Operation Of Wastewater Treatment Plants: A Field Study Training Program, 2Nd Edition, Volume 1

-------
Trickling Filters 183
The important thing in plant operation is to avoid problems,
and the key to avoiding problems is ALERTNESS. Many of the
common problems develop slowly and go undetected in their
early stages. For instance, ponding will occur as a result of a
buildup of heavy slime growths. The alert operator, who care-
fully inspects the filters daily, will detect the developing prob-
lem and make corrections. To the casual observer, this
operator doesn't have any problems!
F5
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 191 and 192.
6.4H What are four possible sources of abnormal condi-
tions?
6.4I How can an operator adjust the trickling-filter process
when excess flows occur?
6.4J How do high flows from the clearance of a main line
sewer stoppage differ from high flows caused by a bro-
ken sewer pipe?
6.4K Why are toxic industrial discharges difficult to detect
until it is too late?
6.4L How are toxic industrial discharges often detected or
suspected?
6.4M Why should an operator only make one change at a
time in trickling filter operation and wait approximately
one week before making another change when at-
tempting to correct a trickling-filter problem?
6.5 MAINTENANCE
6.50 Bearings and Seals (Fig. 6.8)
The bearings in distributors may be located in the base of
the center column or at the top. Both types will have a water
seal at the base to prevent wastewater leakage. This is to
avoid uneven distribution of the wastewater over the media,
and also to protect the bearings when they are located in the
base. Many older distributors utilized a mercury seal. Mercury
should not be used because mercury ions are toxic to living
organisms, including operators.
Generally, the bearings ride on removable races (tracks) in a
bath of oil. The oil usually specified is a turbine oil with oxida-
tion and corrosion inhibitors added. The manufacturer's litera-
ture or the plant 0 & M manual should specify what types of oil
to use. If this information is not available, the representative
from any major oil company can recommend a suitable oil.
Be sure to monitor the oil very carefully. The level and condi-
tion of the oil are crucial to the life of the equipment, and should
be checked weekly. To check, drain out about a pint of oil into a
clean container and, if the oil is clean and free of water, return it
to the unit. If the oil is dirty, drain it and refill with a mixture of
approximately 1/4 oil and 3/4 solvent (such as kerosene), and
operate the distributor for a few minutes. Drain again, and refill
with the correct oil. (Note: Drawing off some of the oil to check
it is important. You can see if the oil is contaminated, and verify
that the oil level sensing line is not plugged.)
Water in the oil will appear at the bottom of the oil in the
container. If water is found in the oil, either the sealing fluid is
low or the gasket must be replaced in mechanical seals. Refer
to the manufacturer's literature or the plant O & M manual for
instructions.
6.51	Distributor Arms
Work on distributor orifices only after the arms have stopped
moving, unless you are using a pressure hose for cleaning and
stand outside the filter wall. The distributor arms should be
flushed weekly by opening the end dump-gates one at a time.
Also clean debris out of the filter each dav. cleaning the orifices
ftS often as paftrtorl Whan thorp ic rnngirWahlo plugging, you
should install a coarse hardware-cloth or similar type screen
ahead of the filters, if possible. Screens are easier to clean and
good distribution is maintained over the filter media. Observe
the distributor daily for smooth operation. If it becomes jumpy,
seems to vibrate, or slows down with the same amount of
wastewater passing through it, the bearings and races are
probably damaged and will require replacement. A thorough oil
check each week will probably keep this from happening. Ad-
just the turnbuckles occasionally on the guy rods to keep the
rotating distributor arms at the proper level to provide even flow
over all of the media.
The speed of rotation of the distributor should not be exces-
sive. Rotation of the distributor is due to the reaction of the
water flowing through the orifices. This is similar to the back-
ward thrust of a water hose or the spinning of some types of
lawn sprinklers. Speed is controlled by regulation of flow
through the orifices. (On larger distributors, approximately 1
rpm is normal. The manufacturer's literature or plant O & M
manual will state the maximum allowable speed.) If the dis-
tributor rotates too fast, it may damage the bearing races on
the turntable.
To reduce the speed of rotation, provision usually is made
on the front of each arm for orifices which are easily installed
(Fig. 6.3, page 164). The reaction of the water flowing through
these orifices cancels some of the thrust of the regular orifices.
If the speed of rotation is too slow, check for mechanical prob-
lems and, if none, increase flow to distributor.
Since most distributors appear rather large and bulky, many
operators are surprised to find that they are delicately bal-
anced. As soon as wastewater begins to flow from the orifices,
the distributor arm should start to move. The fan-like pattern as
the wastewater leaves the deflecting plates should be uniform.
If the plates have developed a slime growth that is affecting
uniform distribution, the slime should be brushed off.
6.52	Fixed Nozzles
Fixed-nozzle trickling-filter beds are similar to lawn sprinkler
systems because the distribution piping system is buried under
the media and feeds into riser pipes spaced evenly across the

-------
MECHANICAL
SEAL
TURNTABLE
I)
DISTRIBUTOR
ARM
OIL FILL AND LEVEL
GAGE
SEAL PLATE
DUST SEALS
THRUST BEARINGS,
RUNNING IN OIL BATH
LEVELING ADJUSTMENT
CENTER WELL
*:.Tr&s
I-B"
oO'JO.
o


Q.? to °

c. o «
00
«
D>
3
o
3
2
d>
3
5>
CENTER ASSEMBLY BEARING AND SEAL ARRANGEMENT
Fig. 6.8 Trickling filter bearing and mechanical seal

O 4
a: o
a.
in ro
« 1-
O u.
MIXING HRS.

7„ REMOVAL
BOD
S s
INF- PRI
30.0
52.+
INF— EFF
64.6
87.2
SLUDGE DATA

1
M
FAIR
1.200
70
7.3
8
110
208
1)2
S5
2.}
7.6
21
21
7.0
2.1
5140
IDO
32
10800
4

7. SOLIDS — AVG.
4.4
2
T
n
l.f«I
6?
77
10
205
£16
143
101
1.1
7.4
SI
24
6.8
2.4
5135
1 10
32
11450
-

LBS. DRY SOLIDS / DAY
1,627

W
„
t 120
6?
7*
II
?Z0
ZZZ
153
ioe
2.0
7.0
23
26
5.1
3.0
5380
10
33
11220
ft

4
T
,,
O.W
70
7.1
1
IS4
201
127
12
2.1
7.2
26
32
£.3
1.8
4765
120
33
11570
8
Sludce to* 1 Bco - It.oooSHI..
7. VOL. SOLIDS — AVG.
76
5
F
CLW
1.008
43
7.0
7
9
232
211
1 SI
2*6
2.10
ZiS
I6£
120
2.0
7.3
7.3
7.2
31
25
8.1
1.1
50I0
1 IS
34
10110
6

LBS. VOL. SOLIDS / DAY
1,388
6
S
H
r i n?
f.A
7?
147
ins
? Z
30
ae
30
21
7.8
74
?.l
5240
120
3?
1 1200
4

7
s
FAIR
o.m
69
73
8
131
18
2.1
2.0
4815
no
32
1 El 00
4

LBS. VOL. SOLIDS/IOOOFT^DAY
27.7
8

GALS. SLUDGE TO BEDS
43,000
9

_ -i

—

CU. YDS. CAKE REMOVED
22
1 1

FT3 GAS/LB. VOL. SOLIDS
8jO
1 2

FT3 GAS/MG FLOW
10,800
14

rn«;T HATA
16

~ -

MAN DAYS_±d_ PAYROLL
1 1,250-
18

POWER PURCHASED
450 ~~
19

OTHER UTILITIES (GAS,H->0)
G0~
2 1

GASOLINE, OIL, GREASE
30~
??

CHEMICALS AND SUPPLIES
95 ~~
24

-----

—

MAINTENANCE
140 —
25

VEHICLE COSTS
70—
27

OTHER
20—
28

TOTAL
» 2,105-
30

—-

j?l

Ml
tx.

OPERATING COST/MG TREATED
| €6.83
MIN.

!E\o
TSo
Too"
2.6
"7.3"
30

OPERATING COST/CAPITA / MO.
t °-21
AVG.

1.016
63
7. /

TJ
¦o
m
z
D
X
-------

Fig. 7.4 Sections of the plastic disc media
(Permission of Autotrol Corporation)
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CHLORINE
CONTACT
BASIN
INFLUENT
SOLIDS TO
TREATMENT
SOLIDS TO
TREATMENT
CHLORINE
COMMINUTOR
SECONDARY
EFFLUENT
SOLIDS TO
DISPOSAL
ROTATING BIO
REACTOR EFFLUENT
GRIT CHAMBER
SECONDARY
CLARIFIER
PRIMARY
CLARIFIER
ROTATING
REACTOR
NO. 1
ROTATING
REACTOR
NO. 2
PRIMARY INFLUENT PRIMARY EFFLUENT
3)
O
0)
3"
ID
O
o
Fig. 7.5 Typical rotating biological contactor £
(reactor) treatment plant "
o
0)
-------
208 Treatment Plants
TABLE 7.1 PURPOSE OF PARTS OF A ROTATING
BIOLOGICAL CONTACTOR
Part
Purpose
1. Concrete or Steel Tank Di-
vided into Bays (Sections)
by Baffles (Bulkheads)
2. Orifice or Weir
Located in Baffle
3. Rotating Media
4. Cover over Contactor
5. Drive Assembly
6. Influent Lines with Valves
7. Effluent Lines with Valves
Tank. Holds the wastewater
being treated and allows the
wastewater to come in contact
with the organisms on the
discs.
Bays and baffles. Prevent
short-circuiting of wastewater.
Controls flow from one stage
to the next stage or from one
bay to the next bay.
Provide support for or-
ganisms. Rotation provides
food (from wastewater being
treated) and air for organisms.
Protects organisms from se-
vere fluctuations in the
weather, especially freezing.
Also contains odors.
Rotates the media.
Influent lines. Transport
wastewater to be treated to
the rotating biological contac-
tor.
Influent valves. Regulate in-
fluent to contactor and also to
isolate contactor for mainte-
nance.
Effluent lines. Convey treated
wastewater from the contac-
tor to the secondary clarifier.
Effluent valves. Regulate
effluent from the contactor
and also isolate contactor for
maintenance.
8. Underdrains
Allow for removal of solids
which may settle out in tank.
-------
Rotating Contactors 209
STAGE 12 3 4
MEDIA
SHAFT
PLAN
MEDIA
INFLUENT
EFFLUENT
PROFILE
LAYOUT NO. 1 ONE SHAFT, FOUR STAGES
FLOW PARALLEL TO SHAFT
STAGE
'MEDIA
¦~-SHAFT
PLAN

t 1
f—1

¦j 1
i l 1

i—i

.MEDIA
SHAFT
INFLUENT
PROFILE
EFFLUENT
LAYOUT NO. 2
FOUR SHAFTS, FOUR STAGES
FLOW PARALLEL TO SHAFT
STAGE 12 3 4
INFLUENT
>» EFFLUENT
PLAN
INFLUENT
MED A
SHAFT
V- EFFLUENT
PROFILE
LAYOUT NO. 3 FOUR SHAFTS, FOUR STAGES
FLOW PERPENDICULAR TO SHAFT
Fig. 7.6 Possible rotating biobgical contactor layouts
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210 Treatment Plants
Fiber glass covers in the shape of the media are easily re-
moved for maintenance. In some areas, the rotating biological
contactors are covered by a building. In other areas only a roof
is placed over the media for protection against sunlight. The
type of cover depends on climatic conditions.
Two types of drive assemblies are used to rotata4he-sbafts_
sOppCrting the media:
1'. Motor with chain drive (Fig. 7.7), and
2. Air drive (Fig. 7.8).
The first type of drive assembly consists of a motor, belt
drive, gear or speed reducer, and chain drive. The other drive
unit consists of plastic cups attached to the outside of the
media (Fig. 7.8). A small air header holnu" *he pHga gf thp
media releases air into the cups. The air in the cups creates a
buoyant force which then makes the shaft turn. With either type
of drive assembly, the main shaft is supported by two main
bearings.
Individual units are usually provided with influent and
effluent line valving to allow isolation for maintenance reasons.
Usually the units are not shut down during the low flow condi-
tions because power consumption is minimal and as the flows
/tefrfiasfi the percent of BOD removal increases.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 225.
7.OA How does a rotating biological contactor (RBC) treat
wastewater?
7.0B What is the purpose of a cover over the RBC unit?
7.0C Why is the RBC process divided into four stages?
7.0D What are the two types of drive units?
7.1 PROCESS OPERATION
Performance by rotating biological contactors is affected by
hydraulic loadings and temperatures below 55°F (13°C). Plants
have been designed to treat flows ranging from 18,000 gpd to
50 MGD. Typical operating and performance characteristics
are as follows:
Characteristic
HYDRAULIC LOADING2
BOD Removal
Nitrogen Removal
ORGANIC LOADING2
SOLUBLE BOD3
BOD Removal
Effluent Total BOD
Effluent Soluble BOD
Effluent NH3-N
Effluent NOa-N
Range
1.5 to 6 gpd/sq ft
1.5 to 1.8 gpd/sq ft
3 to 5 lbs BOD/day/1000 sq ft
80 to 95 percent
15 to 30mgIL
7 to 15 mgIL
1 to 10 mgIL
2 to 7 mgIL
Advantages of rotating biological contactors over trickling
filters include the elimination of the rotating distributor with its
problems, the elimination of the problems cause by ponding on
the media, and filter flies. More efficient use of the media is
achieved due to the even or uniform rotation of the media into
the wastewater being treated. A limitation of the process, as
compared with trickling filters, is the lack of flexibility due to the
absence of provisions for recirculation; however, in most in-
stallations recirculation is not needed.
7.10 Pretreatment Requirements
Rotating biological contactors are usually preceded by pre-
treatment consisting of screening, grit removal, and primary
settling. Grit and large organic matter, if nnt rpmnvpd rap
settle beneath the drums and form sludge deposits which re-
duce the effective tank volume, produce septic conditions
scrape the slimes from the media, and possibly stall the unit.
Some rotating biological contactor plants have aerated flow
equalization tanks instead of primary clarifiers ahead of the
contactors. Flow equalization tanks may be installed to
equalize or balance highly fluctuating flows and to allow for the
dilution of strong wastes and neutralization of highly acidic or
alkaline wastes. These equalization tanks are capable of re-
ducing or eliminating shock loads.
7.11 Start-Up
Prior to plant start-up, become familiar with and understand
the contents of the plant O & M manual. If you have any ques-
tions, be sure to ask the design engineer or the manufacturer's
representative. Both of these persons should instruct the
operator on the proper operation of the plant and maintenance
of the equipment.
See Section 7.5, "Loading Calculations," for procedures
showing how to calculate the hydraulic and organic loadings
on rotating biological contactors.
7.110 Pre-Start Checks tor New Equipment
Before starting any equipment or allowing any wastewater to
enter the treatment process, check the following items:
1. TIGHTNESS
Inspect the following for tightness in accordance with manu-
facturer's recommendations.
a. Anchor bolts
b. Mounting studs
c. Bearing caps
Check any torque limitations.
d. Locking collars
e. Jacking screws
2 Hydraulic and organic loadings depend on influent flow, influent soluble BOD, effluent BOD, temperature and surface area of plastic media.
Manufacturers provide charts converting flow to hydraulic and organic loadings for their media.
3 Soluble BOD Soluble BOD is the BOD of water that has been filtered in the standard suspended solids test.
-------
CHAIN
STAGES (PLASTIC MEDIA)
MOTOR
FRONT MAIN
BEARING
.v.v.;.

mmmm
:VnmViViYiV;V!r

WASTEWATER
LEVEL
INFLUENT—
PRIMARY-1
EFFLUENT
SUMP AREA FOR
PORTABLE PUMP
FOR DRAINAGE
OF TANK
SPEED
REDUCER
FRONT MAIN
BEARING
L-CHANNEL
CHAIN HOUSING
BULKHEADS
(END VIEW)
SPROCKET
AND CHAIN
(SIDE VIEW)
REAR MAIN
BEARING
EFFLUENT
SECONDARY
CLARIFIER
SPEED
REDUCER
ELECTRIC
MOTOR
MAIN SPROCKET
BELTS-
BAFFLES AND ORIFICES BETWEEN BAYS IN BULKHEADS
SJ
o
(Q
o
o
3
tt
O
Fig. 7.7 Motor with chain drive unit °
w
ro
-------
212 Treatment Plants
BEARING
AIR CONTROL
VALVE
MEDIA

AIR CUPS

(W
miiiUiiMiiHU

iiimmimiiM
fftl ::!l:l ill *
]j;j! ::: :
»!:::!:!:! ill is
11 liill! jii lj
lip jifi i i!.!1
iiiiijp
hi

wmmm

i"!

Hijlijfiiji} |{ i:
\V
Fig. 8.5 Package plant (two compartments)
-------
Activated Sludge 245
Fig. 8.6 Package plant (three compartments)
-------
246 Treatment Plants
AERATION
TANK OR
REACTOR
PRIMARY
CLARIFIER
SECONDARY
CLARIFIER
PLANT
INFLUENT
I PLANT
EFFLUENT
^/RETURN
ACTIVATED
SLUDGE
WASTE
ACTIVATED
SLUDGE
CONVENTIONAL ACTIVATED SLUDGE
PLANT
INFLUENT
AERATION
TANK OR
REACTOR
CLARIFIER
RETURN ACTIVATED SLUDGE
EXTENDED AERATION
WASTE
~ activated
SLUDGE
PRIMARY
CLARIFIER
PLANT
INFLUENT
WASTE
ACTIVATED
SLUDGE
RETURN
ACTIVATED
SLUDGE

AERATION
REGENERATION

CONTACT
OR STABILIZATION-

TANK OR
TANK

REACTOR
SECONDARY
CLARIFIER
PLANT
EFFLUENT
CONTACT STABILIZATION
PRIMARY
PLANT J \ CLARIFIER
INFLUENT
WASTE
ACTIVATED
SLUDGE
AERATION
TANK OR
REACTOR
RETURN ACTIVATED SLUDGE
COMPLETE MIX
SECONDARY
CLARIFIER
PLANT
'EFFLUENT
NOTE: ALL FOUR PLANTS HAVE AERATION HEADERS RUNNING THE LENGTH OF THE AERA HON TANK.
COMPLETE MIX ALSO HAS AERATION HEADERS RUNNING ACROSS THE AERATION TANK
AT REGULAR INTERVALS.
Fig. 8.7 Types of package aeration plants
-------
Activated Sludge 247
cally inert residue. Extended aeration does not produce as
much waste sludge as other processes; however, wasting
still is necessary to maintain proper control of the process.
2. Contact Stabilization
Contact stabilization is similar to conventional activated
sludge except that the capture of the waste material and the
digestion of that material by the bugs is done in different
aeration tanks. The bugs can "adsorb" the waste material
on the cell wall in only fifteen to thirty minutes, but it takes
several hours to "absorb' the material through the cell wall.
In conventional activated sludge, adsorption and absorp-
tion are done in one tank, therefore, the wastewater has to
remain there for a longer time. In both cases, the bugs flow
to the clarifier to be separated from the wastewater, but in
contact stabilization the settled bugs still have to digest their
food. Another aeration tank called a stabilization or re-
aeration tank is provided separately for this step. Here the
bugs digest the food and then are returned hungry to the
original aeration tank (contact tank) ready to eat more food.
The mixed liquor suspended solids (MLSS) concentration
of the contact tank should be maintained around 1,500 to
2,000 mg/L. If the MLSS gets too high, the sludge that the
microorganisms form is disposed of or "wasted" as in con-
ventional activated sludge.
In most package plants the adsorption/oxidation is
achieved in one tank.
3. Complete Mix
In an ideal complete-mix activated sludge plant, the con-
tents of the tank are completely mixed (the MLSS are uni-
formly mixed throughout the entire aeration tank). In order
to ensure that this is achieved, special arrangements are
often employed to UNIFORMLY DISTRIBUTE THE IN-
FLUENT AND WITHDRAW THE EFFLUENT FROM THE
AERATION TANK. Attention to the tank shape and to inten-
sive mixing is important. There are some means which the
operator may use to evaluate the degree to which a particu-
lar process operates in the complete mix mode. First and
foremost, the entire contents of the tank should be as uni-
form as possible. This can be confirmed by measurements
of DO and suspended solids. If the tank is thoroughly
mixed, these measurements should be nearly uniform. The
settleability of the complete-mix sludges is generally well
within the accepted range of normal operation. The MLSS
in the aeration tank ranges from 2,000 to 5,000 mgIL.
Most package plants have one influent line and one in-
fluent port. The aeration compartment has one aeration
header and the tank contents are completely mixed in a
very short time. A limitation of the complete mix type is that
the process may be more susceptible to short-circuiting.
8.202 Aeration Methods
Two methods are commonly used to supply oxygen from the
air to the bacteria — MECHANICAL AERATION and DIF-
FUSED AERATION. Both methods are mechanical processes
with the difference being whether the mechanisms are at or in
the aerator or at a remote location.
Mechanical aeration devices agitate the water surface in the
aerator to cause spray and waves by paddle wheels (Fig. 8.8),
mixers, rotating brushes, or some other method of splashing
water into the air or air into the water where the oxygen can be
absorbed.
Mechanical aerators in the tank tend to be lower in installa-
tion and maintenance costs. Usually they are more versatile in
terms of mixing, production of surface area of bubbles, and
oxygen transfer per unit of applied power.
Diffused air systems use a device called a diffuser (Fig. 8.9)
which is used to break up the air stream from the blower sys-
tem into fine bubbles in the mixed liquor. The smaller the bub-
ble, the greater the oxygen transfer due to the greater surface
area of rising air bubbles surrounded by water. Unfortunately,
fine bubbles will tend to regroup into larger bubbles while rising
unless they are broken up by suitable mixing energy and turbu-
lence.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 270.
8.2A How many compartments are there in a typical package
extended aeration plant? What is the purpose of each
compartment?
8.2B What are some common characteristics of all package
aeration plants?
8.21 Pre-Start Check-Out
If the plant is being installed, a hole is dug large enough to
accommodate the plant. Usually the plant is brought to the site
by truck and placed in the excavation (hole) by a crane. The
inlet sewer and discharge lines are connected and the plant is
ready for service after power has been connected.
While the tank is empty, check the following:
1. Tank must be level from one end to the other.
2. If the tank is constructed of metal, is CATHODIC PROTEC-
TION13 required?
3. Condition of paint on exterior and interior.
4. Removal of all rocks and debris from both compartments.
5. If equipped with comminutor or grinder, check lubrication,
clearance of cutters, and operation.
6. Check aeration device:
a. Lubrication
b. Direction of rotation
c. Mechanical aeration — proper agitator depth
d. Compressor, if diffused air
(1) Air filter and oil bath
(2) Air header and valves
(3) Air lift tubes and valves
(4) Diffusers installed
(5) Swing header lifts easily and free
7. Record and file the following data:
a. Plant model and serial number
b. Two copies of plant operation and maintenance manual
c. Name plate data from equipment
(1) Comminutor
(2) Comminutor motor
(3) Aeration motor
(4) Compressor or agitator
(5) Amperage of running equipment
(6) Oils and greases specified for each unit
8. Check influent gate or valve for proper operation.
13 Cathodic Protection (ca-THOD-ick). An electrical system for prevention of rust, corrosion, and pitting of steel and iron surfaces in contact
with water, wastewater or soil.
-------
248 Treatment Plants
Fig. 8.8 ¦ Mechanical aeration device
(Permission ol INFILCO INC.)
-------
Activated Sludge 249

V5
25. Which of the following factors could cause a demand tor
more oxygen (increase in aeration rates) , in an aeration
tank?
. Increase in food (BOD) in aeration tank influent.
2. Increase In inert or inorganic wastes.
^3. Increase in microorganisms.
4. Increase in pH.
5. Increase in toxic substances.
26. Before a package plant is started and before wastewater
is allowed to enter the aeration tank, which of the following
items should be checked?
v*i. Chips in the coating on a steel tank.
V2. Influent gate or valve for proper operation.
*3. Provisions for corrosion control of steel tanks.
4. Sludge age.
5. Tank level from one end to other.
27. A package aeration plant with the potential of odor com-
plaints from nearby homes can handle waste activated
sludge by
1. Applying sludge directly to drying beds.
2. Discharging waste activated sludge into a vacuum fit
3. Disposing of waste activated sludge In an incinerator.
Having septic tank pumper remove waste activated
sludge,
^ 5. Pumping waste activated sludge to aerated holding
tank tor disposal in a aanltaiy iandW.
28. Package planls usually
1. Have an extensive lab testing program.
, 2. Haveanopemtt«tth»ptort24fwuwaday.
^ 3. Operate aa extended aenilon plants.
4. Operate the rnrmm device ooniimua^
Waste about Ave percent of the softfii each week dur-
ing summer operation.
29. Solids In the effluent from a package aeration plant could
be caused by
V— 1. a strong stale septic influent.
v2. Either too high or too low a return sludge rate.
V 3. Either too high or too low an aeration rate.
v 4. Excessive plant inflows.
y5. Something toxic In the influent.
30. Odors from a package plant could be caused by
V1. Aeration rates being too low.
2. Excessive aeration rates.
V 3. Improper disposal of waste activated sludge.
"4. Plugged sludge return line.
y/S. Poor housekeeping.
31. Major components of an oxidation ditch wastewater treat-
ment plant include.
Bar screen.
^*2. Final settling tank.
3. Grit channel.
4. Primary clarifier.
—5. Rotors.
32. A pre-start inspection of an oxidation ditch structure
should include which of the following items?
1. Cleanliness of diffusers.
2. Making sure flights or scrapers move freely.
— 3. Operation of adjustable weir.
— 4. Proper direction of rotor rotation.
— 5. Removal of all debris from ditch.
33. Oxidation ditch solids (MLSS) concentrations are-con-
trolled by regulating
1. Aeration rates.
2. Operation of ditch skimmers.
3. Operation of ditch sludge scrapers.
.4. Return sludge rates,
— 5. Waste sludge rates.
34. Environmental factors that significantly affect an oxidation
ditch treatment process include
1. Air pollution.
<* 2. Ice.
^3. Precipitation and runoff.
V—-4. Temperature.
5. Wind.
35. Regular daily maintenance of oxidation ditches Includes
^1. Amoving andburying debris from bar screen.
V2. Removal of grease and scum from surface of final settl-
ing tank.
— 3. Removal of grit from bottom of dteh.
4. Replacing rotor blades.
VS. Washing down and/or brushing down of ditch and

END OF OBJECTIVE TEST
-------
CHAPTER 9
WASTE TREATMENT PONDS
by
A. Hiatt

-------
276 Treatment Plants
TABLE OF CONTENTS
Chapter 9. Waste Treatment Ponds
Page
OBJECTIVES 278
GLOSSARY 279
LESSON 1
9.1 Use of Ponds 281
9.2 History of Ponds in Waste Treatment 281
9.3 Pond Classifications and Applications 284
9.4 Explanation of Treatment Process 286
9.5 Pond Performance 288
LESSON 2
9.6 Starting the Pond 289
9.7 Daily Operation and Maintenance 290
9.70 Scum Control 290
9.71 Odor Control 290
9.72 Weed and Insect Control 290
9.73 Levee Maintenance 291
9.74 Headworks and Screening 291
9.75 Some Operating Hints 291
9.76 Abnormal Operation 292
9.77 Batch Operation 292
9.78 Shutting Down a Pond 292
9.79 Operating Strategy 293
9.8 Surface Aerators 293
9.9 Sampling and Analysis 296
9.90 Importance 296
9.91 Frequency and Location of Lab Samples 296
9.92 Expected Treatment Efficiencies 297
9.93 Response to Poor Pond Performance 299
9.10 Safety 299
-------
Ponds 277
LESSON 3
9.11 Review of Plans and Specifications 300
9.110 Location 300
9.111 Chemistry of Waste 300
9.112 Headworks and Screening 300
9.113 Flow-Measuring Devices 300
9.114 Inlet and Outlet Structures 301
9.115 Levees 301
9.116 Pond Depths 301
9.117 Fencing and Signs 306
9.118 Surface Aerators 306
9.119 Pond Loading (English and Metric Calculations) 306
9.12 Eliminating Algae from Pond Effluents 309
9.120 Pond Isolation 309
9.121 Water Hyacinth Culture 310
9.13 Acknowledgment 310
9.14 Additional Reading 310
9.15 Metric Calculations 310
9.16 Pond Attachment 312
-------
OBJECTIVES
Chapter 9. WASTE TREATMENT PONDS
Following completion of Chapter 9, you should be able to do
the following:
1. Explain how waste treatment ponds work and what factors
influence and control pond treatment processes,
2. Place a new pond into operation,
3. Schedule and conduct normal and abnormal operational
and maintenance duties,
4. Collect samples, interpret lab results, and make appropri-
ate adjustments in pond operation,
5. Recognize factors that indicate a pond is not performing
properly, identify the source of the problem, and take cor-
rective action,
6. Develop a pond operating strategy,
7. Conduct your duties in a safe fashion,
8. Determine pond loadings,
9. Identify the different types of ponds,
10. Keep records for a waste treatment pond facility, and
11. Review plans and specifications for new ponds.
-------
Ponds 279
GLOSSARY
Chapter 9. WASTE TREATMENT PONDS
ADVANCED WASTE TREATMENT ADVANCED WASTE TREATMENT
Any process of water renovation that upgrades treated wastewater to meet specific reuse requirements. May include general
cleanup of water or removal of specific parts of wastes insufficiently removed by conventional treatment processes.
ALGAE (AL-gee) ALGAE
Microscopic plants which contain chlorophyll and float or are suspended and live in water. They also may be attached to structures,
rocks or other similar substances.
BIOFLOCCULATION (BUY-o-flock-u-LAY-shun) BIOFLOCCULATION
The clumping together of fine, dispersed organic particles by the action of bacteria and algae. This results in faster and more
complete settling of the organic solids in wastewater.
CHEMICAL OXYGEN DEMAND or COD CHEMICAL OXYGEN DEMAND or COD
A measure of the oxygen-consuming capacity of inorganic and organic matter present in wastewater. COD is expressed as the
amount of oxygen consumed from a chemical oxidant in mg/L during a specific test. Results are not necessarily related to the
biochemical oxygen demand because the chemical oxidant may react with substances that bacteria do not stabilize.
COMPOSITE (PROPORTIONAL) SAMPLE COMPOSITE (PROPORTIONAL) SAMPLE
(com-POZ-it)
A composite sample is a collection of individual samples obtained at regular intervals, usually every one or two hours during a
24-hour time span. Each individual sample is combined with the others in proportion to the flow when the sample was collected. The
resulting mixture (composite sample) forms a representative sample and is analyzed to determine the average conditions during the
sampling period.
FACULTATIVE POND (FACK-ul-tay-tive) FACULTATIVE POND
The most common type of pond in current use. The upper portion (supernatant) is aerobic, while the bottom layer is anaerobic.
Algae supply most of the oxygen to the supernatant.
FREE OXYGEN FREE OXYGEN
Molecular oxygen available for respiration by organisms. Molecular oxygen is the oxygen molecule, 02, that is not combined with
another element to form a compound.
GRAB SAMPLE GRAB SAMPLE
A single sample taken at neither a set time nor flow.
MEDIAN MEDIAN
The middle measurement or value. When several measurements are ranked by magnitude (largest to smallest), half of the
measurements will be larger and half will be smaller.
MOLECULAR OXYGEN MOLECULAR OXYGEN
The oxygen molecule, 02, that is not combined with another element to form a compound.
PARALLEL OPERATION PARALLEL OPERATION
When wastewater being treated is split and a portion flows to one treatment unit while the remainder flows to another similar
treatment unit. Also see SERIES OPERATION.
PERCOLATION (PURR-ko-LAY-shun) PERCOLATION
The movement or flow of water through soil or rocks.
-------
280 Treatment Plants
pH pH
pH is an expression of the intensity of the alkaline or acidic strength of a liquid. Mathematically, pH is the logarithm (base 10) of the
reciprocal of the hydrogen ion concentration.
pH = Log J—
(H+)
The pH may range from 0 to 14, where 0 is most acid, 14 is most alkaline, and 7 is neutral. Natural waters usually have a pH
between 6.5 and 8.5.
PHOTOSYNTHESIS (foto-SIN-the-sis) PHOTOSYNTHESIS
A process in which organisms with the aid of chlorophyll (green plant enzyme) convert carbon dioxide and inorganic substances to
oxygen and additional plant material, utilizing sunlight for energy. Land plants grow by the same process.
POPULATION EQUIVALENT POPULATION EQUIVALENT
A means of expressing the strength of organic material in wastewater. In a domestic wastewater system, microorganisms use up
about 0.2 pounds of oxygen per day for each person using the system (as measured by the standard BOD test).
Pop. Equiv., = Flow, MGD x BOD, mgIL x 8.34 lbs/gal
persons 0 2 hjS BOD/day/person
RIPRAP RIPRAP
Broken stones, boulders, or other materials placed compactly or irregularly on levees or dikes for the protection of earth surfaces
against the erosive action of waves.
SERIES OPERATION SERIES OPERATION
When wastewater being treated flows through one treatment unit and then flows through another similar treatment unit. Also see
PARALLEL OPERATION.
SPLASH PAD SPLASH PAD
A structure made of concrete or other durable material to protect bare soil from erosion by splashing or falling water.
STABILIZED WASTE STABILIZED WASTE
A waste that has been treated or decomposed to the extent that, if discharged or released, its rate and state of decomposition would
be such that the waste would not cause a nuisance or odors.
STOP LOG STOP LOG
A log or board in an outlet box or device used to control the water level in ponds.
TERTIARY TREATMENT (TER-she-AIR-ee) TERTIARY TREATMENT
Any process of water renovation that upgrades treated wastewater to meet specific reuse requirements. May include general
cleanup of water or removal of specific parts of wastes insufficiently removed by conventional treatment processes. Typical
processes include chemical treatment and pressure filtration. Also called ADVANCED WASTE TREATMENT.
TOXIC (TOX-ick) TOXIC
Poisonous.
TOXICITY (tox-IS-it-tee) TOXICITY
A condition which may exist in wastes and will inhibit or destroy the growth or function of certain organisms.
h
IT,
-------
Ponds 281
CHAPTER 9. WASTE TREATMENT PONDS
USED FOR TREATMENT OF WASTEWATER AND OTHER WASTES
(Lesson 1 of 3 Lessons)
9.1 USE OF PONDS
Shallow ponds (three- to five-feet or 1 to 1.5 meters deep)
are often used to treat wasTewater and other wastes Instead of,
or in addition to, conventional waste treatment processes.
(See Figs. 9.1 and 9.2 for typical plant layouts and Table 9.1
for purpose of pond parts.) When discharged into ponds,
TABLE 9.1
Part
1. Flow Meter
2. Bar Screen
3. Pond Inlets
PURPOSE OF POND PARTS
Purpose
Measures and records flows
into pond.
Removes coarse material
from pond influent.
4. Pond Depth and Outlet
Control
5. Outlet Baffle
6. Dike or Levee
7. Transfer Line
8. Recirculation Line
9. Chlorination
10. Chlorine Contact Basin
11. Effluent Line
Distribute influent in pond.
Regulates outflow from pond
and depth of water in pond. Al-
lows pond to be drained for
cleaning and inspection.
Prevents scum and other sur-
face debris from flowing to
next pond or receiving waters.
Separates ponds and holds
wastewater being treated in
ponds.
Conveys wastewater from
one pond to another.
Returns pond effluent rich in
algae and oxygen from sec-
ond pond to first pond for
seeding, dilution and process
control.
Applies chlorine to treated
wastewater for disinfection
purposes.
Provides contact time for
chlorine to disinfect pond
effluent.
Conveys treated wastewater
to receiving waters, to point of
reuse (irrigation), or to land
disposal site.
wastes are treated or STABILIZED1 by several natural pro-
cesses acting at the same time. Heavy solids settle to the
bottom where they are decomposed by bacteria. Lighter sus-
pended material is broken down by bacteria in suspension.
Some wastewater is disposed of by evaporation from the pond
surface.
Dissolved nutrient materials, such as nitrogen and phos-
phorous, are utilized by green ALGAE2 which are actually mi-
croscopic plants floating and living in the water. The algae use
carbon dioxide (C02) and bicarbonate to build body proto-
plasm. In so growing, they need nitrogen and phosphorous in
their metabolism much as land plants do. Like land plants, they
release oxygen and some carbon dioxide as waste products.
Ponds can serve as very effective treatment facilities. Ex-
tensive studies of their performance have led to a better un-
derstanding of the natural processes by which ponds treat
wastes. Information is provided here on the natural processes
and ways operators can regulate pond processes for efficient
waste treatment.
9.2 HISTORY OF PONDS IN WASTE TREATMENT
The first wastewater collection systems in the ancient Orient
and in ancient Europe discharged wastewater into nearby
bodies of water. These systems accomplished their intended
purpose until overloading, as in modern systems, made them
objectionable.
In ancient times, ponds and lakes were purposefully fer-
tilized with organic wastes to encourage the growth of algae
which, in turn, greatly increased the production of fish due to
the food supply provided by the algae. This practice still con-
tinues and is a recognized art in Germany.
The first ponds constructed in the United States were built
for the purpose of keeping wastewaters from flowing into
places where they would be objectionable. Once built, these
ponds performed a treatment process that finally became rec-
ognized as such.
The tendency over the years has been to equate pond
treatment effiency with the non-emission of odors. Actually, the
opposite is true as the greatest organic load destroyed per unit
1 Stabilized Wastes. A waste that has been treated or decomposed to the extent that, if discharged or released, its rate and state of
decomposition would be such that the waste would not cause a nuisance or odors.
2 Algae (AL-gee). Microscopic plants which contain chlorophyll and float or are suspended and live in water. They also may be attached to
structures, rocks or other similar substances.
-------
IO
00
IO
EFF.
INF.
FLOW
METER
BAR SCREEN
i PONDS
CHLORINE CONTACT
BASIN
(D
»
3
-------
INF.
BIOLOGICAL
PROCESS
(REMOVE SUS-
PENDED AND
DISSOLVED
SOLIDS)
SCREENING,
GRIT REMOVAL
(REMOVE
COARSE
MATERIAL)
MEASURE,
RECORD
FLOW
SEDIMENTATION
(REMOVE
SETTLEABLE
AND FLOATING
MATERIALS)
(SOLIDS
DISPOSAL)
DISINFECTION
DIGESTION
AND
SLUDGE
HANDLING
3 PONDS
PRIMARY
TREATMENT
PRELIMINARY
TREATMENT
SECONDARY
TREATMENT
FLOW
METER
CHLORI NATION
INFLUENT
mmm
EFFLUENT
SOLIDS TO
DIGESTION
SOLIDS BACK
TO PRIMARY
TREATMENT
TJ
O
3
a
<0
Fig. 9.2 Typical plant; ponds after secondary treatment
to
00
u
-------
284 Treatment Plants
of area (high treatment efficiency) may be accompanied by
objectionable odors.
Since 1958, engineers have designed and constructed a
great number of ponds using research by qualified biological
consultants, current scientific knowledge of ponding, and the
experience of past successes and failures. When operated in a
knowledgeable and purposeful manner, these ponds have
Successfully performed a variety of functions.
As a complete process, the ponding of wastewater offers
many advantages for smaller installations. This is true pro-
vided that land is not costly and the location is isolated from
residential, commercial, and recreational areas. The advan-
tages are that a pond:
1. Does not require expensive equipment;
2. Does not require highly trained operating personnel;
3. Is economical to construct;
4. Provides treatment that is equal or superior to some con-
ventional processes;
5. Is a satisfactory method of treating wastewater on a tem-
porary basis;
— 6. Is adaptable to changing loads;
7. Is adaptable to land application;
8. Consumes little energy;
9. Serves as a wildlife habitat;
10. Has potentially an increased design life;
11. Has no sludge handling and disposal problems; and
12. Is probably the most trouble-free of any treatment process
when utilized correctly, PROVIDED A CONSISTENTLY
HIGH QUALITY EFFLUENT IS NOT REQUIRED.
The limitations are that a pond:
1. May emit odors;
2. Requires a large area of land;
3. Treats wastes somewhat dependent on climatic condi-
tions;
4. May contaminate groundwaters; and
5. May have high suspended solids levels in the effluent.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 313.
9.2A If a pond is giving off objectionable odors, are the
wastes being effectively treated? Explain your answer.
9.2B Discuss the advantages of ponds.
9.3 POND CLASSIFICATIONS AND APPLICATIONS
Ponding of raw wastewater, as a complete treatment pro-
cess, is used to treat the wastes of single families as well as
large cities up to the size of the city of Melbourne, Australia.
Currently a portion of Melbourne's wastewater is disposed of
on a 28,000 acre farm. During the dry season, most of the
treatment is accomplished by broad irrigation and grass filtra-
tion (flowing through grass lands) while during the wet season
most of the 130 MGD flow is handled by ponds and discharged
to receiving waters. Ponds designed to receive wastes with no
prior treatment are often referred to as "raw wastewater (sew-
age) lagoons" or "stabilization ponds" (Fig. 9.3). This requires
sizable areas of land.
Ponds are quite commonly used in series (one pond follow-
ing another) after a primary wastewater treatment plant to pro-
vide additional clarification, BOD removal, and disinfection.
These ponds are sometimes called "oxidation ponds." Pnnrls
.are sometimes used in series after a trickling filter plant, thus
pivin(f5'lDrnTT?f-7tH//>qH sometimes-
called "polishing ponds." Ponds placed in series with each
other can provide a high quality effluent which is acceptable for
discharge into most watercourses. If the detention time is long
enough, many ponds can meet fecal coliform standards.
A great many variations in ponds are possible due to differ-
ences in depth, operating conditions, and loadings. A bold line
of distinction among different types of ponds is often impossi-
ble. Current literature generally uses three broad pond classifi-
cations: AEROBIC, ANAEROBIC, and FACULTATIVE.
AEROBIC ponds are characterized by having dissolved
oxygen distributed throughout their contents practically all of
the time. They usually require an additional source of oxygen
to supplement the rather minimal amount that can be diffused
from the atmosphere at the water surface. The additional
source of oxygen may be supplied by algae during daylight
hours, by mechanical agitation of the surface, or by bubbling
air provided by compressors through the pond.
ANAEROBIC ponds, as the name implies, usually are with-
out any dissolved oxygen throughout their entire depth. Treat-
ment depends on fermentation of the sludge at the pond bot-
tom. This process can be quite odorous under certain condi-
tions, but it is highly efficient in destroying organic wastes.
Anaerobic ponds are mainly used for processing industrial
wastes, although some domestic-waste ponds become
anaerobic when they are badly overloaded.
FACULTATIVE (FACK-ul-TAY-tive) ponds are the most
common type in current use. The upper portion (supernatant)
of-thesa ponds is aerobic, while the bottom layer is anaerobic.
Algae supply most of the oxygen tojha supernatant.-Faculta-
tive ponds are most common Decause it is almost impossible
to maintain completely aerobic or anaerobic conditions all the
time at all depths of the pond.
Pond uses may be classified according to detention time. A
pond with a detention time of less than three days will perform
in ways similar to a sedimentation or settling tank. Some
growth of algae will occur in the pond, but it will not have a
major effect on the treatment of the wastewater.
Prolific growth of algae will be observed in ponds with deten-
tion periods from three to around twenty days, but large
amounts of algae will be found in the pond effluent. In some
effluents, the stored organic material may be greater than the
amount in the influent. Detention times in this range merely
allow the organic material to change form and delay problems
until the algae settle out in the receiving waters. Effluent BODs
may show considerable reductions from influent BODs, but this
is because BOD is a rate estimate (oxygen used during a
3 Tertiary (TER-she-AIR-ee). Tertiary refers to the third treatment process or the process following a secondary treatment process, such as a
trickling filter. Some refer to tertiary treatment as advanced waste treatment, meaning processes that remove wastes not commonly removed
by conventional (secondary) treatment processes.
-------
Ponds 285
INFLUENT
RAW
WASTE-
WATER
POND NO. 2
POND NO. 3
POND NO. 1
STABILIZATION PONDS IN SERIES
EFFLUENT
INFLUENT
RAW
WASTE-
WATER
POND NO. 1
POND NO. 2
STABILIZATION PONDS IN PARALLEL
EFFLUENT
INFLUENT
PRIMARY
CLARIFIER
POND NO. 2
POND NO. I
OXIDATION PONDS IN SERIES
TRICKLING
FILTER
PRIMARY
CLARIFIER
POND NO. 2
POND NO. 1
SECONDARY
CLARIFIER
POLISHING PONDS IN SERIES
Fig. 9.3 Pond Classifications
-------
286 Treatment Plants
five-day period). The rate of oxygen use is temporarily slowed
down, but will increase when anaerobic decomposition of set-
tled dead algae cells starts.
Longer detention periods in ponds provide time for the
sedimentation of algae. Usually, this will occur in ponds with
anaerobic conditions on the bottom and aerobic conditions on
the surface. Combined aerobic-anaerobic treatment provided
by long detention periods produces definite stabilization of the
ihfluent.
Controlled discharge ponds are facultative ponds with long
detention times of up to 180 days or longer. These ponds may
discharge effluent only once (fall) or twice (fall and spring) a
year.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 313.
9.3A What is the difference between raw wastewater (sew-
age) lagoons, oxidation ponds, and polishing ponds?
9.3B What is the difference between the terms "aerobic,"
"anaerobic," and "facultative" when applied to ponds?
9.3C How does the use of a pond vary depending on deten-
tion time?
9.4 EXPLANATION OF TREATMENT PROCESS
As mentioned in the previous section, waste disposal ponds
also are classified according to their dissolved oxygen content.
Oxygen in an aerobic pond is distributed throughout the entire
depth practically all the time. An anaerobic pond is predomi-
nantly without oxygen most of the time because oxygen re-
quirements are much greater than the oxygen supply. In a
facultative pond, the upper portion is aerobic most of the time,
whereas the bottom layer is predominantly anaerobic.
In aerobic ponds or in the aerobic layer of facultative ponds,
organic matter contained in the wastewaterjsfirst converted to
narhnn dioxide and ammonia, and finaiiyTtolitgaeinrthepres-
ence of sunlight. Algae are simple one-cell microscopic plants
which are essential to the successful operation of both aerobic
and facultative ponds.
By utilizing sunlight through PHOTOSYNTHESIS,4 the one-
celled plant uses the oxygen in the water molecule to produce
FREE OXYGEN,5 making it available to the aerobic bacteria
that inhabit the pond. Each pound of aloae in a healthy pond is
capable nf nrnrincinn i « pounds of nxx/nan on a normal sum-
mer day. Algae live on carbon dioxide and other nutrients in the
wastewater. Algae occur naturally in a pond without seeding
and multiply greatly under favorable conditions. Figure 9.4 il-
lustrates the role of algae in treating wastes in a pond.
In anaerobic ponds or in the anaerobic layer of facultative
ponds, the organic matter is first converted by a group of or-
ganisms called the "acid producers" to carbon dioxide, nitro-
gen, and organic acids. In an established pond, at the same
time, a group called the "methane fermenters" breaks down
the acids and other products of the first group to form methane
gas and alkalinity. Water is another end product of organic
decomposition. This process is described in Figure 9.4.
In a successful facultative pond, the processes characteris-
tic of aerobic ponds occur in the surface layers, while those
similar to anaerobic ponds occur in its bottom layers.
During certain periods, sludge decomposition in the
anaerobic zone is interrupted and it begins to accumulate. If
sludge accumulation occurs and decomposition does not set
in, it is probably due to a lack of the right bacteria, low pH,6
pressure of substances that slow or stop the process, or a low
temperature. Under these circumstances, the acid production
will continue at a slower rate, but the rate of gas (methane)
production slows down considerably.
Sludge storage in ponds is continuous with small amounts
stored during warm weather and larger amounts when it is
cold. During low temperatures, the bacteria cannot multiply
fast enough to handle the waste. When warm weather comes,
the "acid producers" begin to decompose the accumulated
sludge deposits built up during the winter. If the organic acid
production is too great, a lowered pH will occur with the pos-
sibilities of an upset pond and resulting hydrogen sulfide odors.
Hydrogen sulfide ordinarily is not a problem in properly de-
signed and bpsrated" ponds because it dissociates (divides)
into hydrogen and hydrosulfide ions at high pH and may form
insoluble metallic sulfides or sulfates, niis high degree of dis-
sociation and the formation of insoluble metallic sulfides are
the reasons that ponds having a pH above 8.5 do not emit
odors, even when hydrogen sulfide is present in relatively large
amounts. An exception occurs in northern climates during the
spring when the pH is low and the pond is just getting started,
then hydrogen sulfide odors can be a problem.
All of the organic matter that finds its way to the bottom of a
stabilization pond through the various processes of sludge de-
composition is subject to METHANE FERMENTATION, pro-
vided that proper conditions exist or become established. In
order for methane fermentation to exist, an abundance of or-
ganic matter must be deposited and continually converted to
organic acids. An abundant population of methane bacteria
must be present. They require a pH level of from 6.5 to 7.5
within the sludge, alkalinity of several hundred mg/L to buffer
(neutralize) the organic acids (volatile acid/alkalinity relation-
ship), and suitable temperatures. Once methane fermentation
is established, it accounts for a considerable amount nf tho
organic load removal?
4 Photosynthesis. A process in which organisms with the aid of chlorophyll (green plant enzyme) convert carbon dioxide and inorganic
substances to oxygen and additional plant material, utilizing sunlight for energy. Land plants grow by the same process.
Light
COj + Hfi ~ CH2Ox + 02
5 Free Oxygen. Molecular oxygen available for respiration by organisms. Molecular oxygen is the oxygen molecule, 02, that is not combined
with another element to form a compound.
6 pH. pH is an expression of the intensity of the alkaline or acid strength of a liquid. Mathematically, pH is the logarithm (base 10) of the
reciprocal of the hydrogen ion concentration.
pH = Log J—
(H+)
The pH may range from 0 to 14, where 0 is the most acid, 14 the most alkaline, and 7 is neutral. Most natural waters usually have a pH
between 6.5 and 8.5.
-------
Ponds 287
AEROBIC
ANAEROBIC
ALGAE OBTAIN
ENERGY FROM
SUNLIGHT
POND SURFACE
ALGAE
ALGAE, UTILIZING SUNLIGHT
THROUGH PHOTOSYNTHESIS,
USE THE OXYGEN IN THE
WATER MOLECULE TO
PRODUCE FREE OXYGEN
ALGAE LIVE
ON C02 AND
NUTRIENTS
_£

ORGANIC MATTER AND

INPUT OR
NUTRIENTS IN WASTES

INFLUENT "
BEING TREATED

AEROBIC
NUTRIENTS
AND AMMONIA
TO ALGAE
CARBON
DIOXIDE
OXYGEN
DEAD
CELLS
AEROBIC BACTERIA
IN POND USE (EAT)
WASTES AND NUTRIENTS
AEROBIC BACTERIA
REMOVE (BREATHE
OR RESPIRATE)
DISSOLVED OXYGEN
FROM WATER
BACTERIA
RELEASE
(RESPIRATION)
ANAEROBIC
NUTRIENTS
AND
k AMMONIA .
HYDROGEN
SULFIDE
CARBON
DIOXIDE
METHANE
ALKALINITY
WATER
DEAD
CELLS
METHANE
FERMENTING
BACTERIA
BREAK DOWN
ACIDS AND
OTHER PRO-
DUCTS TO
METHANE
GAS,C02> HjS,
ALKALINITY
AND WATER
INPUT OR
ORGANIC
ACIDS
INFLUENT
ACID-PRODUCING BACTERIA
CONVERT ORGANIC
^ ANAEROBIC >
BACTERIA
IN POND USE (EAT)
WASTES AND
V NUTRIENTS >
ORGANIC MATTER
AND NUTRIENTS
IN WASTES
BEING TREATED
ACID-PRODUCING BACTERIA
CONVERT ORGANIC
MATTER TO VOLATILE
ACIDS. COo, WATER AND
NITROGEN
Fig. 9.4 Process of decomposition in aerobic and anaerobic
layers of a pond
-------
288 Treatment Plants
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 313.
9.4A How is oxygen produced by algae?
9.4B Where does the algae found in a pond come from?
9.4C What happens to unstable organic matter in a pond?

9.5 POND PERFORMANCE
The treatment efficiencies that can be expected from ponds
vary more than most other treatment devices. Some of the
many variables are:
1. Physical Factors
a.
b.
c.
d.
e.
f.
g-
h.
type of soil
surface area
depth
wind action
sunlight
temperature
short-circuiting
inflow variations
2. Chemical Factors
a. organic material
b. pH
c. solids
d. concentration and nature of waste
3. Biological Factors
a. type of bacteria
b. type and quantity of algae
c. activity of organisms
d. nutrient deficiencies
e. toxic concentrations
The performance expected from a pond depends largely
upon its design. The design, of course, is determined by the
waste discharge requirements or the water quality standards to
be met in the receiving waters. Overall treatment efficiency
may be about the same as primary treatment (only settling of
solids), or it may be equivalent to the best secondary biological
treatment plants. Some ponds, usually those located in hot,
arid areas, have been designed to take advantage of PERCO-
LATION7 and high evaporation rates so that there is no dis-
charge.
Depending on design, ponds can be expected to provide
BOD removals from 50 to 90 percent. Facultative ponds, under
jQormaLdesjgnJoads with 50 to 60 days' detention timeTltfiir
usually remove approxima!ety-90 to 95 percent of the cbliform
bacteria and, 70. to 80 percent of the BOD load approximately
80 percent of the time. Controlled discharge ponds with 180-
Ldetention times can produce BOD removals from 85 to
percentTToTdl susperidScTsoTrasTemovaTs from~8b to 95"per-"
cent, and fecal coliform reductions up to 99 percent.
Physical sedimentation by itself has been found to remove
approximately 90 percent of the suspended solids in three
days. About 80 percent of the dissolved organic solids can be
removed by biologic action in ten days. However, in a pond
with a healthy algae and bacteria population, a phenomenon
known as BIOFLOCCULATION8 can occur. This will remove
approximately 85 percent of both suspended and dissolved
solids within hours. Bioflocculation is accelerated by incres
temperature, wave acfionrand tTtgh'dissoTVSdTOTygerTcontent.
Pond detention times are sometimes specified by regulatory
agencies to assure adequate treatment and removal of bac-
teria. Many agencies specify effluent or receiving water quality
standards in terms of MEDIAN9 and maximum MPN (Most
Probable Number) values that should not be exceeded. In criti-
cal water use areas, chlorination or other means of disinfection
can be used to further reduce the coliform level (see Chapter
10, "Chlorination and Disinfection").
A pond is generally regarded as not fulfilling its function
when it creates a visual or odor nuisance, or leaves a high
BOD, solids, grease, or coliform-group bacteria concentration
in the discharge.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 313.
9.5A What is bioflocculation?
9.5B What biological factors influence the treatment effi-
ciency of a pond?
9.5C What factors indicate that a pond is not fulfilling its func-
tion (operating properly)?

m ofimrwtu&hMU
Please answer the discussion and review questions before
continuing with Lesson 2.
7 Percolation (PURR-ko-LAY-shun). The movement or flow of water through soil or rocks.
8 Bioflocculation (BUY-o-flock-u-LAY-shun). The clumping together of fine, dispersed organic particles by the action of bacteria and algae.
This results in faster and more complete settling of the organic solids in wastewater.
9 Median. The middle measurement or value. When several measurements are ranked by magnitude (largest to smallest), half of the
measurements will be larger and half will be smaller.
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Ponds 289
DISCUSSION AND REVIEW QUESTIONS
Chapter 9. WASTE TREATMENT PONDS
(Lesson 1 of 3 Lessons)
At the end of each lesson in this chapter, you will find some
discussion and review questions that you should work before
continuing. The purpose of these questions is to indicate to you
how well you understand the material in this lesson.
Write the answers to these questions in your notebook be-
fore continuing.
1. When wastewater flows through different treatment pro-
cesses in a plant, where might ponds be located?
2. Why are most ponds "facultative ponds"?
3. Where does the oxygen come from that is produced by
algae in a pond?
4. What is photosynthesis?
5. What are the three types of factors that may influence pond
performance?
CHAPTER 9. WASTE TREATMENT PONDS
(Lesson 2 of 3 Lessons)
9.6 STARTING THE POND
One of the most critical periods of a pond's life is the time
that it is first placed in operation. If at all possible, at least one
foot (n.a m) nf watar should be in the pond before wastes are
introduced. The water should be turned into the pond in ad-
vance to prevent odors developing from waste solids exposed
to the atmosphere. Thus a source of water should be available
when starting a pond.
A good practice is to start ponds during the warmer part of
the year because a shallow starting depth allows the contents
of the pond to cool too rapidly if nights are cold. Generally
speaking, the warmer the pond contents, the more efficient the
treatment processes.
Algal blooms normally will appear from seven to twelve days
after wastes are introduced into a pond, but it generally takes
at least sixty days to establish a thriving biological community.
A definite green color is evidence that a flourishing algae popu-
lation has been established. After this length of time has
elapsed, bacterial decomposition of bottom solids will usually
become established. This is generally evidenced by bubbles
coming to the surface near the pond inlet where most of the
sludge deposits occur. Although the bottom is anaerobic, travel
of the gas through the aerobic surface layers generally pre-
vents odor release.
Wastes should be discharged to the pnnd intermittently dur-
ing the first few weeks with constant monitoring of the pH. The
pH in the pona should be Kept above 7.5 if possible. Initially the
pH of the bottom sludge will be below 7 due to the digestion of
the sludge by acid-producing bacteria. If the pH starts to drop,
discharge to the pond should be diverted to another pond or
diluted with make-up water (water from another source) if
another pond is not available until the pH recovers. A high pH
is essential to encourage a balanced anaerobic fermentation
(bacterial decomposition) of bottom sludge. This high pH also
is indicative of high algal activity since removal of the carbon-
ate from the water in algal metabolism tends to keep the pH
high. A continuing low pH indicates acid production which will
cause odors. Soda ash (sodium bicarbonate) may be added to
the influent to a pond to increase the pH.
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290 Treatment Plants
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 313.
9.6A Why should at least one foot of fresh water cover the
pond bottom before wastes are introduced?
9.6B Why should ponds be started during the warmer part of
the year if at all possible?
9.6C What does a definite green color in a pond indicate?
9.6D When bubbles are observed coming to the pond sur-
face near the inlet, what is happening in the pond?
9.7 DAILY OPERATION AND MAINTENANCE
BECAUSE PONDS ARE DECEPTIVELY SIMPLE, THEY
ARE PROBABLY NEGLECTED MORE THAN ANY OTHER
TYPE OF WASTEWATER TREATMENT PROCESS. Many of
the complaints that arise regarding ponds are the result of
neglect or poor housekeeping. Following are listed the day-
to-day operational and maintenance duties that will help to
insure peak treatment efficiency and to present your plant to its
neighbors as a well-run waste treatment facility. If problems
develop in a pond, refer to this section and Section 9.11, "Re-
view of Plans and Specifications," as troubleshooting guides.
9.70 Scum Control
Scum accumulation is a common characteristic of ponds
and is usually greatest in the spring of the year when the water
warms and vigorous biological activity resumes. Ordinarily,
wind action will dissipate scum accumulations and cause them
to settle; however, in the absence of wind or in sheltered areas,
other means must be used. If scum is not broken up, it will dry
on top and become crusted. Not only is the scum more difficult
to break up then, but a species of blue-green algae is apt to
become established on the scum. This can give rise to dis-
agreeable odors. If scum is allowed to accumulate, it can reach
proportions where it cuts off a significant amount of sunlight
from the pond. When this happens the production of oxygen by
algae is reduced and odor problems can result. Rafts of scum
cause a very unsightly appearance in ponds and can quite
likely become a source of botulism that will have a devastating
effect on waterfowl and shore birds which may be attracted to
the facility.
Many methods of breaking up scum have been used, includ-
ing agitation with garden rakes from the shore, jets of water
from pumps or tank trucks, and the use of outboard motors on
boats in large ponds. Scum is broken up most easily if it is
attended to promptly.
9.71 Odor Control
Eventually, at some time, odors probably will come from a
wastewater treatment plant no matter what kind of process is
used. Most odors are caused by overloading (see Section
9.119 to determine pond loading) or poor housekeeping prac-
tices and can be remedied by taking corrective measures. If a
pond is overloaded, stop loading and divert influent to other
ponds, if available, until the odor problem stops. Then gradu-
ally start loading the pond again. Once a pond develops odor
problems, it is more apt to cause trouble than other ponds.
There are times, such as when unexpected shutdowns oc-
cur, that plant processes may be upset and cause odors. For
these unexpected occurrences, it is strongly advised that a
careful plan for emergency odor control be available. Odors
usually occur during the spring warmup in colder climates be-
cause biological activity has been reduced during cold
weather. When the water warms, microorganisms become ac-
tive, use up all of the available dissolved oxygen, and odors
are produced under these anaerobic conditions.
There are several suggested ways to reduce odors in ponds.
These ways include recirculation from aerobic units, the use of
floating aerators, and heavy chlorination. Recirculation from an
aerobic pond to the inlet of an anaerobic pond (1 part recycle
flow to 6 parts influent flow) will reduce or eliminate odors.
Usually, floating aeration and chlorination equipment are too
expensive to have standing idle waiting for an odor problem to
develop. Odor-masking chemicals also have been promoted
for this purpose and have some uses for concentrated sources
of specific odors. However, in almost all cases, process proce-
dures of the type mentioned previously are preferable. In any
event, it is poor procedure to wait until the emergency arises to
plan for odor control. Often several days are needed to receive
delivery of materials or chemicals if they are required. Try to
have possible alternate methods of control ready to go in case
they are needed.
In some areas, sodium nitrate has been added to ponds as a
source of oxygen for microorganisms rather than sulfate com-
pounds, already in the water, thus preventing odors. To be
effective, sodium nitrate must be dispersed throughout the
water in the pond. Once mixed in the pond, it acts very quickly
because may common organisms (facultative groups) may use
the oxygen in nitrate compounds instead of dissolved oxygen.
Liquid sodium hypochlorite or chlorine solution is a faster act-
ing solution, but not necessarily the best chemical because it
will interfere with biological stabilization of the wastes.
9.72 Weed and Insect Control
Weed control is an essential part of good housekeeping and
is not a formidable task with modern herbicides and soil steril-
ants. Weeds around the edge are most objectionable because
they allow a sheltered area for mosquito breeding and scum
accumulation. In most average ponds, there has been little
need for mosquito control when edges are kept free of weed
growth. Weeds also can hinder pond circulation. Aquatic
weeds, such as tules, will grow in depths shallower than three
feet (1 m), so an operating pond level of at least this depth is
necessary. Tules may emerge singly or be well scattered, but
should be removed promptly by hand as they will quickly multi-
ply from the root system.
Mosquitoes will breed in sheltered areas of standing water
where there is vegetation or scum to which the egg rafts of the
female mosquito can become attached. These egg rafts are
fragile and will not withstand the action of disturbed water sur-
faces such as caused by wind action or normal currents. Keep-
ing the water edge clear of vegetation and keeping any scum
broken up will normally give adequate control. Shallow, iso-
lated pools left by the receding pond level should be drained or
sprayed with a larvacide.
Any of several minute shrimp-like animals may infest the
pond from time to time during the warmer months of the year
(March - November). These predators live on algae and at
times will appear in such numbers as to almost clear the pond
of algae. During the more severe infestations, there will be a
sharp drop in the dissolved oxygen of the pond, accompanied
by a lowered pH. This is a temporary condition because the
predators will outrun the algae supply, and there will be a mass
die-off of insects which will be followed by a rapid greening up
of the pond again. When the algae concentration in a pond is
low under these conditions, ponds operated on a batch basis
may find this a good time for release of water due to low
suspended solids values.
Ordinarily there should be no great concern about these
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Ponds 291
infestations because they soon balance themselves; however,
in the case of a heavily loaded pond, a sustained low dissolved
oxygen content may give rise to noxious odors. In that event,
any of several commercial sprays can be used to control the
shrimp-like animals.
Chironomid midges are often produced in wastewater ponds
in sufficient numbers to be serious nuisances to nearby resi-
dential areas, farm workers, recreation sites, and industrial
plants. When emerging in large numbers, they may also create
traffic hazards. At present the only satisfactory control is
through the use of insecticides. Control measures are time
consuming and may be difficult, particularly if there is a dis-
charge to a receiving stream. If possible, lower the level in the
ponds enough to contain a day's inflow before applying an
insecticide. Holding the insecticide for at least one day will kill
more insects and reduce the effect of the insecticide on receiv-
ing waters. For better results, insecticides should be applied on
a calm day and any recirculation pumps should be stopped.
CAUTION. Before attempting to apply any insecticide or pes-
ticide, contact your local official in charge of approving pes-
ticide applications. This person can tell you which chemicals
may be applied, the conditions of application, and safe proce-
dures.
9.73 Levee Maintenance
Levee slope erosion caused by wave action is probably the
most serious maintenance problem. If allowed to continue, it
will result in a narrowing of the levee crown which will make
accessibility with maintenance equipment most difficult.
If the levee slope is composed of easily erodible material,
the only long-range solution is the use of bank protection such
as stone RIPRAP10 or broken concrete rubble. Good sources
of bank-protection materials include small pieces of broken
street materials, curbs, gutters, and also bricks and other suit-
able materials from building demolition.
Portions of the pond levee or dike not exposed to wave
action should be planted with a low-growing spreading grass to
prevent erosion by surface runoff. Native grasses may natu-
rally seed the levees, or local highway departments may be
consulted for suitable grasses to control erosion. If necessary,
grass may have to be mowed to prevent it from becoming too
high. Do not allow grazing animals to control vegetation be-
cause they may damage the levees near the water line and
possibly complicate erosion problems.
Plants or grasses with long roots, such as willows and al-
falfa, should not be allowed to grow on levees because they
may damage the levees and possibly cause levee failure and
costly repair. Burrowing animals such as muskrats, badgers,
squirrels and gophers also may cause levees to fail. Remove
these animals from levees as soon as possible and repair their
burrowed holes immediately.
Levee tops should be crowned so that rain water will drain
over the side in a sheet flow. Otherwise the water may flow a
considerable distance along the levee crown and gather
enough flow to cause erosion when it finally spills over the side
and down the slope.
If the levees are to be used as roadways during wet weather,
they should be paved or well graveled.
If seepage or leakage from the ponds appears on the out-
side of levees, ask your engineer to investigate and solve this
problem before further damage occurs to the levee.
9.74 Headworks and Screening
Be sure to clean the bar screen as frequently as necessary.
The screen should be inspected at least once or twice a day
with more frequent visits during storm periods. Screenings
should be disposed of daily in a sanitary manner, such as by
burial, to avoid odors and fly breeding. A trench dug by a
backhoe near the bar screen provides a convenient location for
disposal by burial. Another method of disposal is to place
screenings in garbage cans and request that your local gar-
bage service dispose of the screenings at a sanitary-landfill
disposal site.
Many pond installations have grit chambers at the head-
works to protect raw-wastewater lift pumps or prevent plugging
of the influent lines. There are many types of grit-removal
equipment. Grit removed by the various types of mechanical
equipment or by manual means will usually contain small
amounts of organic matter and should therefore be disposed of
in a sanitary manner. Disposal by burial is the most common
method.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 313.
9.7A Why should scum not be allowed to accumulate on the
surface of a pond?
9.7B How can scum accumulations be broken up?
9.7C What are the causes of odors from a pond?
9.7D What precaution would you take to be prepared for an
odor problem which might develop?
9.7E Why are weeds objectionable in and around ponds?
9.7F How can weeds be controlled and removed in and
around ponds?
9.7G Why should insects be controlled?
9.7H Why should a pond be lowered before an insecticide is
applied?
9.75 Some Operating Hints
1. Anaerobic ponds should be covered and isolated for odor
control and followed by aerobic ponds. Floating polystyrene
planks can be used to cover anaerobic ponds and can be
painted white for protection from the sun. These will help to
confine odors and heat and tend to make the anaerobic
ponds more efficient.
2. Placing PONDS IN SERIES11 tends to cause the first pond
to become overloaded and may never allow it to recover;
the overload may be carried to the next pond in series.
PONOS IN SERIES
Ul u
10 Riprap. Broken stones, boulders, or other materials placed compactly or Irregularly on levees or dikes for the protection of earth surfaces
against the erosive action of waves.
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292 Treatment Plants
Feeding PONDS IN PARALLEL11 allows you to distribute
the incoming load evenly between units. Whether ponds
are operated in series or in parallel should depend on the
loading situation.
When operating ponds in series, the accumulation of solids
in the first pond may become a serious problem after a long
period of use. Periodically the flow should be routed around
the first pond. This pond should then be drained and the
solids removed and buried.
3. A large amount of recirculation, say 25 to 100 percent, can
be very helpful. This allows the algae and other aerobic
organisms to become thoroughly mixed with incoming raw
wastewater. At the same time, good oxygen transfer can be
attained by passing the incoming water over a deck and
down steps or other type of aerator. This procedure can
cause heat loss, however.
4. Heavy chlorination at the recirculation point can assist in
odor control, but will probably interfere with treatment.
5. As with any treatment process, it is necessary to measure
the important water quality indicators (DO and solids) at
frequent, regular intervals and plot them so that you have
some idea of the direction the process is taking in time to
take corrective action when necessary.
6. When solids start floating to the surface of a pond during
the spring or fall overturn, the pond may have to be taken
out of service and cleaned. Measurement of the sludge
depth on the bottom of a pond also will indicate when a
pond should be cleaned. Usually ponds are cleaned when
the wet sludge depth is over one-foot (0.3 m) deep.
7. Before applying insecticides or herbicides, be sure to check
with appropriate authorities regarding the long-term effects
of the pesticide you plan to use. Do not apply pesticides that
may be toxic to organisms in the receiving waters.
8. Algae in effluent. Unfortunately there is little an operator
can do by changing pond operating procedures to effec-
tively remove algae from a pond effluent. The best ap-
proach is to operate ponds in series and to draw off the
effluent below the surface by use of a good baffling ar-
rangement.
If the algae must be removed from the effluent of a pond,
additional facilities may be designed and constructed.
Techniques for eliminating algae from pond effluents in-
clude growing a water hyacinth culture in a special final
pond (see Section 9.12, "Eliminating Algae from Pond
Effluent"). Another possibility is constructing extra ponds
and using the Pond Isolation Process. Suitable effluents
have been obtained under favorable field conditions. Other
algae removal processes include microscreening, slow
sand filtration, dissolved air flotation, and algae harvesting.
In final ponds that are operated in series with periodic dis-
charges, alum may be added in doses of less than 20 mg/L
to improve effluent quality before discharge.
9.76 Abnormal Operation
Abnormal operation occurs when ponds are overloaded be-
cause the BOD loads are too high. Excessive BODs can occur
when influent loads exceed design capacity due to population
increases, industrial growth, or industrial dumps. Under these
conditions new facilities must be constructed or the BOD load-
ing must be reduced at the source, such as an industrial dump.
Another type of overloading can occur when too much flow is
diverted to one pond. This can happen when an operator acci-
dentally feeds one pond more than the other or when a pipe
opening is blocked by rags, solids or grit due to low pipe ve-
locities, and thus too much flow is diverted to another pond.
When this happens and the overloaded pond starts producing
odors, take the pond out of service and divert flows to the other
ponds until the overloaded pond recovers. Hopefully the ponds
in service will not become overloaded. Also be sure to remove
any rags, solids or grit which caused the overloading and in-
spect the other pipes to prevent this problem from happening
again in the other ponds.
Usually ponds do not become overloaded during storms and
periods of high runoff because there is not a significant in-
crease in the BOD loading on the ponds.
Large amounts of brown or black scum on the surface of a
pond is an indication that the pond is overloaded. Scum on the
surface of a pond often leads to odor problems. The best way
to control scum is to take corrective action as soon as possible
(see Section 9.70, "Scum Control").
During winter conditions the pond can become covered with
ice and snow. Sunlight is no longer available to the algae and
oxygen cannot enter the water from the atmosphere. Without
dissolved oxygen available for aerobic decomposition,
anaerobic decomposition of the solids occurs. Anaerobic de-
composition takes place slowly because of the low tempera-
tures. By keeping the pond surface at a high level, a longer
detention time and less heat loss will be obtained. During the
period of ice cover, odorous gases formed by anaerobic de-
composition accumulate under the ice and are dissolved into
the wastewater being treated.
Some odors may be observed in the spring just after the ice
cover breaks up because the pond is still in an anaerobic state
and some of these dissolved gases are being released. Melt-
ing of ice in the spring provides dilution water with a high
oxygen content, thus the ponds usually become facultative in a
few days after breakup of the ice if they are not organically
(BOD) overloaded.
9.77 Batch Operation
Some ponds do not discharge continuously. These ponds
may discharge only once (fall) or twice (fall and spring) a year.
Discharges should be made only when necessary and, if pos-
sible, during the nonrecreational season when flows are high in
the receiving waters.
If your pond is allowed to discharge intermittently (controlled
discharge), you must work closely with your pollution control
agency and be sure that you are in compliance with the Na-
tional Pollutant Discharge Elimination System (NPDES) per-
mit. Before and during the discharge, samples should be col-
lected from the pond being emptied and from the receiving
waters both upstream and downstream from the point of dis-
charge. Samples are usually analyzed for DO, BOD, pH, total
suspended solids, and coliform-group bacteria.
Ponds should not be emptied too quickly. Usually ponds are
emptied in two weeks or less depending on how much water is
to be discharged. Normally one to one and a half feet (0.3 to
0.45 m) of water is left in the bottom of the pond.
9.78 Shutting Down a Pond
Ponds may be shut down for short periods of time without
any problems developing. For example, if flow to a pond must
be stopped to repair a pipe or a valve, no precautionary proce-
dures are necessary. If a pond is full and received no flows for
a long period of time, start up the pond with caution and gradu-
ally increase the load. If the full load is applied immediately, the
pond may become overloaded because the microorganism
population in the pond is low and insufficient to treat the load.
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Ponds 293
Stop all flow to a pond when emptying it to remove bottom
deposits, repair inlet or outlet structures, or repair levees. Drain
by use of discharge valves or pump water from one pond to
other ponds. Try to feed the other ponds equally to prevent
them from becoming overloaded. Frequently there is a time lag
between the overloading of a pond and the development of
problems. Therefore, watch the other ponds and lab results
closely for any signs (odors, low pH, low DO, drop in alkalinity,
loss of green color) of potential problems developing.
9.79 Operating Strategy
In order to prevent your ponds from developing odors or
discharging an effluent in violation of the NPDES permit re-
quirements, you should develop a plan to keep your ponds
operating as intended.
A. Maintain constant water elevations in the ponds.
If your NPDES permit allows the discharge of a pond into
receiving waters, keep a constant water level to help maintain
constant loadings. When the water surface elevation starts to
drop, look for the following possible causes:
1. Discharge valve open too far or a STOP LOG12 is missing;
2. Levees leaking due to animal burrows, cracks, soil settle-
ment or erosion; and
3. Inlet lines plugged or restricted and causing wastewater to
back up into the collection system.
When the water surface starts to rise, look for:
1. Discharge valve closed or lines plugged, and
2. Sources of infiltration.
NOTE: Under some conditions you may not want to maintain
constant water levels in your ponds. For example, you
may allow the water surface to fluctuate to
1. Control shoreline aquatic vegetation,
2. Control mosquito breeding and burrowing rodents,
3. Handle fluctuating inflows, and
4. Regulate discharge (continuous, intermittent or
seasonal).
B. Distribute inflow equally to ponds.
All ponds designed to receive the flow should receive the
same hydraulic and organic (BOD) loadings.
C. Keep pond levees or dikes in good condition.
Proper maintenance of pond levees can be a time-saving
activity. Regularly inspect levees for leaks and erosion and
correct any problems before they become serious. If erosion is
a problem at the water line, install riprap. Do not allow weeds to
grow along the water line and keep weeds on the levee
mowed. If insect larvae are observed on the pond surface,
spray with an appropriate insecticide before problems develop.
D. Observe and test pond condition.
Daily visual observations can reveal if a pond is treating the
wastewater properly. The pond should be a deep green color
indicating a healthy algae population. Scum and floating
weeds should be removed to allow sunlight to reach the algae
in the pond.
Once or twice a week tests should be conducted to deter-
mine pond dissolved oxygen level, pH and temperature.
Effluent dissolved oxygen should be measured at this time
also. Other effluent tests should be conducted at least weekly
and include BOD, suspended solids, dissolved solids,
coliform-group bacteria and chlorine residual. If ponds are op-
erated on a batch or controlled discharge basis, these effluent
tests will have to be determined only during periods of dis-
charge.
During warm summer months algae populations tend to be
high and may cause high suspended solids concentrations in
the effluent. An advantage of ponds in arid regions is that this
is also a period of high evaporation rates. Under these condi-
tions effluent flows may drop to almost zero or may be
stopped. In the fall and winter when the weather is cool and
sunlight is reduced, the algae population in ponds and thus the
suspended solids are reduced. This situation could allow
ponds to meet effluent requirements during this period.
If test results reveal that certain water quality indicators
(such as DO, BOD, pH or suspended solids) are tending to
move in the wrong direction, try to identify the cause and take
corrective action. Remember that ponds are a biological pro-
cess and that changes resulting from corrective action may not
occur until a week or so after changes were made.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 314.
9.7I Why are the contents of ponds recirculated?
9.7J When do ponds that are operated on a batch basis
discharge?
9.7K What factors would you consider when developing an
operating strategy for ponds?
9.8 SURFACE AERATORS (Figs. 9.5 and 9.6 and Table
9.2)
Surface aerators have been used in two types of applica-
tions:
1. To provide additional air for ponds during the night, during
cold weather, or for overloaded ponds; and
2. To provide a mechanical aeration device for ponds oper-
ated as an aerated lagoon. Aerated lagoons operate like
activated sludge aeration tanks without returning any set-
tled activated sludge.
12 Stop Log. A log or board in an outlet box or device used to control the water level in ponds.
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294 Treatment Plants
Fig. 9.5 Surface aerator
(Permission of EIMCO)
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Ponds 295
MOTOR
POWER CABLE
GUY WIRE
PROPELLER
FLOAT
DRAFT TUBE
Fig. 9.6 Floating surface aerator
(Permission ol Aqua-Jet)
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296 Treatment Plants
PURPOSE OF AERATOR PARTS
Purpose
Introduces oxygen into pond.
Provides energy to drive
aerator.
TABLE 9.2
Part
1. Aerator
2. Electric Motor
3. Drive Reduction
Gear Box
4. Draft Tube
5. Discharge Guide
6. Jacking Screw
FLOATING AERATOR
7. Pontoons or Floats
8. Guy Wires
9. Power Cable
10. Propeller
(aerator)
Converts torque from motor to
move aerator.
Conveys bottom contents of
pond to surface for aeration.
Regulates spray patterns for
oxygen transfer to water.
Adjusts aerator impeller level
in water to regulate oxygen
transfer.
COMPONENTS (additional)
Provide platform for motor.
Positions floats in ponds and
are anchored to pond levee.
Conveys power to motor.
Pumps water into air to be
aerated.
In both cases, the aerators are operated by time clocks with
established on-off cycles. Laboratory tests on the dissolved
oxygen in a pond indicate the time period for on and off cycles
to maintain aerobic conditions in the surface layers of the
pond. Adjustments in the on-off cycles are necessary when
changes occur in the quantity and quality of the influent and
seasonal weather conditions. Some experienced operators
have correlated their lab test results to pond appearance and
regulate the on-off cycles using the following rule: "If the pond
has foam on the surface, reduce the operating time of the
aerator; and if there is no evidence of foam on the pond sur-
face, increase the operating time of the aerator." If there is a
trace of foam on the surface, the operating time is satisfactory.
Surface aerators may be either stationary or floating. Main-
tenance of surface aerators should be conducted in accord-
ance with manufacturer's recommendations. Always turn off,
tag, and lock out electric current when repairing surface
aerators. Special precautions may be necessary to handle
problems with icing and winter maintenance. Overhead guy
wires have been used to prevent aerators from turning over
when iced up.
Another method of aerating ponds is by the use of air com-
pressors connected to plastic tubes placed across the pond
bottom. Holes are drilled in the plastic tubes which serve as
diffusers to disperse air in the pond. This method of aeration
requires less equipment maintenance than surface aerators,
but diffusers can become plugged and create maintenance
problems.
9.9 SAMPLING AND ANALYSIS
9.90 Importance
Probably the most important sampling that can be accom-
plished easily by any operator is routine pH and dissolved
oxygen analysis. A good practice is to take pH, temperature,
and dissolved oxygen tests several times a week, and occa-
sionally during the night. These values should be recorded
because they will serve as a valuable record of performance.
The time of day should be varied occasionally for the tests so
that the operator becomes familiar with the pond's characteris-
tics at various times of the day. Usually the pH and dissolved
oxygen will be lowest just at sunrise. Both will get progressively
higher as the day goes on, reaching their highest level in late
afternoon.
Be very careful to avoid getting any atmospheric oxygen into
the sample taken to measure dissolved oxygen. This is most
necessary when samples are taken in the early morning or if
the dissolved oxygen in the pond is low from overloading. If
possible, measure the dissolved oxygen with an electric probe,
being careful not to allow the membrane on the end of the
probe to be exposed to the atmosphere.
Ponds often have clearly developed individuality, each being
a biological community that is unique unto itself. Apparently
identical adjacent ponds receiving the same influent in the
same amount often have a different pH and a different dis-
solved oxygen content at any given time. One pond may gen-
erate considerable scum while its neighbor doesn't have any
scum. For this reason, EACH pond should be given routine pH
and dissolved oxygen tests. Such testing may indicate an un-
equal loading because of the internal clogging of influent or
distribution lines that might not be apparent from visual inspec-
tion. Tests also may indicate differences or problems that are
being created by a build-up of solids or solids recycling.
When an operator becomes familiar with operating a pond,
the results of some of the chemical tests can be related to
visual observations. A deep green sparkling color generally
indicates a high pH and a satisfactory dissolved oxygen con-
tent. A dull green color or lack of color generally indicates a
declining pH and a lowered dissolved oxygen content. A grey
color indicates the pond is being overloaded or not working
properly.
9.91 Frequency and Location of Lab Samples
The frequency of testing and expected ranges of test results
vary considerably from pond to pond, but you should establish
those ranges within which your pond functions properly. Test
results will also vary during the hours of the day. Table 9.3
summarizes the typical tests, locations, and frequency of sam-
pling.
Samples should always be collected from the same point or
location. Raw wastewater samples for pond influent tests may
be collected either at the wet well of the influent pump station
or at the inlet control structure. Samples of pond effluent
should be collected from the outlet control structure or from a
well-mixed point in the outfall channel. Pond samples may be
taken from the four corners of the pond. The samples should
be collected from a point eight feet (2.5 m) out from the water's
edge and one foot (0.3 m) below the water surface. Be careful;
try not to stir up material from the pond bottom. Do not collect
pond samples during or immediately after high winds or storms
because solids will be stirred up after such activity.
-------
Ponds 297
TABLE 9.3 FREQUENCY AND LOCATION OF LAB
SAMPLES
Test
Frequency"1 Location
Common Range
pH®
Weekly
Pond
7.5+
Dissolved

Oxygen (DO)a
Weekly
Pond
4- 12 mg/L

Effluent
4- 12 mg/L
Temperature
Weekly
Pond

BOC*
Weekly
Influent
100 - 300 mg/L

Effluent
20- 50 mg/L
Coliform Group
Weekly
Effluent
MPN > 24,000/100 mL
Bacteria

Chlorine Residual
Daily
Effluent
0.5 - 2.0 mg/L
Suspended Solids6
Weekly
Influent
100 - 350 mg/L

Effluent
40 - 80 mg/L
Dissolved Solids
Weekly
Influent
250 - 800 mg/L
a pH values above 9.0 and DO levels over 15 mgIL are not uncom-
mon.
b Contact your regulatory agency to determine whether effluent
samples should be filtered to remove algae before testing. If the
samples must be filtered, the agency will recommend the proper
procedures.
c Effluent suspended solids consist of algae, microorganisms and
other suspended matter.
d Tests may be less frequent for ponds with long detention times
(greater than 100 days).
BOD should be measured on a weekly basis. Samples
should be taken during the day at low flow, medium flow, and
high flow. The average of these three tests will give a reason-
able indication of the organic load of the wastewater being
treated. If it is suspected that the BOD varies sharply during
the day or from day to day, or if unusual circumstances exist,
the sampling frequency should be increased to obtain a clear
definition of the variations. If the pond DO level is supersatu-
rated (see Chapter 16, section on DO tests), the sample must
be aerated to remove the excess oxygen before the BOD test
is performed. A typical data sheet for a plant consisting mainly
of ponds is provided in the Appendix at the end of this chapter.
Figure 9.7 shows the influent and effluent BOD and suspended
solids values from an actual pond.
A GRAB SAMPLE13 is a single sample. Grab samples are
used to measure temperature, pH, dissolved oxygen and
chlorine residual. These tests must be performed immediately
after the sample is collected in order to obtain accurate results.
COMPOSITE SAMPLES14 of pond influent or effluent are col-
lected by gathering individual samples at regular intervals over
a selected period of time. The individual samples are then
mixed together proportionally to the flow at the time of sam-
pling. Pond samples may be composited by mixing equal por-
tions from the four corners of the pond. Composite samples
should be placed in a refrigerator or ice box as soon as possi-
ble after they are collected. BOD and suspended solids are
measured using composite samples.
Tests of pH, DO, and temperature are important indicators of
the condition of the pond, whereas BOD, coliform, and solids
tests measure the efficiency of the pond in treating wastes.
BOD is also used to calculate the loading on the pond.
In order to estimate the organic loading on the pond, the
operator must have some knowledge of the biochemical oxy-
gen demand (BOD) of the waste and the approximate average
daily flow. Influent BOD and solids will vary with time of day,
day of week, and season, but a pond is a good equalizer if not
overloaded.
Tests for pond alkalinity can provide helpful information to an
operator. After you have determined "normal" alkalinity levels
for your pond, a sudden change in alkalinity of 10 to 20 mg/L or
more may indicate that a problem is developing. A change in
alkalinity may be a warning that the pH of the pond could
change in a day or two if corrective action is not taken. If a
trend in changes in alkalinity continues in one direction for two
or three days, the cause of this change should be identified.
For useful results, the alkalinity test should be performed every
day.
9.92 Expected Treatment Efficiencies1 s
Table 9.4 is provided as a guide to indicate probable re-
moval efficiencies of typical ponds.
13 Grab Sample. A single sample taken at neither a set time nor flow.
14 Composite (Proportional) Sample (com-POZ-lt). A composite sample Is a collection of Individual samples obtained at regular Intervals,
usually every one or two hours during a 24-hour time span. Each Individual sample Is combined with the others in proportion to the flow when
the sample was collected. The resulting mixture (composite sample) forms a representative sample and is analyzed to determine the
average conditions during the sampling period.
u
Waste Removal, % = (ln' °ut) x 100%
In
See page 299 for example.
-------
600 - -
400 ¦ -
£
8*
«8
O
O
m
H
Z
UJ
3
_J
u.
z
5 200
E
O*
Q
»-
Z
UJ
3
u.
HI
UJ
3
_i
u.
UL
UJ
MOVING AVERAGE
INFLUENT SS
^INFLUENT BOD
EFFLUENT DO
^EFFLUENT SS
•' V
A—-EFFLUENT BOD
100
25 30
WEEK OF THE YEAR
Fig. 9.7 Pond influent and effluent BOD and suspended solids
values
-------
Ponds 299
TABLE 9.4 EXPECTED RANGES OF REMOVAL BY
PONDS

Detention Time
Expected Removal15
BOD

50 to 90%
BOD (FACULTATIVE POND)™
50 to
60 days
70 to 80%"
Coliform Bacteria
50 to
60 days
90 to 95%
(facultative pond)

Suspended Solids
After
3 days
90%
Dissolved Organic Solids
After
10 days
80%
The calculation of pond BOD removal efficiency is figured in
terms of the percentage of BOD removed.
Example:
The influent BOD to a series of ponds is 300 mg/L, and the
effluent BOD is 60 mg/L. What is the efficiency of BOD re-
moval?
BOD Removal, % = (ln' 0ut) x 100%
In
= (300 mg/L - 60 mg/L) x 100%
300 mg/L
= 240 x 100%
300 mg/L
= 0.80 x 100%
= 80%
9.93 Response to Poor Pond Performance
See Section 9.7, "Daily Operation and Maintenance," espe-
cially 9.75, "Some Operating Hints."
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 314.
9.8A Surface aerators have been used in what two types of
applications?
9.9A If the color of a pond is dull green or colorless, what is
happening in the pond?
9.9B Why should the pH, temperature, and dissolved oxygen
be measured in a pond?
9.9C If the pH and dissolved oxygen are dropping danger-
ously low in a pond, how can this situation be cor-
rected?
9.9D Influent BOD to a series of ponds is 200 mg/L. If the
BOD in the effluent of the last pond is 40 mg/L, what is
the BOD removal efficiency?
9.10 SAFETY
Even though a pond has little mechanical equipment, there
still are hazards. Catwalks should have guardrails and non-
skid walking surfaces. Headworks and any enclosed appurte-
nances should be well ventilated to prevent dangerous gas
accumulations.
WARNING
AN OPERATOR •SHOULD AUVVAVS
AOroAAPAWlEP \ HeLP&C WHtN
PECFOEMlMca ANAV TA^ THACV t-O
(7ANSeeoU6 ^IWCB POMP LOCATION'S
ACE U^UAHV QUITE IS.OL-AT&P.
Be very careful when removing debris from channels and
ponds. Do not attempt to lift too much. Make certain you have
secure footing so you won't slip and fall. Never stand in a boat
or lean over too far to one side, for you could fall into the pond
and also possibly tip over the boat. Always wear a life jacket
when in a boat.
Electrical wires and electrical equipment are always a
source of potential danger. Exercise caution when cutting
weeds or removing vegetation such as trees next to electrical
wires. Electrical wires in damp areas can be dangerous. Be
careful when spraying weeds around electrical wires and
equipment because the spray could act as a conductor. Al-
ways turn off, tag, and lock out electric current when repairing
surface aerators and other equipment operated by electricity.
When applying pesticides or herbicides, be sure they are
approved by the appropriate officials for your specific use and
FOLLOW THE DIRECTIONS EXACTLY. This includes follow-
ing the directions for using the proper mixing or preparing the
solution, applying the solution, disposing of any excess solu-
tion and the containers, and cleaning up before you go home.
Not only can you kill the target pest or weed, but carelessness
can harm nearby grasses, plants, trees, fishes, birds and even
people, including yourself. Also failure to follow directions may
result in harm to the algae and microorganisms in the pond.
Tetanus and typhoid are ever-present dangers when work-
ing around wastewater. Adequate precautions should be ob-
served by cleaning all cuts and scrapes and always washing
before eating or smoking.
Fences should surround ponds to keep unauthorized per-
sons and animals out of the pond area. They should be located
in such a manner that they will not interfere with mechanical or
hand maintenance of levee slopes.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 314.
9.1 OA What safety devices should be provided on catwalks
over ponds?
9.10B Why should an operator be accompanied by a helper
when performing any dangerous task?
BMP Of Li¥>OU %
Of %
ON
wweiftAHmrtbnc*i
Please answer the discussion and review questions before
continuing with Lesson 3.
16 Facultative Pond (FACK-ul-tay-tive). The most common type of pond in current use. The upper portion (supernatant) is aerobic while the
bottom layer is anaerobic. Algae supply most of the oxygen to the supernatant.
17 Expected removal approximately 80 percent of the time with poorer removals during the remainder of the time.
-------
300 Treatment Plants
DISCUSSION AND REVIEW QUESTIONS
Chapter 9. WASTE TREATMENT PONDS
(Lesson 2 of 3 Lessons)
Write your answers in a notebook and then compare your
answers with those on page 314.
6. Why should water be introduced into a new pond before
any wastewater?
7. Why is good housekeeping an important factor in operat-
ing a properly functioning pond?
8. What precautions should be taken when applying an in-
secticide?
9. Why may chlorine compounds or chlorine solution not be
the best method of odor control in a pond?
10. What lab tests measure the condition of a pond?
11. Estimate the BOD removal efficiency of a series of ponds
if the influent BOD is 250 mgIL and the effluent BOD is 50
mgIL.
12. Why should fences be placed around ponds?
CHAPTER 9. WASTE TREATMENT PONDS
(Lesson 3 of 3 Lessons)
9.11 REVIEW OF PLANS AND SPECIFICATIONS
A careful review of the plans and specifications of a pro-
posed pond can provide the operator an opportunity to suggest
design improvements and changes before construction which
will allow the operator and the ponds to do a better job.
Guidelines for reviewing plans and specifications are provided
in this section. If you are having trouble with an existing pond
or ponds, check the items discussed in this section for help in
locating possible sources of problems.
9.110 Location
The general considerations for the location of other types of
wastewater treatment plants also apply to the location of
ponds. Isolation should be as great as can be economically
provided. Attention to the direction of prevailing winds with due
regard for present and projected downwind residential, com-
mercial, and recreational development is of utmost impor-
tance.
Winds can have both favorable and unfavorable impacts on
ponds. Winds are desirable in terms of blowing surface scum
and weeds to one side of the pond where they can be re-
moved. Also winds can be helpful by mixing the contents of a
pond, such as DO, algae and incoming wastes. An undesirable
aspect of winds is the creation of waves which can erode the
pond levee. Both of these factors should be considered when
selecting the location of the ponds and the arrangement or
length of the ponds. If high winds are to be expected in the
area where ponds will be constructed, try to arrange the ponds
so the winds will blow across the short width of the pond rather
than the length in order to reduce levee erosion caused by
waves.
9.111 Chemistry of Waste
Before the design of any pond is undertaken, it should be
determined whether there are any POSSIBLE TOXIC18 EF-
FECTS (interfere with growth of algae or bacteria) from the
waste. Some natural water supplies may have a high sulfur
content or other chemicals that limit the possibility of desired
sludge decomposition.
Certain wastes, such as dairy products and wine products,
are difficult to treat because of their low pH. Any processing
waste must be carefully investigated before one can be certain
that it can be successfully treated by ponding. Some process
wastes contain powerful fungicides and disinfectants that may
have a great inhibitive effect on the biological activity in a pond.
Other wastes may have nutrient deficiencies that could inhibit
the growth of desirable types of algae.
9.112 Headworks and Screening
A headworks with a bar screen is desirable to remove rags,
bones, and other large objects that might lodge in pipes or
control structures.
A trash shredder is a luxury that may not be warranted. Any
material that gets past an adequate bar screen will, in all prob-
ability not harm the influent pump. Any fecal matter will be
pulverized when going through the pump.
9.113 Row-Measuring Devices
An influent-measuring device should be installed to give a
direct reading on the daily volume of wastes that are intro-
duced into the ponds. This information, along with a BOD
measurement of the influent, is required to estimate the or-
ganic loading on the pond. Comparison of influent and effluent
flow rates is necessary for estimating percolation and evapora-
tion losses.
A measuring device provides basic data for prediction of
future plant expansion needs or for detecting unauthorized or
abnormal flows. Reliable, well-kept records on flow volume
help justify budgets and greatly assist an engineer's design of
a plant expansion or new installation.
18 Toxic (TOX-Ick). Poisonous.
-------
Ponds 301
9.114 Inlet and Outlet Structures
Inlet structures should be simple, foolproof, and constructed
of standard manufactured articles so that replacement parts
are readily available. Telescoping friction-fit tubes (see Fig.
9.8) for regulating spill or discharge height should be avoided
because a biological growth may become attached and pre-
vent the tubes from telescoping if they are not cleaned regu-
larly. Occasional dosages of hypochlorite solution can effec-
tively discourage growths. Also the formation of ice can pre-
vent adjustment of the tubes. If freezing is a problem, a
polyethelyne floating ring around the friction tube of the tele-
scopic valve sprayed with urea can prevent freeze-ups. This
device will act as a floating baffle to keep scum and floating
debris from clogging up the tube and entering the effluent.
Figure 9.1 (page 282) shows four inlets to one pond. With
this type of installation, usually only one inlet valve is open at a
time. If all the valves were open, velocities in the pipes might
become too low and solids would settle out in the pipes. To
overcome low velocities, close all but one valve or recycle
pond effluent back to the inlet. When all inlet valves are open,
the load is more evenly distributed throughout the pond.
A submerged inlet will minimize the occurrence of floating
material and will help conserve the heat of the pond by intro-
ducing the warmer wastewater into the depths of the pond.
Warm wastewater introduced at the bottom of a cold water
mass will channel to the surface and spread unless it is
promptly and vigorously mixed with cold water. Warm waste-
water spilled onto the surface of the pond will spread out in a
thin layer on the surface and not contribute to the warmth of the
lower regions of the pond where heat is needed for bacterial
decomposition. Inlet and outlet structures should be so located
in relation to each other to minimize possible short-circuiting.
Outlet structures (Figs. 9.9 and 9.10) should consist of a
baffled and submerged pipe inlet to prevent scum and other
floating surface material from leaving the pond. The actual
level of the pond and rate of outflow can be controlled by the
use of flashboards in the outlet structure. A row boat may be
used when access to the outlet baffle in Figure 9.9 is required.
Valves that have stems extending into the stream flow
should be avoided. Stringy material and rags will collect, form
an obstruction, and may render the valve inoperative.
Free overfalls (Fig. 9.11) at the outlet should be avoided to
minimize release of odors, foaming, and gas entrapment which
may hamper pipe flows. Free overfalls should be converted to
submerged outfalls if they are causing nuisances and other
problems.
If a pond has a surface outlet, floating material can be kept
out of the effluent by building a simple baffle around the outlet.
The baffle can be constructed of wood or other suitable mate-
rial. This baffle should be securely supported or anchored.
9.115 Levees
The selection of the steepness of the levee slope must de-
pend on several variables. A steep slope erodes quicker from
wave wash unless the levee material is of a rocky nature or
else protected by riprap. However, a steep slope minimizes
waterline weed growth. Equipment operation and the perform-
ance of routine maintenance are more difficult on steep slopes.
A gentle slope will erode the least from wave wash. Also, it is
easier to operate equipment and easier to perform routine
maintenance on a gentle slope. However, waterline weed
growth will have a much greater opportunity to flourish.
Ensure that provisions are made to adequately compact
and/or seal the levee banks to prevent leaking. Pipes passing
through levees should be as close to horizontal as possible to
reduce the possibility of leaks. Also cut-off walls should be
installed when pipes pass through levees to prevent leakage
around the outside of the pipes. Proper compaction and seal-
ing is necessary around pipes, SPLASH PADS,™ cleanouts,
valves, inlet and outlet control structures, and also recircula-
tion, transfer and drain lines. Once a leak develops, stopping it
can be very difficult.
The top of the levee should be at least ten feet (3.1 m) wide
to allow for maintenance vehicles. Provisions should be made
for a rounded or sloping top to allow for drainage. Pave or
gravel the levee surface if it will be used as a roadway during
wet weather.
9.116 Pond Depths
The operational depth of ponds deserves considerable at-
tention. Depending upon conditions, ponds of less than three
feet (1 m) of depth may be completely aerobic if there are no
solids on the bottom (unlikely) because oi tne depth of sunlight
penetration. This means that the treatment of wastes is ac-
complished essentially by converting the wastes to algae cell
material. Ponds of this shallow depth with short detention times
are apt to be irregular in performance because algae blooms
will increase to such proportions that a mass die-off will occur.
When this happens, all algae sink to the bottom and thereby
add to the organic load. Such conditions could lead to the
creation of an anaerobic pond. The bottoms of shallow ponds
will become anaerobic when solids collect on the bottom and
after sunset.
Discharges from shallow, aerobic ponds contain large
amounts of algae. To operate efficiently, these ponds should
have some means of removing the algae grown in the pond
before the effluent is discharged to the receiving waters. If the
algae are not removed from the effluent, the organic matter in
the wastewater is not removed or treated and the problem is
merely transferred to some downstream pool. See Section
9.12, "Removal of Algae from Pond Effluents," for a discussion
of possible methods of algae removal.
An observed phenomenon of lightly loaded, shallow secon-
dary ponds and tertiary ponds is that they are apt to become
infested with filamentous algae and mosses that not only limit
the penetration of sunlight into the pond, but hamper circula-
tion of the pond's contents and clog inlet and outlet structures.
When the loading is increased, this condition improves be-
cause these algae and mosses require relatively clean water
(low nutrients) for their environment.
Pond depths of four feet (1.2 m) or more allow a greater
conservation of heat from the incoming wastes. This encour-
ages biological activity as the ratio between pond volume and
jmnri arag h mrra fpunrahin In facultative ponds. depths over
four feet 11.2 m) nrnvida physical storage for dissolved oxygen
accumulated during the day. The stored dissolved oxvoen car-
ries over through the night when no oxygen is released by the
algae, unless floating algae and poor circulation keep all the
oxygen near the surface. This physical storage of DO is very
important during the colder months when nights are long.
i» Splash Pad. A structure made of concrete or other durable material to protect bare soil from erosion by splashing or falling water.
-------
302 Treatment Plants
THREADED STEM
WHEEL HANDLE
VALVE BOX
V-NOTCH
FRICTION FIT
BETWEEN PIPES
POND
OUTLET
Fig. 9.8 Telescoping friction-fit tubes for regulating discharge.
These tubes must be exercised regularly to prevent becoming
stuck.
-------
VALVE
HANDLE
<>
OUTLET
BAFFLE
FLASH
BOARDS
SUBMERGED
PIPE INLET
TO OUTLET
STRUCTURE
OUTLET
VALVE
Fig. 9.9 Pond outlet structure
-------
304 Treatment Plants
FLASH
BOARDS
OUTLET PIPE
Fig. 9.10, Pond outlet control structure
-------
Ponds 305
M.
FOAM
STREAM
POND
FREE OVERFALL--UNDESIRABLE
SCUM BAFFLE
POND
STREAM
SUBMERGED OUTLET--NO FOAMING PROBLEMS
Fig. 9.11 Free overfall and submerged outlet
-------
306 Treatment Plants
A pond operating depth of at least three feet (1 m) is recom-
mended to prevent tule and cattail growth. Weeds that emerge
along the shore line can be effectively controlled by spraying
with any of several products available. Ponds designed for
depths less than three feet (1 m) should be lined to prevent
troublesome weed growth.
9.117 Fencing and Signs
The pond area must be surrounded by a fence capable of
keeping livestock out and discouraging trespassing. A gate
wide enough to allow mowing equipment and other mainte-
nance vehicles to enter the pond facility should be provided. All
access gates should have locks.
Signs should be posted along the fence around the ponds to
indicate the nature of the facility and to forbid trespassing. The
signs should not be more than 300 feet apart.
9.118 Surface Aerators
Provisions must be made for easy access and sufficient
space for maintenance and repair of fixed aerators. Alternate
anchor points should be installed in order to move floating
aerators. Also be sure the electrical cables are long enough to
permit easy movement of the aerator and large enough to
handle anticipated loads.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 314.
9.11A Why are some wastes not easily treated by ponds?
9.11B What is the minimum recommended pond operating
depth?
9.11C Why should the inlet to a pond be submerged?
9.11D Why should the outlet be submerged?
9.11E How could problems created by a surface outlet be
reduced or corrected?
9.11F Why should free overfalls be avoided?
9.11G Why are shallow ponds apt to be irregular in perform-
ance?
9.11H Why should the influent to a pond be metered?
9.119 Pond Loading (English and Metric Calculations)
The waste loading on a pond is generally spoken of in rela-
tion to its area, and may be stated in several different ways:
1. lbs of BOD per day per acre = lbs BOD/day/acre (This is
called "organic loading.");
2. inches (or feet) of depth added per day (This is called "hy-
draulic loading" or "overflow rate."); or
3. persons (or population served) per acre (This is called
"population loading.").
Detention time is related directly to pond hydraulic loading,
which is actually the rate of inflow of wastewater. It may be
expressed as million gallons per day (MGD), or as the number
of acre-inches per day or acre-feet per day (one acre-foot
covers one acre to a depth of one foot or twelve inches and is
equal to 43,560 cu ft). We must know the pond volume in order
to determine detention time; this is most easily computed on an
acre-foot basis.
A. Detention Time
Detention (in days) = Pond Volume
Influent Rate (ac-ft/day)
This equation does not take into consideration water which
may be lost through evaporation or percolation. Detention time
may vary from 30 to 120 days, depending on the treatment
requirements to be met. Controlled discharge ponds may have
minimum detention times of 180 days. Ponds whose dis-
charges are disposed of by land application may have 210-day
minimum detention times.
B. Population Loading
Loading calculated on a population-sej^gd hasip is ex-
pressed simpiyasT~ — ¦
No. of Persons per Acrs_= Population Served, persons
Area of Pond, ac
The population loading may vary from 50 to 500 persons per
acre, depending on many local factors.
C. Hydraulic Loading
The hydraulic loading or overflow rate is expressed as:
Inches per day = Inflow (ac-in per day)
Pond Area, ac
The hydraulic loading may vary from half an inch to several
inches per day, depending on the organic load of the influent.
NOTE: If the wastewater inflow rate is known in million gallons
per day (MGD), it can be converted to an equivalent
number of acre-inches per day as follows:
Inflow, acre-inches per day = (Inflow, MGD) x 36.820
If the pond detention time is known, the hydraulic loading
can also be calculated, as follows:
Inches per day = Depth of Pond, in
Detention Time, days
D. Organic Loading
The organic loading is expressed as:
Organic Load
(lbs BOD per= (BOD, mgIL) (Flow, MGD) (8.34 lbs/gal)21
Per acre> Pond area, ac
Typical organic loadings may range from 10 to 50 lbs BOD
per day per acre. Recirculation will help an overloaded pond.
20 , mgd = 1 >000,000 gal x 1 cu ft x 1 ac x 12 in = 36g acjn
day 7.48 gal 43,560 sq ft 1 ft day
21 Recall lbs/day = (Cone. mglM mg) (M gal/day) (8.34 lbs/gal)
-------
Ponds 307
EXAMPLE CALCULATIONS
NOTE TO OPERATOR: If you have difficulty following the
work shown in Example 1 below, you should refer to Section
9.16, "Pond Attachment," at the end of this chapter for further
details. If you have no trouble, continue with the lesson.
EXAMPLE NO. 1:
Use of the pond loading formulas can be illustrated by exam-
ining a typical situation. The following data should be obtained
so that all the calculations can be performed:
Essential Data
1. Depth of Pond = 4 feet
2. Width of Pond
Bottom =412 feet
Water Surface = 428 feet
Average Width = 420 feet
3. Length of Pond
Bottom = 667 feet
Water Surface = 683 feet
Average Length = 675 feet
4. Side Slopes s.
-------
308 Treatment Plants
the procedures for Example 1 and try to apply them to Example
2.
Suppose that a small wastewater treatment plant must be
completely shut down for major repairs that will require several
months of work. Enough vacant land is near the plant to enable
16 acres of temporary ponds to be constructed as raw waste-
water (sewage) lagoons. Determine if this is feasible, given the
following data:
Influent Rate = 1 MGD
Influent BOD = 150 mg/L
= 150 lbs BOD per million lbs of wastewater
Pond Area =16 acres
Average Operating = 42 inches = 42 in = 3.5 ft
DePth 12 in/ft
Assume that at least a 60-day detention period (average
time the wastewater must take to flow through the pond for
disinfection) is desired for bacterial die-off.
Assume that the organic loading (BOD) should not exceed
50 lbs per day per acre.
Calculate what the WASTE DETENTION TIME would be in
the pond:
One acre-foot = 325,829 gallons
Pond Volume, ac-ft = Pond Area, ac x Pond Depth, ft
= 16 ac x 3.5 ft
= 56 ac-ft
Influent Flow Rate = 1,000,000 gals per day
= 1,000,000 gpd
325,829 gal/ac-ft
= 3.07 ac-ft per day
56 ac-ft
Detention Time
3.07 ac-ft per day
18.2 days
Organic Loading,
lbs BOD/day
Thus the detention time would not be sufficient to satisfy
requirements. Increasing the depth to 5 feet would help.
Calculate the organic loading:
(BOD, mg/L) (Flow, MGD) (8.34 lbs/gal)
= (150 mg/L) (1 MGD) (8.34 lbs/gal)
= 1250 lbs BOD per day
The organic loading per acre of pond would be:
Organic Loading, _ Loading, lbs BOD/day
lbs BOD/day/ac Area, ac
_ 1250 lbs BOD per day
Therefore, the organic loading would exceed the desired
maximum of 50 lbs BOD/day/acre.
QUESTION
Write your answers in a notebook and then compare your
answers with those on pages 314 and 315.
9.111 Given a pond receiving a flow of 2.0 MGD from 20,000
people. Influent BOD is 180 mg/L. Pond area is 24
acres, and the average operating depth is four feet.
Determine the detention time, organic loading, popula-
tion loading, and hydraulic loading.
EXAMPLE METRIC CALCULATIONS
EXAMPLE NO. 1
Use of the pond loading formulas can be illustrated by exam-
ining a typical situation. The following data should be obtained
so that all calculations can be performed:
Essential Data
1. Depth of Pond = 2.0 meters
2. Width of Pond
Bottom = 125 meters
Water Surface = 133 meters
Average Width = 129 meters
3. Length of Pond
Bottom = 200 meters
Water Surface = 208 meters
Average Length= 204 meters
^rPOND SURFACE
'"En
4. Side Slopes
(2 ft horizontal
to 1 ft vertical) = 2:1 2

8
EFFLUENT
ifisili
!j >¦! v"'

09*S*
r/
38. Two ponds serve a summer resort and are operated in
series. They cover an area of 150 ft by 250 ft (average
width and length of both ponds combined). The average
depth is four feet, and the average inflow is 25,000 gpd.
The detention time is approximately
1. 20 days.
V2. 45 days.^
3. 50 days.
4. 55 days.
5. 80 days
jSH£e.*S_!2i±r
2, C, trcO 1 * (I
39. And when the influent BOD is 200 mg/L for the ponds in
problem 38, the organic loading is approximately
1. 40 lb BOD/day/ac.
ISOKT-SO-OyS-V*- AC.
2. 42 lb BOD/day/ac
3. 45 lb BOD/day/ac.
*"4. 48 lb BOD/day/ac.
0 zs xztfo
lb.
h. ho iu DV^L//uay/ou.^s. ' ' $
5. 70 lb BOD/day/ac.
Review Question:
40. Estimate the velocity in a grit channel if a stick travels 30
feet in 40 seconds.
1. 0.50 ft/sec.
*2. 0.75 ft/sec.
3. 1.00 ft/sec.
4. 1.25 ft/sec.
5. 1.33 ft/sec.
ft/
- 0
END OF OBJECTIVE TEST
-------
CLEANWATER, U.S.A.
WATER POLLUTION CONTROL PLANT
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-------
CHAPTER 10
DISINFECTION AND CHLORINATION
by
Leonard W. Horn
(With a special section by J.L. Beals)
Revised
by
Tom Ikesaki
-------
320 Treatment Plants
TABLE OF CONTENTS
Chapter 10. Disinfection and Chlorination
Revised by Tom Ikesaki
Page
OBJECTIVES 324
GLOSSARY 325
LESSON 1
10.0 Need for Disinfection 329
10.00 Effectiveness in Microorganism Removal by Various Treatment Processes 329
10.01 Disinfection 329
10.02 Reaction of Chlorine in Wastewater 331
10.020 Free Chlorine (Cl2) 331
10.021 Hypochlorite (OCI") 331
10.022 Chlorine Dioxide (CI02) 332
10.03 Reactions of Chlorine Solutions with Impurities in Wastewater 332
10.030 Inorganic Reducing Materials 332
10.031 Reaction with Ammonia 332
10.04 Hypochlorination of Wastewater 333
10.05 Factors Influencing Disinfection 333
10.06 Chlorine Requirements 333
LESSON 2
10.1 Points of Chlorine Application 336
10.10 Collection System Chlorination 336
10.11 Prechlorination 336
10.12 Plant Chlorination 336
10.13 Chlorination Before Filtration 336
10.14 Postchlorination 336
10.2 Chlorination Process Control 338
10.20 Chlorinator Control 338
10.200 Manual Control 338
10.201 Start-Stop Control 338
10.202 Step-Rate Control 338
-------
Disinfection 321
10.203 Timed-Program Control 338
10.204 Flow-Proportional Control 338
10.205 Chlorine Residual Control 338
10.206 Compound Loop Control 338
10.21 Chlorination Control Nomogram 339
10.22 Hypochlorinator Feed Rate and Control 341
10.23 Chlorine Solution Discharge Lines, Diffusers, and Mixing 342
10.230 Solution Discharge Lines 342
10.231 Chlorine Solution Diffusers 342
10.232 Mixing 342
10.24 Measurement of Chlorine Residual 342
10.25 Start-Up of Chlorinators 342
10.250 Gas Chlorinators 344
10.251 Liquid Chlorine Chlorinators 344
10.26 Normal and Abnormal Operation 345
10.260 Container Storage Area 345
10.261 Evaporators 345
10.262 Chlorinators, Including Injectors 347
10.27 Shutdown of a Chlorinator 349
10.270 Short-Term Shutdown 349
10.271 Long-Term Shutdown 349
10.28 Operational Strategy 349
10.29 Chlorine Troubleshooting Guide 350
LESSON 3
10.3 Chlorine Safety Program 354
10.30 Chlorine Hazards 354
10.31 Why Chlorine Must be Handled with Care 354
10.32 Protect Yourself from Chlorine 355
10.33 First Aid Measures 355
10.4 Chlorine Handling 356
10.40 Chlorine Containers 356
10.400 Cylinders 356
10.401 Ton Tanks 356
10.402 Chlorine Tank Cars 356
10.41 Removing Chlorine from Containers 362
10.410 Connections 362
10.411 Valves 362
10.412 Ton Tanks 362
i
-------
322 Treatment Plants
10.413 Railroad Tank Cars 362
10.42 Chlorine Leaks 364
LESSON 4
10.5 Chlorination Equipment and Maintenance 366
10.50 Chlorinators 366
10.51 Evaporators 366
10.52 Hypochlorinators 371
10.53 Chlorine Dioxide Facility 371
10.54 Installation and Maintenance 371
10.55 Installation Requirements 373
10.550 Piping, Valves, and Manifolds 373
10.551 Chlorinator Injector Water Supply 373
10.56 Review of Plans and Specifications 374
10.6 Other Uses of Chlorine 374
10.60 Odor Control 374
10.61 Protection of Structures 375
10.62 Aid to Treatment 375
10.620 Sedimentation and Grease Removal 375
10.621 Trickling Filters 375
10.622 Activated Sludge 375
10.623 Reduction of BOD 375
10.7 Acknowledgments 375
LESSON 5
10.8 Dechlorination 376
10.80 Need for Dechlorination 376
10.81 Sulfur Dioxide (S02) 376
10.810 Properties 376
10.811 Chemical Reaction of Sulfur Dioxide with Wastewater 377
10.812 Application Point 377
10.82 Sulfur Dioxide Hazards 377
10.820 Exposure Responses to Sulfur Dioxide 377
10.821 Detection of Leaks 378
10.822 What to Do in Case of Leaks 378
10.823 Employees Authorized to Work on Leaks 378
10.824 Safety with Sulfur Dioxide 378
10.825 First Aid 378
10.826 Emergency Safety Equipment 379
i
-------
Disinfection 323
10.83 Sulfur Dioxide Supply System 379
10.830 Sulfur Dioxide Containers 379
10.831 Supply Piping 379
10.832 Valves 379
10.84 Sulfonation System 380
10.840 Evaporator 380
10.841 Sulfonator 380
10.842 Injector 380
10.85 Sulfonator Controls 380
10.850 Sulfonator Feed-Rate Control 380
10.851 Control Facilities 380
10.852 Selection of Method of Control 381
10.86 Determination of Residual Sulfur Dioxide in Wastewater 381
10.87 Operation of Sulfonator Process 381
10.870 Start-Up of a New System 381
10.871 Start-Up of Gas Sulfonators 382
10.872 Troubleshooting the Gas Sulfonator System 383
10.873 Start-Up of Liquid Sulfonators 384
10.874 Troubleshooting the Liquid Sulfonator System 385
10.875 Normal and Abnormal Operation 386
10.876 Operational Strategy 386
10.877 Troubleshooting Sulfonation System 386
10.878 Sulfonation System Shutdown Procedures 387
10.88 Maintenance of the Sulfur Dioxide Systems 387
10.880 Supply Area 387
10.881 Piping 387
10.882 Evaporators 387
10.883 Sulfonators 387
10.9 Additional Reading 387
10.10 Metric Calculations 388
10.100 Conversion Factors 388
10.101 Problem Solutions 388
-------
324 Treatment Plants
OBJECTIVES
Chapter 10. DISINFECTION AND CHLORINATION
Following completion of Chapter 10, you should be able to
do the following:
1. Explain the principles of wastewater disinfection with
chlorine,
2. Control the chlorination process to obtain the desired
effluent disinfection,
3. Handle chlorine safely,
4. Detect chlorine leaks and take appropriate corrective ac-
tion,
5. Inspect new chlorination facilities for proper installation,
6. Schedule and conduct chlorination operation and mainte-
nance duties,
7. Recognize factors that indicate the chlorination process is
not performing properly, identify the source of the prob-
lem, and take corrective action,
8. Conduct your duties in a safe fashion,
9. Determine chlorine dosages,
10. Explain applications and limitations of uses of chlorine
other than for disinfection,
11. Keep records of chlorination operation, and
12. Safely operate and maintain a sulfur dioxide dechlorina-
tion system.
-------
Disinfection 325
GLOSSARY
Chapter 10. DISINFECTION AND CHLORINATION
QQT4iO~fOL\Wtt4& 'MVPO-
C-HLO B IN 4ipPlf
-------
326 Treatment Plants
CHLORINATION (KLOR-i-NAY-shun) CHLORINATION
The application of chlorine to water or wastewater, generally for the purpose of disinfection, but frequently for accomplishing other
biological or chemical results.
CHLORINE DEMAND CHLORINE DEMAND
Chlorine demand is the difference between the amount of chlorine added to wastewater and the amount of residual chlorine
remaining after a given contact time. Chlorine demand may change with dosage, time, temperature, pH, and nature and amount of
the impurities in the water.
Chlorine Demand, mgIL = Chlorine Applied, mgIL - Chlorine Residual, mgIL
CHLORINE REQUIREMENT CHLORINE REQUIREMENT
The amount of chlorine which is needed for a particular purpose. Some reasons for adding chlorine are reducing the number of
coliform bacteria (Most Probable Number), obtaining a particular chlorine residual, or destroying some chemical in the water. In
each case a definite dosage of chlorine will be necessary. This dosage is the chlorine requirement.
CHLORORGANIC (chlor-or-GAN-nick) CHLORORGANIC
Chlororganic compounds are organic compounds combined with chlorine. These compounds generally originate from, or are
associated with, living or dead organic materials.
COLIFORM (COAL-i-form) COLIFORM
One type of bacteria. The presence of coliform-group bacteria is an indication of possible pathogenic bacterial contamination. The
human intestinal tract is one of the main habitats of coliform bacteria. They may also be found in the intestinal tracts of warm-
blooded animals, and in plants, soil, air, and the aquatic environment. Fecal coliforms are those conforms found in the feces of
various warm-blooded animals; whereas the term "coliform" also includes other environmental sources.
COLORIMETRIC MEASUREMENT COLORIMETRIC MEASUREMENT
A means of measuring unknown concentrations of water quality indicators in a sample by measuring the sample's color intensity.
The color of the sample after the addition of specific chemicals (reagents), is compared with colors of known concentrations.
COMBINED AVAILABLE CHLORINE COMBINED AVAILABLE CHLORINE
The concentration of chlorine which is combined with ammonia (NH3) as chloramine or as other chloro derivatives, yet is still
available to oxidize organic matter.
COMBINED AVAILABLE RESIDUAL COMBINED AVAILABLE RESIDUAL
CHLORINE CHLORINE
That portion of the total residual chlorine which remains in water or wastewater at the end of a specified contact period and reacts
chemically and biologically as chloramines or organic chloramines.
COMBINED RESIDUAL CHLORINATION COMBINED RESIDUAL CHLORINATION
The application of chlorine to water or wastewater to produce a combined chlorine residual. The residual may consist of chlorine
compounds formed by the reaction of chlorine with natural or added ammonia (NH3) or with certain organic nitrogen compounds.
DECHLORINATION (dee-KLOR-i-NAY-shun) DECHLORINATION
The removal of chlorine from the effluent of a treatment plant.
DEGRADATION (de-gray-DAY-shun) DEGRADATION
The conversion of a substance to simpler compounds.
DEW POINT DEW POINT
The temperature to which air with a given quantity of water vapor must be cooled to cause condensation of the vapor in the air.
DISINFECTION (DIS-in-FECK-shun) DISINFECTION
The process designed to kill most microorganisms in wastewater, including essentially all pathogenic (disease-causing) bacteria.
There are several ways to disinfect, with chlorine being most frequently used in water and wastewater treatment plants. Compare
with STERILIZATION.
EDUCTOR (e-DUCK-tor) EDUCTOR
A hydraulic device used to create a negative pressure (suction) by forcing a liquid through a restriction, such as a Venturi. An
eductor or aspirator (the hydraulic device) may be used in the laboratory in place of a vacuum pump; sometimes used instead of a
suction pump.
ELECTRON ELECTRON
An extremely small (microscopic), negatively charged particle. An electron is much too small to be seen with a microscope.
-------
Disinfection 327
ENTERIC ENTERIC
Intestinal.
ENZYMES (EN-zimes) ENZYMES
Enzymes are organic substances which are produced by living organisms and speed up chemical changes.
FILAMENTOUS ORGANISMS (FILL-a-MEN-tuss) FILAMENTOUS ORGANISMS
Organisms that grow in a thread or filamentous form.
FREE AVAILABLE CHLORINE FREE AVAILABLE CHLORINE
The amount of chlorine available in water. This chlorine may be in the form of dissolved gas (Cl2), hypochlorous acid (HOCI), or
hypochlorite ion (OCI~), but does not include chlorine combined with an amine (ammonia or nitrogen) or other organic compound.
FREE AVAILABLE RESIDUAL CHLORINE FREE AVAILABLE RESIDUAL CHLORINE
That portion of the total residual chlorine remaining in water or wastewater at the end of a specified contact period. Residual chlorine
will react chemically and biologically as hypochlorous acid (HOCI) or hypochlorite ion (OCI~).
FREE CHLORINE FREE CHLORINE
Free chlorine is chlorine (Cl2) in a liquid or gaseous form. Free chlorine combines with water to form hypochlorous (HOCI) and
hydrochloric (HCI) acids. In wastewater free chlorine usually combines with an amine (ammonia or nitrogen) or other organic
compounds to form combined chlorine compounds.
FREE RESIDUAL CHLORINE FREE RESIDUAL CHLORINE
The result of the application of chlorine or chlorine compounds to water or wastewater to produce a free available chlorine residual
directly or through the destruction of ammonia (NH3) or certain organic nitrogenous compounds.
HEPATITIS HEPATITIS
Hepatitis is an acute viral infection of the liver. Yellow jaundice is one symptom of hepatitis.
HYPOCHLORINATION (hi-po-KLOR-i-NAY-shun) HYPOCHLORINATION
The application of hypochlorite compounds to water or wastewater for the purpose of disinfection.
HYPOCHLORINATORS (hi-poe-KLOR-i-NAY-tors) HYPOCHLORINATORS
Chlorine pumps or devices used to feed chlorine solutions made from hypochlorites such as bleach (sodium hypochlorite) or
calcium hypochlorite.
HYPOCHLORITE (hi-po-KLOR-ite) HYPOCHLORITE
Hypochlorite compounds contain chlorine and are used for disinfection. These compounds are similar to strong bleach. They are
available as liquids or solids (powder, granules and pellets) in barrels, drums and cans.
MPN (EM-PEA-EN) MPN
MPN is the Most Probable Number of coliform-group organisms per unit volume. Expressed as density or population of organisms
per 100 ml.
MOTILE (MO-till) MOTILE
Motile organisms exhibit or are capable of movement.
NITROGENOUS (nye-TROG-en-ous) NITROGENOUS
Nitrogenous compounds contain nitrogen.
NOMOGRAM NOMOGRAM
A chart or diagram containing three or more scales used to solve problems with three or more variables instead of using mathemati-
cal formulas.
ORTHOTOLIDINE (or-tho-TOL-i-dine) ORTHOTOLIDINE
Orthotolidine is a colorimetric indicator of chlorine residual. If chlorine is present, a yellow-colored compound is produced. This
method is no longer approved for tests of effluent chlorine residual.
OXIDIZING AGENT OXIDIZING AGENT
An oxidizing agent is any substance, such as oxygen (02) and chlorine (Cl2), that can add (take on) electrons. When oxygen or
chlorine is added to wastewater, organic substances are oxidized. These oxidized organic substances are more stable and less
likely to give off odors or to contain disease bacteria. The opposite of REDUCING AGENT.
-------
328 Treatment Plants
PARASITIC BACTERIA (PAIR-a-SIT-tick) PARASITIC BACTERIA
Parasitic bacteria are those bacteria which normally live off another living organism, known as the "host."
PATHOGENIC BACTERIA (path-o-JEN-nick) PATHOGENIC BACTERIA
Bacteria, viruses or cysts which can cause disease (typhoid, cholera, dysentery). There are many types of bacteria which do NOT
cause disease and which are NOT called pathogenic. Many beneficial bacteria are found in wastewater treatment processes
actively cleaning up organic wastes.
POSTCHLORINATION POSTCHLORINATION
The addition of chlorine to the plant discharge or effluent, FOLLOWING plant treatment, for disinfection purposes.
POTABLE WATER (POE-ta-bl) POTABLE WATER
Water that does not contain objectionable pollution, contamination, minerals, or infective agents and is considered safe for domestic
consumption.
PRECHLORINATION PRECHLORINATION
The addition of chlorine at the headworks of the plant PRIOR TO other treatment processes mainly for odor and corrosion control.
Also applied to aid disinfection, to reduce plant BOD load, to aid in settling, 1o control foaming in Imhoff units and to help remove oil.
REAGENT (re-A-gent) REAGENT
A substance which takes part in a chemical reaction and is used to measure, detect, or examine other substances.
REDUCING AGENT REDUCING AGENT
A reducing agent is any substance, such as the chloride ion (CI ~) and the sulfide ion (S~2), that can give up electrons. The opposite
of OXIDIZING AGENT.
RELIQUEFACTION (re-LICK-we-FACK-shun) RELIQUEFACTION
The return of a gas to a liquid. For example, a condensation of chlorine gas returning to the liquid form.
RESIDUAL CHLORINE RESIDUAL CHLORINE
Residual chlorine is the amount of chlorine remaining after a given contact time and under specified conditions.
ROTAMETER ROTAMETER
A device used to measure the flow rate of gases and liquids. The gas or liquid being measured flows vertically up a calibrated tube.
Inside the tube is a small ball or bullet-shaped float (it may rotate) that rises or falls depending on the flow rate. The flow rate may be
read on a scale behind the middle of the ball or the top of the float.
SAPROPHYTES (SAP-pro-fights) SAPROPHYTES
Organisms living on dead or decaying organic matter. They help natural decomposition of the organic solids in wastewater.
SEPTICITY (sep-TIS-it-tee) SEPTICITY
Septicity is the condition in which organic matter decomposes to form foul-smelling products associated with the absence of free
oxygen. If severe, the wastewater turns black, gives off foul odors, contains little or no dissolved oxygen and creates a heavy oxygen
demand.
STERILIZATION (stare-uh-luh ZAY-shun) STERILIZATION
The removal or destruction of all living microorganisms, including pathogenic and saprophytic bacteria, vegetative forms and
spores. Compare with DISINFECTION.
TITRATE (TIE-trate) TITRATE
To TITRATE a sample, a chemical solution of known strength is added on a drop-by-drop basis until a color change, precipitate, or
pH change in the sample is observed (end point). Titration is the process of adding the chemical solution to completion of the
reaction as signaled by the end point.
TOTAL RESIDUAL CHLORINE TOTAL RESIDUAL CHLORINE
The amount of chlorine remaining after a given contact time. The sum of the combined available residual chlorine and the free
available residual chlorine. Also see RESIDUAL CHLORINE.
-------
Disinfection 329
CHAPTER 10. DISINFECTION AND CHLORINATION
(Lesson 1 of 5 Lessons)
10.0 NEED FOR DISINFECTION
10.00 Effectiveness in Microorganism Removal by Vari-
ous Treatment Processes
Homes, hospitals and industrial facilities all discharge liquid
and solid waste materials into the wastewater collection sys-
tem. Diseases from human discharges may be transmitted by
wastewater. Typical disease-causing microorganisms include
bacteria, viruses, and parasites. These microorganisms are
commonly referred to as PATHOGENIC (disease-causing)
MICROORGANISMS.1 These microorganisms can cause the
following types of illnesses:
Bacteria-caused:
Salmonellosis
Shigellosis
Typhoid Fever
Cholera
Paratyphoid
Bacillary Dysentery
Virus-caused:
Polio
Infectious Hepatitis
Internal Parasite-caused:
Amoebic Dysentery
Ascaris (giant roundworm)
Giardiasis
Disease-producing microorganisms are potentially present
in all wastewaters. These microorganisms must be removed or
killed before treated wastewater can be discharged to the re-
ceiving waters. The purpose of disinfection is to destroy
pathogenic microorganisms and thus prevent the spread of
waterborne diseases.

PAT-*-t©
-------
330 Treatment Plants
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-------
Disinfection 331
One of the main uses of chlorine in wastewater treatment is
for disinfection. Chlorine is relatively easy to obtain and cheap
to manufacture. Even at relatively low dosages, chlorine is
extremely effective.
Today people are living more intimately with wastewater
than ever before. Wastewater effluent may be used for irrigat-
ing lawns, parks, cemeteries, freeway planting, golf courses,
college campuses, athletic fields, and other public areas. Rec-
reational lakes used for boating, swimming, water skiing, fish-
m
ing, and other water sports are frequently made up partially
and, in a few cases, solely of treated effluents. As public con-
tact has increased and diluting waters have decreased or be-
come of poor quality, it has become obvious that more consid-
eration must be given to disinfection practices.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 389.
10.0A What is the purpose of disinfection? Why is this impor-
tant?
10.0B How are pathogenic bacteria destroyed or removed
from water?
10.OC Why is chlorination used for disinfection?
10.0D Why are wastes not sterilized?
10.02 Reaction of Chlorine in Wastewater
Chlorine is applied to wastewater as FREE CHLORINE3
(Cl2), as HYPOCHLORITE4 ion (OCI~), or as chlorine dioxide
(CIO?)- In either the free chlorine or hypochlorite ion form,
chlorine is an extremely active chemical and acts as a potent
OXIDIZING AGENT.5 In the chlorine dioxide form, chlorine is
not as potent an oxidizing agent in the pH ranges commonly
found in most wastewaters. Since chlorine is very reactive, it is
often used up by side reactions before disinfection takes place.
These side reactions can be with such substances as organic
material, hydrogen sulfide, phenols, thiosulfate, and ferrous
iron. These side reactions occur first and use up a major por-
tion of the chlorine necessary to meet the CHLORINE DE-
MAND6 for a wastewater.
10.020 Free Chlorine (CI J
Free chlorine combines with water to form hypochlorous and
hydrochloric acids:
. Hypochlorous
Acid
Chlorine + Water;
, Hydrochloric
Acid
Cl2 + H20 ^ HOCI + HCI
In solutions that are dilute and have a pH above 4, the forma-
tion of HOCI (hypochlorous acid) is most complete and leaves
little Cl2 existing. The hypochlorous acid is a weak acid and is
very poorly dissociated (broken up) at levels below a pH of 6.
Thus any free chlorine or hypochlorite (OCI) added to water
will immediately form either HOCI or OCh and what will be
formed is controlled by the pH value of the water. This is ex-
tremely important since HOCI and OCh differ in disinfection
ability. HOCI has a greater disinfection potential than OCI .
Normally in wastewater with a pH of 7.3 (depends on tempera-
ture), 50 percent of the chlorine present will be in the form of
HOCI and 50 percent in the form of OCh. The higher the pH
level, the greater the percent of OCh.
10.021 Hypochlorite (OCI )
When hypochlorite compounds are used in wastewater, they
are usually in the form of sodium hypochlorite (NaOCI). Cal-
cium hypochlorite (Ca(OCI)2) normally is not used because of
its cost, sludge-forming characteristics and explosive nature.
The use of hypochlorite in wastewater follows the reaction
similar to that of chlorine gas.
Sodium . WalBr.
Hypochlorite + vva,er
NaOCI + H20 ¦
Hypochlorous Hypochlorite , Hydrogen
' Acid Ion Ion
^ Sodium
' Hydroxide
NaOH + HOCI + OCI + H +
The difference between chlorine gas and hypochlorite com-
pounds is in the side reactions formed. The reaction of chlorine
gas tends to decrease the pH which favors the HOCI
(hypochlorous acid) formation while the hypochlorite increases
the pH with the formation of hydroxyl ions (OH~) by the forma-
tion of sodium hydroxide. At a high pH of around 10, the
hypochlorous acid (HOCI) dissociates.
Hypochlorous _ Hydrogen Hypochlorite
Acid Ion Ion
HOCI ^ H+ + OCh
This pH condition lasts only a brief time at the contact of the
hypochlorite solution and the wastewater to be treated. Since
the hypochlorite ion (OCh) is a relatively ineffective disinfec-
tant, the sodium hypochlorite solution should be as dilute as
3 Free Chlorine. Free chlorine is chlorine (CI,) in a liquid or gaseous form. Free chlorine combines with water to form hypochlorous (HOCI)
and hydrochloric (HCI) acids. In wastewater free chlorine usually combines with an amine (ammonia or nitrogen) or other organic compounds
to form combined chlorine compounds.
4 Hypochlorite (hi-po-KLOR-ite). Hypochlorite compounds contain chlorine and are used for disinfection. These compounds are similar to a
strong bleach. They are available as liquids or solids (powder, granules, and pellets) in barrels, drums and cans.
5 Oxidizing Agent. An oxidizing agent is any substance, such as oxygen (02) and chlorine (Cl2), that can add (take on) electrons. When
oxygen or chlorine is added to wastewater, organic substances are oxidized. These oxidized organic substances are more stable and less
likely to give off odors or to contain disease bacteria. The opposite of REDUCING AGENT.
6 Chlorine Demand. Chlorine demand is the difference between the amount of chlorine added to wastewater and the amount of RESIDUAL
CHLORINE7 remaining after a given contact time. Chlorine demand may change with dosage, time, temperature, pH, and nature and amount
of impurities in water. Chlorine Demand, mgIL = Chlorine Applied, mg/L - Chlorine Residual, mg/L.
7 Residual Chlorine. Residual chlorine is the amount of chlorine remaining after a given contact time and under specified conditions.
-------
332 Treatment Plants
possible. This is extremely important in wastewater disinfec-
tion.
10.022 Chlorine Dioxide (CIO,)
Chlorine dioxide reacts in the following manner:
Chlorine Water Chlorate + Chlorite + Hydrogen
Dioxide Ion Ion Ions
2 CI02 + HjO - CI03- + CIO" + 2H+.
The oxidizing capability of chlorine dioxide is not all used in
wastewater treatment because reactions with the substances
(,REDUCING AGENTS8) in wastewater only cause the reduc-
tion of chlorine dioxide to chlorite.
Chlorine + Electron _ Chlorite
Dioxide Ion
CI02 + e~ — CI02
Therefore, chlorine dioxide is not as reactive as chlorine and
chlorine is a better oxidant. In waters with a pH above 8.5,
chlorine dioxide is a very effective disinfectant. Chlorine
dioxide usually does not react with ammonia.
Chlorine dioxide is very unstable and must be generated at
the plant site. Generally chlorine dioxide is prepared by the
injection of sodium chlorite into the chlorine solution line from a
chlorinator.
Sodium + Chlorine Sodium + Chlorine
Chlorite Chloride Dioxide
2 NaCI02 +- Cl2 — 2 NaCI + 2 CI02
Chlorine dioxide may find more applications in the water
treatment field than in wastewater treatment because chlorine
dioxide is less likely than chlorine to produce cancer-causing
compounds and to cause tastes and odors in water.
10.03 Reactions of Chlorine Solutions with Impurities in
Wastewater
Since wastewater contains a great number of complex sub-
stances and chemicals, many of these substances have a
serious effect on wastewater chlorination. A few of the major
impurities will be discussed in the following sections.
10.030 Inorganic Reducing Materials
Chlorine reacts rapidly with many reducing agents and more
slowly with others. These reactions complicate the use of
chlorine tor disinfecting purposes. One of the most widely
known inorganic reducing materials is hydrogen sulfide. Hy-
drogen sulfide reacts with chlorine to form sulfuric acid (sul-
fate) or elemental sulfur depending on the concentration of
hydrogen sulfide, pH and temperature.
1. Hydrogen Free + Water Sulfuric + Hydrochloric
Sulfide Chlorine Acid Acid
HjS + 4 Cl2 + 4 H20 - H2S04 + 8 HCI
2. w_.or . Free Hypochlorous . Hydrogen Elemental . Hydrochloric + wflter
Chlorine Acid Sulfide Sulfur Acid
H20 + Cl2 — HOCI + H2S -» S° + HCI + H20
1
One part of hydrogen sulfide (H2S) takes about 8.5 parts of
chlorine in equation 1 and 2.2 parts of chlorine in equation 2.
Since these reactions occur before a chlorine residual occurs,
the demand caused by the inorganic salts must be satisfied
first before any disinfection can take place. Ferrous iron, man-
ganese, and nitrite are examples of other inorganic reducing
agents that react with chlorine.
10.031 Reaction with Ammonia (NHJ
Since ammonia is present in all domestic wastewaters, the
reaction of ammonia with chlorine is of great significance.
When chlorine is added to waters containing ammonia, the
ammonia reacts with hypochlorous acid (HOCI) to form
monochloramine, dichloramine and trichloramine. The forma-
tion of these chloramines depends on the pH of the solution
and the initial chlorine-ammonia ratio.
Ammonia + Hypochlorous chloramine + Water
Acid
NH3 + HOCI —» NH2CI + H20 monochloramine
NH2CI + HOCI NHCI2 + H20 dichloramine
NHCI2 + HOCI —> NCIj + H20 trichloramine
In general at the pH levels that are usually found in wastewa-
ter (pH 6.5 to 7.5), monochloramine and dichloramine exist
together. At pH levels below 5.5, dichloramine exists by itself.
Below pH 4.0, trichloramine is the only compound found.
The mono- and dichloramine forms have definite disinfection
powers and are of interest in the measurement of chlorine
residuals. Dichloramine has a more effective disinfecting
power than monochloramine.
05*
+ AlO
If enough chlorine is added to react with the inorganic com-
pounds and NITROGENOUS9 compounds, then this chlorine
will react with organic matter to produce CHLORORGANIC10
compounds or other combined forms of chlorine, which have
slight disinfecting action. Then if enough chlorine is added to
8 Reducing Agent. A reducing agent is any substance, such as the chloride ion (Cl~) and the sulfide ion (S 2), that can give up electrons.
The opposite of OXIDIZING AGENT.
9 Nitrogenous (nye-TROG-en-ous). Nitrogenous compounds contain nitrogen.
10 Chiororganic (chlor-or-GAN-nick). Chiororganic compounds are organic compounds combined with chlorine. These compounds gener-
ally originate from, or are associated with, living or dead organic materials.
-------
Disinfection 333
react with all the above compounds, any additional chlorine will
exist as FREE AVAILABLE CHLORINE11 which has the high-
est disinfecting action (Fig. 10.2). This situation rarely exists in
wastewater that contains nitrogenous compunds. The term
BREAKPOINT CHLORINATION12 refers to the breakpoint
shown on Fig. 10.2.
The exact mechanism of this disinfection action is not fully
known. In some theories, chlorine is considered to exert a
direct action against the bacterial cell, thus destroying it.
Another theory is that the toxic character of chlorine inactivates
the ENZYMES13 upon which the living microorganisms are de-
pendent for utilizing their food supply. As a result, the or-
ganisms die of starvation. From the point of view of wastewater
treatment, the mechanism of the action of chlorine is much less
important than its effects as a disinfecting agent.
The demand by inorganic and organic materials is referred
to as "chlorine demand." The chlorine that remains in com-
bined forms having disinfecting properties plus any free
chlorine is referred to as "residual chlorine." The sum of the
chlorine demand and the chlorine residual is the chlorine dose.
Chlorine Dose = Chlorine Demand + Chlorine Residual
where
Chlorine Residual = Combined Chlorine Forms + Free Chlorine
10.04 Hypochlorination14 of Wastewater
Hypochlorination is usually not the most common method of
disinfection. Higher costs and the disinfecting deficiencies of
hypochlorination make chlorination the most effective method
in most cases. Some cities recently have switched to
hypochlorination for safety reasons because chlorine gas is
not involved. As previously described, when the pH is in-
creased, the hypochlorite ion (OCI ) formation is increased
and is less efficient than the hypochlorous acid (HOCI). How-
ever, when the hypochlorite solution is added to wastewater,
the solution becomes diluted with the pH usually approaching
that of the wastewater.
Hypochlorination will raise the pH of the wastewater being
treated. The rise in pH will decrease the effectiveness of the
hypochlorite, thereby requiring a higher dosage. This, in turn,
will increase the pH even more.
10.05 Factors Influencing Disinfection
Both CHLORINE ADDITION and CONTACT TIME are es-
sential for effective killing of pathogenic microorganisms. Ex-
perimental determination of the best combination of combined
residual chlorine and contact time is necessary to insure both
proper chlorine dose and minimum use of chlorine. Changes in
pH affect the disinfection ability of chlorine and the operator
must reexamine the best combination of chlorine addition and
contact time when the pH fluctuates. Critical factors influencing
disinfection are summarized as follows:
1. Injection point and method of mixing to get disinfectant in
contact with wastewater being disinfected.
2. Design (shape) of contact chambers are designed in vari-
ous sizes and shapes. Rectangular contact chambers often
allow short-circuiting and consequently reduced contact
times. Baffles often are installed to increase mixing action,
to obtain better distribution of disinfectant, and to reduce
short-circuiting which in turn increases contact time.
Pipelines have proved to be good contact chambers.
3. Contact time. With good initial mixing, the longer the con-
tact time, the better the disinfection. Most chlorine contact
basins are designed to provide a contact time of 30 min-
utes. In general, extending the chlorine contact time is more
effective than increasing the chlorine dose to improve disin-
fection.
4. Effectiveness of upstream treatment processes. The lower
the suspended solids and organic content of the wastewa-
ter, the better the disinfection.
5. Temperature. The higher the temperature, the more rapid
the rate of disinfection.
6. Dose rate and type of chemical. Normally the higher the
dose rate, the quicker the disinfection rate. The form or type
of chemical also influences the disinfection rate.
7. pH. The lower the pH, the better the disinfection.
10.06 Chlorine Requirements
The quantity of chlorine-demanding substances differs from
plant to plant, so that the amount of chlorine that has to be
added to insure proper disinfection also differs. The amount of
chlorine required to satisfy the chlorine-demanding substances
is called the CHLORINE DEMAND. This demand is equal to
the chlorine dose minus the chlorine residual.
Chlorine Demand = Chlorine Dose - Chlorine Residual
The chlorine residual is determined by one of several labora-
tory tests. The method of choice must be one of those ap-
proved by state and federal water pollution control agencies,
otherwise the results will not be recognized. These tests are
discussed in the laboratory section of this manual (Chapter
16). The amount of residual that one should maintain is deter-
mined by the desired microorganism population. The mi-
croorganism population is usually specified by State or Federal
NPDES Permit requirements. The microorganism population
usually is estimated by determining the MP/V15 of COL-
IFORM*6 -group organisms present. This determination does
not test for individual pathogenic microorganisms, but uses the
coliform group of organisms as the indicator organism. Col-
iform organisms usually are found in most wastewaters. See
Chapter 16 for the laboratory test to determine the MPN of
conforms present.
11 Free Available Chlorine. The amount of chlorine available in water. This chlorine may be in the form of dissolved gas (Cl2), hypochbrous
acid (HOCI), or hypochlorite (OCI ), but does not include chlorine combined with an amine (ammonia or nitrogen) or other organic
compound.
12 Breakpoint Chlorination. Addition of chlorine to water or wastewater until the chlorine demand has been satisfied and further additions of
chlorine result in a residual that is directly proportional to the amount added beyond the breakpoint.
13 Enzymes (EN-zimes). Enzymes are organic substances which are produced by living organisms and speed up chemical changes.
14 Hypochlorination (hi-po-KLOR-i-NAY-shun). The application of hypochlorite compounds to water or wastewater for the purpose of disin-
fection.
is MPN (EM-PEA-EN). MPN is the Most Probable Number of coliform-group organisms per unit volume. Expressed as density or population
of organisms per 100 ml.
is Coliform (COAL-i-form). One type of bacteria. The presence of coliform-group bacteria is an indication of possible pathogenic bacterial
contamination. The human intestinal tract is one of the main habitats of coliform bacteria. They may also be found in the intestinal tracts of
warm-blooded animals, and in plants, soil, air, and the aquatic environment. Fecal conforms are those conforms found in the feces of various
warm-blooded animals; whereas the term "coliform" also includes other environmental sources.
-------
334 Treatment Plants
COMBINED
RESIDUAL
CHLORINE
OXIDATION OF
COMBINED RES I -
DUAL MATERIALS
(CHLORAMINES)
CHLORINE
DEMAND
BREAKPOINT
FOR SECONDARY
WASTEWATER,
APPROXIMATELY
CHLORINE
RESIDUAL,
mg/l
FREE CHLORINE
RESIDUAL ON A
1 TO 1 BASIS
CHLORINE DOSAGE, mg/l
Fig. 10.2 Breakpoint chlorination curve
-------
Disinfection 335
Calculations to determine the chlorine dosage and chlorine
demand are illustrated in the following example problem.
EXAMPLE:
A chlorinator is set to feed 50 pounds of chlorine per 24
hours; the wastewater flow is at a rate of 0.85 MGD, and the
chlorine as measured by the chlorine residual test after thirty
minutes of contact time is 0.5 mgIL. Find the chlorine dosage
and chlorine demand in mg IL.
Chlorine Feed
or Dose, mg IL
Pounds of Chlorine
Million Pounds of Water
50 lbs chlorine/day
Chlorine
Demand, mg IL
(0.85 MG/day) (8.34 lbs/gal)
59 lbs chlorine/MG
8.34 lbs/gal
7.1 lbs chlorine/million pounds water
7.1 ppm (Parts Per Million parts)
7.1 mg IL
Chlorine Dose, mg/i.
7.1 mg IL - 0.5 mgIL
6.6 mg/l.
59.
0.85) 50.00
42 5
7 50
7 65
Chlorine Residual, mg IL
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 389.
10.0E
10.OF
10.0G
10.OH
10.01
What does chlorine produce when it reacts with or-
ganic matter and with nitrogenous compounds?
How much chlorine must be added to wastewater to
produce disinfecting action?
How is the chlorine demand determined?
How is the chlorine dosage determined?
Calculate the chlorine demand of treated domestic
wastewater if:
Flow Rate
Chlorinator
Residual
1.2 MGD
70 lbs of chlorine per 24 hours
0.4 mg IL after thirty minutes
The objective of disinfection is the destruction of pathogenic
bacteria, and the ultimate measure of the effectiveness is the
bacteriological result. The measurement of residual chlorine
does supply a tool for practical control. If the residual chlorine
value commonly effective in most wastewater treatment plants
ml
does not yield satisfactory bacteriological kills in a particular
plant, the residual chlorine that does must be determined and
used as a control in that plant. In other words, the 0.5 mg//.
residual chlorine, while generally effective, is not a rigid stan-
dard but a guide that may be changed to meet local require-
ments.
One special case would be the use of chlorine in the effluent
from a plant serving a tuberculosis hospital. Studies have
shown that a residual of at least 2.0 mgIL should be maintained
in the effluent from this type of institution, and that detention
time should be at least two hours at the average rate of flow
instead of the thirty minutes which is normally used for basis of
design. Two-stage chlorination may be particularly effective in
this case.
The following list of chlorine dosages provides a reasonable
guideline to produce chlorine residual adequate for applica-
tions indicated for domestic wastewaters. Individual plants
may require higher or lower dosages, depending upon type
and amount of suspended and dissolved organic compounds
in the chlorinated sample.
APPLICATION
Collection Systems
Slime Control
Corrosion Control
Odor Control
Treatment
Grease Removal
BOD Reduction
Inorganic Compounds
Filter Ponding
Filter Flies
Activated Sludge
Bulking
Digester
Supernatant
Foaming
Disinfection
Raw Wastewater
Primary-Clarifier Effluent
Chemical Precipitation
Trickling-Filter Effluent*
Activated-Sludge Effluent*
Advanced Waste Treatment
"After secondary clarification
DOSAGE RANGE, mg IL
1-15
10-25
10-25
1-10
1-10
2-12
1-10
0.5
1-10
20-150
2-20
10-30
5-20
2-6
3-20
2-8
1-5
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 389.
10.0J What is the objective of disinfection?
10.0K How is the effectiveness of the chlorination process for
a particular plant determined?

BHC
0? 9
OH C7|
Please answer the discussion and review questions before
continuing with Lesson 2.
-------
336 Treatment Plants
DISCUSSION AND REVIEW QUESTIONS
Chapter 10. DISINFECTION AND CHLORINATION
(Lesson 1 of 5 Lessons)
At the end of each lesson in this chapter, you will find dis-
cussion and review questions that you should work before con-
tinuing. The purpose of these questions is to indicate to you
how well you understand the material in the lesson.
Write the answers to these questions in your notebook be-
fore continuing.
1. Why must wastewaters be disinfected?
2. Why is chlorination used to disinfect wastewater?
3. To improve disinfection, which is more effective — increas-
ing the chlorine dose, or extending the chlorine contact
time?
4. What constituents in wastewater are mainly responsible for
the chlorine demand?
5. Calculate the chlorinator setting (lbs per 24 hours) to treat a
waste with a chlorine demand of 12 mg//., when a chlorine
residual of 2 mg/Z. is desired, if the flow is 1 MGD.
6. How do suspended and dissolved organic compounds in an
effluent affect disinfection?
CHAPTER 10. DISINFECTION AND CHLORINATION
(Lesson 2 of 5 Lessons)
10.1 POINTS OF CHLORINE APPLICATION (Fig. 10.3)
10.10 Collection System Chlorination
One of the primary benefits of up-sewer chlorination is to
prevent the deterioration of structures. Other benefits include
odor and septicity control, and possibly BOD reduction to de-
crease the load imposed on the wastewater treatment pro-
cesses. In some instances, the maximum benefit may result
from a single application of chlorine at a point on the main
intercepting sewer before the junction of all feeder sewer lines.
In others, several applications at more than one point on the
main intercepting sewer or at the upper ends of the feeder lines
may prove most effective. Due to high costs CHLORINATION
SHOULD BE CONSIDERED AS A TEMPORARY OR
EMERGENCY MEASURE IN MOST CASES, with emphasis
being placed on proper design of the system. Aeration also is
effective in controlling septic conditions in collection systems.
Although many problems result from improper design or de-
sign for future capacity requirements, the need for hydrogen
sulfide protection exists under the best of conditions in some
locations.
10.11 Prechlorination
"Prechlorination" is defined as the addition of chlorine to
wastewater at the entrance to the treatment plant, ahead of
settling units and prior to the addition of other chemicals. In
addition to its application for aiding disinfection and odor con-
trol at this point, prechlorination is applied to reduce plant BOD
load, as an aid to settling, to control foaming in Imhoff units,
and to help remove oil. Current trends are away from pre-
chlorination to up-sewer aeration or other chemical treatment
for control of odors.
10.12 Plant Chlorination
Chlorine is added to wastewater during treatment by other
processes, and the specific point of application is related to the
results desired. The purpose of plant chlorination may be for
control and prevention of odors, corrosion, sludge bulking, di-
gester foaming, filter ponding, filter flies, and as an aid in
sludge thickening. Here again, chlorination should be an
emergency measure. Extreme care must be exercised when
applying chlorine because it can interfere with or inhibit biolog-
ical treatment processes.
10.13 Chlorination Before Filtration
More stringent discharge requirements are causing many
agencies to provide filtration for solids removal before dis-
charge (Chapter 23). The better designs provide a means of
chlorinating the water before application to the filters to kill
algae and other large biological organisms. Prechlorination
tends to prevent the development of biological growths which
might cause short-circuiting or excessive backwashing in the
filter media. Postchlorination of the effluent from the filter would
be in addition to this application.
10.14 Postchlorination
"Postchlorination" is defined as the addition of chlorine to
municipal or industrial wastewater following other treatment
processes. This point of application should be before a
CHLORINE CONTACT UNIV and after the final settling unit in
the treatment plant. The most effective place for chlorine appli-
cation for disinfection is after treatment and on a well-clarified
effluent. Postchlorination is used primarily for disinfection. As a
result of chlorination for disinfection, some reduction in BOD
17 Chlorine Contact Unit. A baffled basin that provides sufficient detention time for disinfection to occur.
-------
Disinfection 337
COLLECTION SYSTEM
ODOR CONTROL
CORROSION CONTROL
PUMP STATION
PRECHLORINATION
ODOR CONTROL
CORROSION CONTROL
BOD REDUCTION
AID SEDIMENTATION
GREASE REMOVAL
SCREENS
REMOVAL
IN-PLANT
ODOR CONTROL
BOD REDUCTION
SEPTICITY CONTROL
SEDIMENTATION
AND FLOTATION
SLUDGE
DIGESTION
IN-PLANT
RETURN
SLUDGE
TRICKLING
FILTERS
ACTIVATED
SLUDGE
ODOR CONTROL
PSYCHODA FLY
CONTROL
PONDING
CONTROL
BOD REDUCTION
SEPTICITY
SLUDGE
BULKING
AID
SEDIMENTATION
SEDIMENTATION
SEDIMENTATION
MIXED LIQUOR
ODOR CONTROL
AID SEDIMENTATION
POSTCriLORINATION
DISINFECTION
CHLORINE
CONTACT
CHAMBER
Fig. 10.3 Points of chlorine application
-------
338 Treatment Plants
may be observed; however, chlorination is rarely practiced
solely for the purpose of BOD reduction.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 389.
10.1 A What is the purpose of up-sewer chlorination?
10.1 B Where should chlorine be applied in sewers?
10.1C What are the main reasons for prechlorination?
10.1 D Why might chlorine be added to wastewater during
treatment by other processes?
10.1E What is the objective of postchlorination?
10.2 CHLORINATION PROCESS CONTROL
10.20 Chlorinator Control
The control of chlorine flow to points of application is accom-
plished by six basic methods and a seventh method which
combines two of the basic six.
10.200 Manual Control
Feed-rate adjustment and starting and stopping of equip-
ment is done by hand.
10.201 Start-Stop Control
Feed-rate adjustment by hand, starting and stopping (by in-
terrupting injector water supply) controlled by starting of
wastewater pump, flow switch, and level switch.
10.202 Step-Rate Control
Chlorinator feed rate is varied according to the number of
wastewater pumps in service. As each pump starts, a pre-set
quantity of chlorine is added to the flow of chlorine existing at
starting time. This system can be applied conveniently with
installations using up to eight pumps.
10.203 Time-Program Control
Chlorine feed rate is varied on a timed step-rate basis regu-
lated to correspond to the times of flow changes or by using a
time-pattern transmitter which uses a revolving cam cut to
match a flow pattern.
10.204 Flow-Proportional Control
Chlorinator feed rate is controlled by a system which con-
verts wastewater flow information into a chlorinator control
value. This can be accomplished by a variety of flow-metering
equipment, including all process control instrumentation pres-
ently available and nearly all metering equipment now in use
on wastewater systems.
10.205 Chlorine Residual Control
Chlorine feed rate is controlled to a desired chlorine residual
(usually COMBINED AVAILABLE CHLORINE™) level. After
mixing and reaction time (about five minutes maximum), a
wastewater sample is TITRATED19 by an AMPEROMETRIC20
analyzer-recorder (or indicator). As the residual chlorine level
varies above or below the desired (set point) level, the
chlorinator is caused to change its feed rate to bring the
chlorine residual back to the desired level.
10.206 Compound Loop Control
Any "automatic" control system (step-rate, timed program,
flow proportional, or residual) can be employed in two ways:
(1) by positioning the feed-rate valve; or (2) by varying the
vacuum differential across the feed-rate valve. For instance, a
flow-proportional (or step-rate, or timed program) control sys-
tem may position the feed-rate valve, and a residual-control
system may vary the vacuum differential across the feed-rate
valve. Thus, changes in flow cause changes in feed-rate valve
position, but changes in chlorine demand may occur without
any flow change. When this happens, the residual analyzer
detects a change in chlorine residual and, by varying the vac-
uum differential across the feed-rate valve, causes the
chlorinator to change rates to meet the desired chlorine re-
sidual level.
Various combinations of compound loop control can be
employed. Generally speaking, the part of the system requiring
the fastest response should be applied to valve positioning
(since it responds faster). If flow changes are rapid, flow con-
trol should be by valve position. If flow and demand change
rates are nearly the same, the magnitude of change may dic-
tate the selection of control.
The selection of control methods should be based on treat-
ment costs and treatment results (required or desired). A
waste discharger must normally meet a disinfection standard.
A small treatment plant might do this with a compound loop
control system costing several thousand dollars, but may save
less than one hundred dollars a year in chlorine consumed. In
this case the expense would not be justified. A manual system,
which would meet the maximum requirements and over-
chlorinate at minimum requirement periods, might be used. It is
not unheard of for a plant to have maximum chlorine residual
requirements becaue of irrigation and/or marine life tolerances.
In these cases the uncontrolled or haphazard application of
chlorine cannot be considered, no matter how large the added
cost.
A specified chlorine residual level may be required at some
point downstream from the best residual control sample point.
In this case a residual analyzer should be used to monitor and
record residuals at this point. It may also be used to change the
control set point of the controlling residual analyzer.
Ultimate control of dosage for disinfection rests on the re-
sults desired, that is, the bacterial level or concentration ac-
ceptable or permissible at the point of discharge. Determina-
tion of chlorine requirements according to the current edition of
STANDARD METHODS FOR THE EXAMINATION OF WATER
AND WASTEWATER is the best method of control. You must
remember that the chlorine requirement or chlorine dose will
vary with wastewater flow, time of contact, temperature, pH,
and major waste constituents such as hydrogen sulfide, am-
monia, and amount of dead and living organic matter.
18 Combined Available Chlorine. The concentration of chlorine which is combined with ammonia (NHJ as chloramine or as other chloro
derivatives, yet is still available to oxidize organic matter.
19 Titrate (TIE-trate). To TITRATE a sample, a chemical solution of known strength is added on a drop-by-drop basis until a color change,
precipitate, or pH change in the sample is observed (end point). Titration is the process of adding the chemical solution to completion of the
reaction as signaled by the end point. ,
20 Amperometric (am-PURR-o-MET-rick). A method of measurement that records electric current flowing or generated, rather than recording
voltage. Amperometric titration is a means of measuring concentrations of certain substances in water.
-------
Disinfection 339
The chlorine requirements for various flow rates and contact
times can be determined on either a plant or a laboratory scale.
If the determination is made on a laboratory scale, you should
expect the plant requirements to be somewhat higher. This is
to be expected since the mixing and actual contact times can
be more carefully controlled in the laboratory. It is preferable
that the determinations be made by both methods and the
results compared. If the chlorine requirement as determined by
full plant tests is significantly greater than that determined by
laboratory testing, a wastage of chlorine is indicated. The two
major causes of a large discrepancy between laboratory and
plant results are poor mixing at the point of chlorine injection
and short-circuiting in the contact chamber. Either problem can
usually be solved at a relatively small expense as compared to
the savings which can be achieved by the reduced use of
chlorine.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 389.
10.2A How can chlorine gas feed be controlled?
10.2B Control of chlorine dosage depends on the bacterial
desired.
10.2C Define amperometric.
10.21 Chlorlnation Control Nomogram21
Determination of the chlorine residual may give information
that confirms the previous choice of dosage or indicates that
the dosage should be readjusted. The contact period must be
specified since longer contact periods increase chlorine up-
take.
Since feed rate is expressed in pounds per day, the rate
setting of the feeder must be calculated from determination of
chlorine required and the flow. The simplest means of making
the calculation is by a chlorination control nomogram taken
from the WPCF MANUAL OF PRACTICE NO. 11 (MOP 11),
1968 (Fig. 10.4). The following sequence is a guide to using
this nomogram:
1. Lay a straightedge (ruler) on point on Line A, representing
flow, and on point on Line B, representing CHLORINE RE-
QUIRED, 22 and read point on Line C, which shows setting
for chlorine feeder.
2. For any value in excess of maximum indicated on Scales A,
B, or C, introduce proper factor of ten or multiple thereof.
The application of a factor of ten will be presented later in
Example 2.
3. Greatest accuracy will be obtained when the angle of the
straightedge approaches a right angle with Line B. Multi-
pliers of ten may be applied to aid in accomplishing this
objective.
4. If straightedge does not cross all three scales, introduce
necessary factors of ten and move straightedge to point
where all three scales will be crossed.
Let's try some examples using Fig. 10.4. Assume the given
chlorine dosage was selected on the basis of preliminary tests
as capable of producing the desired results.
EXAMPLE 1
Given: Maximum Flow Rate = 0.5 MGD
Chlorine dosage = 1.0 mg/L
Procedure: Place one end of straightedge (ruler) on 0.5
MGD (Line A) and draw a line through the point
on Line B representing a chlorine dosage of 1.0
mg/L. Extend the line to Line C and read the
point indicating the chlorine feed rate.
Answer: Chlorine Feed Rate = 4.2 lbs per 24 hours
Check:
Chlorine
Feed = (Max. Flow, MGD) (Dosage, mg/L) (8.34 lbs/ gal)
Rate
= 0.5 MGX 1.0 -JDtf-3 x 8.34 M "J
day M mg gal u a
4.170
= 4.17, say 4.2 lbs per day
EXAMPLE 2
Given: Maximum Flow Rate = 5.0 MGD
Chlorine Dosage = 1.0 mg/L
Procedure: 5.0 MGD is off our scale on Line A. Reduce flow
by a factor of ten to 0.5 MGD, or 5.0 MGD/10 =
0.5 MGD. The problem is the same as Example
1, and the chart gives a chlorine feed rate of 4.2
lbs per 24 hrs. The flow rate is actually ten times
0.5 MGD (10 x 0.5 MGD = 5 MGD). Therefore
the required chlorine feed rate is 10 x 4.2 lbs per
24 hours (10 x 4.2 = 42) or 42 lbs per 24 hours.
Note: On a cold day, a 150-lb cylinder may not be
adequate to provide this feed rate because the
lines may freeze.
EXAMPLE 3
Given: Maximum Flow Rate = 0.4 MGD
Chlorine Dosage = 5.0 mg/L
Procedure: A line through a flow of 0.4 MGD (Line A) and 5.0
mg/L (Line B) misses line C. The chlorine dos-
age should be reduced by a factor of ten to be
able to use the nomogram.
21 Nomogram. A chart or diagram containing three or more scales used to solve problems with three or more variables instead of using
mathematical formulas.
22 Chlorine Requirement. The amount of chlorine which is needed for a particular purpose. Some reasons for adding chlorine are reducing
the number of coliform bacteria (Most Probable Number), obtaining a particular chlorine residual, or destroying some chemical in the water.
In each case a definite chlorine dosage will be necessary. This dosage is the chlorine requirement.
" Recall concentrations in mgIL are the same as mglM mg.
-------
340 Treatment Plants
10.0
9.0
100
8.0
0.2
200 y
£ 0.3
7.0
CM
UJ
6.0
_i 0.4
CL
Q
300
05
5.0
400 $
O 0.6
4.0 O
UJ
UJ
Ll_
u.
UJ
07
3.0
500
0 8
2.0
600
09
6944
Fig. 10.4 Chlorination control nomogram
(Source: WPCF MOP No. 11,1968)
-------
Disinfection 341
Chlorine Dosage = 5-0 mg/L = Q 5
10
1.7 lbs per 24 hours
(from chart)
= (10) (1.7 lbs per 24 hrs)
= 17 lbs per 24 hrs
Chlorine
Feed Rate
Actual
Feed Rate
The chlorine feed rate must be ten times the rate
from the chart because the chlorine required was
reduced by a factor of ten to use the chart.
The results from the chart should be checked using the
mathematical calculations used in Example 1 to avoid errors.
Note that the chlorine requirement should take into consid-
eration the chlorine demand so that a desired residual is
obtained after a given contact period. As discussed in Sec-
tion 10.06, chlorine requirements vary with the wastewater
characteristics, concentration, flow, and temperature. Ad-
justment of chlorine feeder rates to meet all these variations
is the ultimate goal of good operation practice. More frequent
adjustments are usually required for primary effluent than for
secondary effluent.
Suggested schedule for adjusting manual-feeder rates:
1. In large plants — at least every hour,
2. In medium-sized plants — every two to four hours, and
3. In small plants — every eight hours.
Other methods of chlorinator control have been described
in Section 10.20.
10.22 Hypochlorinator24 Feed Rate and Control
Chlorine for disinfection and other purposes is provided in
some plants by the use of hypochlorite compounds. The
amount of chlorine delivered depends on the type of hypochlo-
rite. For example, HTH (high test hypochlorite) contains 65
percent, by weight, of chlorine, and chlorinated lime contains
34 percent.
Manufacturers of hypochlorite compounds define available
chlorine as the amount of gaseous chlorine required to make
the equivalent hypochlorite chlorine. If you prepare a hypochlo-
rite solution for disinfection and immediately measure the
chlorine residual, you will find the chlorine residual about half
of the expected value based on the manufacturer s amount of
available chlorine. When hypochlorite is mixed with water, ap-
proximately half of the chlorine forms hydrochloric acid (HCI)
and the other half forms hypochlorite (OCh), the chlorine re-
sidual that you measured.
EXAMPLE:
A wastewater requires a chlorine feed rate of 17 lbs per day.
How many pounds of chlorinated lime will be required to pro-
vide the needed chlorine? Assume each pound of chlorinated
lime contains 0.34 lbs of available chlorine.
Chlorinated Lime = Chlorine Required, lbs/day
Feed Rate, lbs/day
Portion of Chlorine in lb of Hypochlorite
17 lbs/day
0.34
50 lbs/day
Hypochlorinators can be installed on either small systems or
large systems. Usually the larger systems use liquid chlorine
because of lower costs. However, some very large cities use
hypochlorite because it is safer. Treatment plants serving
these cities are located in highly populated areas where escap-
ing chlorine gas could threaten the lives of many people.
The items in feed systems of hypochlorinators and their con-
struction are discussed below.
1. Some type of storage system for the solution. The storage
container is made of corrosion-resistant materials such as
plastic or other similar materials.
2. Solution piping which is usually fiber glass or PVC
(polyvinyl chloride).
3. Diffusers that are made of the same material as the piping
systems.
4. Valves and EDUCTORS25 that are made of PVC.
5. Pumps that are made of corrosion-resistant materials.
Epoxy-lined systems have been successful.
6. Flow meters. These meters can be constructed using a
Hastelloy C straight-through metal tube ROTAMETER26
with the float position determined magnetically and the flow
rate transmitted either electrically or pneumatically.
7. Chlorine residual analyzers of the amperometric type are
commonly installed.
8. Automatic controls that consist of a hypochlorite flow con-
troller, recorder and totalizer, a ratio control station, and the
necessary electronic signal converters.
The feed system can usually be operated automatically or by
manual control. The operation of the hypochlorite system will
usually require twice the cost of that of the liquid chlorine sys-
tems. Maintenance of the hypochlorinator system requires
more operator-hours than do the liquid chlorine systems.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 390.
10.2D How is the rate of dosage for a chlorinator deter-
mined?
10.2E Determine the chlorine feed rate, pounds per 24
hours, if you are treating:
1. A flow of 0.5 MGD and the chlorine required is 1.0
mg/L.
2. Flow = 0.8 MGD and chlorine required = 4.0
mg/L.
3. Flow = 6 MGD and chlorine required = 25 mg/L.
10.2F How frequently should feeder rates be adjusted with
manual controls? Why?
10.2G How many pounds of HTH (high test hypochlorite)
should be used per day by a hypochlorinator dosing a
flow of 0.55 MGD at 12 mg/L of chlorine?
24 Hypochlorinator (hi-poe-KLOR-i-NAY-tor). A chlorine pump or device used to feed chlorine solutions made from hypochlorites such as
bleach (sodium hypochlorite) or calcium hypochlorite.
25 Eductor. A hydraulic device used to create a negative pressure (suction) by forcing a liquid through a restriction, such as a Venturi. An
eductor or aspirator (the hydraulic device) may be used in the laboratory in place of a vacuum pump; sometimes used instead of a suction
pump.
26 Rotameter. A device used to measure the flow rate of gases and liquids. The gas or liquid being measured flows vertically up a calibrated
tube. Inside the tube is a small ball or bullet-shaped float (it may rotate) that rises or falls depending on the flow rate. The flow rate may be
read on a scale behind the middle of the ball or the top of the float.
-------
342 Treatment Plants
10.23 Chlorine Solution Discharge Lines, Diffusers, and
Mixing
10.230 Solution Discharge Lines
Solution discharge lines are made from a variety of materials
depending upon the requirements of service. Two primary req-
uisites are that it must be resistant to the corrosive effects of
chlorine solution and of adequate size to carry the required
flows. Additional considerations are pressure conditions, flexi-
bility (if required), resistance to external corrosion and stresses
when underground or passing through structures, ease and
tightness of connections, and the adaptability to field fabrica-
tion or alteration.
Development of plastics in the past several years has con-
tributed greatly to chemical solution transmission. Polyvinyl
chloride (PVC) pipe and black polyethylene flexible tubing
have all but eliminated the use of rubber hose. Both are gener-
ally less expensive and both outlast rubber in normal service.
The use of hose is almost exclusively limited to applications
where flexibility is required or where extremely high back pres-
sures exist.
PVC and polyethylene can be field fabricated and altered.
PVC should be Schedule 80 to limit its tendency to cold flow
and partially collapse under vacuum conditions, or for higher
pressure ratings if required. Schedule 80 PVC may be
threaded and assembled with ordinary pipe tools or may be
installed using solvent-welded fittings.
Rubber-lined steel pipe has been used for many years
where resistance to external stresses is required. It cannot be
field fabricated or altered and is thus somewhat restricted in
application. PVC lining of steel pipe has not yet become eco-
nomically competitive, but other plastics, which can readily
compete with rubber lining and are adaptable to field fabrica-
tion and alteration, have been developed.
Never use neoprene hose to carry chlorine solutions be-
cause it will become hard and brittle in a short time.
10.231 Chlorine Solution Diffusers
These diffusers are normally constructed of the same mate-
rials used for solution lines. Their design is an extremely impor-
tant part of a chlorination program. This importance is almost
completely related to the mixing of the chlorine solution with
the wastewater being treated; however, strength and flexibility
also must be given consideration. In most CIRCULAR, FILLED
conduits flowing at 0.25 ft/sec (0.08 m/sec) or greater, a solu-
tion injected at the center of the pipeline will mix with the entire
flow after flowing ten pipe diameters downstream. Mixing in
open channels can be accomplished by the use of a hydraulic
jump (Fig. 10.5) or by sizing diffuser orifices so that a high
velocity (about 16 ft/sec or 4.8 m/sec) is attained at the diffuser
discharge. This accomplishes two things: (1) introducing a
pressure drop to get equal discharge from each orifice, and (2)
imparting sufficient energy to the surrounding wastewater to
complete the mixing. Generally speaking, a diffuser should be
supplied for each two to three feet (0.6 to 1 meter) of channel
depth. Diffusers should be placed across the width of the
channel rather than in the direction of flow. Mixing also can be
achieved by the use of high speed mechanical mixers specif-
ically designed for this purpose.
HIGH FLO*
VELOCITY
Fig. 10.5 Hydraulic jump
10.232 Mixing
Mixing as well as the speed of mixing are extremely impor-
tant ahead of a chlorine contact tank or a residual sampling
point. Since a contact tank is usually designed for low velocity,
little mixing occurs after wastewater enters it. Mixing must be
achieved before the contact tank is entered. The same is true
for a chlorine residual sampling point. If good mixing does not
occur somewhere upstream from the sampling point, erratic
results will be obtained by the residual analyzing system.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 390.
10.2H Why does little mixing of the chlorine solution with
wastewater occur in chlorine contact basins?
10.21 Chlorine solution discharge lines may be made of
or
10.24 Measurement of Chlorine Residual
Refer to Chapter 16, "Laboratory Procedures and Chemis-
try," for procedures to measure chlorine residual. Amperomet-
ric titration provides for the most convenient, and the most
repeatable results; however, the equipment costs are more
expensive than for the other methods. The starch-iodide test
can be used, but will have limited success in turbid or muddy
waters. DPD TESTS27 can be used and are less expensive
than the other methods, but this also is a colorimetric method.
The orthotolidine method is no longer a test that is recognized
by federal agencies. Figure 10.6 shows a typical automatic
chlorine residual analyzer.
10.25 Start-Up of Chlorinators
Before starting any chlorination system, read the plant Op-
eration and Maintenance Manual and the manufacturer's litera-
ture to become familiar with the equipment. Review the plans
or drawings of the facility. Determine what equipment,
pipelines, pumps, tanks and valves are to be placed into serv-
ice or are in service. The current status of the entire chlorina-
tion system must be known before starting or stopping any
portion of the system. During emergencies you must act
quickly and may not have time to check out each of the steps
outlined above, but you still must follow established proce-
dures.
HYDRAULIC
LOW FLO*
VELOCITY
27 DPD Tests. A colorimetric chlorine residual test. DPD stands for N, N-diethyl-p-phenylenediamine.
-------
Disinfection 343
ACID HFStRVO«
• CONSTANT «40 OCVft*
BUFFER RESERVOIR
BUFFER PUMP
STROKE ADJUSTMENT
41ft CHAMBER
PUMP FEtO
RATE CONTROL
115 VOLT
SUPPLY
SAMPLE
PRESSURE GAUGE
AIR BREAK
CONSTANT LEVEL
DILUTION BOX
ACID PUMP
STRODE ADJUSTTaCNT
FLOW METERS
GRIT STICK
GND
TEMP COMPENSATOR
CELL BLOCK-
PLUNGER
TO RECORDER
OR INDICATOR
ORIFICE
OVERFLOW DRAIN
AMPLE PUMP
UMP FEED
RATE CONTROL
REFERENCE ELECTRODE
MEASURING ELECTRODE
Fig. 10.6 Automatic chlorine residual analyzer
(Permission of Wallace & Tiernan Division, Penwatt Corporation)
-------
344 Treatment Plants
Procedures for start-up, operation, shutdown and
troubleshooting are outlined in this section and are intended to
be typical procedures for all types of chlorinators. For specific
directions, see manufacturer's literature and plant O and M
manual.
10.250 Gas Chlorinators
Start-up procedures for chlorinators using chlorine gas from
containers are outlined in this section.
1. Be sure chlorine gas valve at the chlorinator is closed.
This valve should have been closed since the chlorinator
is out of service.
2. All chlorine valves on the supply line should have been
closed during shutdown. Be sure they are still closed. If
any valves are required to be open for any reason, this
exception should be indicated by a tag on the valve.
3. Inspect all tubing, manifold and valve connections for po-
tential leaks and be sure all joints are properly gasketed.
4. Check chlorine-solution distribution lines to be sure that
system is properly valved to deliver chlorine solution to
desired point of application.
5. Open chlorine metering orifice slightly by adjusting
chlorine feed-rate control.
6. Start the injector water supply system. Usually the source
of water is plant effluent (with a minimum of suspended
solids) or potable water (after an AIR-GAP28 or air-break
system) supply. Injector water is pumped at an appropri-
ate flow rate and the flow through the injector creates
sufficient vacuum in the injector to draw chlorine. Chlorine
is absorbed and mixed in the water at the injector. This
chlorine solution is conveyed to the point of application.
7. Examine injector water supply system.
a. Note reading of injector-supply pressure gage. If read-
ing is abnormal (different from usual reading), try to
identify cause and correct.
b. Note reading of injector vacuum gage. If system does
not have a vacuum gage, have one installed. If the
vacuum reading is less than normal, the machine may
function at a lower feed rate, but will be unable to
deliver at rated capacity.
8. Inspect chlorinator vacuum lines for leaks.
9. Crack open the chlorine container valve and allow gas to
enter the line. Inspect all joints for leaks by placing an
ammonia-soaked rag near each joint. The formation of a
white cloud or vapor will indicate a chlorine leak. Start with
the valve at the chlorine container, move down the line
and check all joints between this valve and the next one
downstream. If the downstream valve passes the am-
monia test, open the valve and continue, to the next valve.
If there are no leaks to the chlorinator, continue with the
start-up procedure.
10. Inspect the chlorinator.
a. Chlorine gas pressure at the chlorinator should be
between 20 and 30 psi (1.4 to 2.1 kg/sq cm).
b. Operate chlorinator at complete range of feed rates.
c. Check operation on manual and automatic settings.
11. Chlorinator is ready for use. Log in the time the system is
placed into operation and the application point.
10.251 Liquid Chlorine Chlorinators
Start-up procedures for chlorinators using liquid chlorine
from containers are outlined in this section.
1. Inspect all joints, valves, manifolds and tubing connec-
tions in chlorination system, including application lines for
proper fit and for leaks. Make sure that all joints have
gaskets.
2. If chlorination system has been broken open or exposed to
the atmosphere, verify that the system is dry. Usually once
a system has been dried out, it is never opened again to
the atmosphere. However, if moisture enters the system in
the air or by any other means, it readily mixes with chlorine
and forms hydrochloric acid which will corrode the pipes,
valves, joints and fittings.
To verify that the system is dry, determine the DEW
POINT29 (must be lower than 40°F or 5°C). If not dry, turn
the evaporator on, pass dry air through the evaporator and
force this air through the system. If this step is omitted and
moisture is in the system, serious corrosion damage can
result and the entire system may have to be repaired.
3. Start up the evaporators. Fill the water bath and adjust the
device according to the manufacturer's directions.
4. Turn on the heaters on the evaporators.
5. Wait until the temperature of the evaporators reaches
180°F (82°C). This may take over an hour on large units.
6. Inspect and close all valves on the chlorine supply line.
7. Open the chlorine-metering orifice slightly. This is to pre-
vent damage to the rotameter.
8. Start the injector water supply system.
9. Examine injector water supply system.
a. Note reading of injector water supply pressure gage. If
gage reading is abnormal (different than usual read-
ing), try to identify the cause and correct it.
28 Air Gap. An open vertical drop, or vertical empty space, between a drinking (potable) water supply and the point of use in a wastewater
treatment plant. This gap prevents back siphonage because there is no way wastewater can reach the potable water. See Chapter 15,
Section 15.2, paragraph 18, "Air-Gap Separation Systems."
29 Dew Point Test. Dew point is the temperature to which air with a given quantity of water vapor must be cooled to cause condensation of the
vapor in the air. One way to measure the dew point is with a special dew point apparatus. This apparatus consists of a small box. The gas or
air being tested enters the box on one side and leaves on the opposite side. One of the other sides has an observation window. A polished
cup is inserted firmly in the top.
Pass a sample of air or gas being tested through this apparatus. Adjust the flow so it can be felt against wetted lips, but not readily felt by
the hand. Pour acetone into the cup. Allow the sample to pass through the cup for about five minutes. Add small amounts of crushed dry ice
to the acetone. Stir continuously with a thermometer. Carefully add dry ice to the acetone as necessary to slowly lower the temperature.
When dew or moisture first appears on the outside polished surface of the cup, read the temperature from the thermometer. This tempera-
ture is the DEW POINT. The lower the dew point, the less moisture in the air. The amount of moisture in the air can be determined from a dew
point temperature chart or table provided by manufacturers of dew point measuring equipment.
-------
Disinfection 345
b. Note reading of injector vacuum gage. If system does
not have a vacuum gage, have one installed. If the
vacuum reading is less than normal, the machine may
function at a lower feed rate, but will be unable to
deliver at rated capacity.
10. Inspect chlorinator vacuum lines for leaks.
11. Close all valves on the supply line.
12. Crack open the CHLORINE GAS LINE at the chlorine con-
tainer. All liquid chlorine systems should be checked by
using gas because of the danger of leaks (gas is less
dangerous). Inspect the joints between this valve and the
next one downstream. If this valve passes the ammonia
leak test, continue to the next valve down the line. Follow
this procedure until the evaporator is reached. Before al-
lowing chlorine to enter the evaporator and the chlorinator,
make sure that all valves between the evaporator and the
chlorinator are open. Heat in the evaporator will expand
the gas, and if the system is closed, there could be prob-
lems. Chlorine should never be trapped in a line between
the evaporator and the chlorinator.
13. If no problems develop, the gas line can be put in service
by opening the valve 11/2 to 2 turns.
14. Check the operation of the chlorinator.
a. Operate over complete range of chlorine feed rates.
b. Check operation on manual and automatic settings.
15. Inspect the liquid chlorine control valve. If OK, open the
liquid chlorine control valve.
16. After admitting liquid chlorine to the system, wait until the
temperature of the evaporator again reaches 180°F (82°C)
and full working pressure (100 psi or 7 kg/sq cm). Inspect
the evaporator by looking for leaks around pipe joints,
unions and valves.
17. The system is ready for normal operation.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 390.
10.2J What would you do before attempting to start any
chlorination system?
10.2K How is the chlorination system inspected for leaks?
10.26 Normal and Abnormal Operation
Normal operation of the chlorination process requires regu-
lar observation of facilities and a regular preventive mainte-
nance program. When something abnormal is observed or dis-
covered, corrective action must be taken. This section outlines
normal operation procedures and also responses to abnormal
conditions.
10.260 Container Storage Are a
Daily
1. Inspect building or area for ease of access by authorized
personnel to perform routine and emergency duties.
2. Be sure fan and ventilation equipment are operating prop-
erly.
3. Read scales, charts or meters at the same time every day
to determine use of chlorine and any other chemicals.
Notify plant superintendent when chlorine supply is low.
4. Look at least once per shift for chlorine and chemical leaks.
5. Try to maintain temperature of storage area below tempera-
ture of chlorinator room.
6. Determine manifold pressure before and after chlorine
pressure regulating valve.
7. Be sure all chlorine containers are properly secured.
Weekly
1. Clean building or storage area.
2. Check operation of chlorine leak-detector alarm.
Monthly
1. Exercise all valves, including flex connector's auxiliary,
manifold, filter bypass, and switchover valves.
2. Inspect all flex connectors and replace any that have been
kinked or flattened.
3. Inspect hoisting equipment.
a. Cables: frayed or cut.
b. Beams and hooks: cracked or bent.
c. Controls: operate properly; do not stick or respond
sluggishly; cords not frayed; safety chains or cables in
place.
4. Examine building ventilation.
a. Ducts and louvers: clean and operate freely.
b. Fans and blowers: operate properly; guards in place;
equipment properly lubricated.
5. Perform preventive maintenance as scheduled.
a. Lubricating equipment.
b. Repacking of valves and regulators.
c. Cleaning and replacing of valve seats and stems.
d. Cleaning filters and replacing glass wool. (CAUTION:
Glass wool soaked with liquid chlorine or chlorine im-
purities may burn your skin or give off sufficient chlorine
gas to be dangerous.)
e. Painting of equipment.
10.261 Evaporators
Evaporators are used to convert liquid chlorine to gaseous
chlorine for use by gas chlorinators.
Dally
1. Check evaporator water bath to be sure water level is at
midpoint of sight glass.
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346 Treatment Plants
2. Be sure water bath temperature is between 160 to 195°F
(71 to 91°C). Low alarm should sound at 160°F (71°C) and
high alarm should sound at 200°F (93°C).
3. Determine chlorine inlet pressure to evaporator. Pressure
should be same pressure as on supply manifold from con-
tainers (20 to 100 psi or 1.4 to 7 kg/sq cm).
4. Measure chlorine outlet temperature from evaporator. Typi-
cal range is 90 to 105°F (32 to 41°C). High alarm should
sound at 110°F (43°C). At low temperatures the chlorine
pressure-reducing valve (CPRV) will close due to the low
temperature in the water bath.
5. Check CPRV for open-closed position.
6. If evaporator is equipped with water bath recirculation pump
at back of evaporator, determine if pump is operating prop-
erly.
7. Look for leaks and repair any discovered.
Abnormal Evaporator Conditions
1. Evaporator water level low. Water level not visible in sight
glass!
Troubleshooting Measurements.
a. Determine actual level of water.
b. Measure temperature of water.
c. Check temperature and pressure of chlorine in
evaporator system and feed lines back to containers
and chlorinators for possible overpressure of system
(pressure should not exceed 100 psi or 7 kg/sq cm).
Corrective Action
a. If chlorine pressure on system is near or over 100 psi (7
kg/sq cm), close supply-container valves to stop
chlorine addition to the system, increase feed rate of
chlorinator to use chlorine in the system, and drop the
pressure back down to a safe range. NOTE: Alarm sys-
tem is usually set to sound at 110 psi (7.7 kg/sq cm). If
system pressure was at or over 110 psi (7.7 kg/sq cm),
inspect alarm circuit to determine failure of alarm.
b. If temperature of water bath is at an abnormal level, find
the cause. Water bath levels are usually set in the fol-
lowing sequence:
1) 160°F or 71°C: low temperature alarm.
2) 185 to 195°F or 85 to 91 °C: normal operating range.
3) 185°F or 85°C: actuates pressure reducing valve
(PRV) to open position.
4) 200°F or 93°C: high temperature alarm.
If water temperature is above 200°F (93°C), alarm
should have sounded. Open control switch on
evaporator heaters to stop current flow to heating ele-
ments. If temperature is in normal range, return to cor-
recting the original problem of a low water level.
c. Evaporator water levels are controlled by a solenoid
valve. First check to see if drain valve is fully closed and
then use the following steps.
1) Override solenoid valve and fill water bath to proper
level.
2) If water cannot be added, take evaporator out of
service:
a. Switch to another evaporator, or
b. Switch supply to gas side of containers.
3) Repair valve and actuating sensor.
2. Low water temperature in evaporator.
a. Check chemical (chlorine) flow-through rate. Rate may
have exceeded unit's capacity and may require two
evaporators to be on line to handle chemical feed rate.
b. Inspect immersion heaters for proper operation. First
examine control panel for thermal overload on breaker.
Most evaporators are equipped with two to three heat-
ing elements. An inspection of the electrical system will
indicate if the breakers are shorted or open and will
locate the problem. Replace any heating elements that
have failed.
c. If no spare evaporators are available, operate from the
valves on the chlorine gas supply. If necessary, reduce
the chlorine feed rate to keep the chlorination system
working properly.
3. No chlorine gas flow to the chlorinator.
a. Inspect pressure-reducing valve downstream from
evaporator and determine if valve is in the open or
closed position.
1) Valve may be closed due to low water temperature
in evaporator (less than 185°F or 85°C).
2) Valve may be closed due to loss of vacuum on sys-
tem or loss of continuity of electrical control circuits
which may have been caused by a momentary
power drop. Correct problem and reset valve.
3) Valve may be out of adjustment and restricting gas
flow through the valve due to a low pressure setting.
b. Inspect supply containers and manifold. Possible
sources of lack of chlorine gas flow to chlorinators in-
clude:
1) Containers empty.
2) Container chlorine supply lines incorrectly con-
nected to gas instead of liquid side of containers.
High flow rates of gas will freeze chlorine, thus frost-
ing valves and flex connectors.
3) Chlorine manifold filters plugged. Check pressure
upstream and downstream from filter. Pressure
drop should not exceed 10 psi (0.7 kg/sq cm). Frost
on manifold will indicate a restriction in the filters.
4) Inspect manifold and system for closed valves. Most
systems operate properly with all chlorine valves at
only ONE TURN OPEN position.
Monthly
1. Exercise all valves, including inlet, outlet, pressure reducing
(PRV), water, drain and fill valves.
2. Inspect evaporator cathode-protection meter (if so
equipped). Cathodic protection protects the metal water
tank (on SULFONATORS30) and piping from corrosion due
to electrolysis. Electrolysis is the flow of electrical current
and is the reverse of metal plating. In electrolysis, the flow
away of certain compounds from the metal causes corro-
sion and holes in a short time. This type of corrosion is
30 Sulfonators (see Section 10.8, "Dechlonnstion ) ars slrnilor to chlotinotofs.
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Disinfection 347
controlled by either a sacrificial anode made of magnesium
and zinc or by applied small electrical currents to suppress
or reverse the normal corroding current flow.
3. Check setting of PRV (pressure reducing valve) in order to
maintain desired pressure of chlorine gas to chlorinators.
4. Inspect heating and ventilation equipment in chlorinator
area.
5. Perform scheduled routine preventive maintenance.
a. Drain and flush water bath.
b. Clean evaporator tank.
c. Repack gasket and reseat pressure-reducing valves.
d. Check heater elements.
e. Replace anodes.
f. Paint system.
10.262 Chlorinators, Including Injectors
Daily
1. Check injector water-supply pressure. Pressures will range
from 40 to 90 psi (2.8 to 6.3 kg/sq cm) depending on sys-
tem.
2. Determine injector vacuum. Values will range from 15 to 25
inches (38 to 64 cm) of mercury.
3. Check chlorinator vacuum. Values will range from 5 to 10
inches (13 to 25 cm) of mercury.
4. Determine chlorinator chlorine-supply pressure. Values will
range from 20 to 40 psi (1.4 to 2.8 kg/sq cm).
5. Read chlorinator feed rate on rotameter tube. Is feed rate at
required level? Record rotameter reading and time.
6. Examine and record mode of control.
a. Manual
b. Automatic (single input)
c. Automatic (dual input)
7. Measure chlorine residual at application point.
8. Inspect system for chlorine leaks.
9. Inspect auxiliary components.
a. Flow signal input. Does chlorinator feed rate change
when flow changes? Chlorinator response is normally
checked by biasing (adjusting) flow signal which may
drive dosage control unit on chlorinator to full open or
closed position. When switch is released, chlorinator
will return to previous feed rate. During this operation
the unit should have responded smoothly through the
change. If the response was not smooth, look for me-
chanical problems of binding, lubrication, or vacuum
leaks.
b. If chlorinator also is controlled by a residual analyzer,
be sure the analyzer is working properly. Check the
following items.
1) Actual chlorine residual is properly indicated.
2) Recorder alarm set point.
3) Recorder control set point.
4) Sample water flow.
5) Sample water flow to cell block after dilution with
fresh water.
6) Adequate flow of dilution water.
7) Filter system and drain.
8) Cell block
a) Buffer pump and solution feed correct. Run pH
test of cell block.
b) Check amount of grit in cell block and add more
grit if amount is low. Grit is used to keep the
electrode free of slimes and chemical scales in
order to provide quick and accurate readings.
c) Cell block hydraulics purger.
9) Run comparison tests of chlorine residuals. Do tests
match with analyzer output readings?
10) If residual analyzer samples two streams, start
other stream flow and compare tested residual of
that stream with analyzer output readings. Stan-
dardize analyzer output readings against tested re-
siduals. Enter changes and corrections in log.
11) Change recorder chart daily.
12) Check recorder output signal controlling chlorinator
for control responses on feed rate. Correct feed
rates through ratio controller.
Weekly
1. Put chlorinator on manual control. Operate feed-rate ad-
justment through full range from zero to full scale (250,500,
1000, 2000, 4000, 6000, 8000, or 10,000 pounds/day). At
each end of scale check:
a. Chlorinator vacuum.
b. Injector vacuum.
c. Solution line pressure.
d. Chlorine pressure at chlorinator.
If any of the readings do not produce normal set points,
make proper adjustments.
1) Injector should produce necessary vacuum at
chlorinator (5 to 10 inches or 13 to 25 centimeters of
mercury).
2) Adjust PRV to obtain sufficient pressure and chemi-
cal feed for full feed-rate operation of chlorinator.
2. If unit performs properly through complete range of feed
rates, return unit to automatic control. If any problems
develop, locate source and correct.
3. Clean chlorine residual analyzer, including the following
items:
a. Clean filters.
b. Clean sample line.
c. Clean hydraulic dilution wells and baffles.
d. Flush discharge hoses and pipes.
e. Clean and flush cell block.
f. Fill buffer reservoirs.
g. Check buffer pump and feed rate.
h. Wipe machine clean and keep it clean.
Monthly
1. Exercise all chlorine valves.
2. Inspect heaters and room ventilation equipment.
3. Check chlorinator vent line to outside of structure for any
obstructions that could prevent free access to the atmos-
phere. Bugs and wasps like vent lines for nests.
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348 Treatment Plants
4. Inspect unit for vacuum leaks.
5. Clean rotameter sight glass.
6. Inspect all drain lines and hoses.
7. Perform scheduled routine maintenance.
a. Disassemble, clean and regasket chlorinator (once a
year).
b. Repack seat and stem of valves.
c. Inspect tubing and fittings for leaks. Wash and dry thor-
oughly before reassembling.
d. Inspect control system.
1) Electrical and electronics
2) Pneumatics
3) Lubrication
4) Calibration of total system
e. Chlorine analyzer.
1) Lubrication of chart drives, filter drives and pumps.
2) Clean and flush all piping and hoses, filters, tubing,
cell blocks and hydraulic chambers.
3) Replace electrodes in cell block.
4) Replace buffer pumps and system solenoids. Clean
acid and iodide reservoirs.
5) Calibrate unit with known standards.
6) Repaint unit.
f. Inspect safety equipment, including self-contained
breathing equipment and repair kits.
Possible Abnormal Conditions
1. Chlorine leak in chlorinator.
Shut off gas flow to chlorinator. Leave injector on line. Allow
chlorinator to operate and empty chlorine gas for three to
five minutes with zero psi showing on the chlorine pressure
gage. Repair leak or switch to another chlorinator and re-
pair leak.
2. Gas pressure too low, less than 20 psi (1.4 kg/sq cm).
Alarm indicated. Check chlorine supply:
a. Empty containers, switch to standby units.
b. Evaporator shut down. See section 10.261,
"Evaporators."
c. Inspect manifold for closed valves or restricted filters.
Correct by switching to another manifold or setting
valves and controls to proper position.
3. Injector vacuum too low.
a. Adjust injector to achieve required vacuum.
b. Inspect injector water supply system.
1) Pump off: start pump.
2) Strainers dirty: clean strainers.
3) Pump worn out and will not deliver appropriate flow
and pressure to injector: use other unit and/or repair
or replace pump.
c. Inspect solution line discharge downstream from injec-
tor. Check for the following items:
1) Valve closed or partially closed.
2) Line broken or restriction reducing flow or increas-
ing back pressure.
3) Diffuser plugged, thus restricting flow and creating a
higher back pressure on discharge line and injector.
Clean diffuser and flush pipe.
4. Low Chlorine Residual. Alarm indicator is on from chlorine
residual analyzer.
Determine actual chlorine residual and compare with re-
sidual reading from chlorine analyzer. If residual analyzer is
off, recalibrate analyzer and readjust. If chlorine residual
analyzer is correct and chlorine residual is low, check the
following items:
a. Sample pump
1) Operation, flow and pressure.
2) Sample lines clean and free of solids or algae that
could create a chlorine demand.
3) Strainer dirty and restricting flow, thus preventing
adequate pressure (15 to 20 psi or 1.0 to 1.4 kg/sq
cm) at analyzer.
b. Control system if chlorinator is on automatic control. If
chlorine feed rate remains too low, take chlorinator off
of automatic control and switch to manual control. Set
chlorinator to proper feed rate as determined by previ-
ous adequate feed rates (see Section 10.28, "Opera-
tional Strategy").
c. Chlorine demand higher than the amount one
chlorinator can supply. Place additional chlorinator on
line.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 390.
10.2L Normal operation of a chlorinator includes daily in-
spection of what facilities or areas?
10.2M What is the purpose of evaporators?
10.2N What abnormal conditions could be encountered
when operating an evaporator?
10.2O How can you determine if chlorine residual analyzer is
working properly?
10.2P What are possible chlorinator abnormal conditions?

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Disinfection 349
10.27 Shutdown of a Chlorinator
10.270 Short-Term Shutdown
The following is a typical procedure for shutting down a
chlorinator for a time period of less than one week.
1. Close chlorine-container gas outlet valve.
2. Allow chlorine gas to completely evacuate the system
through the injector. Chlorine gas pressure gages will fall to
zero psi on the manifold and the chlorinator.
3. Close chlorinator gas discharge valve. The chlorinator may
remain in this condition indefinitely and is ready to be
placed back in service by reopening the chlorinator dis-
charge valve and chlorine-container gas outlet valve. After
these valves have been reopened, inspect for chlorine
leaks throughout the chlorination system.
10.271 Long-Term Shutdown
1. Perform steps one, two and three above for short-term
shutdown.
2. Turn off chlorinator power switch, lock out and tag.
3. Secure chlorinator gas manifold and chlorinator valve in
closed position.
10.28 Operational Strategy
The operator should strive to keep the chlorination system
well maintained and operational. There will be occasions when
pieces of equipment will be out of service for maintenance and
repair. These activities should be scheduled during the times
of the year when demands on the chlorination system are low.
Plants may be required to provide chlorination services for:
1. Disinfection: postchlorination of effluent.
2. Process Control: activated sludge and trickling filter treat-
ment processes.
3. Odor Control: usually seasonal during the warmer
months from May through October.
4. Dechlorination: usually seasonal during July through
November (see Section 10.8, "Dechlori-
nation." Chlorination and dechlorination
facilities are similar).
Under these circumstances, maintenance of chlorination
facilities requiring tearing down, cleaning, repairing and reas-
sembling should be done during the winter months of
November through April. If a chlorination unit fails, there will be
standby capabilities for at least post-chlorination to disinfect
the plant effluent. Even if all systems fail, the operator is still
expected to meet discharge disinfection requirements. A sup-
ply of HTH or other dry hypochlorite compound should be
available for emergencies of this nature because dry hypochlo-
rite compounds can be fed manually while repairs are being
made. A table of dosages or calculation procedures and a
calibrated measuring container should be available so the
proper dosage of chemical can be applied.
Usually wastewater treatment plants are designed and
equipped with standby or backup capabilities so at least the
effluent can be disinfected. In this case, two areas could cause
trouble:
1. Run out of chlorine.
This problem is strictly the operator's problem. You are
the only person who maintains the chlorine supply inven-
tory. Vou must request more chlorine with sufficient lead
time for the vendor to acquire and deliver the chlorine.
Therefore, your plant should never run out of chlorine or
any other chemical.
Care must also be exercised that the connected contain-
ers do not empty and that sufficient containers are con-
nected so that the maximum dosage rates can be achieved
without exceeding maximum withdrawal rates from the
connected containers. Weighing scales or automatic
switchover equipment should always be provided. The lat-
ter is highly desirable particularly when the plant is unat-
tended part of the day. Even in this case, it is important to
note when the switchover has occurred so that the empty
containers can be replaced with full ones before the second
set empties.
2. Failure of automatic control equipment.
Assume you are operating a chlorination system on
"auto" control to meet NPDES-permit coliform require-
ments. A 4.5 mgIL chlorine residual must be maintained at
the outlet of the chlorine contact basin to meet this require-
ment at your plant. If the plant operators have recorded the
past chlorinator feed rates every two hours during daily
routine checks, a history of feed rates at various times dur-
ing the day will have been established for "auto" control.
With this information available, manual operation only re-
quires setting the feed rate to correspond to the same hour
and flow conditions. Daily flows at most treatment plants
are consistent (except during storm flows) where feed rates
are known for every day of the year. By reviewing dates for
the same day for three previous weeks, the information
below can be obtained and calculations can be made for
intermediate hours (1000 and 1200 hours). To calculate
these suggested manual feed rates, determine the average
feed rate between the 0900 and 1100 average feed rates
and also between the 1100 and 1300 average feed rates.
See Chapter 17, "Basic Arithmetic and Treatment Plant
Problems" for procedures on how to calculate the average
(Section 17.4).

Two
Thraa

Suggoatad

Last
WMki
WMki

Manual
Tim*
WNk
Ago
Ago
Avaraga
Faod Rataa
0900
1055 lb/day
1065 lb/day
1060 lb/day
1060 lb/day
1060 lb/day
1000
—
—
—

1500 tb/day
1100
1900 lb/day
1900 lb/day
1800 tb/day
1900 lb/day
1900 lb/day
1200
—
—
—
—
1900 lb/day
1300
1800 lb/day
1850 lb/day
1850 lb/day
1850 tb/day
1850 ib/day
By recording readings of chlorine feed rates, it is very simple
to manually program equipment and maintain high plant per-
formance during instrumentation or equipment failures. In this
example, note that the suggested feed rate is adjusted manu-
ally every hour in an attempt to provide adequate disinfection
at all times.
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350 Treatment Plants
10.29 Chlorine Troubleshooting Guide
CHLORINE CONTACT CHAMBER
Operating Symptoms
Increase in coliform level
Probable Cause
Low residual
Organic strength increase in effluent
Mixing problems
Drop in chlorine residual
Short-circuiting
Solids accumulation in chamber
Large variation in flow (surges)
Diffuser plugged
Organic strength increase
Solids accumulation in chamber
Flow change
Equipment failure
Increase in chlorine residual Organic strength decrease
Flow change
BREAKOUT OF CHLORINE31 Overfeeding chlorine
Insufficient flow in injector water supply
Mixing
Diffuser
Remedy
Increase chlorine dose.
Improve biological treatment process in-
cluding secondary clarification and/or in-
crease chlorine dose.
Baffle the chamber.
Install mixer.
Install baffles.
Take chamber out of service and clean.
Change to steady flow.
Clean diffuser.
Increase dosage. Inspect rest of plant for
possible problems. Check dischargers into
the system, especially industrial dis-
charges.
Take chamber out of service and clean.
Adjust dosage for flow.
Repair.
Lower dosage.
Correct dosage.
Decrease chlorine feed rate.
Increase flow in injector water supply
Turn off mixer because mixing can encour-
age release of chlorine gas under breakout
conditions. If chlorine gas continues to be
released, corrosion damage can occur to
mixer and structure.
Lower diffuser.
or
Install a larger diffuser to cover a bigger
area.
3' Breakout of Chlorine. A point at which chlorine leaves solution as a gas because chlorine feed rate is too high. The solution is saturated and
cannot dissolve any more chlorine.
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Disinfection 351
CHLORINATOR AND EVAPORATOR
Operating Symptoms
Loss of chlorine pressure at the
chlorinator
Liquid through manometer
Loss of vacuum
High vacuum
Misting
Low temperature alarm on evaporator
Chlorinator will not come up to full feed.
Gas pressure adequate
Chlorinator feeds OK at high rates but
will not control feed at low rates.
Chlorinator controls OK at low feeds but
are erratic when full feed is attempted.
Injector vacuum is OK
Chlorinator does not feed. Gas pressure
is adequate. Injector vacuum OK
A variable vacuum-control chlorinator
formerly working normally, now won't go
below about 30% feed. Signal levels OK
A variable vacuum-control chlorinator
reaches full feed, but won't go below
about 45 to 50% feed. CPRV is OK
Probable Cause
Plugged chlorine gas filter on gas phase
Out of chlorine
Supply valve closed or partly closed
Defective evaporator
Dosage too high
Plugged diffuser
Injector problems
Loss of water pressure
Vacuum leak in chlorinator
Loss of chlorine supply
Defective evaporator
Evaporator undersized
Water bath
Power loss
Heater element burned out
Injector vacuum does not develop
Chlorinator pressure reducing valve
(CPRV) not working properly
Possibly a bad diaphragm in vacuum
Reducing valve is causing bypassing of
V-notch control valve
Not enough chlorine for demand
Dirty CPRV or partially clogged gas line
Tube connection from upstream of V
notch to top of differential valve is dis-
connected or leaking
CPRV not throttling sufficiently for low
feeds
Signal vacuum is too high because of air
leak through diaphragm or control vac-
uum check valve is bypassing restrictor
Remedy
Clean filter.
Switch to another container.
Open valve.
Repair evaporator.
Lower dosage. Use another chlorinator.
Repair diffuser.
Repair injector.
Check water supply.
Locate and stop leak. Usually leak is
caused by unseated rotameter tube,
leaky gasket or ruptured diaphragm.
Check supply system.
Repair evaporator.
Operate two evaporators or reduce
chlorine feed rate.
Clean water bath.
Check electrical system.
Repair by replacing heater element.
Repair injector. Clean piping.
Clean CPRV. Check for leaks in CPRV
diaphragm.
Replace diaphragm.
Replace valve.
Clean CPRV cartridge.
Clean high-pressure gas line.
Supply adequate chlorine gas pressure.
Reconnect tube line.
Replace tube if cracked, kinked or defec-
tive at ends.
Tighten tube nuts.
Clean CPRV cartridge.
Readjust CPRV bias.
Replace diaphragm, gasket or stem as
tests indicate source of leak.
Clean and dry or replace filter disc.
Clean converter nozzle.
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352 Treatment Plants
CHLORINE SUPPLY SYSTEM
Operating Symptoms
Discoloration at joint. Green scum on
cadmium plating gone and replaced by
reddish color
Small droplet of liquid on joint
Leaks at gas gages or pressure switches
Gooey, taffy-like mass
High-pressure alarm
Cold or freezing areas on the supply sys-
tem
Probable Cause
Leaks
Leaks
Leaks
Moisture in supply
Defective silver diaphragm on gage or
pressure switch
Restriction in line
Withdrawal rate too rapid
Remedy
Repair by replacing.
Repair as quickly as possible.
Repair gage or pressure switch.
Clean filters. Taffy caused in manufactur-
ing process.
Repair diaphragm or switch.
Repair.
Lower withdrawal rate.
Place more chlorine containers on line.
-------
Disinfection 353
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 390.
10.2R What are two areas that could hinder your ability to
meet NPDES-permit coliform requirements when your
plant is equipped with standby or backup capabilities?
10.2Q List the steps for a short-term shutdown of a
chlorinator.
Please answer the discussion and review questions before
continuing with Lesson 3.

DISCUSSION AND REVIEW QUESTIONS
Write the answers to these questions in your notebook be-
fore continuing. The problem numbering continues from Les-
son 1.
Chapter 10. DISINFECTION AND CHLORINATION
(Lesson 2 of 5 Lessons)
10. Determine the chlorine feed rate for a flow of 0.75 MGD
and a chlorine dosage of 18 mg/L?
7. Where might chlorine be applied in the treatment of
wastewater?
8. Where is chlorine usually applied for disinfection pur-
poses?
9. What is the ultimate control of chlorine dosage for disinfec-
tion?
11. Why must the chlorine solution be well mixed with the
wastewater?
12. What precautions would you take before starting any
chlorination system?
13. When should the maintenance and repair of chlorination
systems be scheduled?
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354 Treatment Plants
CHAPTER 10. DISINFECTION AND CHLORINATION
(Lesson 3 of 5 Lessons)
10.3 CHLORINE SAFETY PROGRAM
Every good safety program begins with cooperation be-
tween the employee and the employer. The employee must
take an active part in the overall program. The employee must
be responsible and should take all necessary steps to prevent
accidents. This begins with the attitude that as good an effort
as possible must be made by everyone. Safety is everyone's
problem. The employer also must take an active part by sup-
porting safety programs. There must be funding to purchase
equipment and to enforce safety regulations required by OSHA
and industrial safety programs. The following items should be
included in all safety programs.
1. Establishment of a safety program.
2. Written rules.
3. Periodic hands-on training using safety equipment:
a) Leaks-detection equipment
b) Gas masks
c) Atmospheric monitoring devices
4. Establishment of emergency procedures for chlorine leaks
and first aid.
5. Establishment of a maintenance and calibration program
for safety devices and equipment.
All persons handling chlorine should be thoroughly aware of
its hazardous properties. Personnel should know the location
and use of the various pieces of protective equipment and be
instructed in safety procedures. In addition, an emergency
procedure should be established and each individual should
be instructed how to follow the procedures. An emergency
checklist also should be developed and available. For addi-
tional information on this topic, see the Water Pollution Control
Federation's Manual of Practice No.1, SAFETY IN WASTEWA-
TER WORKS, and the Chlorine Institute's CHLORINE MAN-
UAL, 4th edition.32 Also see Chapter 14, "Plant Safety and
Good Housekeeping."
10.30 Chlorine Hazards
Chlorine is a gas, heavier than air, extremely toxic and cor-
rosive in moist atmospheres. Dry chlorine gas can be safely
handled in steel containers and piping, but with moisture must
be handled in corrosion-resisting materials such as silver,
glass, teflon, and certain other plastics. Chlorine gas at con-
tainer pressure should never be piped in silver, glass, teflon, or
any other plastic material. Even in dry atmospheres, the gas is
very irritating to the mucous membranes of the nose, to the
throat, and to the lungs; a very small percentage in the air
causes severe coughing. Heavy exposure can be fatal. (See
Table 10.1).
WARNING I
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-------
Disinfection 355
iting, and difficulty in breathing. Chlorine is particularly irritating
to persons suffering from asthma and certain types of chronic
bronchitis. Liquid chlorine causes severe irritation and blister-
ing on contact with the skin.
10.32 Protect Yourself From Chlorine
Every person working with chlorine should know the proper
ways to handle it, should be trained in the use of self-contained
breathing apparatus, and should know what to do in case of
emergencies.
Self-contained air supply and demand-breathing equipment
must fit properly and be used properly. Pressure demand and
rebreather kits may be safer. Pressure demand units use more
air from the air bottle which reduces the time a person may
work on a leak.
Before entering an area with a chlorine leak, wear protective
clothing. Gloves and a rubber suit will prevent chlorine from
contacting the sweat on your body and forming hydrochloric
acid. Rubber suits are very cumbersome, but should be worn
when the weather is hot and humid and the chlorine concentra-
tion is high. Otherwise, use your own judgment regarding
whether or not to wear protective clothing.
The best protection that one can have when dealing with
chlorine is to respect it. Each individual should practice rules of
safe handling and good PREVENTIVE MAINTENANCE.
Prevention is the best emergency tool you have.
Plan ahead.
1. Have your fire department tour the area so that they know
where the facilities are located. Give them a clearly
marked map indicating the location of the chlorine storage
area, chlorinators, and gas masks.
2. Have emergency drills using chlorine gas masks and
chlorine repair kits.
3. Have a supply of ammonia available to detect chlorine
leaks.
4. Write emergency procedures:
Prepare a CHLORINE EMERGENCY LIST of names or
companies and phone numbers of persons to call during
an emergency. This list should include:
a. Fire department,
b. Chlorine emergency personnel, and
c. Chlorine supplier.
5. Follow established procedures during all emergencies.
a, Never work alone during chlorine emergencies.
b. Obtain help immediately and quickly repair the prob-
lem. PROBLEMS DO NOT GET BETTER.
c. Only authorized and properly trained persons with
adequate equipment should be allowed in the danger
area to correct the problem.
d. If you are caught in a chlorine atmosphere without a
gas mask, shallow breathing is safer than breathing
deeply. Recovery depends upon the duration and
amount of chlorine inhaled, so it is important to keep
that amount as small as possible.
e. If you discover a chlorine leak, leave the area im-
mediately unless it is a very minor leak. Small leaks
can be found by using a rag soaked with ammonia. A
white gas will form near the leak so it can be located
and corrected.
f. Notify your police department that you need help if it
becomes necessary to stop traffic on roads and to
evacuate persons in the vicinity of the chlorine leak.
6. Develop emergency evacuation procedures for use during
a serious chlorine leak. Coordinate these procedures with
your police department and other officials.
7. Post emergency procedures in all operating areas.
8. Inspect equipment and routinely make any necessary re-
pairs.
9. At least twice weekly, inspect area where chlorine is
stored and where chlorinators are located. Remove all
obstructions from the area.
10. Schedule routine maintenance on ALL chlorine equipment
at least once every six months or more frequently.
11. Have health appraisal for employees on chlorine
emergency duty. All those who have heart and respiratory
problems should not be allowed on emergency teams.
Remember:
Small amounts of chlorine cause large problems. Leaks
never get better.
10.33 First Aid Measures
Mild Cases
Whenever you have a mild case of chlorine exposure which
does happen from time to time around chlorination equipment,
you should first leave the contaminated area. Move slowly,
breathe lightly without exertion, remain calm, keep warm and
resist coughing. Notify other operators and have them repair
the leak immediately.
If clothing has been contaminated, remove as soon as pos-
sible. Otherwise the clothing will continue to give off chlorine
gas which will irritate the body even after leaving the contami-
nated area. Immediately wash off area affected by chlorine.
Shower and put on clean clothes.
If victim has slight throat irritation, immediate relief can be
accomplished by drinking milk. Drinking spirits of peppermint
also will help reduce throat irritation.
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-------
356 Treatment Plants
Extreme Cases
1. Follow established emergency procedures.
2. Always use proper safety equipment. Do not enter area
without gas masks with a self-contained breathing ap-
paratus.
3. Remove patient from affected area immediately.
4. First aid:
a. Remove contaminated clothes to prevent clothing giv-
ing off chlorine gas which will irritate the body.
b. Keep patient warm and cover with blankets if neces-
sary.
c. Place patient in a comfortable position on back.
d. EYES\
If even a small amount of chlorine gets into the eyes,
they should be flushed with water. The flushing should
continue so that all traces of chlorine are flushed from
the eyes.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 390.
10.3A What are the hazards of chlorine gas?
10.3B What type of breathing apparatus is recommended
when repairing a chlorine leak?
10.3C What first aid measures should be taken if a person
comes in contact with chlorine?
10.4 CHLORINE HANDLING
10.40 Chlorine Containers
10.400 Cylinders
Cylinders containing 100- to 150-pounds (45- to 68-kg) of
chlorine are convenient for very small treatment plants with
capacities less than 0.5 MGD (1890 cu m/day). These cylin-
ders are usually of seamless steel construction (Fig. 10.7).
A Jusible plug is placed in the valve below the valve seat
ig. 10.8). This plug is a safety device. The fusible metal
softens or melts at 158° to 165°F (70° to 74°C) to prevent
buildup of excessive pressures and the possibility of rupture
due to a fire or high surrounding temperatures.
Cylinders will not explode and can be handled safely.
The following are procedures for handling chlorine cylinders.
1. Move cylinders with a properly balanced hand truck with
clamp supports that fasten at least two-thirds of the way up
the cylinder.
2. 100- and 150-pound (45- to 68-kg) cylinders can be rolled in
a vertical position. Lifting of these cylinders should be
avoided except with approved equipment. Never lift with
chains, rope slings, or magnetic hoists.
3. Protective cap should always be replaced when moving a
cylinder.
4. Cylinders should be kept away from direct heat (steam
pipes or radiators).
5. Cylinders should be stored in an upright position.
6. Cylinders must be firmly secured to an immovable object.
10.401 Ton Tanks
Ton tanks are of welded construction and have a loaded
weight of as much as 3700 pounds (1680 kg). They are about
80 inches (200 cm) in length and 30 inches (75 cm) in outside
diameter. The ends of the tanks are crimped inward to pro-
vided a substantial grip for lifting clamps (Fig. 10.9).
The following are some characteristics of and procedures for
handling ton tanks.
Most ton tanks have eight openings for fusible plugs and
valves (Figs. 10.9 and 10.10). Generally, two operating valves
are located on one end near the center. There are six or eight
fusible metal safety plugs, three or four on each end. These
are designed to melt within the same temperature range as the
safety plug in the cylinder valve.
j^WARNINQ^J
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TANK VJ\LL B£ ttlJEASb&Z?.
Ton tanks are shipped by rail in multi-unit tank cars. They
also may be transported by truck or semi-trailer.
Ton tanks should be handled with a suitable lift clamp in
conjunction with a hoist or crane of at least two-ton capacity
(Fig. 10.9).
Ton tanks should be stored and used on their sides, above
the floor or ground, on steel or concrete supports. They should
not be stacked more than one high.
Ton tanks should be placed on trunnions (pivoting mounts)
which are equipped with rollers so that the withdrawal valves
may be positioned one above the other. The upper valve will
discharge chlorine gas, and the lower valve will discharge liq-
uid chlorine (see Fig. 10.9). Trunnion rollers should not exceed
3-1/2 inches (9 cm) in diameter so that the containers will not
rotate too easily and be turned out of position. Roller shafts
should be equipped with a zerk-type lubrication fitting. Roller
bearings are not advised because of the ease with which they
rotate. Locking devices should be used when these rules are
observed to prevent ton tanks from rolling while connected.
10.402 Chlorine Tank Cars
Chlorine tank cars are of 16-, 30-, 55-, 85-, or 90-ton capac-
ity. All have four-inch (10 cm) cork board insulation protected
by a steel jacket. The dome of the standard car contains four
angle valves plus a safety valve. The two angle valves located
on the axis line of the tank are equipped for discharging liquid
chlorine. The two angle valves at right angles to the axis of the
tank deliver gaseous chlorine (Fig. 10.11).
Unloading of tank cars should be performed by trained per-
sonnel in accordance with Interstate Commerce Commission
(ICC) regulations.
In most situations, chlorine is withdrawn from tank cars as a
liquid and then passed through chlorine evaporators. Some-
times DRY air is passed into the tank car through one of the
gas valves to assist in liquid withdrawal. This practice is re-
ferred to as AIR PADDING.3*
14 Air Padding. Pumping dry air Into a container to assist with the withdrawal of a liquid or to force a liquid gas such as chlorine or sulfur
dioxide out of a container.
-------
Disinfection 357
Chlorine Cylinder
Protection
Hood
Valve
Neck Ring
Cylinder
Body
—¦ Foot Ring
Net
Cylinder
Contents
Approx.
Tare,
Lbs.*
Dimensions,
Inches
A
B
100 Lbs.
73
8 V«
54'A
1 50 Lbs.
92
10V«
54 Vi
•Stamped tare weight on cylinder shoulder
does not include valve protection hood.
Fig. 10.7 Chlorine cylinder
(Courtesy of PPG Industries, Inc., Chemical Division)
-------
358 Treatment Plants
GASKET
Poured Type Fusible Plug
Screwed Type Fusible Plug
STANDARD CYLINDER VALVE
r$TEM
' \. J
PACKING GLAND
PACKING NUT
PACKING
PACKING COLLAR
OUTLET CAP
(Special straight threads)
Fig. 10.8 Standard cylinder valve
(Reproduced with permission of the Dow Chemical Company (1959, 1966))
-------
Disinfection 359
Protection-
Hood
Chlorine'
Liquid
Net Weight of Chlorine. . ,2000 lbs. 2-Ton Minimum 1%«"
Tare Wt. of Tank (average) 1550 Jbs. Capacity Hoist 7
-------
360 Treatment Plants
Ton Tank Valve
100 and 150 lb. Cylinder Valve
-Stem-
Packing Gland Nut
Packing Gland
Ring Packing
Packing Retainer
Cap
Disc
Fusible Plug
Special 3/4" Straight Thread
Body
Standard 3/4" Pipe Thread
kw—
Fig. 10.10
Comparison of ton tank valve with cylinder valve
(Courtesy of PPG Industries, Inc., Chemical Division)
-------
-EXPANSION CHAMMI (HEATH*
1/ CMO VALVf)
SAaOMCTttC LEG*

VALVE
VALVES
CHLORINE
GAGE—s.

hi car
DOME . FLANGE
COVER-«\uNfONS
LIQUID
VALVE
LIQUID
CHLORINE
FLEXIBLE
CONNECTOftS
LIQUID CHLORINE
TO PROCESS
(PREFERRED METHOD)
CHLORINE GAS TO PROCESS
I
THERMOMETER
STEAM

^CHLORINE GAGE
^/-CONDENSATE
VVVVVSAVVOOvVs
5V
(NO VALVE)
SEAL POT (NO TRAP)
VVWWVVVVWV
i«-AIR LINE
TO GAS
VALVE
A
SHUT OFF VALVES
CHECK f tEUEf VALVE -165 LBS
jry-SHUT OFF VALVE
|t-OIL-WATER SEPARATOR
GAGE /®iSS^-A,R COMPRESSOR ONOFF CONTROL
v 0 125-150 LBS PRESSURE
\WV\WV wwvvwvwwvwW
REGENERATIVE TTPE AIR
DRYERS - 40° DEW POINT
Fig. 10.11 Typical chlorine tank car unloading arrangement
(Reproduced with permission of The Dow Chemical Company (1959, 1966)}
-------
362 Treatment Plants
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 390.
10.4A How may chlorine be delivered to a plant?
10.4B What is the purpose of the fusible plug?
10.41 Removing Chlorine From Containers
10.410 Connections
Outlet threads on container valves are not tapered pipe
threads. Use fittings and gaskets for connections furnished by
your chlorine supplier or chlorinator equipment manufacturer.
Do not try to use regular pipe thread fittings. Whenever a new
connection is made, a new gasket should be used.
Flexible 3/8-inch 2000-pound (psi) (0.95 cm, 140 kg/sq cm)
annealed (hardened) copper tubing is recommended for con-
nections between chlorine containers and stationary piping.
Care should be taken to prevent sharp bends in the tubing
because this will weaken it and eventually the tubing will start
leaking. Many operators recommend use of a sling to hold the
tubing when disconnecting it from an empty cylinder to prevent
the tubing from flopping around and getting kinked or getting
dirt inside it.
A shutoff valve is needed after the container valve or at
beginning of stationary piping to simplify changing of contain-
ers.
10.411 Valves
Do not use wrenches longer than six inches (15 cm), pipe
wrenches, or wrenches with an extension on container valves.
To unseat, strike end of wrench with heel of hand to rotate the
valve stem in a counterclockwise direction. Then open slowly.
One complete turn permits maximum discharge. Do not
force valve beyond this point.
If valve is too tight to open, loosen the packing gland nut
(Fig. 10.10) slightly to free the stem.
10.412 Ton Tanks
One-ton tanks (Fig. 10.9) must be PLACED ON THEIR
SIDES WITH THE VALVES IN A VERTICAL POSITION. Con-
nect the flexible tubing to the TOP VALVE to remove chlorine
gas from a tank. The BOTTOM VALVE is used to remove liquid
chlorine and is used only with a chlorine evaporator. The
valves are similar to those on the smaller chlorine cylinders
(fusible plugs are not located at valves on ton containers) and
must be handled with the same care.
10.413 Railroad Tank Cars
Unloading of tank cars must be performed by trained per-
sonnel in accordance with Interstate Commerce Commission
(ICC) regulations. Figure 10.12 shows the layout of a facility for
unloading a railroad tank car. This section lists the procedures
to follow to safely receive, connect and disconnect railroad
tank cars. Your facility may be slightly different. This procedure
can be made more specific for your facility by numbering each
valve in the procedures.
Receiving Tank Cars
1. Inspect and refuse delivery if car is damaged or has corro-
sion that would make it unsafe. Once the tank car has been
uncoupled, the railroad is relieved of all responsibility.
Check that the invoice numbers match with the numbers on
the car.
2. Spot the tank car so the draw bridge matches up or lines up
with the car carwalk.
3. Verify that the railroad has set the brakes.
4. Set two wheel chocks, one before and one after, on the rail
nearest the chlorine tower.
5. Place warning light and sign one car length from tank car.
6. Close and lock derailing mechanism.
7. Record on log sheet the date and time the tank car arrived
and was accepted or rejected on treatment plant property.
8. Sign name on log sheet.
Connecting Tank Cars
1. Material needed before leaving office.
a. Keys to tool locker on chlorine tower.
b. Electrical safety tag.
c. A buddy; no one is to work alone on the chlorine tow-
er.
2. Verify that valves are closed.
3. Tag pad air compressor so it will not be turned off during
purging operations.
4. Check eyewash and shower for operation.
5. Put on escape respirator.
6. Lower and lock down draw bridge.
7. Check that initial valves are closed.
8. Open pad air valve if pad is higher than chlorine.
9. Open tank car lid and verify that all car valves are closed.
10. Remove plug from tank car valve farthest from the chlorine
tower and install gage assembly.
11. Record pressure.
12. Install flex air hose.
13. Open valves to initiate purging of chlorine flex line. Valves
should be opened only slightly until the chlorine flex line is
completely connected.
14. Remove plug from tank car valve and connect chlorine flex
line. USE A NEW LEAD WASHER IN THE AMMONIA
COUPUNG.
15. After no leaks can be heard from connections, close
valves.
16. Remove flex air hose.
17. Open valve on tank car. TEST WITH AMMONIA GAS.
-------
MAIN RAILROAD LINE
CAUTION
SIGNS v-
TANK CAR DOME
r=L
DERAIL'
SWITCH
LOCK &
SIGNAL
BARRIER
STOP
50 FT
BLUE
LIGHT
CAUTION
SIGNS
UNLOADING
PLATFORM
Fig-
10.12 Layout for unloading railroad tank car
-------
364 Treatment Plants
18. Open valves. TEST WITH AMMONIA GAS.
19. Record downstream pressure.
20. Open valves. This will connect chlorine tower to chlorine
building.
21. Store all gear and lock tool cabinet.
22. Remove compressor tag.
23. Change sign on valves.
24.
25.
26.
27.
Disconnecting Tank Cars
1. Materials needed before leaving office.
a. Keys to tool locker on chlorine tower.
b. Electrical safety tag.
c. A buddy; no one is to work alone on the chlorine tow-
er.
2. Verify valves are closed.
3. Tag pad air compressor so it will not be turned off during
purging operations.
4. Check eyewash and shower for operation.
5. Put on escape respirator.
6. Close valve that disconnects the chlorine tower from the
chlorine building.
7. Verify that pad air pressure is higher than liquid chlorine
line.
8. Open pad air supply valve to chlorine tower.
9. Install flex air hose.
10. Open valves that will allow the air to force the chlorine
back into the tank car.
11. Wait five minutes.
12. Close valve on chlorine tank car.
13. Close valves and then crack open slightly. Loosen am-
monia coupling and test with ammonia gas until no
chlorine gas is escaping.
14. Remove chlorine flex line.
15. Reassemble and cap chlorine flex line and verify that no
air is escaping.
16. Close tank car valve farthest from the chlorine tower.
17. Remove gage assembly slowly and test with ammonia
gas. Put cap on gage assembly.
18. Put plugs back in chlorine tank car valves and secure lid.
DON'T LEAVE VALVE HANDLE IN CHLORINE TANK CAR
19. Close valves.
20. Remove flex air hose.
21. Store all gear and lock tool cabinet.
22. Raise and lock draw bridge.
23. Change Department of Transportation placards to read
"danger chlorine empty."
24. Place warning light and sign at the end of the spur.
25. Place wheel chocks at the end of the spur.
26. Unlock and open derailing mechanism.
27. Remove compressor tag.
Verify that valves are properly tagged.
Call railroad and notify them to pick up empty tank car.
Record name of railroad official contacted.
Record date and time of disconnect on log sheet.
32. Sign Bill of Lading.
33. Sign name on log sheet to indicate that job is completed.
10.42 Chlorine Leaks
Chlorine leaks must be taken care of immediately or they will
become worse.
Corrective measures should be undertaken only by trained
operators wearing proper safety equipment. All operators
should be trained to safely repair chlorine leaks.
All other persons should leave the danger area until condi-
tions are safe again.
If the leak is large, all persons in the adjacent areas should
be warned and evacuated. Obtain police help. You must al-
ways consider your neighbors ... PEOPLE, animals, and
plants.
1. BEFORE ANY NEW SYSTEM IS PUT INTO SERVICE, it
should be cleaned, dried, and tested for leaks. Pipelines
may be cleaned and dried by flushing and steaming from
the high end to allow condensate and foreign materials to
drain out. After the empty line is heated thoroughly, dry air
may be blown through the line until it is dry. After drying,
the system may be tested for tightness with 150 psi (10.5
kg/sq cm) dry air. Leaks may be detected by application of
soapy water to the outside of joints. Small quantities of
chlorine gas may now be introduced into the line, the test
pressure built up with air, and the system tested for leaks.
Whenever a new system is tested for leaks, at least one
chlorinator should be on the line to withdraw chlorine from
the system in case of a leak. The same is true in case of
an emergency leak at any installation. If a chlorinator is not
running, at least one or more should be started. Prefera-
bly, all available chlorinators should be put on the tine.
2. TO FIND A CHLORINE LEAK, tie a rag on a stick, DIP THE
RAG35 in a strong ammonia solution, and hold the rag
near the suspected points. White fumes will indicate the
exact location of the leak. Location of leaks by this method
may not be possible for large leaks which diffuse the gas
over large areas. Do not use an ammonia spray bottle
because the entire room could turn white if it is full of
chlorine gas.
3. IF THE LEAK IS IN THE EQUIPMENT in which chlorine is
being used, close the valves on the chlorine container at
once. Repairs should not be attempted while the equip-
ment is in service. All chlorine piping and equipment that is
Record date and time job was completed on log sheet. 28.
Sign name on log sheet. 29.
Record date and time tank car was placed in service. 30.
Record date and time tank car was taken out of service. 31.
38 A one-Inch (2.5 cm) paint brush may be used Instead of a rag.
-------
Disinfection 365
to be repaired by welding should be flushed with water or
steam. Before returning equipment to use, it MUST be
cleaned, dried, and tested as previously described.
4. IF THE LEAK IS IN A CHLORINE CYLINDER OR CON-
TAINER, use the emergency repair kit supplied by most
chlorine suppliers. These kits can be used to stop most
leaks in a chlorine cylinder or container and can usually be
delivered to a plant within a few hours if one is not already
at the site of the leak. IT IS ADVISABLE TO HAVE
EMERGENCY REPAIR KITS AVAILABLE AT YOUR
PLANT AT ALL TIMES AND TO TRAIN PERSONNEL IN
THEIR USE. Location of such kits should be posted out-
side chlorine storage areas.
5. If chlorine is escaping as a liquid from a cylinder or a ton
tank, turn the container so that the leaking side is on top.
In this position, the chlorine will escape only as a gas, and
the amount which escapes will be only 1/15 as much as if
the liquid chlorine were leaking. Keeping the chlorinators
running also will reduce the amount of chlorine gas leaking
out of a container. Increase the feed rate to cool the supply
tanks as much as possible.
6. FOR SITUATIONS IN WHICH A PROLONGED OR UN-
STOPPABLE LEAK is encountered, emergency disposal
of chlorine should be provided. Chlorine may be absorbed
in solutions of caustic soda, soda ash, or agitated hyd-
rated lime slurries (Table 10.2). Chlorine should be
passed into the solution through an iron pipe or a properly
weighted rubber hose to keep it immersed in the absorp-
tion solution. The container should not be immersed be-
cause the leaks will be aggravated due to the corrosive
effect, and the container may float when partially empty. In
some cases it may be advisable to move the container to
an isolated area. Discuss the details of such precautions
with your chlorine supplier.
7. NEVER PUT WATER ON A CHLORINE LEAK. A mixture
of water and chlorine will increase the rate of corrosion of
the container and make the leak larger. Besides, water
may warm the chlorine, thus increasing the pressure and
forcing the chlorine to escape faster.
8. LEAKS AROUND VALVE STEMS can often be stopped by
closing the valve or tightening the packing gland nut.
Tighten the nut or stem by turning it clockwise.
9. LEAKS AT THE VALVE DISCHARGE OUTLET can often
be stopped by replacing the gasket or adapter connection.
10. LEAKS AT FUSIBLE PLUGS AND CYLINDER VALVES
usually require special handling and emergency equip-
ment. Call your chlorine supplier immediately and obtain
an emergency repair kit for this purpose if you do not have
a kit readily available.
11. PIN HOLE LEAKS in the walls of cylinder and ton tanks
can be stopped by using a clamping pressure saddle with
a turn-buckle available in repair kits. This is only a tempo-
rary measure, and the container must be emptied as soon
as possible.
If a repair kit is not available, use your ingenuity. One
operator stopped a pin hole leak temporarily until a repair
kit arrived by placing several folded layers of neoprene
packing over a leak, a piece of scrap steel plate over the
packing, wrapping a chain around the cylinder and steel
plate, and applying leverage pressure with a crowbar.
12. A LEAKING CONTAINER must not be shipped. If the con-
tainer leaks or if the valves do not work properly, keep the
container until you receive instructions from your chlorine
supplier for returning it. If a chlorine leak develops in
transit, keep the vehicle moving until it reaches an open
area.
13. Do not accept delivery of containers showing evidence of
leaking, stripped threads, or abuse of any kind.
14. If a chlorine container develops a leak, be sure your
supplier does not charge you for the unused chlorine.
15. Chlorine leaks may be detected by sniffleators and other
detection devices. Alarm systems may be connected to
these devices. Be sure to follow manufacturer's recom-
mendations regarding frequency of checking and testing
detection devices and alarm systems.
TABLE 10.2 CHLORINE ABSORPTION SOLUTIONS*
Absorption Solution

Alkali
(lb)
Water
(9«l)
Caustic Soda (100%)
a
125
40

b
188
60

c
2500
800
Soda Ash
a
300
100

b
450
150

c
6000
2000
Hydrated Lime"
a
125
125

b
188
188

•-D

-------
406 Treatment Plants
Project Pronunciation Key
by Warren L. Prentice
The Project Pronunciation Key is designed to aid you in the
pronunciation of new words. While this key is based primarily
on familiar sounds, it does not attempt to follow any particular
pronunciation guide. This key is designed solely to aid
operators in this program.
You may find it helpful to refer to other available sources for
pronunciation help. Each current standard dictionary contains
a guide to its own pronunciation key. Each key will be different
from each other and from this key. Examples of the difference
between the key used in this program and the Webster's NEW
WORLD DICTIONARY "Key"1 are shown below;
In using this key, you should accent (say louder) the syllable
which appears in capital letters. The following chart is pre-
sented to give examples of how to pronounce words using the
Project Key.
SYLLABLE
WORD
1st
2nd
3rd
4th
5th
acid
AS
id

coagulant
CO
AGG
you
lent

biological
BUY
0
LODGE
ik
cull
The first word, ACID, has its first syllable accented. The
second word, COAGULANT, has its second syllable ac-
cented. The third word, BIOLOGICAL, has its first and third
syllables accented.
We hope you will find the key useful in unlocking the pro-
nunciation of any new word.
Te r m
Proje c t Key
Web s te r Key
acid
AS-id
a sad
c o I i f o r m
COA L-i-for m
k o - ld-f o r m
biological
B U Y-o-LO DG E -i k-c u II
b i-e-l a j-i-ka I
1 The Webster's NEW WORLD DICTIONARY,
availability to the operator.
College Edition,
1968, was chosen rather than an unabridged
dictionary because of Its
-------
Glossary 407
GLOSSARY
ABS ABS
Alkyl Benzene Sulfonate. A type of surfactant, or surface active agent, present in synthetic detergents in the United States before
1965. ABS was especially troublesome because it caused foaming and resisted breakdown by biological treatment processes. ABS
has been replaced in detergents by linear alkyl sulfonate (LAS) which is biodegradable.
ABSORPTION (ab-SORP-shun) ABSORPTION
Taking in or soaking up of one substance into the body of another by molecular or chemical action (as tree roots absorb dissolved
nutrients in the soil).
ACID ACID
(1) A substance that tends to lose a proton. (2) A substance that dissolves in water with the formation of hydrogen ions. (3) A
substance containing hydrogen which may be replaced by metals to form salts.
ACIDITY ACIDITY
The capacity of water or wastewater to neutralize bases. Acidity is expressed in milligrams per liter of equivalent calcium carbonate.
Acidity is not the same as pH because water does not have to be strongly acidic (low pH) to have a high acidity. Acidity is a measure
of how much base can be added to a liquid without causing a great change in pH.
ACTIVATED SLUDGE (ACK-ta-VATE-ed slug) ACTIVATED SLUDGE
Sludge particles produced in raw or settled wastewater (primary effluent) by the growth of organisms (including zoogleal bacteria) in
aeration tanks in the presence of dissolved oxygen. The term "activated" comes from the fact that the particles are teeming with
bacteria, fungi, and protozoa. Activated sludge is different from primary sludge in that the sludge particles contain many living
organisms which can feed on the incoming wastewater.
ACTIVATED SLUDGE PROCESS (ACK-ta-VATE-ed sluj) ACTIVATED SLUDGE PROCESS
A biological wastewater treatment process which speeds up the decomposition of wastes in the wastewater being treated. Activated
sludge is added to wastewater and the mixture (mixed liquor) is aerated and agitated. After some time in the aeration tank, the
activated sludge is allowed to settle out by sedimentation and is disposed of (wasted) or reused (returned to the aeration tank) as
needed. The remaining wastewater then undergoes more treatment.
ADSORPTION (add-SORP-shun) ADSORPTION
The gathering of a gas, liquid, or dissolved substance on the surface or interface zone of another substance. nf
ADVANCED WASTE TREATMENT ADVANCED WASTE TREATMENT
Any process of water renovation that upgrades treated wastewater to meet specific reuse requirements. May Include general
cleanup of water or removal of specific parts of wastes insufficiently removed by conventional treatment processes. Typical
processes include chemical treatment and pressure filtration. Also called TERTIARY TREATMENT.
AERATION (air-A-shun) AERATION
The process of adding air. In wastewater treatment, air is added to freshen wastewater and to keep solids in suspension. With
mixtures of wastewater and activated sludge, adding air provides mixing and oxygen for the microorganisms treating the wastewa-
ter.
AERATION LIQUOR (air-A-shun) AERATION LIQUOR
Mixed liquor. The contents of the aeration tank including living organisms and material carried into the tank by either untreated
wastewater or primary effluent.
AERATION TANK (air-A-shun) AERATION TANK
The tank where raw or settled wastewater is mixed with return sludge and aerated. The same as aeration bay, aerator, or reactor.
-------
408 Treatment Plants
AEROBES AEROBES
Bacteria that must have molecular (dissolved) oxygen (DO) to survive.
AEROBIC (AIR-O-bick) AEROBIC
A condition in which "free" or dissolved oxygen is present in the aquatic environment.
AEROBIC BACTERIA (AIR-O-bick back-TEAR-e-ah) AEROBIC BACTERIA
Bacteria which will live and reproduce only in an environment containing oxygen which is available for their respiration (breathing),
namely atmospheric oxygen or oxygen dissolved in water. Oxygen combined chemically, such as in water molecules (HzO), cannot
be used for respiration by aerobic bacteria.
AEROBIC DECOMPOSITION (AIR-O-bick) AEROBIC DECOMPOSITION
The decay or breaking down of organic material in the presence of "free" or dissolved oxygen.
AEROBIC DIGESTION (AIR-O-bick) AEROBIC DIGESTION
The breakdown of wastes by microorganisms in the presence of dissolved oxygen. Waste sludge is placed in a large aerated tank
where aerobic microorganisms decompose the organic matter in the sludge. This is an extension of the activated sludge process.
AEROBIC PROCESS (AIR-O-bick) AEROBIC PROCESS
A waste treatment process conducted under aerobic (in the presence of "free" or dissolved oxygen) conditions.
AGGLOMERATION (a-GLOM-er-A-shun) AGGLOMERATION
The growing or coming together of small scattered particles into larger floes or particles which settle rapidly. Also see FLOC.
AIR BINDING AIR BINDING
The clogging of a filter, pipe or pump due to the presence of air released from water.
AIR GAP
AIR GAP AIR GAP
Dflttwmo
WATCH
An open vertical drop, or vertical empty space, between a drinking (potable) water A
supply and the point of use in a wastewater treatment plant. This gap prevents u^aAr
back siphonage because there is no way wastewater can reach the drinking water.
own
tank


OPERATION
OF
WASTEWATER
TREATMENT
PLANTS
Volume I
A
Field
Study
Training
Program
•	ENVIRONMENTAL PROTECTION AGENCY •
• OFFICE OF WATER PROGRAMS •
•	DIVISION OF MANPOWER AND TRAINING •

-------
Environmental Protection Agency Review Notice
This training manual has been reviewed by the Office of Water Program
Operations, U.S. Environmental Protection Agency, and approved for publi-
cation. Approval does not signify that the contents necessarily reflect the
views and policies of the Environmental Protection Agency. Mention of trade
names or commercial products does not constitute endorsement or recom-
mendation for use by the Environmental Protection Agency, California State
University, Sacramento, California Water Pollution Control Association, au-
thors of the chapters or project reviewers and directors.

-------
OPERATION OF WASTEWATER
TREATMENT PLANTS
Second Edition
VOLUME I
A Field Study Training Program
prepared by
California State University, Sacramento
(formerly Sacramento State College)
Department of Civil Engineering
in cooperation with the
California Water Pollution Control Association
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~A
Kenneth D. Kerri, Project Director
Bill B. Dendy, Co-Director
John Brady, Consultant and Co-Director
William Crooks, Consultant
*A*****************************************-*********
for the
Environmental Protection Agency
Office of Water Program Operations
Municipal Permits and Operations Division
First Edition, Technical Training Grant No. 5TT1-WP-16-03 (1970)
Second Edition, Grant No. T900690010
1980
i

-------
NOTICE
This manual is revised and updated before each printing based on com-
ments from persons using the manual.
FIRST EDITION
First printing, 1971
5,000
Second printing, 1972
7,000
Third printing, 1973
9,000
Fourth printing, 1974
6,000
Fifth printing, 1975
4,000
Sixth printing, 1977
11,000
Seventh printing, 1979
4,000
SECOND EDITION
First Printing, 1980	7,000
ii

-------
PREFACE TO THE FIRST EDITION
The purposes of this home study program are:
a. to develop qualified treatment plant operators;
b. to expand the abilities of existing operators, permitting better service to both their employers and the public;
and
c. to prepare operators for CERTIFICATION EXAMINATIONS.1
To provide you with information needed to operate wastewater treatment plants as efficiently as possible,
experienced plant operators prepared the material on treatment plant processes. Each chapter begins with an
introduction and then discusses start up, daily operation, interpretation of lab results and possible approaches to
solving operational problems. This order of topics was determined during the testing program on the basis of
operators' comments indicating the information they needed most urgently. Additional chapters discuss mainte-
nance, safety, sampling, laboratory procedures, hydraulics, records, analysis and presentation of data, and report
writing.
Plant influents (raw wastewater) and the efficiencies of treatment processes vary from plant to plant and from
location to location. The material contained in this program is presented to provide you with an understanding of the
basic operational aspects of your plant and with information to help you analyze and solve operational problems.
This information will help you operate your plant as efficiently as possible.
Wastewater treatment is a rapidly advancing field. To keep pace with scientific advances, the material in this
program must be periodically revised and updated. This means that you, the operator, must recognize the need to
be aware of new advances and the need for continuous training beyond this program.
Originally the concepts for this manual evolved from Mr. Larry Trumbull, 1967 Chairman of the Operator Training
Committee of the California Water Pollution Control Association. Messrs. Bill Dendy and Kenneth Kerri, Project
Directors, investigated possible means of financial support to develop and test the manual and prepared a success-
ful application to the Federal Water Pollution Control Administration (5TT1-WP-16-03). The chapters were written,
tested by pilot groups of operators and potential operators, reviewed by consultants and the Federal Water Quality
Administration, and rewritten in accordance with the suggestions from these sources.
The project directors are indebted to the many operators and other persons who contributed to the manual. Every
effort was made to acknowledge material from the many excellent references in the wastewater treatment field.
Special thanks are due Messrs. John Brady and William Crooks who both contributed immensely to the manual. Mr.
F.J. Ludzack, Chemist, National Training Center, Environmental Protection Agency, Water Quality Office, offered
many technical improvements. A note of thanks is also due our typists, Miss Linda Smith, Mrs. Gloria Uri, Mrs. Daryl
Rasmussen, Mrs. Vicki Sadlem, Mrs. Peggy Courtney, and Mrs. Pris Jernigan. Illustrations were drawn by Mr.
Martin Garrity.
Following the first year of use by over 6500 operators and persons interested in operation, minor editing changes
were necessaiy to correct typing errors and omissions and also to rewrite and expand questions and sections that
could be clarified. Improvements suggested by operators using the manual were summarized and forwarded to a
special Technical Advisory Task Force composed of operators familiar with the manual. This Task Force was
formed as a subcommittee of the Water Pollution Control Federation's Personnel Advancement Committee and was
chaired by Mr. Sam Warrington. We gratefully thank John Brady, Carlos Doyle, Otto Havens, Wilbur Hoist, William
Johnson, F.J. Ludzack and David Vandersommen for their efforts to improve our original version.
Kenneth D. Kerri
Bill Dendy
1973
1 Certification examination. An examination administered by a state or professional association that operators take to indicate a level of
professional competence. In most states the Chief Operator of a plant must be "certified" (successfully pass a certification examination),
and in a few states certification is voluntary. Current trends indicate that certification of operators will be mandatory in all states in the near
future.
iii

-------
PREFACE TO THE SECOND EDITION
During the 1970's many people decided that something must be done to control water pollution. The United
States Congress passed the "Federal Water Pollution Control Act Amendments of 1972" (PL 92-500) and sub-
sequent amendments. The objective of this Act is to restore and maintain the quality of the Nation's waters. In order
to achieve this objective, the Act contains provisions for a financial grant program to assist municipalities with the
planning, construction, start up and training of personnel in publicly-owned wastewater treatment plants. Grant
funds have been used to build many new plants to date and many more plants will be built in the future. These plants
are becoming more complex and are requiring operators with higher levels of knowledge and skills in order to insure
that the plants produce a high quality effluent.
This manual, OPERATION OF WASTEWATER TREATMENT PLANTS, was used by over 40,000 persons inter-
ested in the operation of treatment plants during the 1970's. Every year when more manuals were printed, the
manual was updated on the basis of comments and suggestions provided by persons using the manual. After six
years of use by operators, the authors, the California Water Pollution Control Association, and the U.S. Environmen-
tal Protection Agency (EPA) decided that the contents of the manual should be reexamined, updated and revised.
To accomplish this task, EPA provided the Foundation of California State University, Sacramento, with a grant to
conduct the necessary studies, writing and field tests.
Recently the U.S. Environmental Protection Agency and the Association of Boards of Certification (ABC) have
undertaken studies to document "need to know" tasks performed by wastewater treatment plant operators, skills
required, alternative methods of training, training material needs and availability, and the development of instruc-
tional materials for certification examinations. Every effort has been made to incorporate the results of these studies
in this Second Edition of OPERATION OF WASTEWATER TREATMENT PLANTS.
The project directors are indebted to the many operators and other persons who contributed to the Second
Edition. Material from the many excellent references in the wastewater treatment field has been acknowledged
wherever possible. Joe Bahnick, Ken Hay, Adelaide Lilly, Frank Lapensee and Bob Rose, U.S. Environmental
Protection Agency, served ably as resource persons, consultants and advisers. Special thanks are due our project
consultants, Mike Mulbarger, Carl Nagel and Al Petrasek who provided technical advice. Our education reviewers
were George Gardner and Larry Hannah. Christine Umeda and Marlene Itagaki administered the national field
testing program. A note of thanks was well earned by our typists Charlene Arora, Elaine Saika and Gladys
Kornweibel. Illustrations were drawn by Martin Garrity.
Kenneth D. Kerri
John Brady
1980
iv

-------
USES OF THIS MANUAL
Originally this manual was developed to serve as a home-study course for operators in remote areas or persons
unable to attend formal classes either due to shift work, personal reasons or the unavailability of suitable classes.
This home-study training program used the concepts of self-paced instruction where you are your own instructor
and work at your own speed. In order to certify that a person had successfully completed this program, an objective
test was included at the end of each chapter and the training course became a correspondence or self-study type of
program.
Once operators started using this manual for home study, they realized that it could serve effectively as a textbook
in the classroom. Many colleges and universities have used the manual as a text in formal classes often taught by
operators. In areas were colleges were not available or were unable to offer classes in the operation of wastewater
treatment plants, operators and utility agencies joined togehter to offer their own courses using the manual.
Occasionally a utility agency has enrolled from three to over 300 of its operators in this training program. A manual
is purchased for each operator. A senior operator or a group of operators are designated as instructors. These
operators help answer questions when the persons in the training program have questions or need assistance. The
instructors grade the objective tests at the end of each chapter, record scores and notify California State University,
Sacramento, of the scores when a person successfully completes this program. This approach avoids the long wait
while papers are being graded and returned by CSUS.
This manual was prepared to help operators run their treatment plants. Please feel free to use it in the manner
which best fits your training needs and the needs of other operators. We will be happy to work with you to assist you
in developing your training program. Please feel free to contact
Ken Kerri, Project Director
Operation of Wastewater Treatment Plants
California State University, Sacramento
6000 Jay Street
Sacramento, California 95819
Phone (916)454-6142
or 454-6366
v

-------
INSTRUCTIONS TO PARTICIPANTS
IN HOME-STUDY COURSE
Procedures for reading the lessons and answering the
questions are contained in this section.
To progress steadily through this program, you should
establish a regular study schedule. For example, many
operators in the past have set aside two hours during
two evenings a week for study.
The study material is contained in three volumes di-
vided into 29 chapters. Some chapters are longer and
more difficult than others. For this reason, many of the
chapters are divided into two or more lessons. The time
required to complete a lesson will depend on your back-
ground and experience. Some people might require an
hour to complete a lesson and some might require three
hours; but that is perfectly all right. THE IMPORTANT
THING IS THAT YOU UNDERSTAND THE MATERIAL
IN THE LESSON!
Each lesson is arranged for you to read a short sec-
tion, write the answers to the questions at the end of the
section, check your answers against suggested an-
swers; and then YOU decide if you understand the mate-
rial sufficiently to continue or whether you should read
the section again. You will find that this procedure is
slower than reading a normal textbook, but you will re-
member much more when you have finished the lesson.
At the end of each chapter, you will find an "objective
test." Mark your answers on the special answer sheet
provided for each chapter. Some discussion and review
questions are provided following each lesson in the later
chapters. These questions review the important points
you have covered in the lesson.
The objective test at the end of each lesson contains
true or false, multiple-choice, fill-in-the-blank, or match-
the-answers types of questions. The purposes of this
exam are to review the chapter and to give experience in
taking different types of exams. MAIL TO THE PRO-
GRAM DIRECTOR ONLY YOUR ANSWERS TO OB-
JECTIVE TESTS ON THE PROVIDED ANSWER
SHEETS.
After you have completed the last objective test, you
will find a final examination. This exam is provided for
you to review how well you remembered the material.
You may wish to review the entire manual before you
take the final exam. Some of the questions are essay-
type questions which are used by some states for
higher-level certification examinations. After you have
completed the final examination, grade your own paper
and determine the areas in which you might need addi-
tional review before your next examination.
You are your own teacher in this program. You could
merely look up the suggested answers from the answer
sheet or copy them from someone else, but you would
not understand the material. Consequently, you would
not be able to apply the material to the operation of your
plant nor recall it during an examination for certification
or a civil service position.
YOU WILL GET OUT OF THIS PROGRAM WHAT
YOU PUT INTO IT.
vi

-------
SUMMARY OF PROCEDURE
OPERATOR (YOU)
1.	Read what you are expected to learn in each
chapter (from Chapter 4 on, the major topics are
listed at the beginning of the chapter).
2.	Read sections in lesson.
3.	Write answers to questions at end of sections in
your notebook. You should write the answers to
the questions just like you would if these were
questions on a test.
4.	Check your answers with suggested answers.
5.	Decide whether to reread section or to continue
with the next section.
6.	Write answers to discussion and review ques-
tions at the end of lessons in your note book.
7.	Mark answers to objective test on answer sheet.
8.	Mail material to project director.
Ken Kerri, Project Director
Operation of Wastewater Treatment Plants
California State University, Sacramento
6000 Jay Street
Sacramento, California 95819
7
AVAL L
PROJECT DIRECTOR
1.	Mails answer sheet for each chapter to operator.
2.	Corrects tests, answers any questions, and re-
turns results to operators.
C. ORDER OF WORKING LESSONS
To complete this program you will have to work all of
the chapters. You may proceed in numerical order, or
you may wish to work some lessons sooner. Chapter 17,
"Basic Arithmetic and Treatment Plant Problems," may
be worked before Chapter 4 because Chapter 4 requires
the use of simple arithmetic. If you have trouble with the
problems in Chapter 4 or some of the following chapters,
you may find it helpful to refer to the arithmetic chapter
or you may decide to work the arithmetic chapter first.
Chapter 16, "Laboratory Procedures and Chemistry,"
may be studied with Chapter 5 because the operation of
sedimentation and flotation treatment processes re-
quires some laboratory tests. Again, you may wish to
refer to the lab chapter while working on Chapter 5 and
the other chapters, or you may wish to work the lab
chapter first.
SAFETY IS A VERY IMPORTANT TOPIC. Everyone
working in a treatment plant must always be safety con-
scious. You must take extreme care with your personal
hygiene to prevent the spread of disease to yourself and
your family. Operators in treatment plants daily en-
counter situations and equipment that can cause a seri-
ous disabling injury or illness if the operator is not aware
of the potential danger and does not exercise adequate
precautions. For these reasons, you may decide to work
on the chapter on "Plant Safety and Good Housekeep-
ing" early in your studies. In each chapter SAFE PRO-
CEDURES ARE ALWAYS STRESSED.
vii

-------
COURSE OUTLINE
VOLUME I, SECOND EDITION
Chapter Topic	Page
1	The Treatment Plant Operator	1
2	Why Treat Wastes?	11
3	Wastewater Treatment Facilities	25
4	Racks, Screens, Comminutors and Grit Removal 55
5	Sedimentation and Flotation	101
6	Trickling Filters	155
7	Rotating Biological Contactors	197
8	Activated Sludge	227
(Package Plants and Oxidation Ditches)
9	Waste Treatment Ponds	275
10 Disinfection and Chlorination	319
Final Examination	397
Glossary	405
Index	435
TECHNICAL CONSULTANTS, FIRST EDITION
TECHNICAL CONSULTANTS, SECOND EDITION
Mike Mulbarger
viii

-------
COURSE OUTLINE
VOLUME II, SECOND EDITION
Chapter	Topic
11	Activated Sludge
(Conventional Activated Sludge Plants)
12	Sludge Digestion and Solids Handling
13	Effluent Disposal
14	Plant Safety and Good Housekeeping
15	Maintenance
16	Laboratory Procedures and Chemistry
17	Basic Arithmetic and Treatment Plant Problems
18	Analysis and Presentation of Data
19	Records and Report Writing
Final Examination
Glossary
Index
VOLUME III, SECOND EDITION
20	Odor Control
21	Activated Sludge
(Pure Oxygen and Operational Control Alternatives)
22	Solids Handling and Disposal
23	Solids Removal from Secondary Effluents
24	Phosphorus Removal
25	Wastewater Reclamation
26	Instrumentation
27	Industrial Waste Monitoring
28	Industrial Waste Treatment
29	Support Systems
Final Examination
Glossary
Index
ix

-------
CHAPTER 1
THE TREATMENT PLANT OPERATOR
by
Larry Trumbull
and
William Crooks

-------
TABLE OF CONTENTS
Chapter 1. The Treatment Plant Operator
Page
1.0	What is a Treatment Plant Operator?		3
1.01	What does a Treatment Plant Operator do?		3
1.02	Who does the Treatment Plant Operator work for?		3
1.03	Where does the Treatment Plant Operator work?		3
1.04	What pay can a Treatment Plant Operator expect? 		3
1.05	What does it take to be a Treatment Plant Operator? 		3
1.1	Your Personal Training Course		4
1.2	What Do You Already Know? 		4
1.3	The Water Quality Protector: YOU 		4
1.4	Your Qualifications		5
1.41 Your Job		5
1.5	Manpower Needs and Future Job Opportunities 		6
1.6	Training Yourself to Meet the Needs 		7

-------
CHAPTER 1. THE TREATMENT PLANT OPERATOR
This portion of Chapter 1 was prepared especially for the
new or the potential WASTEWATERS treatment plant operator.
If you are an experienced operator, you may find some new
viewpoints.
1.0 WHAT IS A TREATMENT PLANT OPERATOR?
Before modern society entered the scene, water was
purified in a natural cycle as shown below:
(CLOUD4
JRAIN 0
4<4dh6
LAMP
Simplified natural purification cycle
But modern society and the intensive use of the water re-
source and the resulting water pollution could not wait for sun,
wind, and time to accomplish the purification of soiled water;
consequently, treatment plants were built. Thus, nature was
given an assist by a team consisting of designers, builders,
and treatment plant operators. Designers and builders occupy
the scene only for an interval, but operators go on forever.
They are the final and essential link in maintaining and protect-
ing the aquatic environment upon which all life depends.
1.01 What does a Treatment Plant Operator do?
Simply described, the operator keeps a wastewater (sew-
age) treatment plant working. Physically the operator turns
valves, pushes switches, collects samples, lubricates equip-
ment, reads gages and records data.
An operator may also maintain equipment and plant area by
painting, weeding, gardening, repairing and replacing. Men-
tally an operator inspects records, observes conditions, makes
calculations to determine that the plant is working effectively,
and predicts necessary maintenance and facility needs to as-
sure continued effective operation of the plant. The operator
also has an obligation to explain to supervisors, councils, civic
bodies, and the general public what the plant does, and most
importantly, why its continued and expanded financial support
is vital to the welfare of the community.
1.02 Who does the Treatment Plant Operator work for?
An operator's paycheck usually comes from a city, sanitation
district, or other public agency. The operator may, however, be
employed by one of the many large industries which operate
their own treatment plants. As an operator you are responsible
to your employer for maintaining an economically and effi-
ciently operating facility. An even greater obligation rests with
the operator because the great numbers of people who rely
upon downstream water supplies are totally dependent upon
the operator's competence and trustworthiness for their wel-
fare. In the final analysis, the operator is really working for
these vitally affected downstream water users.
1.03 Where does the Treatment Plant Operator work?
Obviously the operator works in a wastewater treatment
plant. But the different types and locations of treatment plants
offer a wide range of working conditions. From the mountains
to the sea, wherever people congregate into communities,
wastewater treatment plants will be found. From a unit process
operator at a complex municipal facility to a one-person man-
ager of a small town plant, you can select your own special
place in treatment plant operation.
1.04 What pay can a Treatment Plant Operator expect?
In dollars? Prestige? Job satisfaction? Community service?
In opportunities for advancement? By whatever scale you use,
returns are what you make them. If you choose a large munici-
pality, the pay is good and advancement prospects are tops.
Choose a small town and pay may not be as good; but job
satisfaction, freedom from time-clock hours, community serv-
ice, and prestige may well add up to outstanding personal
achievement. Total reward depends on you.
The operator's duties
1.05 What does It take to be a Treatment Plant Operator?
Desire. First you must choose to enter this profession. You
can do it with a grammar school, a high school, or a college
education. While some jobs will always exist for manual labor,
the real and expanding need is for TRAINED OPERATORS.
New techniques, advanced equipment, and increasing in-
strumentation require a new breed of operator, one who is
V/AfE'R
50IU
1 Wastewater. The used water and solids from a community that flow to a treatment plant. Storm water, surface water, and groundwater
infiltration also may be included in the wastewater that enters a plant. The term "sewage" usually refers to household wastes, but this word is
being replaced by the term "wastewater."

-------
4 Treatment Plants
willing to learn today, and gain tomorrow, for surely your plant
will move towards newer and more effective operating proce-
dures and treatment processes. Indeed, the truly service-
minded operator assists in adding to and improving the plant
performance on a continuing basis.
Tomorrow's forgotten operator stopped learning yesterday
You can be an operator tomorrow by beginning your learning
today; or you can be a better operator, ready for advancement,
by accelerating your learning today.
This training course, then, is your start towards a better to-
morrow, both for you and for the public who will receive better
water from your efforts.
QUESTIONS
Place an "X" by the correct answer or answers. After you
have answered all the questions, check your answers with
those given at the end of the chapter on page 8. Reread any
sections you did not understand and then proceed to the next
section. You are your own teacher in this training program, and
YOU should decide when you understand the material and are
ready to continue with new material.
EXAMPLE
This is a training course on
A. Accounting
B. Engineering
X c. Wastewater Treatment Plant Operation
D. Salesmanship.
1.0A. Wastewater is the same thing as:
A. Rain
B. Soil
C. Sewage
D. Condensation.
1 OB. What does an operator do?
A. Collect samples.
B. Lubricate equipment.
C. Record data.
1.0C. Who employs Treatment Plant Operators?
A. Cities.
B. Sanitation districts.
C. Industries.
Check your answers on page 8.
1.1 YOUR PERSONAL TRAINING COURSE
Beginning on this page, you are embarking on a training
course which has been carefully prepared to allow you to im-
prove your knowledge of and ability to operate a wastewater
treatment plant. You will be able to proceed at your own pace;
you will have an opportunity to learn a little or a lot about each
topic. The course has been prepared this way to fit the various
needs of operators, depending on what kind of plant you have
or how much you need to learn about it. To study for certifica-
tion examinations, you will have to cover all the material. You
will never know everything about your plant or about the
wastewater which flows through it, but you can begin to answer
some very important questions about how and when certain
things happen in the plant. You can also learn to manipulate
your plant so that it operates at maximum efficiency.
1.2 WHAT DO YOU ALREADY KNOW?
If you already have some experience operating a wastewa-
ter treatment plant, you may use the first three chapters for a
review. If you are relatively new to the wastewater treatment
field, these chapters will provide you with the background in-
formation necessary to understand the later chapters. The re-
mainder of this introductory chapter describes your role as a
PROTECTOR OF WATER QUALITY, your QUALIFICATIONS
to do your job, a little about manpower needs in the wastewater
treatment field, and some information on other TRAINING OP-
PORTUNITIES.
1.3 THE WATER QUALITY PROTECTOR: YOU
Historically Americans have shown a great lack of interest in
the protection of their water resources. We have been content
to think that "the solution to pollution is dilution." For years we
were able to dump our wastes with little or no treatment back
into the nearest RECEIVING WATERS.2 As long as there was
enough dilution water to absorb the waste material, nature took
care of our disposal problems for us. As more and more towns
and industry sprang up, waste loads increased until the natural
purification processes could no longer do the job. Many water-
ways were converted into open sewers. Unfortunately, for
many areas this did not signal the beginning of a clean-up
campaign. It merely increased the frequency of the cry: "We
don't have the money for a treatment plant," or the ever-
popular, "If we make industries treat their wastes they will
move to another state." Thus, the pollution of our waters in-
creased.
f
Water quality protector
Within the last few years, we have seen many changes in
this depressing picture. We now realize that we must give
nature a hand by treating wastes before they are discharged.
Adequate treatment of wastes will not only protect our health
and that of our downstream neighbors; it can also increase
property values, allow game fishing and various recreational
uses to be enjoyed, and attract water-using industries to the
area. Today we are seeing massive efforts being undertaken
to control water pollution and improve water quality throughout
the nation. This includes the efforts not only of your own com-
munity, county and state, but also the federal government
Great sums of public and private funds are now being in-
2 Receiving Water. A stream, river, lake, or ocean into which treated or untreated wastewater is discharged.

-------
The Operator 5
vested in large, complex municipal and industrial wastewater
treatment facilities to overcome this pollution; and you, the
treatment plant operator, will play a key role in the battle. With-
out efficient operation of your plant, much of the research,
planning, and building that has been done and will be done to
accomplish the goals of water quality control in your area will
be wasted. You are the difference between a facility and a
performing unit. You are, in fact, a WATER QUALITY PRO-
TECTOR on the front line of the water pollution battle.
Pollution
The receiving water quality standards and waste discharge
requirements that your plant has been built to meet have been
formulated to PROTECT the water users downstream from
your plant. These uses may include domestic water supply,
industrial water supply, agricultural water supply, stock and
wildlife watering, propagation of fish and other aquatic and
marine life, shellfish culture, swimming and other water contact
sports, boating, esthetic enjoyment, hydroelectric power, navi-
gation, and others.
Therefore, you have an obligation to the users of the water
downstream, as well as to the people of your district or munici-
pality. You are the KEY WATER QUALITY PROTECTOR and
must realize that you are in a responsible position.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 8.
1,3A Why must municipal and industrial wastewaters receive
adequate treatment?
1.3B How did many receiving waters become polluted?
1.4. YOUR QUALIFICATIONS
The skill and ability required for your job depend to a large
degree on the size and type of treatment plant where you are
employed. You may work at a large modern treatment plant
serving several hundred thousand persons and employing a
hundred or more operators. In this case you are probably a
specialist in one or more phases of the treatment process.
On the other hand, you may operate a small plant serving
only a thousand people or fewer. You may be the only operator
at the plant or, at best, have only one or two additional employ-
ees. If this is the case, you must be a "jack-of-all trades" be-
cause of the diversity of your tasks.
1.41 Your Job
To describe the operator's duties, let us start at the begin-
ning. Let us say that the need for a new or improved wastewa-
ter treatment plant has long been recognized by the commu-
nity. The community has voted to issue the necessary bonds to
finance the project, and the consulting engineers have submit-
ted plans and specifications. It is to the best interests of the
community and the consulting engineer that you be in on the
ground floor planning. If it is a new plant, you should be present
or at least available during the construction period in order to
become completely familiar with the entire plant, including the
equipment and machinery and their operation. This will provide
you with the opportunity to relate your plant drawings to actual
facilities.
You and the engineer should discuss how the treatment
plant should best be run and the means of operation the de-
signer had in mind when the plant was designed. If it is an old
plant being remodeled, you are in a position to offer excellent
advice to the consulting engineer. Your experience provides
valuable technical knowledge concerning the characteristics of
wastewater, its sources, and the limitations of the present
facilities. Together with the consultant, you are a member of an
expert team able to advise the district or city.
Once the plant is operating, you become an administrator. In
a small plant your duties may not include supervision of per-
sonnel, but you are still in charge of records. You are responsi-
ble for operating the plant as efficiently as possible, keeping in
Visitors touring a treatment plant.

-------
6 Treatment Plants
mind that the primary objective is to protect the receiving water
quality by continuous and efficient plant performance. Without
adequate, reliable records of every phase of operation, the
effectiveness of your operation has not been documented (re-
corded).
Vou may also be the budget administrator. Most certainly
you are in the best position to give advice on budget require-
ments, management problems, and future planning. You
should be aware of the necessity for additional expenditures,
including funds for plant enlargement, equipment replacement,
and laboratory requirements. You should recognize and define
such needs in sufficient time to inform the proper officials to
enable them to accomplish early planning and budgeting.
You are in the field of public relations and must be able to
explain the purpose and operation of your plant to visitors, civic
organizations, school classes, representatives of news media,
and even to city council or directors of your district. Public
interest in water quality is increasing, and you should be pre-
pared to conduct plant tours that will contribute to public accep-
tance and support. A well-guided tour for officials of regulatory
agencies or other operators may provide these people with
sufficient understanding of your plant to allow them to suggest
helpful solutions to operational problems.
Special care and safety must be practiced when visitors are
taken through your treatment plant. An accident could spoil all
of your public relations efforts.
The appearance of your plant indicates to the visitor the type
of operation you maintain. If the plant is dirty and rundown with
flies and other insects swarming about, you will be unable to
convince your visitors that the plant is doing a good job. YOUR
RECORDS SHOWING A HIGH-QUALITY EFFLUENT3 WILL
MEAN NOTHING TO THESE VISITING CITIZENS UNLESS
YOUR PLANT APPEARS CLEAN AND WELL-MAINTAINED
AND THE EFFLUENT LOOKS GOOD.
Another aspect of your public relations duties is your deal-
ings with the downstream water user. Unfortunately, the
operator is often considered by the downstream user as a
polluter rather than a water quality protector. Through a good
public information program, backed by facts supported by reli-
able data, you can correct the impression held by the
downstream user and establish "good neighbor" relations.
This is indeed a challenge. Again, you must understand that
you hold a very responsible position and be aware that the sole
purpose of the operation of your plant is to protect the
downstream user, be that user a private property owner,
another city or district, an industry, or a fisherman.
You are required to understand certain laboratory proce-
dures in order to conduct various tests on samples of wastewa-
ter and receiving waters. On the basis of the data obtained
from these tests, you may have to adjust the operation of the
treatment plant to meet stream standards or discharge re-
quirements.
As an operator you must have a knowledge of the compli-
cated mechanical principles involved in many treatment
mechanisms. In order to measure and control the wastewater
flowing through the plant, you must have some understanding
Clean Stream
of hydraulics. Practical knowledge of electrical motors, cir-
cuitry, and controls is also essential.
Safety is a very important operator responsibility. Unfortu-
nately too many operators take safety for granted. This is one
reason why the wastewater treatment industry has one of the
worst safety records of any industry. YOU have the responsibil-
ity to be sure that your treatment plant is a safe place to work
and visit. Everyone must follow safe procedures and under-
stand why safe procedures must be followed at all times. All
operators must be aware of the safety hazards in and around
treatment plants. You should plan or be a part of an active
safety program. Chief operators frequently have the responsi-
bility of training new operators and should encourage all
operators to become certified.
Clearly then, the modern day wastewater treatment plant
operator must possess a broad range of qualifications.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 8.
1.4A Why is it important that the operator be present during
the construction of a new plant?
1,4B How does the operator become involved in public rela-
tions?
1.5 MANPOWER NEEDS AND FUTURE JOB
OPPORTUNITIES
The wastewater treatment field, like so many others, is
changing rapidly. New plants are being constructed, and old
plants are being modified and enlarged to handle the wastewa-
ter from our growing population and to treat the new chemicals
being produced by our space age technology. Operators,
maintenance personnel, foremen, managers, instrumentation
experts, and laboratory technicians are sorely needed.
3 Effluent. Wastewater or other liquid - raw, partially or completely treated - flowing FROM a basin, treatment process, or treatment plant.

-------
»The Operator 7
A look at past records and future predictions indicates that
wastewater treatment is a rapidly growing field. Municipalities
employed approximately 20,000 operators in 1967 and over
67,000 operators in 1974. Industry employed approximately
3,500 operators in 1967 and around 12,000 plant operators by
1972. The need for trained operators is increasing rapidly and
is expected to continue in the future.4
1.6 TRAINING YOURSELF TO MEET THE NEEDS
This training course is not the only one available to help you
improve your abilities. The states have offered various types of
both long- and short-term operator training through their health
departments or water pollution control associations have pro-
vided training classes conducted by members of the associa-
tions, largely on a volunteer basis. The Water Pollution Control
Federation has developed two visual aid training courses to
complement its Manual of Practice No. 11. State and local
colleges have provided valuable training under their own
sponsorship or in partnership with others. Many state, local
and private agencies have conducted both long- and short-
term training as well as interesting and informative seminars.
The California Water Pollution Control Association has pre-
pared two textbooks, one on laboratory procedures and one on
mathematics. Excellent textbooks have been written by many
state agencies. Those of the New York State Health Depart-
ment and the Texas Water Utilities Association deserve spe-
cial attention. The Canadian government has developed very
good training manuals for operators.
Listed below are several very good references in the field of
wastewater treatment plant operation that are frequently re-
ferred to throughout this course. The name in quotes repre-
sents the term usually used by operators when they mention
the reference. Prices listed are those available when this man-
ual was published and will probably increase in the future.
1. "MOP 11." OPERATION OF WASTEWATER TREATMENT
PLANTS, WPCF Manual of Practice No. 11, Water Pollution
Control Federation, 2626 Pennsylvania Avenue, N.W.,
Washington, D.C. 20037. Price $8.00 to members; $16.00
to others.
2. "NEW YORK MANUALMANUAL OF INSTRUCTION
FOR SEWAGE TREATMENT PLANT OPERATORS, dis-
tributed in New York by the New York State Department of
Health, Office of Public Health Education, Water Pollution
Control Board, Distributed outside of New York State by
Health Education Service, P.O. Box 7126, Albany, New
York 12224. Price $2.59.
3. "TEXAS MANUAL." MANUAL OF WASTEWATER OPER-
ATIONS, prepared by Texas Water Utilities Association.
Obtainable from Texas Water Utilities Assocation, 6521
Burnet Lane, Austin, Texas 78757. Price $15.00.
These publications cover the entire field of treatment plant
operation. At the end of many of the chapters yet to come, lists
of other references will be provided.
n

4 Data contained in this paragraph were obtained from "Manpower and Training Needs in Water Pollution Control," Report of the Department
of the Interior, Federal Water Pollution Control Administration to the Congress of the United States, Senate Document No. 49, 90th Congress,
First Session, Washington, D.C., 1967 and from "Study of Municipal Wastewater Treatment Plant Manpower and Training Needs and
Resources," Municipal Permits and Operations Division, Office of Water Program Operations, U.S. Environmental Protection Agency,
Washington, D.C., 1974.

-------
8 Treatment Plants
SUGGESTED ANSWERS
Chapter 1. THE TREATMENT PLANT OPERATOR
You are not expected to have the exact answer suggested
for questions requiring written answers, but you should have
the correct idea. The numbering of the questions refers to the
section in the manual where you can find the information to
answer the questions. Answers to questions numbered 1.0 can
be found in Section 1.0, What is a Treatment Plant Operator?
Answers to questions on page 4.
1.0A. C
1.0B. A, B, C
1.0C. A, B, C
^swers to questions on page 5.
1.3A. Municipal and industrial wastewaters must receive
adequate treatment to protect receiving water users.
1.3B. Receiving waters became polluted by a lack of public
concern for the impact of waste discharges and by
discharging wastewater into a receiving water beyond
its natural purification capacity.
Answers to questions on page 6.
1.4A The operator should be present during the construction
of a new plant in order to become familiar with the plant
before the operator begins operating it.
1,4B The operator becomes involved in public relations by
explaining the purpose and operation of the plant to
visitors, civic organizations, newspaper people, and
supervisors.
9
DIRECTIONS FOR WORKING OBJECTIVE TEST
Chapter 1. THE TREATMENT PLANT OPERATOR
1.	You have been provided with a special answer sheet for
each chapter. Be sure you follow the special directions pro-
vided with the answer sheets. If you lose an answer sheet
or have any problems, please notify the Project Director.
2.	Mark your answers on the answer sheet with a dark lead
pencil. Do not use ink.
For example, Question 2 has three correct answers (1, 2
and 3). Therefore, you should place a mark under Columns
1, 2 and 3 on the answer sheet.
Questions 4 through 7 are true or false questions. If a ques-
tion is true, then mark Column 1, and if false mark Column
2. The correct answer to Question 4 is true; therefore, place
a mark in Column 1.
Please mark your answers in your workbook for your record
because answer sheets will not be returned to you.
Mail answer sheet to the Project Director immediately after
you have completed the test.
Answer sheets may be folded (but not into more than 3
equal parts) and mailed in a 4 x 9'/2 standard white en-
velope.

-------
The Operator 9
OPERATION OF WASTEWATER TREATMENT PLANTS
IMPORTANT
PLEASE READ INSTRUCTIONS ON REVERSE SIDE BEFORE COMPLETING THIS FORM.
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Sacramento, California 95819

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Use black lead pencil only ( # 2 or softer).
Make heavy black marks that fill the circle completely.
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Make no stray marks on this answer sheet.
EXAMPLE
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10 Treatment Plants
OBJECTIVE TEST
Chapter 1. THE TREATMENT PLANT OPERATOR
Please mark correct answers on the answer sheet.
1.	The used water and solids from a community that flow to a
treatment plant are called	?
1.	Effluent	3. Sludge
2.	Mixed Liquor	4. Wastewater
2.	Receiving water uses protected by an operator include
1.	Boating.	3. Fishing.
2.	Drinking water supply. 4. None of these
3.	What kinds of jobs are available in the wastewater treat-
ment field in addition to those available for operators?
1.	Foremen
2.	Instrumentation experts
3.	Laboratory technicians
4.	Maintenance personnel
5.	Manager
TRUE OR FALSE:
4.	In many treatment plants the operator must be a "jack-of-
all-trades."
1.	True
2.	False
5.	A treatment plant operator is a WATER QUALITY protector.
1.	True
2.	False
6.	Plant visitors are impressed by records showing efficient
plant operation, and their opinions are never influenced by
the appearance of the plant and grounds.
1.	True
2.	False
7.	After finishing this program, an operator will need to con-
tinue to study in order to keep pace with changes occurring
in the field.
1.	True
2.	False
END OF OBJECTIVE TEST

-------
CHAPTER 2
WHY TREAT WASTES?
by
William Crooks

-------
12 Treatment Plants
TABLE OF CONTENTS
Chapter 2. Why Treat Wastes?
Page
PRONUNCIATION KEY	13
GLOSSARY	14
2.0	Prevention of Pollution	16
2.1	What is Pure Water? 	16
2.2	Types of Waste Discharges	16
2.3	Effects of Waste Discharges	17
2.30	Sludge and Scum	17
2.31	Oxygen Depletion 	17
2.32	Human Health 	18
2.33	Other Effects 	18
2.4	Solids in Wastewater	18
2.40	Types of Solids 	19
2.41	Total Solids	19
2.42	Dissolved Solids 		19
2.43	Suspended Solids	19
2.44	Organic and Inorganic Solids	20
2.45	Floatable Solids	20
2.5	Natural Cycles	20
2.6	NPDES Permits	21
2.7	Additional Reading	21
2.8	Review 	21

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Waste Treatment 13
PROJECT PRONUNCIATION KEY
by Warren L. Prentice
The Project Pronunciation Key is designed to aid you in the
pronunciation of new words. While this Key is based primarily
on familiar sounds, it does not attempt to follow any particular
pronunciation guide. This Key is designed solely to aid
operators in this program.
You may find it helpful to refer to other available sources for
pronunciation help. Each current standard dictionary contains
a guide to its own pronunciation Key. Each Key will be different
from each other and from this Key. Examples of the differences
between the Key used in this program and the WEBSTERS
NEW WORLD DICTIONARY "Key1" are shown below:

1 Te r m
Pro jo c: t Key
Webster Key
1 ac id
AS-i ci
as <3cl
Jj co 1 i f o r in
C 0 A L-1 ¦ f o r ni
k o - la-f o r m
3 b i o 1 o tj i c, a 1
B U Y-o-LO DC E - i k-c u 11
bi-o-l a )- i-ka 1

In using this Key, you should accent (say louder) the syllable
which appears in capital letters. The following chart is pre-
sented to give examples of how to pronounce words using the
Project Key.
Syllable

1st
2nd
3rd
4th
5th
Word
acid
AS
id

coagulant
CO
AGG
you
lent

biological
BUY
0.
LODGE
ik
cull
The first word ACID has its first syllable accented. The sec-
ond word, COAGULANT, has its second syllable accented.
The third word, BIOLOGICAL, has its first and third syllables
accented.
We hope you will find the Key useful in unlocking the pro-
nunciation of any new word.
1 The WEBSTER'S NEW WORLD DICTIONARY, College Edition, 1968, was chosen rather than an unabridged dictionary because of its
availability to the operator. Other editions may be slightly different.

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14 Treatment Plants
GLOSSARY
Chapter 2. WHY TREAT WASTES?
AEROBIC BACTERIA
AEROBIC BACTERIA
(AIR-O-bick back-TEAR-e-ah)
Bacteria which will live and reproduce only in an environment containing oxygen which is available for their respiration (breathing),
namely atmospheric oxygen or oxygen dissolved in water. Oxygen combined chemically, such as in water molecules (H20), cannot
be used for respiration by aerobic bacteria.
ANAEROBIC BACTERIA ANAEROBIC BACTERIA
(AN-air-O-bick back-TEAR-e-ah)
Bacteria that live and reproduce in an environment containing no "free" or dissolved oxygen. Anaerobic bacteria obtain their oxygen
supply by breaking down chemical compounds which contain oxygen, such as sulfate (S04).
BIOCHEMICAL OXYGEN DEMAND (BOD)
BIOCHEMICAL OXYGEN DEMAND
The rate at which microorganisms use oxygen in water or wastewater while stabilizing decomposable organic matter under aerobic
conditions. In decomposition, organic matter serves as food for the bacteria and energy results from its oxidation.
BIOCHEMICAL OXYGEN DEMAND (BOD) TEST BIOCHEMICAL OXYGEN DEMAND TEST
A procedure that measures the rate of oxygen use under controlled conditions of time and temperature. Standard test conditions
include dark incubation at 20°C for a specified time (usually five days).
COLIFORM (COAL-i-form) COLIFORM
One type of bacteria. The presence of coliform-group bacteria is an indication of possible pathogenic bacterial contamination. The
human intestinal tract is one of the main habitats of coliform bacteria. They may also be found in the intestinal tracts of warm-
blooded animals, and in plants, soil, air, and the aquatic environment. Fecal coliforms are those coliforms found in the feces of
various warm-blooded animals; whereas the term "coliform" also includes other environmental sources.
DISINFECTION (dis-in-FECK-shun) DISINFECTION
The process designed to kill most microorganisms in wastewater, including essentially all pathogenic (disease-causing) bacteria.
There are several ways to disinfect, with chlorination being most frequently used in water and wastewater treatment plants.
Compare with STERILIZATION.
EFFLUENT (EF-lu-ent) EFFLUENT
Wastewater or other liquid — raw, partially or completely treated — flowing FROM a basin, treatment process, or treatment plant.
IMHOFF CONE
A clear, cone-shaped container marked with graduations. The cone is used to measure the
volume of settleable solids in a specific volume of wastewater.
IMHOFF CONE
INORGANIC WASTE (IN-or-GAN-nick) INORGANIC WASTE
Waste material such as sand, salt, iron, calcium, and other materials which are only slightly affected by the action of organisms.
Inorganic wastes are chemical substances of mineral origin; whereas organic wastes are chemical substances usually of animal or
vegetable origin.
MILLIGRAMS PER LITER, mgIL
MILL-i-GRAMS per LEET-er)
MILLIGRAMS PER LITER, mgIL
A measure of the concentration by weight of a substance per unit volume. For practical purposes, one mgIL is equal to one part per
million parts (ppm). Thus, a liter of water with a specific gravity of 1.0 weighs one million milligrams; and if it contains 10 milligrams of
dissolved oxygen, the concentration is 10 milligrams per million milligrams, or 10 milligrams per liter (10 mg/L), or 10 parts of oxygen
per million parts of water, or 10 parts per million (10 ppm).
NUTRIENT CYCLE NUTRIENT CYCLE
The transformation or change of a nutrient from one form to another until the nutrient has returned to the original form, thus
completing the cycle. The cycle may take place under either aerobic or anaerobic conditions.

-------
Waste Treatment 15
NUTRIENTS NUTRIENTS
Substances which are required to support living plants and organisms. Major nutrients are carbon, hydrogen, oxygen, sulfur,
nitrogen, and phosphorus. Nitrogen and phosphorus are difficult to remove from wastewater by conventional treatment processes
because they are water soluble and tend to recycle. Also see NUTRIENT CYCLE.
ORGANIC WASTE (or-GAN-nick) ORGANIC WASTE
Waste material which comes mainly from animal or vegetable sources. Organic waste generally can be consumed by bacteria and
other small organisms. Inorganic wastes are chemical substances of mineral origin.
PATHOGENIC BACTERIA PATHOGENIC BACTERIA
(path-o-JEN-nick)
Bacteria, viruses or cysts which can cause disease (typhoid, cholera, dysentery). There are many types of bacteria which do NOT
cause disease and which are NOT called pathogenic. Many beneficial bacteria are found in wastewater treatment processes
actively cleaning up organic wastes.
pH (PEA-A-ch) pH
Technically, this is the logarithm of the reciprocal of the hydrogen-ion concentration, which is explained in Chapter 16, "Laboratory
Procedures and Chemistry." For now, it is sufficient to understand that pH expresses the intensity of the acid or alkaline condition of
a liquid. The pH may range from 0 to 14, where 0 is most acid and 14 is most alkaline, and 7 is neutral. Most natural waters have a
pH between 6.5 and 8.5.
POLLUTION POLLUTION
Any change in the natural state of water which interferes with its beneficial reuse or causes failure to meet water-quality require-
ments.
PRIMARY TREATMENT PRIMARY TREATMENT
A wastewater treatment process that takes place in a rectangular or circular tank and allows those substances in wastewater that
readily settle or float to be separated from the water being treated.
RECEIVING WATER RECEIVING WATER
A stream, river, lake or ocean into which treated or untreated wastewater is discharged.
SECONDARY TREATMENT SECONDARY TREATMENT
A wastewater treatment process used to convert dissolved or suspended materials into a form more readily separated from the
water being treated. Usually the process follows primary treatment by sedimentation. The process commonly is a type of biological
treatment process followed by secondary clarifiers that allow the solids to settle out from the water being treated.
SEPTIC (SEP-tik) SEPTIC
This condition is produced by anaerobic bacteria. If severe, the wastewater turns black, gives off foul odors, contains little or no
dissolved oxygen and creates a heavy oxygen demand.
STABILIZE STABILIZE
To convert to a form that resists change. Organic material is stabilized by bacteria which convert the material to gases and other
relatively inert substances. Stabilized organic material generally will not give off obnoxious odors.
STERILIZATION (stare-uh-luh-ZAY-shun) STERILIZATION
The removal or destruction of all living microorganisms, including pathogenic and saprophytic bacteria, vegetative forms, and
spores. Compare with DISINFECTION.
TRANSPIRATION (TRAN-spear-RAY-shun) TRANSPIRATION
The process by which water vapor is lost to the atmosphere from living plants.

-------
16 Treatment Plants
CHAPTER 2. WHY TREAT WASTES?
2.0 PREVENTION OF POLLUTION
The operator's main job is to protect the many users of re-
ceiving waters. As an operator you must do the best you can to
remove any substances which will unreasonably affect these
users.
Many people think ANY discharge of waste to a body of
water is pollution. However, with our present system of using
water to carry away the waste products of home and industry, it
would be impossible and perhaps unwise to prohibit the dis-
charge of all wastewater to oceans, streams, and groundwater
basins. Present day technology is capable of treating wastes in
such a manner that existing or potential receiving water uses
are not unreasonably affected. Definitions of pollution include
any interference with beneficial reuse of water or failure to
meet water quality requirements. Any questions or comments
regarding this definition must be settled by the appropriate
enforcement agency.
2.1 WHAT IS PURE WATER?
Water is a combination of two parts hydrogen and one part
oxygen, or H2O. This is true, however, only for "pure" water
such as might be manufactured in a laboratory. Water as we
know it is not "pure" hydrogen and oxygen. Even the distilled
water we purchase in the store has measurable quantities of
various substances in addition to hydrogen and oxygen. Rain
water, even before it reaches the earth, contains many sub-
stances. These substances, since they are not found in "pure"
water, may be considered "impurities." When rain falls through
the atmosphere, it gains nitrogen and other gases. As soon as
the rain flows overland, it begins to dissolve from the earth and
rocks such substances as calcium, magnesium, sodium,
chloride, sulfate, iron, nitrogen, phosphorus, and many other
materials. Organic matter (matter derived from plants and ani-
mals) is also dissolved by water from contact with decaying
leaves, twigs, grass, or small insects and animals. Thus it
should be realized that a fresh flowing mountain stream may
pick up many natural "impurities," some possibly in harmful
amounts, before it ever reaches civilization or is affected by the
waste discharges of society. Many of these substances, how-
ever, are needed in small amounts to support life and be useful
to humans. Concentrations of impurities must be controlled or
regulated to prevent harmful levels in receiving waters.
I
6
Water + Impurities
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 23.
2.1 A What are some of the dissolved substances in water?
2.1 B How does water pick up dissolved substances?
2.2 TYPES OF WASTE DISCHARGES
The waste discharge that first comes to mind in any discus-
sion of stream pollution is the discharge of domestic wastewa-
ter. Wastewater contains a large amount of ORGANIC
WASTE.1 Industry also contributes substantial amounts of or-
ganic waste. Some of these organic industrial wastes come
from vegetable and fruit packing; dairy processing; meat pack-
ing; tanning; and processing of poultry, oil, paper and fiber
(wood), and many more.
Another classification of wastes is INORGANIC WASTES,2
1 Organic Waste (or-GAN-nick). Waste material which comes mainly from animal or vegetable sources. Organic waste generally can be
consumed by bacteria and other small organisms. Inorganic wastes are chemical substances of mineral origin.
2 Inorganic Waste (IN-or-GAN-nick). Waste material such as sand, salt, iron, calcium, and other materials which are only slightly affected by
the action of organisms. Inorganic wastes are chemical substances of mineral origin; whereas organic wastes are chemical substances
usually of animal or vegetable origin.

-------
Waste Treatment 17
Domestic wastewater contains inorganic material as well as
organic, and many industries discharge inorganic wastes
which add to the mineral content of receiving waters. For in-
stance, a discharge of salt brine (sodium chloride) for water
softening will increase the amount of sodium and chloride in
the receiving waters. Some industrial wastes may introduce
inorganic substances such as chromium or copper, which are
very toxic to aquatic life. Other industries (such as gravel wash-
ing plants) discharge appreciable amounts of soil, sand or grit,
which also may be classified as inorganic waste.
There are two other major types of wastes that do not fit
either the organic or inorganic classification. These are heated
(thermal) wastes and radioactive wastes. Waters with temper-
atures exceeding the requirements of the enforcing agency
may come from cooling processes used by industry and from
thermal power stations generating electricity. Radioactive
wastes are usually controlled at their source, but could come
from hospitals, research laboratories, and nuclear power
plants.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 23.
2.2A Several of the following contain significant quantities of
organic material. Which are they?
a. Domestic Wastewater
b. Cooling Water from Thermal Power Stations
c. Paper Mill Wastes
d. Metal Plating Wastes
e. Tanning Wastes
2.2B List four types of pollution.
2.3 EFFECTS OF WASTE DISCHARGES
Certain substances not removed by wastewater treatment
processes can cause problems in receiving waters. This sec-
tion reviews some of these substances and discusses why
they should be treated.
2.30 Sludge and Scum
If certain wastes (including domestic wastewater) do not re-
ceive adequate treatment, large amounts of solids may ac-
cumulate on the banks of the receiving waters, or they may
settle to the bottom to form sludge deposits or float to the
surface and form rafts of scum. Sludge deposits and scum are
not only unsightly but, if they contain organic material, they
may also cause oxygen depletion and be a source of odors.
PRIMARY TREATMENT3 units in the wastewater treatment
plant are designed and operated to remove the sludge and
scum before they reach the receiving waters.
2.31 Oxygen Depletion
Most living creatures need oxygen to survive, including fish
and other aquatic life. Although most streams and other sur-
face waters contain less than 0.001 % DISSOLVED OXYGEN
(10 milligrams of oxygen per liter of water, or 10 mgIL* most
fish can thrive if there are at least 5 mg1L and other conditions
are favorable. When oxidizable wastes are discharged to a
stream, bacteria begin to feed on the waste and decompose or
break down the complex substances in the waste into simple
chemical compounds. These bacteria also use dissolved oxy-
gen (similar to human respiration or breathing) from the water
and are called AEROBIC BACTERIA.5 As more organic waste
is added, the bacteria reproduce rapidly; and as their popula-
tion increases, so does their use of oxygen. Where waste flows
are high, the population of bacteria may grow large enough to
use the entire supply of oxygen from the stream faster than it
can be replenished by natural diffusion from the atmosphere.
When this happens, fish and most other living things in the
stream which require dissolved oxygen die.
Oxygen depletion
Therefore, one of the principal objectives of wastewater
treatment is to prevent as much of this "oxygen-demanding"
organic material as possible from entering the receiving water.
The treatment plant actually removes the organic material the
same way a stream does, but it accomplishes the task much
more efficiently by removing the wastes from the wastewater.
SECONDARY TREATMENT6 units are designed and operated
to use natural organisms such as bacteria IN THE PLANT to
STABILIZE7 and to remove organic material.
Another effect of oxygen depletion, in addition to the killing of
fish and other aquatic life, is the problem of odors. When all the
dissolved oxygen has been removed, ANAEROBIC BAC-
TERIA8 begin to used the oxygen which is combined chemi-
cally with other elements in the form of chemical compounds,
such as sulfate (sulfur and oxygen), which are also dissolved in
3 Primary Treatment. A wastewater treatment process which takes place In a rectangular or circular tank and allows those substances In
wastewater that readily settle or float to be separated from the water being treated.
4 Milligrams per Liter, mg/L (MILL-i-GRAMS per LEET-er). A measure of the concentration by weight of a substance per unit volume. For
practical purposes, one mg/L is equal to one part per million parts (ppm). Thus, a liter of waste with a specific gravity of 1.0 weighs one million
milligrams; and if it contains 10 milligrams of dissolved oxygen, the concentration Is 10 milligrams per million milligrams, or 10 milligrams per
liter (10 mg//.), or 10 parts of oxygen per million parts of water, or 10 parts per million (10 ppm).
5 Aerobic Bacteria (AIR-O-blck back-TEAR-e-ah). Bacteria which will live and reproduce only In an environment containing oxygen which Is
available tor their respiration (breathing), namely atmospheric oxygen or oxygen dissolved In water. Oxygen combined chemically, such as in
water molecules (HJD), cannot be used for respiration by aerobic bacteria.
6 Secondary Treatment. A wastewater treatment process used to convert dissolved or suspended materials into a form more readily
separated from the water being treated. Usually the process tollows primary treatment by sedimentation. The process commonly is a type of
biological treatment process followed by secondary clarifiers that allow the solids to settle out from the water being treated.
7 Stabilize. To convert to a form that resists change. Organic material is stabilized by bacteria which convert the material to gases and other
relatively Inert substances. Stabilized organic material generally will not give off obnoxious odors.
* Anaerobic Bacteria (AN-air-O-blck back-TEAR-e-ah). Bacteria that live and reproduce In an environment containing no "free" or dissolved
oxygen. Anaerobic bacteria obtain their oxygen supply by breaking down chemical compounds which contain oxygen, such as sulfate
(SOJ and nitrate (NOJ.

-------
18 Treatment Plants
the water. When anaerobic bacteria remove the oxygen from
sulfur compounds, hydrogen sulfide (H2S), which has a "rotten
egg" odor, is produced. This gas is not only very odorous, but it
also erodes concrete and can discolor and remove paint from
homes and structures. Hydrogen sulfide also may form explo-
sive mixtures with air and is capable of paralyzing your re-
spiratory center. Other products of anaerobic decomposition
(putrefaction: PU-tree-FACK-shun) also can be objectionable.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 23.
2.3A What causes oxygen depletion when organic wastes
are discharged to the water?
2.3B What kind of bacteria cause hydrogen sulfide gas to be
released?
2.32 Human Health
Up to now we have discussed the physical or chemical ef-
fects that a waste discharge may have on the uses of water.
More important, however, may be the effect on human health
through the spread of disease-causing bacteria and viruses.
Initial efforts to control human wastes evolved from the need to
prevent the spread of diseases. Although untreated wastewa-
ter contains many billions of bacteria per gallon, most of these
are not harmful to humans, and some are even helpful in
wastewater treatment processes. However, humans who have
a disease which is caused by bacteria or viruses may dis-
charge some of these harmful organisms in their body wastes.
Many serious outbreaks of communicable diseases have been
traced to direct contamination of drinking water or food
supplies by the body wastes from a human disease carrier.
Some known examples of diseases which may be spread
through wastewater discharges are

Diseases
Fortunately these bacteria that grow in the intestinal tract of
diseased humans are not likely to find the environment in the
wastewater treatment plant or receiving waters favorable for
their growth and reproduction. Although many of these
PATHOGENIC BACTERIA9 are removed by natural die-off dur-
ing the normal treatment processes, sufficient numbers can
remain to cause a threat to any downstream use involving
human contact or consumption. If these uses exist
downstream, the treatment plant must also include a DISIN-
FECTION10 process.
The disinfection process historically employed is the addition
of chlorine. In most cases proper chlorination of a WELL-
TREATED WASTE will result in essentially a complete kill of
these pathogenic bacteria. The operator must realize, how-
ever, that breakdown or malfunction of equipment could result
in the discharge at any time of an effluent which contains
pathogenic bacteria.
2.33 Other Effects
Some wastes adversely affect the clarity and color of the
receiving waters, making them unsightly and unpopular for rec-
reation.
Many industrial wastes are highly acid or alkaline (basic),
and either condition can interfere with aquatic life, domestic
use, and other uses. An accepted measurement of a waste's
acid or alkaline condition is its p/-/.11 Before wastes are dis-
charged, they should have a pH similar to that of the receiving
water.
Waste discharges may contain toxic substances, such as
heavy metals or cyanide, which may affect the use of the re-
ceiving water for domestic purposes or for aquatic life. Plant
effluents chlorinated for disinfection purposes may have to be
dechlorinated to protect receiving waters from the toxic effects
of residual chlorine.
Taste- and odor-producing substances may reach levels in
the receiving water which are readily detectable in drinking
water or in the flesh of fish.
Treated wastewaters contain NUTRIENTS12 capable of en-
couraging excess algae and plant growth in receiving waters.
These growths hamper domestic, industrial, and recreational
uses. Conventional wastewater treatment plants do not re-
move a major portion of the nitrogen and phosphorus nutrients.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 23.
2.3C Where do the disease-causing bacteria in wastewater
come from?
2.3D What is the term which means "disease-causing"?
2.3E What is the most frequent means of disinfecting treated
wastewater?
2.4 SOLIDS IN WASTEWATER (Fig. 2.1)
One of the primary functions of a treatment plant is the re-
moval of solids from wastewater.
9 Pathogenic Bacteria (path-o-JEN-nick). Bacteria, viruses or cysts which can cause disease. There are many types of bacteria which do
NOT cause disease and which are NOT called pathogenic. Many beneficial bacteria are found in wastewater treatment processes actively
cleaning up organic wastes.
10 Disinfection (dis-in-FECK-shun). The process designed to kill most microorganisms in wastewater, including essentially all pathogenic
(disease-causing) bacteria. There are several ways to disinfect, with chlorination being most frequently used in water and wastewater
treatment plants. Compare with STERILIZATION.
11 pH. Technically, this is the logarithm of the reciprocal of the hydrogen-ion concentration, which is explained in Chapter 16, "Laboratory
Procedures and Chemistry." For now, It Is sufficient to understand that pH expresses the intensity of the acid or alkaline condition of a liquid.
The pH may range from 0 to 14, where 0 is most acid and 14 Is most alkaline, and 7 is neutral. Most natural waters have a pH between 6.5
and 8.5.
12 Nutrients. Substances which are required to support living plants and organisms. Major nutrients are carbon, hydrogen, oxygen, sulfur,
nitrogen and phosphorus. Nitrogen and phosphorus are difficult to remove from wastewater by conventional treatment processes because
they are water soluble and tend to recycle. Also see NUTRIENT CYCLE.

-------
Waste Treatment 19
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W.9/4
fllSSOVVCP
SOW PS
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zenueASLt
SOUPS
P|44-OlVfcp
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jze-4i vu&
-fofAL 4<0LlP£
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-^tnl/imuugr gfc-f^e-4AM&A4 mg/17
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urge by v^ht*
4u4PeMt?et7
NOMflLfePA&L^
R&4tc7ue-
F/'fif. 2.1 Typical composition of solids in raw wastewater
(floatable solids not shown)
2.40 Types of Solids
In Section 2.2 you read about the different TYPES of pollu-
tion: organic, inorganic, thermal, and radioactive. For a normal
municipal wastewater which contains domestic wastewater as
well as some industrial and commercial wastes, the concerns
of the treatment plant designer and operator usually are to
remove the organic and inorganic SUSPENDED SOLIDS, to
remove the DISSOLVED ORGANIC SOUDS (the treatment
plant does little to remove DISSOLVED INORGANIC SOLIDS),
and to kill the PATHOGENIC ORGANISMS by disinfection.
THERMAL and RADIOACTIVE wastes require special treat-
ment processes.
Since the main purpose of the treatment plant is removal of
solids from the wastewater, a detailed discussion of the types
of solids is in order. The figure above will help you understand
the different terms.
2.41 Total Solids
For discussion purposes assume that you obtain a one-liter
sample of raw wastewater entering the treatment plant. Heat
this sample enough to evaporate all the water and weigh all the
solid material left (residue); it weighs 1000 milligrams. Thus,
the TOTAL SOLIDS concentration in the sample is 1000 millig-
rams per liter (mgIL). This weight includes both DISSOLVED
and SUSPENDED solids.
2.42 Dissolved Solids
How much is dissolved and how much is suspended? To
determine this you could take an identical sample and filter it
through a very fine mesh filter such as a membrane filter or
fiberglass. The suspended solids will be caught on the filter,
and the dissolved solids will pass through with the water. You
can now evaporate the water and weigh the residue to deter-
mine the weight of DISSOLVED SOLIDS. In the figure above
the amount is shown as 800 mg/L The remaining 200 mgIL is
suspended solids. Dissolved solids are also called FILTERA-
BLE RESIDUE.™
2.43 Suspended Solids
Suspended solids are composed of two parts: settleable and
nonsettleable. The difference between settleable and nonset-
tleable solids depends on the size, shape, and weight per unit
volume of the solid particles; large-sized particles tend to settle
more rapidly than smaller particles. The amount of settleable
solids in the raw wastewater should be estimated in order to
design settling basins (primary units), sludge pumps, and
sludge handling facilities. Also, measuring the amount of set-
tleable solids entering and leaving the settling basin allows you
to calculate the efficiency of the basin for removing the settle-
able solids. A device called an IMHOFF CONE™ is used to
measure settleable solids in milliliters per liter, ml IL. (The
example in the figure above shows a settleable solids concen-
tration of 130 mg/L. The settled solids in the Imhoff Cone had
to be dried and weighed by proper procedures to determine
their weight.)
You may calculate the weight of nonsettleable solids by sub-
stracting the weight of dissolved and settleable solids from the
weight of total solids. In the figure above the nonsettleable
solids concentration is shown as 70 mgIL. Suspended solids
are also called NONFILTERABLE RESIDUE.13
,3 "Standard Methods" (also Chapter 16, Section 16.5, "Laboratory Procedures for NPDES Monitoring") defines FILTERABLE
residue as solids that PASS THROUGH a filter and nonfilterable residue as those solids that DO NOT PASS THROUGH a filter.
14 Imhoff Cone. A clear, cone-shaped container marked with graduations. The cone Is used to measure the volume of settleable
solids In a specific volume of wastewater.

-------
20 Treatment Plants
TREATMENT
PLANT
DISCHARGE
RECEIVING
STREAM
NITRATE
(NO3) IN
EFFLUENT
ALGAE
TAKES
UPNO3
FISH EAT
ALGAE &
PRODUCE
AMINO ACIDS,
UREA &
ORGANIC
RESIDUES
FISH DIE &
NITROGEN
COMPOUNDS
CONVERTED
TO AMMONIUM
(NHj)
„ IN THE PRESENCE
OF DISSOLVED
OXYGEN IN THE
WATER. AMMONIUM-
(nhJ)
- NITRITE ¦
(NOj)
>• NITRATE
(NOJg.
CYCLE
REPEATS
Fig. 2.2 Simplified illustration of nitrogen cycle
2.44 Organic and Inorganic Solids
For total solids or for any separate type of solids, such as
dissolved, settleable, or nonsettleable, the relative amounts of
organic and inorganic matter can be determined. This informa-
tion is important for estimating solids handling capacities and
for designing treatment processes for removing the organic
portion in waste. The organic portion can be very harmful to
receiving waters.
2.45 Floatable Solids
There is no standard method for the measurement and
evaluation of floatable solids. Since treatment units are de-
signed to remove these solids in raw wastewater and treated
effluent. Floatable solids are undesirable in the plant effluent
from an aesthetic viewpoint because the sight of floatables in
receiving waters indicates the presence of inadequately
treated wastewater.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 23.
2.4A An Imhoff Cone is used to measure - solids.
2.4B Why is it necessary to measure settleable solids?
2.4C Total solids consist of and solids,
both of which contain organic and inorganic matter.
2.5 NATURAL CYCLES (Fig. 2.2)
When the treated wastewater from a plant is discharged into
RECEIVING WATERS15 such as streams, rivers or lakes, natu-
ral cycles in the aquatic (water) environment may become up-
set. Whether any problems are caused in the receiving waters
depends on the following factors:
1. Type or degree of treatment,
2. Size of flow from the treatment plant,
3. Characteristics of wastewater from treatment plant,
4. Amount of flow in the receiving stream or volume of receiv-
ing lake that can be used for dilution,
5. Quality of the receiving waters,
6. Amount of mixing between EFFLUENT16 and receiving
waters, and
7. Uses of receiving waters.
Natural cycles of interest in wastewater treatment include
the natural purification cycles such as the cycle of water from
evaporation or TRANSPIRATION17 to condensation to precipi-
tation to runoff and back to evaporation, the life cycles of aqua-
tic organisms, and the cycles of nutrients. These cycles are
occurring continuously in wastewater treatment plants and in
receiving waters at different rates depending on environmental
conditions. Treatment plant operators control and accelerate
these cycles to work for their benefit in treatment plants and in
receiving waters rather than have these cycles cause plant
operational problems and disrupt downstream water uses.
NUTRIENT CYCLES18 are a special type of natural cycle
because of the sensitivity of some receiving waters to nut-
rients. Important nutrients include carbon, hydrogen, oxygen,
sulfur, nitrogen and phosphorus. All of the nutrients have their
own cycles, yet each cycle is influenced by the other cycles.
These nutrient cycles are very complex and involve chemical
changes in living organisms.
To illustrate the concept of nutrient cycles, a simplified ver-
sion of the nitrogen cycle will be used as an example. A
wastewater treatment plant discharges nitrogen in the form of
nitrate (NO-j~Jin the plant effluent to the receiving waters. Algae
take up the nitrate and produce more algae. The algae are
eaten by fish which convert the nitrogen to amino acids, urea
and organic residues. If the fish die and sink to the bottom,
15 Receiving Water. A stream, river, lake, or ocean Into which treated or untreated wastewater is discharged.
18 Effluent (EF-lu-ent). Water or other liquid - raw, partially or completely treated - flowing FROM a basin, treatment process, or treatment
plant.
17 Transpiration (TRAN-spear-RAY-shun). The process by which water vapor Is lost to the atmosphere from living plants.
18 Nutrient Cycle. The transformation or change of a nutrient from one form to another until the nutrient has returned to the original form, thus
completing the cycle. The cycle may take place under either aerobic or anaerobic conditions.

-------
Waste Treatment 21
these nitrogen compounds can be converted to ammonium
(NH^.In the presence of dissolved oxygen and special bac-
teria, the ammonium is converted to nitrite (NO,), then to nit-
rate (NO 3), and finally the algae can take up tne nitrate and
start the cycle all over again.
If too much nitrogen is discharged to receiving waters, too
many algae could be produced. Water with excessive algae
can be unsightly. Bacteria decomposing dead algae from oc-
casional die offs can deplete the dissolved oxygen and cause a
fish kill. Thus, the nitrogen cycle has been disrupted, as well as
the other nutrient cycles. If no dissolved oxygen is present in
the water, the nitrogen compounds are converted to am-
monium (NH 4), the carbon compounds to methane (CH4), and
the sulfur compounds to hydrogen sulfide (H2S). Ammonia
(NH3) and hydrogen sulfide are odorous gases. Under these
conditions the receiving waters are SEPTIC;19 they stink and
look terrible. Throughout this manual you will be provided in-
formation on how to control these nutrient cycles in your treat-
ment plant in order to treat wastes and to control odors, as well
as to protect receiving waters.
2.6 NPDES PERMITS (Fig. 2.3)
NPDES stands for National Pollutant Discharge Elimination
System. NPDES permits are required by the Federal Water
Pollution Control Act Amendments of 1972 with the intent of
making the Nation's waters suitable for swimming and for fish
and wildlife. The permits regulate discharges into navigable
waters from all point sources of pollution, including industries,
municipal treatment plants, large agricultural feed lots and re-
turn irrigation flows. An industry discharging into municipal col-
lection and treatment systems need not obtain a permit but
must meet certain specified pretreatment standards. These
permits may outline a schedule of compliance for a wastewater
treatment facility such as dates for the completion of plant
design, engineering, construction and/or treatment process
changes. Instructions for completing NPDES reporting forms
and the necessary forms are available from the regulatory
agency issuing the permit.
Your main concern as an operator is the effluent (discharge)
limitations specified in the NPDES permit for your plant. The
permit may specify monthly average and maximum levels of
settleable solids, suspended solids (nonfilterable residue),
biochemical oxygen demand (BOO)20 and the most probable
number (MPN) of COLIFORM21 group bacteria. Larger plants
must report effluent temperatures because of the impact of
temperature changes on natural cycles. Also, average and
maximum flows may be identified as well as an acceptable
range of pH values. Almost all effluents are expected to con-
tain virtually no substances which would be toxic to organisms
in the receiving waters. The NPDES permit will specify the
frequency of collecting samples and the methods of reporting
the results. Details on how to comply with NPDES permits will
be provided throughout this manual.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 23.
2.5A Why should an operator have an understanding of natu-
ral cycles?
2.5B What can happen when nutrient cycles are disrupted
and there is no dissolved oxygen in the receiving water?
2.6A What does NPDES stand for?
2.7 ADDITIONAL READING
For a detailed discussion of the physical and chemical com-
position of wastewater, you may wish to refer to the following
sources:
1. MOP 11, Chapter 3, "Characterization of Wastewater*."
2. NEW YORK MANUAL, Chapter 1, "Sewage."
3. TEXAS MANUAL, Chapter 1, "Wastewater, Its Composi-
tion, Chemistry and Biology."
4. TREATMENT OBJECTIVES FOR OPERATING WATER
AND WASTEWATER TREATMENT PLANTS, by J.C.
Meredith, Deeds & Data, WPCF, August 1977.
* Actual chapter number and title may depend on edition.
2.8 REVIEW
In this chapter you have read why it is necessary to treat
wastewater, something about the types of waste discharges
and their effects, and a brief description of the different kinds of
solids in wastewater. This is intended to be only a general
discussion of these subjects; you will find more detail in later
chapters.
You are now ready to go on to Chapter 3 which deals with a
description of the basic elements of the wastewater collection
and treatment systems. Chapter 3 actually begins the discus-
sion of HOW to treat wastewater. Chapter 2 has told you WHY
you need to do so.
<3 w/wv y wow 0>
•GO
19 Septic (SEP-tlck). This condition is produced by anaerobic bacteria. If severe, the wastewater turns black, gives off foul odors, contains
little or no dissolved oxygen and creates a heavy oxygen demand.
20 Biochemical Oxygen Demand (BOD). The rate at which microorganisms use oxygen in water or wastewater while stabilizing decomposa-
ble organic matter under aerobic conditions. In decomposition, organic matter serves as food for the bacteria and energy results from its
oxidation.
21 Coliform (COAL-i-form). One type of bacteria. The presence of coliform-group bacteria is an indication of possible pathogenic bacterial
contamination. The human intestinal tract is one of the main habitats of coliform bacteria. They may also be found in the intestinal tracts of
warm-blooded animals, and In plants, soil, air, and the aquatic environment. Fecal conforms are those conforms found in the feces of various
warm-blooded animals; whereas the term "coliform" also includes other environmental sources.

-------
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to
MONTHLY OPERATION REPORT OF WASTEWATER TREATMENT FACILITY
STABILIZATION PONDS
NAME OF FACILITY
MAX PERMIT CONDITION
S*r.d to MINNESOTA POLLUTION CONTROL AGENCY
1935 W£ST COUNTY KOAO 8 2
ftOSEVILLE, MINNESOTA 55113
ATTN: COMPLIANCE ft ENFORCEMENT SECTION
REPORTED FREQUENCY OF ANALYSIS
PERMIT CONDITION FREQUENCY" Of ANALYSIS
REPORTED SAMPLE TYPE
PERMIT CONDITION SAMPLE TYPE
TYPE OF POND (PRIMARY, SECONDARY, AERATED, ETC.)

POND

ACRES

CRES

WEEK OF THE MONTH
1 at
2 nd
3 "S
4 th
5 th
i at
2nd
3rd
4 rh
5th
1 at
2 nd
3rd
4 th
5th
1 DATE OF TEST OR OBSERVATION

2. ODOR (YES OR NO )

9. AQUATIC PLANTS (% OF COVERAGE, TYPE}

4. FLOATING NATS (% OF COVERAGE , TYPE )

5. PONO WATER DEPTH (NEAREST INCH)

«. MUSKRATS. RODENTS ETC. (YES OR NO )

7. DIKE CONDITION (EROSION ETC.)

$. ICE COVER (%
GENERAL
OF COVERAGE)