; an

other environmental consi erations.A sites hydraulic suitability for a wastewater treatment plant is determined primarily

y site elevation an topography. The typical site elevation is low-lying, which facilitatesthe flow of wastewater from the service area y gravity an minimizes costly pumping inthe collection system. Such a site, however, may require floo protection. The ifferencein hea etween the plant influent sewer an the receiving water o y is the hea avail-able for the treatment plant. If available head does not exceed the plants head require-ments, a itional hea can e provi e y pumping the wastewater. Selecting processeswith lower head requirements can also reduce the need for pumping. Pumping of waste-water, especially untreate wastewater, shoul e avoi e when possi le ue to potential

operational ifficulties of han ling the associate rags, grit, stringy material an otherlarge soli s. A mil , continuous slope usually provi es optimal gravity flow con itions.Relatively flat sites often necessitate higher pumping hea s. Sites on a severe, unevenslope or slopes can require costly hydraulic and structural features, and should be avoid-e when possi le.

22.4.1.7 Plant layout. The selecte treatment processes esta lish the major space an

hy raulic requirements nee e to evelop initial plant layouts. Also, provisions for future

unit process additions and plant capacity expansions should be included both spatially and

hy raulically. Support facilities, such as maintenance, la oratory an a ministrative

facilities, must also be considered.

Arranging process elevations to generally follow plant site topography minimizes theamount of structural excavation. Site geology constraints may limit the practical depth and

elevation of the processes. In such cases, a itional pumping facilities may e necessary

to provi e sufficient hea for the require water surface elevation.

When arranging treatment processes, a preliminary hy raulic profile shoul e evel-

ope as iscusse elow. The plant hy raulic profile an site topography an geology

information together determine the location having the optimal elevation for each process.






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Other o jectives when eveloping a plant layout at a selecte site inclu e: close proxim-

ity of processes to associate facilities; structure grouping accor ing to process;

transportation equipment an staff traffic pattern efficiency; minimization of process

piping; an safe, isolate hazar ous chemical an material locations.

When preparing layouts for a ition of a new process to an existing plant, the existing

plant hydraulic profile should be consulted to determine the amount of head available for

the new process. If a equate hy raulic hea is not availa le for the new process, new

pumping facilities will be necessary.

22.4.1.8 Hy rau ic profi e an ca cu ations. A hy raulic profile shoul e prepare forthe flow train to graphically epict the results of hy raulic calculations an site layouts.Details in a profile should include free water surface elevations throughout the flow train,inclu ing unit treatment processes, interconnecting piping an channels, junction cham-

bers, flowmeters and flow control devices, as well as structural profiles. Figure 22.21shows a typical hy raulic profile. Both high an low water levels are shown to illustratethe range of liqui levels anticipate at each structure. Sufficient free oar must e pro-vi e to prevent liqui or floating material from splashing over the si es un er con itionsof high water level. Low water levels are important when esigning evices requiring amimimum amount of submergence, such as surface skimmers or baffles.

In a ition to normal high an low water levels, hy raulic calculations shoul a ressother potential con itions. For example, for each process having re un ant structures, thelargest capacity unit shoul e assume to e out of service uring maximum flow forconsi eration of a worst case. The process structure shoul always e hy raulicallycapable of accommodating the change in elevation due to the worst case. head require-ments without liqui overtopping the walls.

The process head requirement is the amount of head lost by the wastewater as it pass-es through a process at maximum flow. The hea requirement for a specific process canvary with flow rate, influent water quality, process equipment size, process equipment lay-out, process equipment components inclu e , an process equipment manufacturer.

22.4.2 Typical Unit Process Hydraulics

22.4.2.1 Bar screens. Process cr ter a. The first unit operation typically encountere in

a wastewater treatment plant is screening. A schematic iagram of a typical ar screen sys-tem is shown in Fig. 22.22. A screen is comprised of a screening element with circular orrectangular openings esigne to retain coarse sewage soli s. The screens are esignateas han cleane or mechanically cleane ase on the metho of cleaning. Base on thesize of the openings, screens are esignate as coarse or fine. The general ivi ing linebetween coarse and fine screens is an opening size of 6 mm (1/4 in). A ar screen is acoarse screen designed to remove large solids or trash that could otherwise damage orinterfere with the ownstream operations of treatment equipment, such as pumps, valves,mechanical aerators, and biological filters. The bar screens are oriented vertically or at aslope varying from 30 80 with the horizontal.

Key hydraulic design parameters. The key hydraulic design parameters for barscreens inclu e the approach channel, effective ar opening, an operating hea loss.

Approac c anne . Velocity istri ution in the approach channel is an important fac-tor in successful ar screen operation. A straight channel ahea of the channel provi esgoo velocity istri ution across the screen an promotes effectiveness of the evice. Useof a configuration other than a straight approach channel has often resulte in uneven flow






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FIGU

RE22.22

Schematicdiagramofbarscreensystem.





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tanks an aerate grit cham ers are still popular. Depen ing on the type of grit removalprocess use , the remove grit is often further concentrate in a cyclone, classifie , anthen washed to remove light organic material captured with the grit.

Key y rau ic esign parameters. The key hy raulic esign parameters for grit tanksinclu e the inlet channel or inlet affle, an effluent weir.

In et c anne /in et aff e. For aerate grit cham ers, the tank inlet an outlet shoul epositioned so that the flow through the tank is perpendicular to the roll pattern created by theiffuse air. Inlet an outlet affles serve to issipate energy an minimize short circuiting.

For vortex tanks, the flow into the vortex tank shoul e straight, smooth an stream-line . As a goo practice, the straight inlet channel length shoul e seven times the wi thof the inlet channel or 15 ft, whichever is greater. The ideal velocity in the influent chan-nel ranges from 0.6 to 0.9 m/s (23 ft/s) and should be used for flows between 40 and 80

percent of the peak flow. The minimum acceptable velocity for low flow is 0.15 m/s (0.5ft/s). A baffle, located at the entrance, helps control the flow system in the tank and alsoforces the grit ownwar as it enters the tank.

For etritus tanks, the performance relies on well- istri ute flow into the settlingbasin. Allowances for inlet and outlet turbulence, as well as short circuiting, are necessaryto etermine the total tank area require .

For horizontal flow grit chambers, velocity control throughout the chamber at approx-imately 0.3 m/s (1 ft/s) is important. An allowance for inlet an outlet tur ulence is nec-essary to etermine the actual length of the channel.


TABLE 22.8 Example Hydraulic Calculation of a Typical Bar Screen System

Initial Operation Design Operation

Parameter Min Day Avg.Day Avg.Day Max Hour Max Hour

1. Wastewater flow rate, Q (m /s) 1.0 1.6 2.0 3.2 3.2

(mgd) 23 36 46 73 73

Bar screens

Total number of units 3 3 3 3 3

Number of units in operation 2 2 2 2 2Number of units on standby 1 1 1 1 1

Flow rate per screen in operation, (m3/s) 0.5 0.8 1.0 1.1 1.6

Width of each bar screen, (m) 2.5 2.5 2.5 2.5 2.5

2.At point 8

Pump wetwell HGL at high water level,HGL7(m) 100.60 100.60 100.60 100.60 100.60

(pump starts at EL 100.60 and stops at EL 100.00)

Pump well bottom EL (m) 99.00 99.00 99.00 99.00 99.00

Critical depth in a rectangular channel,

Yc=(q /g/w2 1/3 0.16 0.22 0.25 0.26 0.35

Bar screen channel depth= 1.10 1.10 1.10 1.10 1.10

pump WW HGL - channel bottom EL (m)(Water level at pump well controls upstream

hydraulics if bar screen channel depth is higher

than c)

Is bar screen channel depth higher than Yc? yes yes yes yes yes

3.Point 8 to point 7

Channel bottom EL (m) 99.50 99.50 99.50 99.50 99.50





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Parameter Min Day Avg.Day Avg.Day Max Hour Max Hour

Depth in channel,y7(m) 1.10 1.10 1.10 1.10 1.10

Velocity, V7(m/s) 0.18 0.29 0.36 0.39 0.58

Exit loss from channel to pump well

Exit loss coeficient, Kexit

1.0 1.0 1.0 1.0 1.0

Headloss,Hle7=Kexit. V72

/2g (m) 0.00 0.00 0.01 0.01 0.02

HGL at point 7,HGL7 HGL8+H e7(m) 100.60 100.60 100.61 100.61 100.62

4.Point 7 to Point 6

Friction headloss through channel

Length of approach channel,L6(m) 7 7 7 7 7

Mannings number for concrete channel, n 0.013 0.013 0.013 0.013 0.013

Channel width, w6(m) 2.50 2.50 2.50 2.50 2.50

Water depth, h (m) 1.10 1.10 1.11 1.11 1.12

Velocity, V6(m/s) 0.18 0.29 0.36 0.39 0.57

Hydraulic radius,R (h w )/2 h w ) 0.59 0.59 0.59 0.59 0.59

Headloss,Hlf6 (V6 n/r62/3

)2 L6(m) 0.00 0.00 0.00 0.00 0.00

HGL at Point 6,HGL HGL7 + Hlf (m) 100.60 100.60 100.61 100.61 100.62


Bar width (m) 0.010 0.010 0.010 0.010 0.010

Bar shape factor, bsf 2.42 2.42 2.42 2.42 2.42

Cross-sectional width of bars, w (m) 0.89 0.89 0.89 0.89 0.89

Clear spacing of bars, b (m) 1.61 1.61 1.61 1.61 1.61

Upstream velocity head, (m) 0.0041 0.0104 0.0163 0.0186 0.0418

Angle of bar screen with horizontal, p (degrees) 60 60 60 60 60

(Kirschmers eq),.H s s w/

1.33 h sinp (m) 0.01 0.02 0.03 0.03 0.06

Allow 0.15 m head for blinding

by screenings,Ha (m) 0.15 0.15 0.15 0.15 0.15

HGL upstream of bar screen,HGL5

HGL6 H s Ha (m) 100.76 100.77 100.78 100.79 100.83


Friction headloss through channelLength of approach channel,L4 (m) 7.00 7.00 7.00 7.00 7.00

Mannings number for concrete channel n 0.013 0.013 0.013 0.013 0.013

Channel width, 4 (m) 2.50 2.50 2.50 2.50 2.50

Channel bottom elevation (m) 99.65 99.65 99.65 99.65 99.65

Water depth, (m) 1.11 1.12 1.13 1.14 1.18

Channel velocity, V (m/s) 0.18 0.29 0.35 0.38 0.54

Hydraulic radiusR

4/(2 h w4) 0.59 0.59 0.59 0.60 0.61

Headloss ,H (V *

n/R

4 (2/3)

2 L4 (m) 0.00 0.00 0.00 0.00 0.00

HGL at Point 4,HGL4 HGL5 H (m) 100.76 100.77 100.78 100.79 100.83


Headloss at sluice gate contraction

Kgate 1.0 1.0 1.0 1.0 1.0

Sluice gate width (m) 1.2 1.2 1.2 1.2 1.2

Sluice gate height (m) 0.9 0.9 0.9 0.9 0.9

Velocity through sluice gate, Vs (m/s) 0.38 0.59 0.74 0.78 1.13





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The primary se imentation tank receives the wastewater passe through ar screensan /or grit tanks. The o jectives of primary se imentation are to pro uce a liqui effluentsuitable for downstream biological treatment and to achieve solids separation. The solids

result in a slu ge that can e conveniently an economically treate efore ultimateisposal. On an average asis, the primary se imentation tank removes approximately

60 and 30 percent of influent total suspended solids (TSS) and 5-day biological oxygeneman (BOD ), respectively.

The secondary sedimentation tank receives mixed liquor from the aeration tank. Mixeiquor is a suspen e iological growth stream containing microorganisms an treate

wastewater. The microorganisms settle with other settleable solids and the clear water is dis-charge from the se imentation tank as an effluent. The se imentation process also thickensthe settle soli s, a major part of which is returne to the aeration tank an the remain er iswaste as secon ary slu ge. Se imentation tank performance is critical for meeting effluent

limits for TSS an BOD . The secon ary se imentation effluents are usually esigne toproduce 30 mg/L or lower for TSS or BOD , depending on the effluent requirement.

Both primary an secon ary se imentation tanks are commonly arrange in eitherrectangular or circular shape. Key design parameters include surface overf ow rate (SOR),tank water epth, hy raulic etention time, an weir loa ing rate. Soli s loa ing rate is anoth-er important parameter for the secon ary se imentation tank. A properly esigne se imen-tation tank will provi e similar performance for oth rectangular an circular shapes. Choiceof the shape epen s on the site constraints, construction cost, an esigner preference.

Key y rau ic esign parameters. The key hydraulic design parameters for sedimen-tation tanks inclu e the inlet con itions, inlet channel, inlet flow istri ution, inlet affle,

outlet con itions, overflow weir, an effluent laun er.

In et con itions. Inlets shoul e esigne to issipate the inlet port velocity, istri -ute flow and solids equally across the cross-sectional area of the tank, and prevent shortcircuiting in the se imentation tank. The minimum istance etween the inlet an outletshoul e 3 m (10 ft) unless the tank inclu es special provisions to prevent shortcircuiting.

In et c anne . Inlet channels should be designed to maintain velocities high enough toprevent soli s eposition. The minimum channel velocity is typically 0.3 m/s (1 ft/s).Alternatively, inlet channel aeration or water jet nozzles can e esigne to prevent soli seposition.

In et f ow istri ution. Inlet flow can be distributed by inlet weirs, submerged ports,or orifices with velocities between 0.05 and 0.15 m/s (0.150.5 ft/s), and sluice gates orgate valves. Uniform flow to the sedimentation tanks can be achieved by locating inletports away from si es, a ing partitions or affles in the inlet zone to re irect the influ-ent, an creating a higher hea loss in the inlet ports relative to that in the inlet channel.Alternatively, splitter oxes are use for equally splitting the flow as well as soli s con-taine in the liqui into multiple se imentation tanks.

In et aff e. Inlet affles are esigne to issipate the energy of the inlet velocities.Baffles are usually installed 0.60.9 m (23 ft) downstream of the inlet port and

submerged 0.450.6 (1.52 ft), depending on tank depth. The top of the baffle should befar enough elow the water surface to allow scum to pass over the top. Circular tanks typ-ically have a feed well with a diameter 15 to 20 percent of the tank diameter. Thesu mergence varies epen ing on the manufacturer.

Out et con itions. Effluent should be uniformly withdrawn to prevent localized highvelocity zones an short circuiting. Typically, effluent is with rawn from a se imentation






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Parameter Min Day Avg.Day Avg.Day Max Hour Pea

Length of weir,L (m) 3.00 3.00 3.00 3.00 3.00

Head over end contracted weir,

He (assumed) 0.20 0.28 0.32 0.34 0.45

Headloss,He8 ( /1.84 (L 0.2He)(2/3) (m) 0.20 0.28 0.32 0.34 0.45

H e8 He (must be zero) 0.00 0.00 0.00 0.00 0.00

HGL at Point 8,HGL8 weir

EL Hle8 (m) 106.20 106.28 106.32 106.34 106.45

4. Point 8 to Point 7Channel width, w7 (m) 3.00 3.00 3.00 3.00 3.00

Channel bottom EL (m) 105.00 105.00 105.00 105.00 105.00

Water depth, 7 (m) 1.20 1.28 1.32 1.34 1.45

Velocity, V7 (m/s)

Exit headloss from channel to effluent weir

Exit headloss coefficient Kxit 1.0 1.0 1.0 1.0 1.0 1.0

Headloss,H e7 Kxit V72/2g (m) 0.0010 0.0022 0.0032 0.0036 0.0069

HGL at Point 7,HGL7HGL H e7(m) 106.20 106.28 106.33 106.34 106.45


Channel width, 6 (m) 2.50 2.50 2.50 2.50 2.50

Channel bottomEL (m) 105.00 105.00 105.00 105.00 105.00

Water depth, 6 (m) 1.20 1.28 1.33 1.34 1.45

Velocity, V6 (m/s) 0.17 0.25 0.30 0.32 0.44

Friction headloss through channel

Length of approach channel,L6 (m) 10.00 10.00 10.00 10.00 10.00

Mannings number for concrete channel .013 0.013 0.013 0.013 0.013

Hydraulic radius,R6 (h6 w6)/

(2 x 6 6) (m) 0.61 0.63 0.64 0.65 0.67

HeadlossHlf

[(V6

n/R

6(2/3)]2

L6(m)0.0001 0.0002 0.0003 0.0003 0.0006

Fitting headloss through 90 bend

Fitting headloss coefficient

Kbend

1.0 1.0 1.0 1.0 1.0 1.0

Headloss,Hlb6 Kbend

V6

2/2g(m) 0.0014 0.0032 0.0046 0.0051 0.0099

HGL at Point 6,HGL6 HGL7

Hlf

Hlb6 (m) 106.21 106.28 106.33 106.35 106.46


Headloss through sluice gate

Sluice gate headloss coefficient

Kgate 1.0 1.0 1..0 1.0 1.0 1.0

Sluice gate width (m) 1.5 1.5 1.5 1.5 1.5

Sluice gate height (m) 1.0 1.0 1.0 1.0 1.0

Water depth, h5 (m) 1.20 1.28 1.33 1.34 1.45

Sluice gate height or 5,

whichever is smaller (m) 1.0 1.0 1.0 1.0 1.0

Velocity through sluice gate,

V5 (m/s) 0.33 0.53 0.67 0.71 1.07





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Critical depth,yc ( c2/(g w62 0.33 (m) 0.19 0.26 0.23 0.31 0.41

Water depth at upstream end

of channel,yu 2 (yc (yc

(S*L/3)

2]0.5 (2 Sc L/3) (m) 0.21 0.33 0.28 0.42 0.58

Channel bottom El at upstream

end of trough, 104.70 104.70 104.70 104.70 104.70

ELuc EL c EL i (m)

HGL at trough downstream,

HGL6 EL c (m) 104.75 104.82 104.79 104.87 104.97

HGL at trough upstream,

HGL6 ELuc (m) 104.91 105.03 104.98 105.12 105.28


Allowance to Weir from

high trough HGL (m) 0.10 0.10 0.10 .010 0.10

Weir elevation,Elwe, max.

HGL6 a owance (m) 105.38 105.38 105.38 105.38 105.38

Headloss over V notch weirs

Number of weirs per tank,Nw 1 1 1 1 1

Tank diameter,Dt, (m) 45.00 45.00 45.00 45.00 45.00

Weir length,Lw (Dt 3.14 (m) 141.30 141.30 141.30 141.30 141.30

Hydraulic load, o /Lw, [(m /s)/m] 0.0035 0.0057 0.0047 0.0075 0.0113

Weir angle,A, degrees) 90.00 90.00 90.00 90.00 90.00

V-notch height, Vh (m) 0.10 0.10 0.10 0.10 0.10

V-notch width, Vw 2

(TAN(A

/2) Vh (m) 0.20 0.20 0.20 0.20 0.20

Space between notches,Esv (m) 0.03 0.03 0.03 0.03 0.03

Number of notches per weir,

Lw/(Ew Esv) 614 614 614 614 614

Flow per notch, Qcw /nv (m3/s) 0.0008 0.0013 0.0011 0.0017 0.0026

Weir coefficient for 90 notch,Cw

1.34 1.34 1.34 1.34 1.34Water depth over the weir, hle5

(Qcw/Cw 1/2.48) 0.05 0.06 0.06 0.07 0.08

hle5 < Vh? (If not, need to

readjust calculations) Yes Yes Yes Yes Yes

HGL at Point 5,HGL5

ELwe e5 (m) 105.44 105.45 105.44 105.45 105.47


Headloss through primary

sedimentation tanks

Number of tanks,Nt 2 2 3 3 2

Flow per tank, q (m /s) 0.50 0.80 0.67 1.07 1.60Tank diameter,Dt(m) 45.00 45.00 45.00 45.00 45.00

Side water depth,Dsw (m) 4.30 4.30 4.30 4.30 4.30

Tank bottom elevation,

ELt HGL5 Dsw (m) 101.14 101.14 101.14 101.14 101.14

Tank floor slope, St(%) 8.33 8.33 8.33 8.33 8.33





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Entrance headloss from

primary sedimentation

tank influent distribution box

to influent pipe

Pipe diameter,Dp (m) 1.20 1.20 1.20 1.20 1.20

Flow per pipe, q (m /s) 0.50 0.80 0.67 1.07 1.60

Velocity, V (m/s) 0.44 0.71 0.59 0.94 1.42

Entrance headloss coefficient

Kentrance 0.5 0.50 0.50 0.50 0.50 0.50

Headloss,Hle1

Kentrance V12/2 (m) 0.0050 0.0128 0.0089 0.0227 0.0511

HGL at Point 1,HGL1

HGL2 H e1 (m) 105.52 105.60 105.56 105.68 105.90

Allowance to grit tank

effluent weir from maximum 0.10 0.10 0.10 0.10 0.10

HGL1,Ha (m)

Grit tank effluent elevation,ELgr

HGL1 Ha (m) 106.00 106.00 106.00 106.00 106.00

itches are more popular an for larger plants, plug flow is favore . Various mo ificationsof plug flow systems inclu e conventional, tapere aeration, step aeration, mo ifie aera-tion, an contact sta ilization.

P ysica configuration. Various physical configurations are use in the aeration tankdesign, including rectangular, circular, oval, and octagonal shapes.

Se ector esign. Selectors are small compartments for aero ic, anoxic or anaero icprocessing usually located in the front end of the aeration tank. The purpose of the selec-

tors is to promote the growth of floc-forming microorganisms y provi ing a favora leoo to microorganisms (F:M) ratio while suppressing filamentous growth. Typicallyselectors are esigne with low HRTs an high F:M ratio.

Key y rau ic esign parameters. The key hy raulic esign parameters for aerationtanks inclu e the istri ution ox, inlet channel, inlet flow istri ution, inlet affles, aer-ation equipment, RAS, effluent weir, and effluent channel.

Distri ution ox. Sluice gates, weirs, gate valves or orifices installe in a istri utionox are often use to istri ute the upstream flow to multiple aeration tanks an to a sec-

on ary treatment ypass line. Design shoul provi e the esire rate of flow istri utionat all flow conditions with minimum headloss. Provisions to minimize solids deposition

in the istri ution ox an appurtenances shoul e consi ere .

In et c anne . Inlet channels shoul e esigne to maintain velocities high enough toprevent soli s eposition ut low enough to minimize hea loss. A velocity of 0.3 m/s(1 ft/s) is typically used to keep organic solids in suspension. Alternatively, inlet channelaeration with diffused air, fed at a rate of 0.50.8 m /min (2030 scfm), is often use .

In et f ow istri ution. Inlet flow can e istri ute y inlet weirs, su merge ports ororifices, an sluice gates or gate valves. Return activate slu ge may e intro uce prior





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FIGURE22.25

Schematicdiagramoffinalsedimentationtank.

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chapter 22 - water and wastewater treatment plant hydraulics

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