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
          Operability, Flexibility

                          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

                          TABLE OF CONTENTS
Section                                                  Page
      4.12  Disinfection                                 30
      4.13  Lagoon-Oxidation Ponds                       30
      4.14  Laboratory Facilities                        31
      4.15  Metering                                     32


                          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.


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).

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.

                             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

       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

       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
            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

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
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.

                      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
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.

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

       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

       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
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

       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.

                      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
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

       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.

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
  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
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

       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
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
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

       is recommended.  A means of viewing the sludge is also
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
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
4.5.12      Gravity sludge flow systems should have back-up pumping
  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.

4.6.2       Lift stations located immediately upstream of secondary
       clarifiers shall have flow-paced controls to reduce shock
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
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
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.

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.

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
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

       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
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
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
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.

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
4.7.18      Separate return and waste sludge pumps should be
  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
  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
4.9.2       Fixed nozzle ABF towers  should  be divided into  at  least
       two (2) separate units separated by  a solid wall with

       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
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
4.10.4      Gravity sludge thickener solids and hydraulic design
       loading criteria should be used for flow through gravity

       separation supernating facilities located in either a
       separate compartment or a baffled area within the aerobic
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
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
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.

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	
4.11.9      Digester heating systems should be automatically con-
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-
       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

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
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
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.

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.

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
4.11.13     All cells should have staff gauges for liquid depth
  4.14 Laboratory Faci1it ies
4.14.1      All mechanical treatment plants will have  laboratory
       facilities with sufficient equipment to conduct operational

       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
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  -  —
4.14.3      Safety equipment, such as eye wash stations, emergency
       showers, first aid kits, and fire extinguishers, will be
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

        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
            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.

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.