EPA-43O-99-74-OOI
SUPPLIMENT TO FEDERAL GUIDELINES: DESIGN, OPERATION, AND
MAINTENANCE OF WASTEWATER TREATMENT FACILITIES
DESIGN CRITERIA FOR
MECHANICAL, ELECTRIC,
AND FLUID SYSTEM AND
COMPONENT RELIABILITY
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Water Program Operations
Washington, D.C. 20460
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TECHNICAL BULLETIN
DESIGN CRITERIA FOR MECHANICAL, ELECTRIC,
AND FLUID SYSTEM AND COMPONENT RELIABILITY
Supplement to Federal Guidelines for Design,
Operation, and Maintenance of Waste Water
Treatment Facilities
Office of Water Program Operations
U. S. Environmental Protection Agency
Washington, D. C. 20460
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price 85 cents
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FOREWORD
In response to the recent clean water legislation, this country
will undertake an unprecedented building program for new and
improved municipal wastewater treatment works. It is the
responsibility of the EPA to ensure that the Federal funds
authorized under Title II of PL 92-500 for this program will
be justifiably spent. Accordingly, we must ensure that these
works have been designed with a high degree of technical
excellence and will operate effectively day in and day out.
As a part of this effort, this Technical Bulletin provides
a national standard to help ensure that unacceptable degradation
of the works' effluent does not occur from time to time as
a result of periodic maintenance or the malfunctioning of
mechanical, electric, and fluid systems and components.
To assure a workable and effective document, we have involved
all sectors of the wastewater treatment industry in the develop-
ment and review of this Technical Bulletin. In this regard,
I particularly wish to thank the EPA Technical Advisory Group
for Municipal Waste Water Systems for their advice and counsel.
The design criteria contained in this Technical Bulletin are
meant to be specific enough to have force and meaning, yet
have administrative flexibility so as to permit innovation as
to how the intent of the criteria will be met in each individual
case. It is our intent to update and revise these criteria
as experience dictates.
I am confident that through the continued efforts and coopera-
tion of the engineering profession, the objective of improved
reliability of wastewater treatment works will be achieved.
^,~~k -^
Robert L. Sansom
Assistant Administrator
for Air and Water Programs
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TABLE OF CONTENTS
Foreword i
Purpose 1
Applicability of Technical Bulletin 1
Definitions 2
Terms Used in Specifying Criteria 4
Reliability Classification 5
100, Works Design Criteria 7
200. System Design Criteria 14
210. Wastewater Treatment System 15
220. Sludge Handling and Disposal System 30
230. Electric Power System 38
240. Instrumentation and Control Systems 47
250. Auxiliary Systems 49
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DESIGN CRITERIA FOR MECHANICAL,
ELECTRIC, AND FLUID SYSTEM AND
COMPONENT RELIABILITY
Purpose
The purpose of this Technical Bulletin is to amplify and
supplement the Federal Guidelines for Design, Operation, and Mainte-
nance of Wastewater Treatment Facilities with regard to establishing
minimum standards of reliability for mechanical, electric, and fluid
systems and components. This Technical Bulletin provides reliability
design criteria for wastewater treatment works projects seeking
Federal financial assistance under PL 92-500.
Applicability of Technical Bulletin
New treatment works and additions or expansions to existing
treatment works shall comply with this Technical Bulletin. Portions
of existing works, for which the addition or expansion is dependent for
reliable operation, shall comply with this Technical Bulletin to the
degree practicable. There may be some treatment works for which
fulfillment of some of the design criteria may not be necessary or
appropriate. There will be other cases in which these criteria are
insufficient, and additional criteria will be identified by the Regional
Administrator. It is expected that additional criteria may be needed
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for unusual environmental conditions and for new processes. Within
this context, the design criteria should be used as a reference, allowing
additions or deletions as an individual case may warrant.
A basic requirement specified in these criteria is component
backup. However, system reliability can also be attained through
flexibility in the design and operation of systems and components. This
document does not attempt to define requirements for system flexibility.
Definitions
The following definitions apply to the terms used in this
Technical Bulletin:
Component - A single piece of equipment which performs a specific
function in the wastewater treatment works. In this context a
component may be an entire piece of process equipment (e.g.,
sedimentation basin or vacuum filter) or may be a single piece of
equipment (e0g. , a valve or a pump).
Controlled Diversion - Diversion in a controlled manner of
inadequately treated wastewater around the treatment works to
navigable waters.
Design Flow - That flow used as the basis of design of a component
and/or system.
Design Period - The period of time from first operation to the year
at which the treatment works is expected to treat the design flow.
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Effluent Limitation - Any restriction established by a State or the
EPA Administrator on quantities, rates, and concentrations of
chemical, physical, biological, and other constituents which are
discharged from point sources into navigable waters, the waters of
the contiguous zone, or the ocean, including schedules of compliance.
Fluid System - A system within the treatment works which contains
liquid or gaseous fluids. This includes the main wastewater treat-
ment system, parts of the sludge handling and disposal system, and
auxiliary systems.
Hydraulic Capacity - The maximum flow capacity of a component
which does not result in flooding or overflowing.
Navigable Waters - The waters of the United States, including the
territorial seas, as defined in PL 92-500.
Peak Wastewater Flow - The maximum wastewater flow expected
during the design period of the treatment works.
Reliability - A measurement of the ability of a component or system
to perform its designated function without failure. In this Technical
Bulletin, reliability pertains to mechanical, electric, and fluid
systems and components only and includes the maintainability of
those systems and components. Reliability of biological processes,
operator training, process design, or structural design is not within
the scope of this Technical Bulletin. The reliability aspects related
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to works' influent from combined sewers are not within the
scope of this Technical Bulletin.
Unit Operation - An operation involving a single physical or chemical
process. Examples of a unit operation are comminuting, mixing,
sedimentation, aeration, and flocculation.
Vital Component - A component whose operation or function is
required to prevent a controlled diversion, is required to meet
effluent limitations, or is required to protect other vital components
from damage.
Wastewater Treatment Works - The works that treats the waste-
water, including the associated wastewater pumping or lift stations,
whether or not the stations are physically a part of the works.
Holding ponds or basins are considered included, whether or not
the ponds or basins are physically a part of the works.
Terms Used in Specifying Criteria
The following are clarifications of terms used in specifying
criteria in this Technical Bulletin:
° Shall - Used to specify criteria which are mandatory. Depar-
ture from these criteria requires a Departure Request to be
submitted by the Grant Applicant and approval of the request
by the Regional Administrator.
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0 Permissible - Used to clarify the intent of mandatory criteria
by giving examples of designs which are in conformance with
the criteria.
0 Consideration and Where Practicable - Used to specify criteria
which shall be considered by the Grant Applicant, but which are
not mandatory.
Reliability Classification
This Technical Bulletin establishes minimum standards of
reliability for three classes of wastewater treatment works. Unless
identified as applying to a particular class, all criteria contained in
this document apply equally to all three classes. The reliability classi-
fication shall be selected and justified by the Grant Applicant, subject
to the approval of the Regional Administrator, and shall be based on
the consequences of degradation of the effluent quality on the receiving
navigable waters. This document does not specify requirements for
classifying works; however, suggested guidelines are:
Reliability
Class I Works which discharge into navigable waters that could
be permanently or unacceptably damaged by effluent
which was degraded in quality for only a few hours.
Examples of Reliability Class I works might be those
discharging near drinking water reservoirs, into
shellfish waters, or in close proximity to areas used
for water contact sports.
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Reliability
Class II
Reliability
Class III
Works which discharge into navigable waters that would
not be permanently or unacceptably damaged by short-
term effluent quality degradations, but could be damaged
by continued (on the order of several days) effluent
quality degradation. An example of a Reliability Class II
works might be one which discharges into recreational
waters.
Works not otherwise classified as Reliability Class I
or Class II.
Note: Pumping stations associated with, but physically
removed from, the actual treatment works could have
a different classification from the works itself,,
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Works Design Criteria
100. WORKS DESIGN CRITERIA
Page
110. Works Location 8
120. Provisions for Works Expansion and/or Upgrading 9
130. Piping Requirements 9
131. Pipes Subject to Clogging 9
132. Provisions for Draining Pipes 10
133. Maintenance and Repair of Feed Lines 10
140. Component Maintenance and Repair Requirements 11
141. Component Repair 11
142. Component Access Space 12
143. Component Handling 12
144. Essential Services 13
150. Isolation of Hazardous Equipment 13
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Works Design Criteria
100. WORKS DESIGN CRITERIA
110. WORKS LOCATION
The potential for damage or interruption of operation due to
flooding shall be considered when siting the treatment works.
The treatment works' structures and electrical and mechanical
equipment shall be protected from physical damage by the
maximum expected one hundred (100) year flood. The treatment
works shall remain fully operational during the twenty-five (25)
year flood, if practicable; lesser flood levels may be permitted
dependent on local situations, but in no case shall less than a
ten (10) year flood be used. Works located in coastal areas
subject to flooding by wave action shall be similarly protected
from the maximum expected twenty-five (25) and one hundred
(100) year wave actions.
Existing works being expanded, modified, upgraded or rehabili-
tated shall comply with these criteria to the degree practicable.
The flood and wave action elevations used to implement these
criteria shall be determined and justified by the Grant Applicant,
using available data sources where appropriate. Elevations for
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Works Design Criteria
a specific location may be available from local or state studies
as well as studies by the following Federal organizations: U.S.
Army Corps of Engineers, U.S. Geological Survey, U.S. Soil
Conservation Service, National Oceanic and Atmospheric
Administration, and Tennessee Valley Authority.
The works shall be accessible in all normal seasonal conditions,
including the expected annual floods.
120. PROVISIONS FOR WORKS EXPANSION AND/OR UPGRADING
All new works and expansions to existing works shall be designed
for further expansion except where circumstances preclude the
probability of expansion. During a works1 upgrading or expansion
the interruption of normal operation shall be minimized and
shall be subject to the approval of the Regional Administrator.
130. PIPING REQUIREMENTS
131. Pipes Subject to Clogging
131. 1 Provisions for Flushing of Pipes
The works shall have provisions for flushing with water
and/or air all scum lines, sludge lines, lime feed and
lime sludge lines, and all other lines which are subject to
clogging. The design shall be such that flushing can be
accomplished without causing violation of effluent limita-
tions or without cross-connections to the potable water
system.
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Works Design Criteria
131.2 Provisions for Mechanical Cleaning of Pipes
All piping subject to accumulation of solids over a long
period of time shall have sufficient connections and shall
be arranged in a manner to facilitate mechanical cleaning.
This may include the main wastewater treatment process
piping, service water system piping, and sludge process
piping. Special attention shall be paid to piping containing
material which has a tendency to plug, such as scum lines,
drain lines, and lime sludge lines. System design shall
be such that the mechanical cleaning can be accomplished
without violation of effluent limitations.
132. Provisions for Draining Pipes
Where practicable, all piping shall be sloped and/or have
drains (drain plug or valve) at the low points to permit com-
plete draining. Piping shall be installed with no isolated
pockets which cannot be drained.
133. Maintenance and Repair of Feed Lines
Lines feeding chemicals or process air to basins, wetwells,
and tanks shall be designed to enable repair or replacement
without drainage of the basins, wetwells or tanks.
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Works Design Criteria
140. COMPONENT MAINTENANCE AND REPAIR REQUIREMENTS
141. Component Repair
Every vital mechanical component (mechanical components
include such items as pumps, bar screens, instrumentation
and valves, but not piping, tanks, basins, channels, or wells)
in the works shall be designed to enable repair or replace-
ment without violating the effluent limitations or causing a
controlled diversion. To comply with this requirement, it
is permissible to use the collection system storage capacity
or holding basins and to perform maintenance during the low
influent flow periods. This requirement applies to shutoff
and isolation valves. Provisions shall be made in the initial
works design to permit repair and replacement of these types
of valves.
Example: This criterion applies to the isolation valves of
main wastewater pumps. The following are examples of ways
these valves could be maintained. Pump suction isolation
valves can be maintained if the works has a two compartment
main pump wetwell and if the works can continue operation
(during the diurnal low flow period, for example) with one
part of the wetwell isolated. Pump discharge isolation valves
connected to a pressurized outlet header can be maintained
if the collection system storage capacity is sufficiently large
to permit all main wastewater pumps to be stopped (collection
system storage capacity is used) while the valve in question
is removed and blind flanges installed.
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Works Design Criteria
142. Component Access Space
Adequate access and removal space shall be provided around
all components to permit easy maintenance and/or removal
and replacement without interfering with the operation of
other equipment. Components located inside buildings or
other structures shall be removable without affecting the
structural integrity of the building or creating a safety hazard.
Normal disassembly of the component is permissible for
removal and replacement. This criterion is not intended to
be applicable to the removal or replacement of large tanks,
basins, channels, or wells.
Note: This criterion requires that consideration be given to
the sizing of doors, stairways, hallways, hatches, elevators
and other access ways in the initial works design. It also
requires that special thought be given to the physical layout
of piping systems and components in the initial design,
especially to components located above and below the ground
level of buildings and to unusually large components. The
complete path of removal from in-plant location, through
hatches, doors and passageways, to a truck or other service
vehicle should be checked and defined for each component.
143. Component Handling
The works shall have lifting and handling equipment available
to aid in the maintenance and replacement of all components.
In addition, the placement of structures and other devices,
such as pad-eyes and hooks, to aid component handling shall
be considered in the initial design. This is particularly
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Works Design Criteria
important for large and/or heavy components which require
special handling and lifting equipment. Means shall be
provided for removal of components located above and below
the ground level of buildings and other structures. This
criterion is not intended to be applicable to the removal or
replacement of large tanks, basins, channels, or wells.
144. Essential Services
Essential services, such as water, compressed air, and
electricity, shall be made available throughout the works
where required for cleaning, maintenance, and repair work.
To facilitate cleaning wetwells, tanks, basins and beds, water
(supplied from a non-potable water system or the works'
effluent) shall be supplied at these points by means of a
pressurized water system with hydrants or hose bibs having
minimum outlet diameters of one inch.
150. ISOLATION OF HAZARDOUS EQUIPMENT
Equipment whose failure could be hazardous to personnel or to
other equipment shall have means for isolation, such as shutoff
valves, or shutoff switches and controls located away from the
equipment to permit safe shutdown during emergency conditions.
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System Design Criteria
200. SYSTEM DESIGN CRITERIA
Page
210. Wastewater Treatment System 15
211. System Requirements 15
212. Component Backup Requirements 18
213. Component Design Features and Maintenance 25
Requirements
220. Sludge Handling and Disposal System 30
221. System Requirements 30
222. Component Backup Requirements 31
223. Component Design Features and Maintenance 35
Requirements
230. Electric Power System 38
240. Instrumentation and Control Systems 47
250. Auxiliary Systems 49
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System Design Criteria
200. SYSTEM DESIGN CRITERIA
210. WASTEWATER TREATMENT SYSTEM
The wastewater treatment system includes all components from
and including the bar screens and wastewater pumps to and
including the works outfall.
211. System Requirements
The wastewater treatment system shall be designed to
include the following:
211.1 Trash Removal or Comminution
The system shall contain components to remove and/or
comminute trash and all other large solids contained in
the wastewater.
211.2 Grit Removal
The system shall contain components to remove grit and
other heavy inorganic solids from the wastewater. This
requirement shall not apply to types of treatment works
which do not pump or dewater sludge, such as waste
stabilization ponds.
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System Design Criteria
211.3 Provisions for Removal of Settled Solids
All components, channels, pump wells and piping prior to
the degritting facility or primary sedimentation basin
shall be accessible for cleaning out settled solids. The
provisions shall enable manual or mechanical cleaning of
equipment on a periodic basis without causing a controlled
diversion or causing violation of effluent limitations.
211.4 Treatment Works Controlled Diversion
Wastewater treatment works shall be provided with a
controlled diversion channel or pipe sized to handle peak
wastewater flow. Actuation of the controlled diversion
shall be by use of a gravity overflow. The overflow
elevation shall be such that the maximum feasible storage
capacity of the wastewater collection system will be utilized
before the controlled diversion will be initiated. The
controlled diversion flow shall be screened to remove
large solids unless the wastewater flow has been previously
screened. The actuation of a controlled diversion shall be
alarmed and annunciated (see Paragraph 243 of this
Technical Bulletin), and the flow shall be measured and
recorded.
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System Design Criteria
All Reliability Class I wastewater treatment works shall
have a holding basin to augment the storage capacity of
the collection system. The controlled diversion system
and the holding basin shall be designed to permit the
wastewater retained by the holding basin to be fully treated
in the wastewater treatment works. The capacity of the
holding basin shall be sized by the Grant Applicant based
on the constraints and conditions applicable to that specific
treatment works.
2' 11. 5 Unit Operation Bypassing
The design of the wastewater treatment system shall
include provisions for bypassing around each unit opera-
tion, except as follows. The term unit operation does not
apply to pumps in the context of this criterion. Unit
operations with two or more units and involving open basins,
such as sedimentation basins, aeration basins, disinfectant
contact basins, shall not be required to have provisions
for bypassing if the peak wastewater flow can be handled
hydraulically with the largest flow capacity unit out of
service. All other unit operations with three or more
units shall not be required to have provisions for bypassing
if the peak wastewater flow can be handled hydraulically
with the two largest flow capacity units out of service.
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System Design Criteria
The comminution facility shall be provided with a means
for bypassing regardless of the number and flow capacity
of the comminutors.
The bypassing system for each unit operation shall be
designed to provide control of the diverted flow such that
only that portion of the flow in excess of the hydraulic
capacity of the units in service need be bypassed. With
the exception of the comminution facility, which shall have
a gravity overflow, the actuation of all other unit operation
bypasses shall require manual action by operating personnel.
All power actuated bypass valve operators shall be designed
to enable actuation with loss of power and shall be designed
so that the valve will fail as is, upon failure of the power
operator. A disinfection facility having a bypass shall
contain emergency provisions for disinfection of the bypassed
flow.
212. Component Backup Requirements
Requirements for backup components for the main wastewater
treatment system are specified below for Reliability Class I,
II, and III works.
Except as modified below, unit operations in the main waste-
water treatment system shall be designed such that, with the
largest flow capacity unit out of service, the hydraulic
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System Design Criteria
capacity (not necessarily the design-rated capacity) of the
remaining units shall be sufficient to handle the peak waste-
water flow. There shall be system flexibility to enable the
wastewater flow to any unit out of service to be distributed
to the remaining units in service.
Equalization basins or tanks shall not be considered a substi-
tute for component backup requirements.
212. 1 Reliability Class I
For components included in the design of Reliability Class I
works, the following backup requirements apply.
212. 1. 1 Mechanically-Cleaned Bar Screens or Equivalent Devices
A backup bar screen shall be provided. It is permissible
for the backup bar screen to be designed for manual
cleaning only. Works with only two bar screens shall
have at least one bar screen designed to permit manual
cleaning.
212. 1. 2 Pumps
A backup pump shall be provided for each set of pumps
which performs the same function. The capacity of the
pumps shall be such that with any one pump out of
service, the remaining pumps will have capacity to
handle the peak flow. It is permissible for one pump
to serve as backup to more than one set of pumps.
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System Design Criteria
212.1.3 Comminution Facility
If comminution of the total wastewater flow is provided,
then an overflow bypass with an installed manually- or
mechanically-cleaned bar screen shall be provided.
The hydraulic capacity of the comminutor overflow
bypass shall be sufficient to pass the peak flow with all
comminution units out of service.
212.1.4 Primary Sedimentation Basins
There shall be a sufficient number of units of a size,
such that with the largest flow capacity unit out of
service, the remaining units shall have a design flow
capacity of at least 50 percent of the total design flow
to that unit operation.
2 12o 1. 5 Final and Chemical Sedimentation Basins, Trickling
Filters, Filters and Activated Carbon Columns
There shall be a sufficient number of units of a size,
such that with the largest flow capcity unit out of
service, the remaining units shall have a design flow
capacity of at least 75 percent of the total design flow
to that unit operation.
212.1.6 Activated Sludge Process Components
212.1.6.1 Aeration Basin
A backup basin shall not be required; however, at
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System Design Criteria
least two equal volume basins shall be provided.
(For the purpose of this criterion, the two zones of
a contact stabilization process are considered as
only one basin. )
212. 1.6.2 Aeration Blowers or Mechanical Aerators
There shall be a sufficient number of blowers or
mechanical aerators to enable the design oxygen
transfer to be maintained with the largest capacity
unit out of service. It is permissible for the backup
unit to be an uninstalled unit, provided that the
installed unit can be easily removed and replaced.
However, at least two units shall be installed.
212.1.6.3 Air Diffusers
The air diffusion system for each aeration basin
shall be designed such that the largest section of
diffusers can be isolated without measurably
impairing the oxygen transfer capability of the
system,,
212.1.7 Chemical Flash Mixer
At least two mixing basins or a backup means for
adding arid mixing chemicals, separate from the basin,
shall be provided. If only one basin is provided, at
least two mixing devices and a bypass around the basin
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System Design Criteria
shall be provided. It is permissible for one of the
mixing devices to be uninstalled, provided that the
installed unit can be easily removed and replaced.
212.1.8 Flocculation Basins
At least two flocculation basins shall be provided.
212.1.9 Disinfectant Contact Basins
There shall be a sufficient number of units of a size,
such that with the largest flow capacity unit out of
service, the remaining units shall have a design flow
capacity of at least 50 percent of the total design flow
to that unit operation.
212.2 Reliability Class II
The Reliability Class I requirements shall apply except
as modified below.
212.2.1 Primary and Final Sedimentation Basins and Trickling
Filters
There shall be a sufficient number of units of a size
such that, with the largest flow capacity unit out of
service, the remaining units shall have a design flow
capacity of at least 50 percent of the design basis flow
to that unit operation.
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System Design Criteria
212.2.2 Components Not Requiring Backup
Requirements for backup components in the wastewater
treatment system shall not be mandatory for components
which are used to provide treatment in excess of typical
biological (L e. , activated sludge or trickling filter),
or equivalent physical/chemical treatment, and disin-
fection. This may include such components as:
Chemical Flash Mixer
Flocculation Basin
Chemical Sedimentation Basin
Filter
Activated Carbon Column
212.3 Reliability Class III
The Reliability Class I requirements shall apply except
as modified below.
212.3.1 Primary and Final Sedimentation Basins
There shall be at least two sedimentation basins.
21203.2 Activated Sludge Process Components
2 120 3. 2, I Aeration Basin
A single basin is permissible.
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System Design Criteria
212.3.2.2 Aeration Blowers or Mechanical Aerators
There shall be at least two blowers or mechanical
aerators available for service. It is permissible
for one of the units to be uninstalled, provided that
the installed unit can be easily removed and replaced.
212.3.2.3 Air Diffusers
The Reliability Class I requirements shall apply.
212.3.3 Components Not Requiring Backup
Requirements for backup components in the wastewater
treatment system shall not be mandatory for components
which are used to provide treatment in excess of primary
sedimentation and disinfection, except as modified
above. This may include such components as:
Trickling Filter
Chemical Flash Mixer
Flocculation Basin
Chemical Sedimentation Basin
Filter
Activated Carbon Column
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System Design Criteria
213. Component Design Features and Maintenance Requirements
213. 1 Provisions for Isolating Components
Each component shall have provisions to enable it to be
isolated from the flow stream to permit maintenance and
repair of the component without interruption of the works'
operation. Where practicable, simple shutoff devices,
such as stop logs and slide gates, shall be used.
213. 1. 1 Main Wastewater System Pump Isolation
The use of in-line valves to isolate the main wastewater
pumps shall be minimized. It is permissible to place
shutoff valves on the suction and discharge lines of
each pump. However, in such a case, alternate means
shall be provided for stopping flow through the pump
suction or discharge lines to permit maintenance on the
valves.
Example: Pump discharge isolation and check
valves are not needed if the pumps have a free
discharge into an open channel rather than dis-
charging into a pressurized discharge header.
Pump suction isolation valves can be maintained
if the plant has a two compartment wetwell design
and if the plant can continue operation (during the
diurnal low-flow period, for example) with one
part of the wetwell isolated.
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System Design Criteria
213.2 Component Protection
213.2.1 Protection from Overload
Components or parts of components subject to clogging,
blockage, binding or other overloads shall be protected
from damage due to the overload. Examples of com-
ponents requiring protection include the rake mechanism
of bar screens, comminuting equipment, the grit-
removal mechanism in degritting facilities, and sludge
and scum arms of sedimentation basins.
213. 2,2 Protection from Freezing
Components or parts of components which are wetted
and subject to freezing shall be designed to ensure
that the components will be operable during winter
climatic conditions anticipated at the works. Examples
of components or parts of components which may require
protection include bar screens, comminuting equipment,
the grit-removal mechanism in degritting facilities,
mechanical aerators and the scum arm of sedimentation
basins.
213.2.3 Protection from Up-Lift Due to Ground Water
In-ground tanks and basins shall be protected from
up-lift due to ground water. If sufficient ballast is not
provided in each tank or basin, other means for ground
water relief shall be provided.
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System Design Criteria
213.3 Slide Gates
Consideration shall be given to providing mechanical
operators or other mechanical assistance for slide gates
which, due to their size or infrequent use, may not be
easily removable by manual means alone.
213.4 Bar Screens or Equivalent Devices
213.4. 1 Provisions for Manual Cleaning
Manually-cleaned bar screens or mechanically-cleaned
bar screens which can be manually cleaned shall have
accessible platforms above the bar screen from which
the operator can rake screenings easily and safely when
the screens are in operation.
213.4.2 Provisions for Lifting and Handling Equipment
The design of the equipment and the works shall contain
provisions for easily and safely lifting and handling all
parts of a mechanically-cleaned bar screen. Special
attention shall be given to the proper location of eyes,
rails, and hooks located above the equipment to facilitate
lifting and handling.
213.5 Comminution Equipment and Degritting Facility
All mechanical components shall be easily removable for
maintenance and repair.
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System Design Criteria
213.6 Sedimentation Basins
The main drive mechanism and reducing gears shall be
maintainable and repairable without draining the basin.
The number of other operating parts which require draining
the basin for repair and maintenance shall be minimized.
Z1307 Aeration Equipment
2 130 1, 1 Component Maintenance
Mechanical aerators or air diffusers shall be easily
removable from the aeration tank to permit maintenance
and repair without interrupting operation of the aeration
tank or inhibiting operation of the other aeration equip-
ment.
Z13.7.2 Filtration of Air
If air is supplied to fine bubble diffusers, air filters
shall be provided in numbers, arrangement and capac-
ities to furnish at all times an air supply sufficiently
free from dust to minimize clogging of the diffusers.
213.8 Chemical Mixing Basin and Flocculation Basin
213. 8. 1 Component Maintenance
The mixing and flocculating devices shall be completely
removable from the basin to allow maintenance and
repair of the device, preferably without draining the
basin.
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System Design Criteria
213. 8. 2 Chemical Feed Line Cleaning
Chemical feed lines shall be designed to permit their
being cleaned or replaced without draining the mixing
basin or interrupting the normal flow through the basin.
213. 8. 3 Provisions for Isolation
Isolation valves or gates for the mixing or flocculation
basin shall be designed to minimize the problems
associated with operation of these devices after long
periods of idleness and the resulting buildup of chemical
deposits. Access and capability for cleaning debris
and deposits which interfere with valve or gate closure
shall be provided.
213.9 Filters and Activated Carbon Columns
There shall be easy access to the interior of carbon
columns and filters to permit maintenance and repair of
internal mechanisms.
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System Design Criteria
220. SLUDGE HANDLING AND DISPOSAL SYSTEM
This system includes all components and unit processes from
the sludge pumps servicing the sedimentation basins to the
final disposal of waste products, including ancillary components.
Sludge disposal includes the special handling and treatment of
sludge bypassing a normal stage of treatment. In some treatment
works the system may also include processes such as recalci-
nation of lime or regeneration of activated carbon.
221. System Requirements
The sludge handling and disposal system shall be designed
to include the following:
221. 1 Alternate Methods of Sludge Disposal and/or Treatment
Alternate methods of sludge disposal and/or treatment
shall be provided for each sludge treatment unit operation
without installed backup capability.
221.2 Provisions for Preventing Contamination of Treated
Wastewater
All connections (sludge, scum, filtrate, supernatant, or
other contaminated water flows), direct or indirect, from
the sludge handling system to the wastewater treatment
system shall be at a point in the wastewater treatment
system that will ensure adequate treatment.
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System Design Criteria
222. Component Backup Requirements
For components included in the design of the sludge handling
and disposal system of Reliability Class I, II, or III works
the following backup requirements apply.
222. 1 Sludge Holding Tanks
Holding tanks are permissible as an alternative to com-
ponent or system backup capability for components down-
stream of the tank, provided the following requirements
are met. The volume of the holding tank shall be based
on the expected time necessary to perform maintenance
and repair of the component in question. If a holding tank
is used as an alternative to backup capability in a sludge
treatment system which is designed for continuous operation,
the excess capacity in all components downstream of the
holding tanks shall be provided to enable processing the
sludge which was retained together with the normal sludge
flow.
222. 2 Pumps
A backup pump shall be provided for each set of pumps
which performs the same function. The capacity of the
pumps shall be such that with any one pump out of service,
the remaining pumps will have capacity to handle the peak
flow. It is permissible for one pump to serve as backup
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System Design Criteria
to more than one set of pumps. It is also permissible
for the backup pump to be uninstalled, provided that the
installed pump can be easily removed and replaced.
However, at least two pumps shall be installed.
222. 3 Anaerobic Sludge Digestion
222. 3. 1 Digestion Tanks
At least two digestion tanks shall be provided. At least
two of the digestion tanks provided shall be designed to
permit processing all types of sludges normally digested.
222.302 Mixing Equipment
If mixing is required as part of the digestion process,
then each tank requiring mixing shall have sufficient
mixing equipment or flexibility in system design to
ensure that the total capability for mixing is not lost
when any one piece of mechanical mixing equipment is
taken out of service. It is permissible for the backup
equipment not to be installed (eģ g, , a spare uninstalled
digester gas compressor is permissible if gas mixing
is used); not be normally used for sludge mixing (e. g. ,
sedimentation basin sludge pumps may be used); or not
be full capacity (e. g. , two 50 percent-capacity recircu-
lation pumps would comply with this requirement).
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System Design Criteria
222.4 Aerobic Sludge Digestion
222. 4. 1 Aeration Basin
A backup basin is not required.
222.4.2 Aeration Blowers or Mechanical Aerators
At least two blowers or mechanical aerators shall be
provided. It is permissible for less than design oxygen
transfer capability to be provided with one unit out of
service. It is permissible for the backup unit to be an
uninstalled unit, provided that the installed unit can be
easily removed and replaced.
222.4.3 Air Diffusers
The air diffusion system for each aeration basin shall
be designed such that the largest section of diffusers
can be isolated without measurably impairing the oxygen
transfer capability of the system.
222. 5 Vacuum Filter
There shall be a sufficient number of vacuum filters to
enable the design sludge flow to be dewatered with the
largest capacity vacuum filter out of service.
Note: Since the design basis of sludge dewatering equip-
ment is often not continuous operation, this criterion does
not necessarily require additional vacuum filter capacity
if the installed equipment is operated on less than a 24
hour-per-day basis and if the normal operating hours can
be extended on the remaining units to make up the capacity
lost in the unit out of service.
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System Design Criteria
222. 5. 1 Auxiliary Equipment
Each vacuum filter shall be serviced by two vacuum
pumps and two filtrate pumps. It is permissible for
the backup to the normal vacuum or filtrate pump to be
an uninstalled unit, provided that the installed unit can
be easily removed and replaced; or to be a cross -
connect line to the appropriate system of another
vacuum filter.
222.6 Centrifuges
There shall be a sufficient number of centrifuges to enable
the design sludge flow to be dewatered with the largest
capacity centrifuge out of service. It is permissible for
the backup unit to be an uninstalled unit, provided that the
installed unit can be easily removed and replaced.
Note: Since the design basis of sludge dewatering equip-
ment is often not continuous operation, this criterion does
not necessarily require additional equipment if the installed
equipment is operated on less than a 24 hour-per-day basis
and if the normal operating hours can be extended on the
remaining units to make up the capacity lost in the unit
out of service.
222. 7 Incinerators
A backup incinerator is not required (see Paragraph 221. 1
for requirements for alternate sludge disposal capability).
Auxiliary incinerator equipment whose failure during
incinerator operation could result in damage to the
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System Design Criteria
incinerator shall be provided with backups (e. g. , failure
of a center shaft cooling fan could result in damage to the
center shaft of a multi-hearth incinerator). In such cases,
automatic actuation of the backup auxiliary equipment
shall be provided.
223. Component Design Features and Maintenance Requirements
223. 1 Provisions for Isolating Components
Each component shall have provisions to enable it to be
isolated from the flow stream to permit maintenance and
repair of the component without interruption of the works'
operation. Where practicable, simple shutoff devices,
such as stop logs and slide gates, shall be used.
223.2 Component Protection
223.2. 1 Protection from Overload
Components or parts of components subject to clogging,
blockage, binding or other overloads shall be protected
from damage due to the overload.
223. 2. 2 Protection from Freezing
Components or parts of components which are wetted
and subject to freezing shall be designed to ensure that
components will be operable during winter climatic
conditions anticipated at the works.
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System Design Criteria
223.2.3 Protection from Up-Lift Due to Ground Water
In-ground tanks and basins shall be protected from
up-lift due to ground water. If sufficient ballast is not
provided in each tank or basin, other means for ground
water relief shall be provided.
223.3 Slide Gates
Consideration shall be given to providing mechanical
operators or other mechanical assistance for slide gates
which, due to their size or infrequent use, may not be
easily removable by manual means alone.
223.4 Aeration Equipment
223.4. 1 Component Maintenance
Mechanical aerators or air diffusers shall be easily
removable from the aeration tank to permit maintenance
and repair without interrupting operation of the aeration
tank or inhibiting operation of the other aeration equip-
ment.
223.4.2 Filtration of Air
If air is supplied to fine bubble diffusers, air filters
shall be provided in numbers, arrangement and capa-
cities to furnish at all times an air supply sufficiently
free from dust to minimize clogging of the diffusers.
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System Design Criteria
223. 5 Anaerobic Sludge Digester
At Least three access manholes shall be provided in the
top of the tank. One opening shall be large enough to
permit the use of mechanical equipment to remove grit
and sand. A separate side wall manhole shall also be
provided,
223.6 Incinerators
There shall be easy access to the interior of incinerators
to permit maintenance and repair of internal mechanisms.
Multi-hearth incinerators shall have a manhole on each
hearth level.
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System Design Criteria
230. ELECTRIC POWER SYSTEM
The following criteria shall apply only to those portions of the
system supplying power to vital components.
23 10 Power Sources
Two separate and independent sources of electric power shall
be provided to the works from either two separate utility
substations or from a single substation and a works based
generator. If available from the electric utility, at least one
of the works' power sources shall be a preferred source
(i. e. , a utility source which is one of the last to lose power
from the utility grid due to loss of power generating capacity).
In geographical areas where it is projected that sometime
during the design period of the works, the electric utility may
reduce the rated line voltage (i. e. , "brown out") during peak
utility system load demands, a works based generator shall
be provided as an alternate power source, where practicable.
As a minimum, the capacity of the backup power source for
each class of treatment works shall be:
Reliability
Class I Sufficient to operate all vital components,
during peak wastewater flow conditions,
together with critical lighting and ventilation.
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System Design Criteria
Reliability
Class II Same as Reliability Class I, except that vital
components used to support the secondary
processes (i. e. , mechanical aerators or
aeration basin air compressors) need not be
included as long as treatment equivalent to
sedimentation and disinfection is provided.
Reliability
Class III Sufficient to operate the screening or
comminution facilities, the main wastewater
pumps, the primary sedimentation basins,
and the disinfection facility during peak
wastewater flow condition, together with
critical lighting and ventilation.
Note: This requirement concerning rated capacity of electric
power sources is not intended to prohibit other forms of
emergency power, such as diesel driven main wastewater
pumps.
232. Power Distribution External to the Works
The independent sources of power shall be distributed to the
works' transformers in a way to minimize common mode
failures from affecting both sources.
Example: The two sets of distribution lines should not be
located in the same conduit or supported from the same
utility pole. The two sets of overhead distribution lines,
if used, should not cross nor be located in an area where
a single plausible occurrence (e. g. , fallen tree) could
disrupt both lines. Devices should be used to protect the
system from lightning.
233. Transformers
Each utility source of power to the works shall be transformed
to usable voltage with a separate transformer. The trans-
formers shall be protected from common mode failure by
physical separation or other means.
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System Design Criteria
234. Power Distribution Within the Works
234. 1 Service to Motor Control Centers
The internal power distribution system shall be designed
such that no single fault or loss of a power source will
result in disruption (i. e. , extended, not momentary) of
electric service to more than one motor control center
associated with the Reliability Class I, II, or III vital
components requiring backup power per Paragraph 231,
above.
234.2 Division of Loads at Motor Control Centers
Vital components of the same type and serving the same
function shall be divided as equally as possible between
at least two motor control centers. Nonvital components
shall be divided in a similar manner, where practicable.
234. 3 Power Transfer
Where power feeder or branch circuits can be transferred
from one power source to another, a mechanical or
electrical safety device shall be provided to assure that
the two power'sources cannot be cross-connected, if
unsynchronized. Automatic transfer shall be provided in
those cases when the time delay required to manually
transfer power could result in a failure to meet effluent
limitations, a failure to process peak influent flow, or
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System Design Criteria
cause damage to equipment. Where automatic pump
control is used, the control panel power source and pump
power source shall be similarly transferred. The
actuation of an automatic transfer switch shall be alarmed
and annunciated.
Example: An example for feeder distribution and bus
transfer which meets these criteria is shown in Figure 1.
The two power sources from utility substations are
connected to the motor control centers through circuit
breakers. A circuit breaker is provided to cross-
connect the two motor control centers in the event one
of the two normally energized power feeders fail.
Additional backup capability has been achieved for the
main pump by connecting one of the three pumps to the
motor control center cross-connect. This assures
that two out of three pumps will be available in the
event of a panel fire or panel bus short circuit.
235. Breaker Settings or Fuse Ratings
Breaker settings or fuse ratings shall be coordinated to effect
sequential tripping such that the breaker or fuse nearest the
fault will clear the fault prior to activation of other breakers
or fuses to the degree practicable.
236. Equipment Type and Location
Failures resulting from plausible causes, such as fire or
flooding, shall be minimized by equipment design and location.
The following requirements apply:
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System Design Criteria
FROM
POWER
sounet
NO. 1
FROM
POWER
SOURCE
NO. 2
S~Y-V-Y~Y-Y-\
)
TRANSFORMER
TRANSFORMER
rYYVWI
SOURCE NO. 1 BUS
SOURCE NO. 2 BUS
I MOTOR CONTROL CENTER;
BUS
TIE BREAKER
NORMALLY
OPEN
j MOTOR CONTROL CENTERJ
MOTOR CONTROL
CENTER
TIE BREAKER
BLOWER SLUDGE SLOWED
no. i PUMP wo. s
NO. 1
BLOWER SLUDGE
NO. 1 PUMP
NO. 2
FEEDER DISTRIBUTION AND POWER TRANSFER
FIGURE 1
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System Design Criteria
236. 1 Switchgear Location
Electric switchgear and motor control centers shall be
protected from sprays or moisture from liquid processing
equipm ent and from breaks in liquid handling piping.,
Where practicable, the electric equipment shall be located
in a separate room from the liquid processing equipment.
Liquid handling piping shall not be run through this room.
The electric switchgear and motor control centers shall
be located above ground and above the one hundred (100)
year flood (or wave action) elevation.
236.2 Conductor Insulation
Wires in underground conduits or in conduits that can be
flooded shall have moisture resistant insulation as identified
in the National Electric Code.
236. 3 Motor Protection from Moisture
All outdoor motors shall be adequately protected from the
weather. Water-proof, totally enclosed or weather-protected,
open motor enclosures shall be used for exposed outdoor
motors. Motors located indoors and near liquid handling
piping or equipment shall be, at least, splash-proof design.
Consideration shall be given to providing heaters in motors
located outdoors or in areas where condensation may
occur.
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System Design Criteria
The following criteria shall apply to motors (and their
local controls) associated with vital components. All
outdoor motors, all large indoor motors (i. e. , those not
readily available as stock items from motor suppliers),
and, where practicable, all other indoor motors shall be
located at an elevation to preclude flooding from the one
hundred (100) year flood (or wave action), or from clogged
floor drains. Indoor motors located at or below the one
hundred year flood (or wave action) elevation shall be
housed in a room or building which is protected from
flooding during the one hundred year flood (or wave action).
The building protection shall include measures such as
no openings (e.g., doors, windows, hatches) to the outside
below the flood elevation and a drain sump pumped to an
elevation above the flood elevation.
236.4 Explosion Proof Equipment
Explosion proof motors, conduit systems, switches and
other electrical equipment shall be used in areas where
flammable liquid, gas or dust is likely to be present.
236. 5 Routing of Cabling
To avoid a common mode failure, conductors to components
which perform the same function in parallel shall not be
routed in the same conduit or cable tray. Conduits housing
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System Design Criteria
such cables shall not be routed in the same underground
conduit bank unless the conduits are protected from
common mode failures (such as by encasing the conduit
bank in a protective layer of concrete).
236.6 Motor Protection
Three phase motors and their starters shall be protected
from electric overload and short circuits on all three
phases.
Large motors shall have a low voltage protection device
which on the reduction or failure of voltage will cause and
maintain the interruption of power to that motor.
Consideration shall be given to the installation of tempera-
ture detectors in the stator and bearings of large motors
in order to give an indication of overheating problems.
237. Provisions for Equipment Testing
Provisions shall be included in the design of equipment
requiring periodic testing, to enable the tests to be accom-
plished while maintaining electric power to all vital components.
This requires being able to conduct tests, such as actuating
and resetting automatic transfer switches, and starting and
loading emergency generating equipment.
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System Design Criteria
238. Maintainability
The electric distribution system and equipment shall be
designed to permit inspection and maintenance of individual
items without causing a controlled diversion or causing
violation of the effluent limitations.
239. Emergency Power Generator Starting
The means for starting a works based emergency power
generator shall be completely independent of the normal
electric power source. Air starting systems shall have an
accumulator tank(s) with a volume sufficient to furnish air
for starting the generator engine a minimum of three (3)
times without recharging. Batteries used for starting shall
have a sufficient charge to permit starting the generator
engine a minimum of three (3) times without recharging.
The starting system shall be appropriately alarmed and
instrumented to indicate loss of readiness (e. g. , loss of
charge on batteries, loss of pressure in air accumulators,
etc. ).
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System Design Criteria
240. INSTRUMENTATION AND CONTROL SYSTEMS
These criteria cover the requirements for the instrumentation
and control systems:
241. Automatic Control
Automatic control systems whose failure could result in a
controlled diversion or a violation of the effluent limitations
shall be provided with a manual override. Those automatic
controls shall have alarms and annunciators to indicate
malfunctions which require use of the manual override. The
means for detecting the malfunction shall be independent of
the automatic control system, such that no single failure
will result in disabling both the automatic controls and the
alarm and annunciator.
242. Instrumentation
Instrumentation whose failure could result in a controlled
diversion or a violation of the effluent limitations shall be
provided with an installed backup sensor and readout. The
backup equipment may be of a different type and located at
a different point, provided that the same function is performed.
No single failure shall result in disabling both sets of parallel
instrumentation.
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System Design Criteria
243. Alarms and Annunciators
Alarms and annunciators shall be provided to monitor the
condition of equipment whose failure could result in a
controlled diversion or a violation of the effluent limitations.
Alarms and annunciators shall also be provided to monitor
conditions which could result in damage to vital equipment
or hazards to personnel. The alarms shall sound in areas
normally manned and also in areas near the equipment.
Treatment works not continuously manned shall have the
alarm signals transmitted to a point (e. g. , fire station,
police station, etc. ) which is continuously manned. The
combination of alarms and annunciators shall be such that
each announced condition is uniquely identified. Test circuits
shall be provided to enable the alarms and annunciators to
be tested and verified to be in working order.
244. Alignment and Calibration of Equipment
Vital instrumentation and control equipment shall be designed
to permit alignment and calibration without requiring a
controlled diversion or a violation of the effluent limitations.
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System Design Criteria
250. AUXILIARY SYSTEMS
The auxiliary systems include typical systems such as:
° Drain system, for
Components
Systems
Treatment works
Compressed air system, for
Pneumatic controls
Pneumatic valve operators
Hydropneumatic water systems
Air lift pumps
0 Service water systems, for
High pressure water
Gland seals
General service
0 Fuel supply system, for
Digester heaters
Incinerators
Building heat
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System Design Criteria
° Lubrication oil system, for
- Pumps
Blowers
Motors
Chemical supply and addition system, for
Disinfection
Sludge conditioning
Chemical treatment of wastewater
The reliability requirements of these systems are dependent on
the function of each system in the wastewater treatment works.
If a malfunction of the system can result in a controlled diversion
or a violation of the effluent limitations, and the required function
cannot be done by any other means, then the system shall have
backup capability in the number of vital components (i. e. , pumps,
motors, mechanical stirrers) required to perform the system
function. If the system performs functions which can be performed
manually or by some other means, then backup components shall
not be required.
Example: A compressed air system supplying air to air lift
pumps, which are pumping return activated sludge from the
secondary sedimentation basin to the aeration tanks, is an
example of an auxiliary system whose failure could degrade
effluent quality. If no other means for supplying air or pump-
ing sludge were available, then this system would be required
to have backup vital components, such as compressors.
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System Design Criteria
Example: If the compressed air system only supplied air to
pneumatic controls which could not affect effluent quality,
then the system would not require any backup components.
251. Backup Components
Auxiliary systems requiring backup components shall have
a sufficient number of each type of component such that the
design function of the system can be fulfilled with any one
component out of commission. Systems having components
of different capacities shall meet this criterion with the
largest capacity component out of commission. It is
permissible for the backup component to be uninstalled,
provided that the installed component can be easily removed
and replaced. However, at least two components shall be
installed.
Example: A chemical addition system supplying chlorinated
water to the contact chamber and having six chlorinators
and one water supply pump which just meets capacity
requirements, would be required by this criterion to have
one additional chlorinator and one additional pump.
252. Requirements for System, Component and Treatment Works
Drains and Overflows
All system, component and works drains and overflows shall
discharge to an appropriate point in the main wastewater
treatment process to ensure adequate treatment. Drains
flowing to a two-compartment wetwell shall be designed to
discharge to either compartment of the wetwell.
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System Design Criteria
252. 1 Works Drains
The works shall have sufficient drains to enable all spilled
or leaked raw or partially treated wastewater, sludge,
chemicals or any other objectionable substance to freely
drain out of the area of concern. Special attention shall
be given to specifying sufficient cleanouts in drain lines
which are likely to clog (e.g. , drain lines handling lime).
All floors within buildings and structures shall be sloped
to permit complete draining.
252.2 Sump Pumps
Sump pumps shall be of a non-clog type. Sump pumps are
considered vital components and each sump shall be
provided with two full capacity sump pumps.
252. 3 Equipment Overflows
All equipment located within buildings and which can
overflow shall be equipped with an adequately sized
overflow pipe. The overflow shall be directed to a gravity
drain.
252.4 Surface Water Drains
The works' grounds shall be graded and drains provided
in order to prohibit surface water from draining into
pump wells, tanks, basins, beds, or buildings. Drains
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System Design Criteria
which handle uncontaminated water only shall not be
connected to the contaminated drain system.
252,, 5 Component Dewatering
All pump wells, tanks, basins and beds, with the exception
of aeration tanks, shall be designed to enable complete
dewatering in a reasonable length of time in order to
minimize the component downtime for maintenance or
repairs. Where practicable, these components shall have
sloped bottoms to enable the units to be completely drained,,
252, 6 Drain Backflow
Drains shall be designed to prevent backflow from other
sources which would cause flooding or violation of the
effluent limitations. The drain system shall be designed
to prevent the entrance of storm water during the one
hundred year flood (or wave action) condition.
253. Continuity of Operation
The failure of a mechanical component in an auxiliary system
shall not result in disrupting the operating continuity of the
wastewater treatment system or sludge handling and disposal
system to the extent that flooding, failure, malfunctioning
or damage to components in those systems results.
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System Design Criteria
Example: A seal water system with normal and backup
water supplies must transfer automatically to the backup
upon failure of the normal supply in order to protect the
equipment which needs the seal water to prevent damage.
254. Emergency Fuel Storage
If a vital component requires fuel for operation, then the
fuel supply system design shall include provisions for fuel
storage or a standby fuel source. The capacity of stored
gaseous or liquid fuel shall be determined by the Grant
Applicant based on the plausible downtime of the normal fuel
supply and the expected consumption rate. The emergency
system shall be physically separate from the normal fuel
supply up to its connection to the fuel distribution system
within the works.
255. Disinfectant Addition System
The capacity of the disinfectant addition system shall be
designed with due consideration of abnormal operating
conditions, such as having a disinfectant contact basin out
of service. It is permissible for the additional capacity
required for abnormal conditions to be separate and
independent from the normal disinfectant addition system.
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