collection systems

Wastewater CollectionWastewater Collection(Sewer Alternatives)(Sewer Alternatives)

Sewer BasicsSewer Basics Collection and transportCollection and transport of wastewater from each of wastewater from each

home/building to the point where treatment occurs.home/building to the point where treatment occurs.

Wastewater CharacterizationWastewater Characterization• SolidsSolids• LiquidsLiquids

Pipe SystemPipe System• PlasticPlastic• Ductile ironDuctile iron• Concrete/linedConcrete/lined

Satellite Wastewater ManagementSatellite Wastewater Management

Also called Also called ““decentralizeddecentralized”” or or ““distributeddistributed””

Undertaken by utilities for a variety of reasons:Undertaken by utilities for a variety of reasons: EconomicsEconomics To reuse water locallyTo reuse water locally To avoid expanding “centralized facilitiesTo avoid expanding “centralized facilities

As communities expand, the distances from the new As communities expand, the distances from the new developments to existing wastewater treatment facilities developments to existing wastewater treatment facilities becomes so great as to not be economically feasiblebecomes so great as to not be economically feasible

SustainableSustainable Cost Effective, good for the public and the environmentCost Effective, good for the public and the environment

Collection System AlternativesCollection System Alternatives

1.1. Conventional Gravity sewersConventional Gravity sewers2.2. Septic Tank Effluent Gravity (STEG)Septic Tank Effluent Gravity (STEG)3.3. Septic Tank Effluent Pump (STEP)Septic Tank Effluent Pump (STEP)4.4. Pressure Sewers with Grinder PumpsPressure Sewers with Grinder Pumps5.5. Vacuum SewersVacuum Sewers

Conventional Gravity vs. Pressure SewersConventional Gravity vs. Pressure Sewers

Sewer Alternatives and CharacteristicsSewer Alternatives and Characteristics

Conventional Gravity SewerConventional Gravity Sewer Large pipe (8” minimum), manholes spaced 300-500 feetLarge pipe (8” minimum), manholes spaced 300-500 feet Designed to transport solidsDesigned to transport solids Minimum velocity >2 fps Minimum velocity >2 fps (to avoid the deposition of solids)(to avoid the deposition of solids) Max Max

velocity = 15 fpsvelocity = 15 fps Infiltration and Inflow (I & I)Infiltration and Inflow (I & I) Uniform Slope between manholes Uniform Slope between manholes

• Sewer sizeSewer size Minimum slope (feet/100 ft)Minimum slope (feet/100 ft)• 8-inch8-inch 0.400.40• 10-inch10-inch 0.280.28• 12-inch12-inch 0.220.22• 14-inch14-inch 0.170.17• 16-inch16-inch 0.140.14• 18-inch18-inch 0.120.12• 24-inch24-inch 0.080.08

Conventional Gravity SewerConventional Gravity Sewer

Conventional Gravity SewerConventional Gravity SewerAlignment:Alignment: 24-inch sewers (or smaller) should be laid with 24-inch sewers (or smaller) should be laid with

straight alignment between manholes.straight alignment between manholes.

Changes in pipe size:Changes in pipe size: When a smaller sewer joins a larger When a smaller sewer joins a larger one (at a manhole), the invert (bottom) of the larger sewer one (at a manhole), the invert (bottom) of the larger sewer should be lowered sufficiently to overcome head losses. An should be lowered sufficiently to overcome head losses. An approximate method is to place the 0.8 depth point of both approximate method is to place the 0.8 depth point of both sewers at the same elevation.sewers at the same elevation.

Sewer Materials:Sewer Materials: many types, materials and bedding shall many types, materials and bedding shall prevent damage from external loads, and joints shall prevent prevent damage from external loads, and joints shall prevent leakageleakage

0.8 depths are aligned

ManholesManholes* Located at changes in sewer size, direction, or slope

* Or every 300-500 feet

* Provides access for maintenance (cleanout, etc.)

* Problematic because of Infiltration and Inflow (I&I)


Bedding:Bedding: specified by an engineer for pipe type and anticipated loads specified by an engineer for pipe type and anticipated loads


Backfill:Backfill: suitable material, free of debris, stones, etc.suitable material, free of debris, stones, etc. DO NOT DISTURB SEWER ALIGNMENTDO NOT DISTURB SEWER ALIGNMENT

Separation from Water Lines:Separation from Water Lines:• 10 feet horizontal10 feet horizontal• Water line 18-inches above sewerWater line 18-inches above sewer

Crown CorrosionCrown Corrosion

H2S + H2O H2SO4

H2S

H2SO4

Estimating FlowrateEstimating Flowrate Equivalent Dwelling Unit (EDU)Equivalent Dwelling Unit (EDU)

A residence with a given number of people (say 3.5)A residence with a given number of people (say 3.5) Represents the average household flowrateRepresents the average household flowrate

Design Peak Flowrate (DPF)Design Peak Flowrate (DPF) Flowrate expected in the collection system, assuming a given number of Flowrate expected in the collection system, assuming a given number of

EDUs are discharging at the same timeEDUs are discharging at the same time Typical values for systems with >50 EDUs is 0.35 to 0.5 gal/min-EDUTypical values for systems with >50 EDUs is 0.35 to 0.5 gal/min-EDU Total DPF QTotal DPF QDPDP = 0.5 N = 0.5 N

Septic Tank Effluent GravitySeptic Tank Effluent GravitySTEGSTEG

Small diameter plastic pipeSmall diameter plastic pipe Conveys effluent from a septic tankConveys effluent from a septic tank

• with an effluent filterwith an effluent filter No solids to transport No solids to transport (no minimum velocity required)(no minimum velocity required) Can be installed at variable (flat) gradesCan be installed at variable (flat) grades No manholesNo manholes Air-release valves needed at high pointsAir-release valves needed at high points

Septic Tank Effluent GravitySeptic Tank Effluent GravitySTEGSTEG

STEG Sewer ComponentsSTEG Sewer Components

Pipe Size and VelocityPipe Size and Velocity

Septic Tank Effluent PumpSeptic Tank Effluent PumpSTEPSTEP

High-head turbine pump used to pump screened septic tank High-head turbine pump used to pump screened septic tank effluent into a pressurized collection system.effluent into a pressurized collection system.

Small diameter, plastic pipe (2-inch)Small diameter, plastic pipe (2-inch) No Solids transport No Solids transport (no minimum velocities required)(no minimum velocities required) Installed shallowInstalled shallow Can follow terrainCan follow terrain Air-release valves incorporatedAir-release valves incorporated

STEP ComponentsSTEP Components Building sewer (from house to septic tank)Building sewer (from house to septic tank) Septic Tank (or interceptor tank)Septic Tank (or interceptor tank) Vaults/pump basins (effluent filter and pump)Vaults/pump basins (effluent filter and pump) Pumps (submersible, high-head, turbine)Pumps (submersible, high-head, turbine) Service lateral (1.25-inch typical)Service lateral (1.25-inch typical) Check Valves (at pump outlet and at edge of property)Check Valves (at pump outlet and at edge of property)

Septic Tank Effluent PumpSeptic Tank Effluent PumpSTEPSTEP

STEP System Design DataSTEP System Design Data

STEP System Interceptor TankSTEP System Interceptor Tank

Pressure Sewer with Grinder PumpsPressure Sewer with Grinder Pumps

Discharge pump with chopper blades in a small pump basinDischarge pump with chopper blades in a small pump basin Small diameter, pressure line, installed shallowSmall diameter, pressure line, installed shallow Solids and greases are transportedSolids and greases are transported Relatively simple installationRelatively simple installation Somewhat higher O&MSomewhat higher O&M No I&INo I&I

Pressure SewerPressure SewerGrinder Pump basinGrinder Pump basin

Grinder Grinder PumpPumpBasinBasin

Vacuum SewerVacuum Sewer Central vacuum source maintains a Central vacuum source maintains a

vacuum on a small diameter sewervacuum on a small diameter sewer Pulls wastewater to a central locationPulls wastewater to a central location Ideal application:Ideal application:

• Flat terrainFlat terrain• High water tableHigh water table• 70-100 connections to be economical70-100 connections to be economical

Vacuum SewerVacuum Sewer

Vacuum Sewer ComponentsVacuum Sewer Components

Vacuum StationVacuum Station

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