United States Region 10 91 0979Ut> I
5711 Environmental Protection 1200 Sixth Avenue
Agency Seattle WA 98101
September 1978
Waste water Treatment Plant
Design Guidelines
For
Operability, Flexibility
And
Maintainability
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TABLE OF CONTENTS
Section Page
1. INTRODUCTION 4
1.1 Design Summary 5
2. GENERAL 7
2.1 Plans 7
2.2 Specifications 7
2.3 Revisions to Approved Plans 10
3. DESIGN CONSIDERATION 11
3.1 Hydraulic Loading 11
3.2 Organic Loading 11
3.3 General 11
4. PROCESS UNIT DESIGN 16
4.1 Reliability 16
4.2 Influent/In-Plant Lift Station 16
4.3 Solids Grinding Equipment 16
4.4 Grit Removal 18
.4.5 Primary Clarifier 19
4.6 Secondary Clarifier 2Q
4.7 Aeration Tanks 22
4.8 Activated Sludge "Package Plants" 25
4.9 Activated Biofliters 25
4.10 Aerobic Digestion 26
4.11 Anaerobic Digestion 27
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TABLE OF CONTENTS
Section Page
4.12 Disinfection 30
4.13 Lagoon-Oxidation Ponds 30
4.14 Laboratory Facilities 31
4.15 Metering 32
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WASTEWATER TREATMENT PLANT DESIGN GUIDELINES
for
OPERABILITY, FLEXIBILITY AND MAINTAINABILITY
1. INTRODUCTION
Many municipal wastewater treatment plants have not met their
designed treatment efficiencies. This has been in part due to
untrained plant personnel and in part due to designs which can not;"
for various reasons, be adequately operated and/or maintained.
Operator training programs have been and are being initiated to
alleviate the problem of untrained operations personnel. These
guidelines are intended to supplement recognized design guidelines"^'
such as ASCE-MEP-No. 36 "Sewage Treatment Plant Design," to insure
that municipal wastewater treatment plants are designed in a manner
which provides for operability, flexibility, and maintainability.
These design guidelines will be used by EPA Region 10 and state
agencies in the review of plans and specifications for construction
of municipal wastewater treatment facilities constructed with the
aid of federal funds.
DEVIATIONS FROM THESE GUIDELINES WILL BE CONSIDERED ON A CASE-BY-
CASE BASIS WHEN IT CAN BE SHOWN THAT THE DEVIATIONS WILL PROVIDE FOR
EFFICIENT AND EFFECTIVE OPERABILITY, FLEXIBILITY, AND MAINTAINABILITY.
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1.1 Design Summary
A design summary shall accompany the plans and specifi-
cations when submitted for EPA or state agency approval. A
preliminary draft design summary should be submitted prior to
10 percent completion of design. The summary shall include,
but not be limited to,the following:
a. Hydraulic and organic loadings—minimum, average,
maximum and effect on each process unit for both
dry and wet weather flows and initial start-up.
b. Quantity and type of industrial wastes which the
plant is designed to treat, and what factors of
design are affected by the industrial wastes.
c. Process unit dimensions and volumes.
d. Flow rates and velocities within process compart-
ments and piping at minimum, average, and maximum
loading for both dry and wet weather flows and
initial start-up.
e. Detention time for each process compartment at
minimum, average, and maximum flow rates for both
dry and wet weather flows and initial start-up.
f. Expected ranges of BOD,- and/or COD, and S.S.
concentrations of all process side streams.
g. Expected mixed liquor suspended solids (MLSS)
concentrations, food/mass (F/M) ratios, and mean
cell residence time (MCRT).
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h. Recycle flow rates—minimum, average, and maximum
for both dry and wet weather flow conditions and
initial start-up.
i. List chemical additives and their control.
j. List or denote in schematic form physical controls
for each process compartment (e.g., gates, valves,
weirs, measuring devices, etc.).
k. Removals—effluent BODg and/or COD, and S.S.
concentrations for each process unit handling solid
and liquid fractions.
1. Process diagrams including:
1. Process units.
2. Interconnecting piping with direction of flow.
3. Flexibility including direction of flow.
4. Hydraulic profiles at minimum, average, and
maximum flows for both dry and wet weather and
initial start-up conditions.
m. List of physical and laboratory control tests needed
to control each treatment unit.
n. Adequate description of any features not otherwise
covered by the plans or specifications.
o. Estimated staffing requirements, both initial and
at design capacity for the entire facility, with a
per shift breakdown when applicable.
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2. GENERAL
2.1 Plans
The plans shall be drawn to a scale which will allow all
necessary information to be plainly shown. Datum used shall
be indicated. Locations and logs of test borings, when made,
shall be shown.
Detail plans shall contain plan view, elevations, sec-
tions, and supplementary views which, in conjunction with the
specifications and general layouts, provide sufficient infor-
mation for the construction of the treatment facilities. The
plans must include dimensions and relative elevations of
structures; the location and outline form of equipment; loca-
tion and size of valves, clean outs, and piping; water levels;
slopes of piping and floors including tank bottoms; sump
locations; ground elevations; hydraulic profiles; design
parameters; and other information as necessary to fully des-
cribe intended works.
2.2 Specifications
Complete technical construction specifications shall
accompany the plans. The specifications shall include, but
not be limited to, the following:
2.2.1 All construction information not shown in detail on the
plans which is necessary to indicate design requirements such
as the quality of materials, workmanship, and fabrication of
the project and the type, size, strength, operating
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characteristics, and rating of equipment, including machinery,
valves, piping, and jointing of pipes; electrical apparatus,
electronic and pneumatic control apparatus, wiring, and
meters; laboratory fixtures and equipment; operating tools;
safety equipment; construction materials; miscellaneous
appurtenances; chemicals; instructions for testing materials
and equipment as necessary to meet design standards; operating
tests for the completed facility and/or separate units (wet
testing is preferred); and start-up training requirements for
the operating personnel for specific units as applicable.
2.2.2 The specifications shall require one (1) set of special
tools for each different piece of equipment along with a list
by name and part numbers of the special tools. A special
tool is defined as a tool necessary to disassemble, assemble,
or adjust the piece of equipment and which would not normally-
be found in the treatment plant or municipal maintenance
shop; duplication of tools must be avoided.
2.2.3 The specifications shall require equipment identifica-
tion/specification tags to be composed of materials which
will be durable in the environment to which they will be
subjected. The tags should have stamped or cut lettering and
be screwed, riveted, or bolted to the equipment.
2.2.4 A minimum of two (2) sets of manufacturer's operation and
maintenance (O&M) manuals will be provided with each piece of
equipment. The manuals will be delivered to the design
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engineer within sixty (bO) days after the equipment purchase
order is signed. Where a manual also contains information on
equipment not installed, the extraneous information will be
marked out to avoid confusion.
2.2.5 The equipment manufacturer and/or vendor will provide
for each piece of equipment a complete maintenance summary
which wiII include:
a. Name of manufacturer with address and phone
number of nearest representative.
b. Complete identification/specification tag data
including serial number of equipment.
c. A list of spare parts including part numbers
and other information needed to order parts. .
d. A complete listing of routine maintenance,
including time intervals for lubrication,
adjustments, etc., and a list of acceptable
equivalent lubricants from at least three (3)
different major manufacturers whose products
are locally available.
e. Weight of individual components of each piece
of equipment weighing over 4b kg (100
pounds).
It is recommended that the designer develop a suitable
form to obtain the above information. Manufacturer and/or
vendor response such as "see instruction manual" will not be
acceptable.
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2.2.6 The specifications shall indicate clear lines of respon-
sibility where components of a unit are provided by different
manufacturers, vendors, etc. Also guaranteed performance of
equipment and instrumentation will be required.
2.2.7 The specifications will indicate the ambient conditions
and maintenance acceptable for equipment in storage and in
place during construction prior to plant start-up.
2.2.8 The specifications shall provide a written program for
meeting the level of treatment required of the owner by the
state agency during construction. Treatment plant personnel
should have input in developing the program and in approving
deviations by the contractor. Deviations by the contractor
will need approval by the state agency prior to their
initiation.
2.3 Revisions to Approved Plans and Specifications
All deviations from the approved plans and specifications
affecting capacity, flow, operation of units or compartments,
methods of process control, or level of treatment of existing
facilities shall be approved in writing by the state agency
(and/or EPA where required by regulation) before such changes
are made.
2.3.1 At least one set of "As Built" plans and design summary
(Section 1.1) will be provided to the state regulatory agency
and two sets to the municipality within 30 days of completion
of construction.
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3. DESIGN CONSIDERATION
3.1 Hydraulic Loading
Where peak waste flows are expected to be greater than
2h times design flow, some form of flow equalization should
.be considered when needed to prevent significant reduction of
treatment efficiency.
3.2 Organic Loading
The organic design of the treatment units will be ad-
dressed in the same manner as hydraulic loading. Shock
loading, industrial wastes, and process unit return streams
must be given careful consideration.
3.3 General
3.3.1 Treatment units shall be arranged for operating conven-
ience, flexibility and maintainability, and to facilitate
installation of planned future units.
3.3.2 Control rooms should be designed and located to afford
operators a commanding view of the plant and grounds as is
practical.
3.3.3 All large buildings should have man doors on all sides,
where practicable.
3.3.4 The prevailing wind should be considered when laying out
the process units to prevent aerosols from blowing towards
control and office buildings and to direct scum towards scum
collection equipment.
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3.3.5 Process units should be located to provide access by
locally available mobile equipment (cranes, front end loaders,
trucks, etc.).
3.3.6 Process units should be designed to provide easy access
for sampling.
3.3.7 Process tanks should have a minimum free-board of 0.6 m
(2 feet).
3.3.8 When the outside of the peripheral wall of process tanks,
channels, chambers, etc., is greater than 1.2 m (4 feet)
above ground level or above water, a catwalk at least 0.76 m
(2% feet) wide should be provided where access is needed.
3.3.9 Treatment compartments shall be designed in such a manner
as to allow each individual compartment to be removed from
service and/or dewatered without the need of removing other
compartments from service.
3.3.10 Inside corners of treatment units should be filleted as
needed to enhance circulation, reduce dead areas, and prevent
deposition of solids.
3.3.11 Process units designed for parallel operation should
have an adjustable method of equalizing or dividing the waste
flows entering the units. Splitter boxes, channels, etc.,
should be designed to avoid creating septic conditions in
unused portions or areas.
3.3.12 Process units, channels, etc., shall have dewatering
sumps or drains to facilitate complete dewatering and
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cleaning. The drains must return to a process unit located
upstream of the unit being dewatered. Where practicable,
dewatering facilities should be capable of dewatering each
unit within four (4) to eight (8) hours.
3.3.13 Bottoms (floors) of process units, channels, etc., should
slope toward unit sumps or drains to facilitate cleaning when
units are dewatered.
3.3.14 Building, gallery, dry well, etc., floors should slope
toward floor drains.
3.3.15 Floor drains or sumps with sump pumps should be strate-
gically located near sources of spills in buildings,
galleries, dry wells, etc.
3.3.16 OSHA safety requirements shall be incorporated into all
treatment facility designs. In addition, motor kill switches
should be installed adjacent to motors where a breaker or
control switch is not within sight of the unit.
3.3.17 Exterior equipment pads, walkways, etc., should be ade-
quately sloped to prevent standing water. Surfaces should be
slip resistant. Slip resistance will be required where oil
may be present.
3.3.18 All piping should be painted according to the standard
color code recommended by the Water Pollution Control Federa-
tion, except as otherwise required by OSHA.
3.3.19 Large plants should have a loading dock on the plant
site for loading and unloading delivery trucks. Overhead
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clearance must be sufficient to accommodate enclosed
transport trucks.
3.3.20 Mechanical treatment plants larger than 189 cu m/day
(0.05 MGD) should have storage areas for spare parts,
cleaning agents, etc., and a shop area for routine preventive
maintenance of the plant equipment.
3.3.21 Every reasonable effort should be made to standardize
equipment to minimize confusion and maximize utilization of
spare parts.
3.3.22 Valves located higher than 1.8 m (6 feet) above the
floor level should have mechanical operators that provide for
operation of the valve from an elevation of no higher than
1.5 m (5 feet) from floor level.
3.3.23 Valves should be marked with name or number by permanent
tags.
3.3.24 Mechanical equipment (pumps, motors, blowers, etc.)
where individual components weigh in excess of 45 kg (100
pounds) should be arranged to allow for a means of
mechanically lifting the unit for the purpose of removal,
installation, and/or maintenance. Weight of individual
components will be listed on the maintenance summary sheet
(Section 2.2.5).
3.3.25 Mechanical eqi/ipment requiring routine maintenance
should have a minimum of 0.6 m (2 feet) clearance on all
sides of the equipment where access for maintenance is
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needed. Take-down couplings should be used for inlet and
outlet pipe connections. A convenient method of removing
equipment from buildings, tunnels, etc., should be considered.
3.3.26 Oil filled stationary equipment (hydraulic controls,
pumps, blower gear drives, etc.) should have built-in catch
basins or channel grooves to contain any leaking oil. Units
will have drain valves with safety plugs; drains should be
piped for access to drain pans.
3.3.27 Exposed water lines, seal water tubing, pneumatic and
hydraulic control systems, etc., should be protected from
freezing where ambient temperatures are below freezing.
3.3.28 Electrical controls should be protected from splash
during wash down operations.
3.3.29 Critical process units should have malfunction alarms
and, where possible, the alarms should be incorporated into a
central dispatch system that is monitored 24 hours per day.
3.3.30 Portable lighting should be provided to allow for
emergency equipment maintenance and repair at night.
3.3.31 Wash water system pressure should be a minimum of 3.5
kg/cm2 (50 PSI) at point of use; 4.9 to 6.3 kg/cm2 (70 -
90 PSI) is preferred.
3.3.32 Hose bibs should be located to allow washdown of process
units with no more than 15.24 m (50 feet) of hose. A 2.54 cm
(1 inch) diameter hosebib should be considered.
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4. PROCESS UNIT DESIGN
4.1 Reliability
Design guidelines for reliability are provided in the
following technical bulletins:
1. Design Criteria for Mechanical, Electric, and Fluid
System and Component Reliability, EPA-430-99-74-001.
2. Protection of Shellfish Waters, EPA/9-74-010.
4.2 Influent/In-Plant Lift Stations
4.2.1 Influent and in-plant lift stations should be sized and
controlled in such a manner as to prevent adverse hydraulic
shock loading of subsequent treatment units. Generally
in-plant on-off pumping of plant flow should not precede
clarifiers.
4.2.2 Water sealed pumps should be considered where large
amounts of grit are present in the waste flow. A method of
removing scum and grit from the wet well should be considered.
4.2.3 Pump discharge piping should be designed to preclude
settling of solids and grit into discharge riser of pumps not
in use.
4.2.4 Dehumidifers or adequate ventilation should be provided
in pump rooms to minimize corrosion.
4.3 Solids Grinding and Screening Equipment
4.3.1 When only one grinding device (comminutor, barminutor,
etc.) or mechanically cleaned screen is used, it should be
designed to carry the maximum expected flow. The design
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shall incorporate a means of bypassing the grinding/screen-
ing device through a bar screen for maintenance purposes and
include an emergency overflow weir whereby flows would bypass
through the bar screen prior to overtopping or flooding the
primary grinding/screening device. Where more than one
grinding/screening device is used, the sizing and bypassing
capability will be in accordance with reliability
requirements (Section 4.1).
4.3.2 Rock traps should be considered in all channels upstream
of grinding devices. The trap should be 0.3 m (1 foot) deep
and the full width of the channel. Accessibility and method
of cleaning should be incorporated into the bypassing scheme
(Section 4.3.1.).
4.3.3 All grinding and screening devices will be located to
provide easy access for maintenance. Where possible, narrow
channels should be avoided; channels must be wide enough to
allow personnel to work.
4.3.4 When bar screens are located so that the elevation at
which the debris is manually removed is more than 0.9 m (3
feet) below ground level, a mechanical method of lifting the
debris should be considered. In all cases, a debris
dewatering platform should be provided.
4.3.5 The channel ahead of the bar screen should be designed
to assure that equal hydraulic velocity is distributed across
the bar screen.
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4.3.6 Hand cleaned bar screens should have a slope with the
horizontal between 30 degrees and 45 degrees.
4.3.7 The design must consider the ultimate disposal of
screenings.
4.4 Grit Removal
4.4.1 Grit removal facilities should be provided for
mechanical treatment facilities utilizing anaerobic sludge
digestion and/or when the collection system is known to have
abnormal infiltration/inflow and/or combined sanitary/storm-
water systems.
4.4.2 All gravity grit removal chambers will incorporate a
method of hydraulic velocity control,' preferably adjustable.
4.4.3 All manually cleaned chambers should incorporate
parallel units to facilitate cleaning. When the bottom of
the chamber is more than 0.9 m (3 feet) below ground level, a
mechanical method of lifting the grit should be considered.
A drive or walkway should be provided to facilitate the
vehicle used to haul the grit.
4.4.4 Mechanically cleaned chambers will have a bypass or
sufficient duplication to allow dewatering of individual
units.
4.4.5 Grit storage-dewatering (draining) facilities should be
considered an integral part of all grit removal facilities
and be protected from freezing or a means provided to prevent
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ice build-up where the ambient temperature is below freezing
for extended periods.
4.4.6 All facilities not provided with positive hydraulic
velocity control should contain grit washing equipment.
4.4.7 All aerated grit removal facilities must have a metered
and adjustable air supply.
4.4.8 The design should insure that grit will be removed from
all portions of the grit chamber floor.
4.5 Primary Clarifier
4.5.1 The inlet shall be designed to dissipate the inlet hy-
draulic velocity and to equally distribute the flow to reduce
short-circuiting.
4.5.2 Clarifier walkways, handrails, etc., should provide easy
access for maintenance and protection of personnel.
4.5.3 Overflow weirs should be adjustable to allow for future
re-leveling.
4.5.4 Clarifiers should have scum baffles ahead of the effluent
weirs. Facilities designed for flows of 378.6 m /day (0.1
MGD) and greater should have mechanical scum removal equip-
ment. A method of conveying the scum across the water sur-
face to the point of removal should be included, such as
water or air spray. Baffles should be designed to ensure
scum capture at minimum and maximum flow rates.
4.5.5 Provisions should be made to sample the sludge during
removal; a 3.81 cm (1 1/2 inch) minimum quick opening valve
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is recommended. A means of viewing the sludge is also
desirable.
4.5.6 Sludge removal lines should be a minimum of 15.24 cm (6
inches) in diameter. Each point of sludge withdrawal should
be individually valved.
4.5.7 Scum holding tanks should be provided with a method of
removing the excess water. The scum should be premixed with
sludge when discharged to anaerobic digesters. Scum piping
should be glass lined or equivalent.
4.5.8 Large scum sumps should have a mixing device (pneumatic,
hydraulic, or mechanical) to keep the scum mixed when being
pumped.
4.5.9 Scum pump start-stop switches should be located adjacent
to scum holding tanks. '
4.5.10 Launders should have flat interior bottoms and be
accessible for easy cleaning.
4.5.11 Since closely spaced multiple overflow weirs tend to
increase hydraulic velocities, their spacing should be
conservative.
4.5.12 Gravity sludge flow systems should have back-up pumping
capabilities.
4.6 Secondary Clarifier
4.6.1 Primary clarifier Section 4.5.1 to Section 4.5.11 shall
also apply to secondary claritiers except minimum size of
sludge piping.
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4.6.2 Lift stations located immediately upstream of secondary
clarifiers shall have flow-paced controls to reduce shock
loading.
4.6.3 Activated sludge, including all modifications of the
process, should be continuously removed from clarifiers.
Provisions for intermittent removal should also be
incorporated in small plants.
4.6.4 Provisions should be made to control the rate of sludge
withdrawal from each individual point of withdrawal. ' In
addition, provisions should be made to isolate each point of
withdrawal.
4.6.5 When two or more clarifiers are used, provisions shall
be made to control and measure the rate of sludge withdrawal
from each clarifier.
4.6.6 The rate of activated sludge withdrawal should be infi-
nitely variable from ten percent (10%) of plant average design
flow to the maximum designed sludge withdrawal rate without
plugging.
4.6.7 Circular clarifiers, 30.48 m (100 feet) in diameter and
larger, should have two sets of concentric launder troughs
and weirs separated by a distance of approximately 1/10 of
the clarifier diameter.
4.6.8 Square clarifiers with circular sludge withdrawal
mechanisms shall be designed such that corner hydraulic
velocities do not cause sludge carry over.
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4.6.9 Consideration should be given to removing activated
sludge from the effluent end of rectangular clarifiers.
4.6.10 A method of determining the activated sludge blanket
level should be available.
4.6.11 The up-flow rate shall not be greater than the surface
overflow rate at any location within the solids separation
zone of a clarifier.
4.6.12 Overflow weirs should be of the notched type; straight
edged weirs are not recommended.
4.6.13 Clarifiers following activated sludge should provide a
minimum of 3.65 m (12 feet) side wall water depth.
4.6.14 Designs should consider the possible need for future
modifications to add chemicals such as flocculants.
4.6.15 Large circular clarifiers require consideration of
hydraulic overloading of leeward weir due to wind action.
4.6.16 A method of foam control should be considered for all
inlet channels and feed wells in activated sludge systems.
4.7 Aeration Tanks
4.7.1 Aeration tank systems, except extended aeration, should
be designed to accommodate at least three (3) modes of opera-
tion (such as plug flow, complete mix, contact-stabilization,
step aeration, etc.). Two (2) modes of operation for extended
aeration systems larger than 1893 m /day (0.5 MGD) should
be considered.
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4.7.2 When two or more tanks are installed, both series and
parallel flow schemes should be available.
4.7.3 Where flows (return sludge and/or plant flow) enter
aeration tanks through two or more ports, a means of measuring
and control ling the flow rate at each entrance port should be
provided.
4.7.4 The aeration (mixing) devices used shall provide a mini-
mum of one foot per second hydraulic velocity throughout the
entire aeration tank at all times.
4.7.5 The air input rate shall be readily controllable and be
capable of maintaining the dissolved oxygen concentration
between one and three mg/1 in each aeration compartment at
all anticipated loadings, including the initial start-up
loading. (See EPA 600/2-77-032, "Design Procedures for
Dissolved Oxygen Control of Activated Sludge Processes" for
additional guidance.)
4.7.6 Air flow rate meters should be provided for each
aeration compartment in addition to a total air flow rate
meter for each group of blowers, compressors, etc.
4.7.7 A method of control ling the air rate to each aeration
tank should be provided.
4.7.8 Diffused air systems will be installed such that the
diffusers can be removed, inspected, and cleaned without
dewatering the aeration tank, except where the tank can be
dewatered without reducing treatment efficiency. A
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mechanical means of removing the diffuser header must be
provided when the procedure would present a safety or
equipment hazard. Consideration must be given to the weight
of the diffusers plus entrapped debris when being removed.
Adequate room must be provided for the mechanical removal
equipment.
4.7.9 A method of foam supression should be provided for all
aeration tanks.
4.7.10 Mechanical aeration systems should be protected from
freezing and a means provided to prevent ice build-up where
the ambient temperature is below freezing for extended
periods.
4.7.11 Where ambient temperatures are below freezing for ex-
tended periods of time, beams, catwalks, etc., should be lo-
cated and/or designed to preclude spray and foam from
freezing on their surfaces.
4.7.12 All modes of the activated sludge process will have a
positive method of measuring the return and waste sludge flow
rates. For plants of 378.6 rrr/day (0.1 MGD) and larger the
flow rate measuring devices should incorporate totalizing
capabilities.
4.7.13 All activated sludge plants will have sludge handling
facilities to accommodate waste activated sludge.
4.7.14 Adjustable aeration tank outlet weirs are desirable with
mechanical aerators.
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4.7.15 Aeration devices in small plants should have time clock
on-off control available.
4.7.16 Plants with initial flows of less than one-half design
should have at least two aeration basins.
4.7.17 Return and waste activitated sludge must be accessable
for sampling and should be visible at some point in the
system.
4.7.18 Separate return and waste sludge pumps should be
provided.
4.8 Activated Sludge "Package Plants"
4.8.1 All guidelines pertaining to activated sludge systems,
also apply to package plants. Systems smaller than 378.6
m3/day (0.1 MGD) may be exempt from sections 4.7.1, 4.7.3,
4.7.6, and 4.7.18.
4.8.2 Each process compartment shall be constructed with load
bearing walls to allow dewatering each process compartment
individually.
4.9 Activated Biofliters
4.9.1 All guidelines pertaining to activated sludge systems
will also apply to ABF systems when short term aeration is
included, except section 4.7.1. When short term aeration is
not included, sections 4.7.12, 4.7.13, 4.7.17 and 4.7.18 will
apply.
4.9.2 Fixed nozzle ABF towers should be divided into at least
two (2) separate units separated by a solid wall with
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appropriate valving to allow each unit to be independently
removed from service.
4.9.3 Direct recirdilation of the tower should be provided in
such a manner as to provide positive control of the recircu-
lation rate when the facility is subject to highly varying
load rates and/or initial start-up load is less than 50% of
design load.
4.9.4 A method of controlling the air flow rate through the
ABF tower should be provided.
4.9.5 All ABF systems should include short-term aeration
facilities.
4.9.6 Systems treating greater than 10 percent industrial
waste should have a means of flushing solids from the tower.
4.10 Aerobic Digestion
4.10.1 All guidelines pertaining to aeration tanks, except
sections 4.7.1, 4.7.2, 4.7.3, and 4.7.12, will also apply to
aerobic digesters.
4.10.2 Aerobic digestion systems in treatment plants designed
for flows of 1893 m3/day (0.5 MGD) and greater should
contain at least two compartments with provision for
alternate feed. A single compartment may be used in
conjunction with the extended aeration process.
4.10.3 A means of supernating (solids separation) shall be
provided.
4.10.4 Gravity sludge thickener solids and hydraulic design
loading criteria should be used for flow through gravity
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separation supernating facilities located in either a
separate compartment or a baffled area within the aerobic
digester.
4.10.5 The supernatant draw-off level should be adjustable in
either batch or flow through systems.
4.10.6 The supernatant should be returned to the waste stream
at the influent to the aeration tank or upstream.
4.11 Anaerobic Digestion
4.11.1 A gas meter with bypass should be provided to meter the
gas production from each primary digester. In addition, a
gas meter with bypass should be provided to meter the total
production and consumption at each point of use; e.g., boiler,
waste burner, etc. Only gas meters compatible with digester
gas shall be used.
4.11.2 Provisions should be made for gas sampling from each
digester.
4.11.3 Thermometers should be provided to show the temperature
in each digester. They should be located to show the
temperature of the active sludge zone and be removable for
checking and calibration without affecting operation of the
digester.
4.11.4 A high-low gas pressure alarm device should be incorpo-
rated in the gas piping near the digesters and at each vital
point of consumption; e.g., boiler, internal combustion
engine, etc.
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4.11.5 Measuring devices should be provided to indicate gas
pressure in each digester and at all points of consumption;
e.g., boiler, waste burner, etc. Where mechanical gauges are
used, diaphram protectors will be installed.
4.11.6 Each digester should have a vacuum/pressure relief valve
with flame trap. All gas piping must be sloped with a
condensate trap at each low point.
4.11.7 Easy access should be provided to each vacuum/pressure
relief valve, condensate trap, and flame trap with sufficient
room for maintenance. Drain lines from condensate traps
should be piped to floor drains or sumps.
4.11.8 All heated digesters should be provided with mixing
facilities. Mechanical or gas mixing is acceptable;
generally, mixing by liquid recirculation is inadequate by
itself.
4.11.9 Digester heating systems should be automatically con-
trolled.
4.11.10 A method of measuring the volume of sludge discharged
into each primary digester should be provided.
4.11.11 Adequate piping and valving will be provided to facili-
r
tate cleaning the digesters. It may be desirable for large
installations to permanently install the pumps necessary to
facilitate cleaning; whenever portable pumps are used, the
availability of such pumps will be indicated prior to
approval.
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4.11.12 All digesters should have side hatches to facilitate
cleaning operations. It is recommended that the bottom of
the hatch be located 1.52 m (5 feet) above the digester
floor, but not below exterior grade, with a minimum opening
of 0.91 m by 0.91 m (3 feet by 3 feet).
4.11.13 Digesters should have sufficient sludge withdrawal points
to maximize concentration of solids.
4.11.14 Digesters should have sufficient supernatant withdrawal
points and elevation control to minimize supernatant solids
concentrations.
4.11.15 Sludge handling shall be provided (such as drying beds,
holding tanks, lagoons, dewatering equipment and/or incinera-
tion equipment, or valves and piping for liquid hauling) so
that year-round disposal is available.
4.11.16 Overflow and gas pipes should be positioned to avoid
plugging with surface scum.
4.11.17 A means of adding chemical solutions into the digester
without opening the digester lid should be provided.
4.11.18 Sludge density must be considered in the selection of
pumps.
4.11.19 Timers or variable speed units should be used on raw
sludge pumps.
4.11.20 Extreme caution must be used in selecting pumps used for
pumping sludge containing significant quantities of grit.
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4.11.21 Sump pumps in sludge handling areas should be capable of
pumping sludge.
4.11.21 Sludge pumps should be positioned to have positive
suction head.
4.12 Disinfection
Disinfection facilities will be designed in accordance
with "Disinfection Chlorination, Design, Operation and Main-
tenance Guidelines," June 1977, U.S. EPA Region X.
4.13 Lagoons-Oxidation Ponds
4.13.1 A minimum of three cells should be used. The cells
should be interconnected in such a manner to provide for
series, parallel, and parallel series operation.
4.13.2 Grit removal facilities should be considered when the
collection system is known to have abnormal infiltra- ,
tion/inflow and/or combined sanitary/stormwater systems,,
4.13.3 Comminutors and/or bar screens should be provided when
the facility is serving dischargers that characteristically
contribute large volumes of debris, such as penal and mental
institutions, hospitals, resident schools, etc.
4.13.4 The liquid depth should be controllable, no greater than
15.24 cm (6-inch) increments, from 0.6 m (2 feet) to maximum
design depth, and provide for a maximum liquid elevation
reduction in the last cell of 5.08 cm (2 inches) per day.
4.13.5 All transfer structures should have submerged inlets.
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4.13.6 Cell inlets should be located down-wind from the outlet
structure, according to the prevailing wind direction.
4.13.7 Adequate piping and valving should be provided to allow
isolating and completely dewatering any individual cell
without draining into the receiving waters. Portable Dumps
and piping may be acceptable.
4.13.8 Effluent structures should provide for multi-level draw-
off from the final cell(s). The lowest draw-off at 30.48 cm
(12 inches) from the cell bottom with additional draw-offs at
30.48 cm (12-inch) increments up to 45.72 cm (18 inches)
below the highest operational level anticipated.
4.13.9 The space between dikes and fences should have
sufficient width to accommodate mowing equipment.
4.13.10 Nonfloating rip rap material should extend to the toe
of the inner dike.
4.13.11 Short circuiting should be reduced as practical by cell
shape or non-load bearing baffles.
4.13.12 Piping and valving-should be considered for recircula-
tion between ce-lls. Portable pumps and pipe may be
acceptable.
4.11.13 All cells should have staff gauges for liquid depth
measurement.
4.14 Laboratory Faci1it ies
4.14.1 All mechanical treatment plants will have laboratory
facilities with sufficient equipment to conduct operational
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control tests indicated in the design summary (Section 1.1).
Coliform testing by an off-site laboratory may be allowed on
a case-by-case basis. Laboratory facilities must be avail-
able to non-mechanical plants; on-site facilities are
recommended.
4.14.2 EPA-430/9-74-002, "Estimating Laboratory Needs for
Municipal Wastewater Treatment Facilities," June 1973, should
be used to determine the physical size, layout and ancillary
equipment (water, sinks, power, etc.) of the laboratory - —
facilities.
4.14.3 Safety equipment, such as eye wash stations, emergency
showers, first aid kits, and fire extinguishers, will be
required.
4.14.4 Storage of tools, lubricants, spare parts, etc., in
laboratories will not be allowed.
4.14.5 The laboratory should not be located in the same
building with mechanical equipment which may cause vibration
or excessive noise, such as blowers, pumps, etc., unless
adequate sound and vibration isolation is provided.
4.15 Metering
4.15.1 Mechanical plants greater than 378.6 m /day (0.1 MGD)
should have a flow measuring device incorporating a recording
chart and totalizer.
4.15.2 Mechanical plants 378.6 m3/day (0.1 MGD) and smaller
should have a flow measuring device incorporating a
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totalizer. Pump hour meters may be acceptable in some cases
if calibrated after installation.
4.15.3 Lagoons, ponds, etc., should have as minimum influent
and effluent flow measuring weirs; effluent flow totalizer
-capabilities are preferred.
,f.l5v4-;. The following side streams should have flow rate
indicators with totalizers (See Sections 4.7, 4.8, 4.9,
4.10, and 4,11):
a. Return activated sludge.
b. Waste activated sludge.
c. Sludge to anaerobic digesters.
d. ABF recirculation streams.
4.15.5 The following side streams should have flow rate
indicators:
a. Flows to parallel units.
b. Sludge thickeners—influent and supernatant.
c. Mechanical sludge dewatering units.
d. Air supply to each aeration basin.
4.15.6 Flow and air rate indicators should be located within
visual contact of flow and air rate controls.
4.15.7 Hydraulic velocities should be considered in the
location of flow measuring devices to assure calibration
curves match field conditions.
4.15.8 A method of calibration should be considered when
locating flow measuring devices.
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4.15.9 All lift station pumps should have hour meters.
4.15.10 Suction and discharge pressure gauge taps should be
considered for all pumps.
4.15.11 Process air systems should have a pressure indicator.
4.15.12 Large electric motors should have ampere meters.
4.15.13 All motors shall have ampere meters when the motor can
be overloaded by control changes. The ampere meter will be
located within visual contact of the controller.
4.15.14 Portable dissolved oxygen meters should be provided for
activated sludge plants and are recommended for all other
aerobic treatment plants. Two probes are recommended, one
for measuring D.O. in. process tanks and a separate probe with
attached stirring device for laboratory use.
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