Onsite Wastewater Treatment Onsite Wastewater Treatment TechnologiesTechnologies

Modified from the work of

Dave LenningWashington Onsite Sewage Association

AcknowledgementAcknowledgement

This work was supported [in part] by the National This work was supported [in part] by the National Decentralized Water Resources Capacity Development Project Decentralized Water Resources Capacity Development Project with funding provided by the U.S. Environmental Protection with funding provided by the U.S. Environmental Protection

Agency through a Cooperative Agreement (EPA No. Agency through a Cooperative Agreement (EPA No. CR827881CR827881--0101--0) with Washington University in St. Louis.0) with Washington University in St. Louis. The The

results have not been reviewed by EPA or Washington results have not been reviewed by EPA or Washington University in St. Louis. The views expressed in this University in St. Louis. The views expressed in this

presentation are solely those of NCSU, and University of presentation are solely those of NCSU, and University of Arkansas and EPA and Washington University in St. Louis do Arkansas and EPA and Washington University in St. Louis do not endorse any products or commercial services mentioned in not endorse any products or commercial services mentioned in

the presentation.the presentation.

Onsite Treatment TechnologiesOnsite Treatment TechnologiesDecentralized Wastewater Treatment Systems Decentralized Wastewater Treatment Systems (DWTS)(DWTS)

NSFCNSFC

ObjectivesObjectivesInvestigate the technologies that are available for Investigate the technologies that are available for the renovation of domestic wastewaterthe renovation of domestic wastewater

Treatment is either onsite or nearTreatment is either onsite or near--site from source of site from source of wastewaterwastewaterBasics on how these systems operateBasics on how these systems operateWhy and where they should be usedWhy and where they should be used

Why Not Sewer all Residential Why Not Sewer all Residential Areas?Areas?

Money and RealityMoney and RealityIt does not make financial senseIt does not make financial senseAll treated water would be returned to surface All treated water would be returned to surface sourcesource

However, we need to treat sewageHowever, we need to treat sewagePublic health concernsPublic health concernsEnvironmental quality concernsEnvironmental quality concerns

We need to find acceptable level of riskWe need to find acceptable level of riskCentralized systems are monitored and maintainedCentralized systems are monitored and maintainedDecentralized systems ?Decentralized systems ?

Wastewater Infrastructure:Wastewater Infrastructure:

For centralized sewers For centralized sewers –– a means to transmit a means to transmit wastewater from sources to treatment & wastewater from sources to treatment & dispersal componentsdispersal components

NSFC

Wastewater Infrastructure:Wastewater Infrastructure:

Collection/Transmission

For decentralized systems For decentralized systems -- the same the same components are required, but on a smaller components are required, but on a smaller scalescale

Pretreatment Final Treatment/Dispersal

Typical Onsite SystemTypical Onsite System

Source

Pretreatment

Final treatment & dispersal

Reserve area

Big PictureBig PictureWastewater Infrastructure must be able to:Wastewater Infrastructure must be able to:

CollectCollectTransportTransportTreatTreatDisperseDisperse

Today’s focus for decentralized systemsToday’s focus for decentralized systemsPrePre--treatmenttreatmentTreatmentTreatmentDispersalDispersal

Treatment OptionsTreatment Options

Traditionally, have been categorized as:Traditionally, have been categorized as:Primary Primary

•• liquid liquid -- solid separationsolid separation•• septic or primary tanksseptic or primary tanks

Secondary Secondary •• BOD and suspended solids removalBOD and suspended solids removal•• biological reactorsbiological reactors

Tertiary Tertiary •• nutrient removal and nutrient removal and disinfectiondisinfection

Primary TreatmentPrimary TreatmentSeptic TanksSeptic Tanks

Separate solids from liquidSeparate solids from liquidAnaerobic decompositionAnaerobic decompositionAttenuate surgesAttenuate surges

NSFC

Septic TankSeptic Tank

Dense solids sink and Solids less dense than Dense solids sink and Solids less dense than water will floatwater will float

Most common unit for OWTSMost common unit for OWTSUsed alone or with other pretreatment unitsUsed alone or with other pretreatment unitsSimple and generally inexpensive ($100s)Simple and generally inexpensive ($100s)3030--50% reduction BOD50% reduction BOD55, 60, 60--80% reduction TSS80% reduction TSS

Septic TankSeptic Tank

Design considerationsDesign considerations1 or 2 compartments1 or 2 compartments

Septic TankSeptic TankDesign considerationsDesign considerations

RisersRisersGas deflectors

USEPA Manual, 1980

Gas deflectors

USEPA Manual, 1980

Septic TankSeptic TankDesign considerationsDesign considerations

Effluent screenEffluent screen

NSFC

Septic TankSeptic TankOther pertinent informationOther pertinent information

Septage must be properly handledSeptage must be properly handledAccess is neededAccess is neededActivated carbon filters can help with odorsActivated carbon filters can help with odorsAdditives not needed!Additives not needed!

Grease InterceptorGrease Interceptor

Grease separatorGrease separatorfor food preparation businesses for food preparation businesses that are serviced by an onsite that are serviced by an onsite systemsystemhigh maintenance productshigh maintenance productshistorically, not good historically, not good performanceperformance

•• high temperature automatic dish high temperature automatic dish washers keep grease soluble washers keep grease soluble

Secondary TreatmentSecondary TreatmentAerobic treatment unitsAerobic treatment units

small activated sludge plantssmall activated sludge plantssuspended growth suspended growth bioreactorsbioreactors

PackedPacked--bed media filtersbed media filterssmall trickling filterssmall trickling filtersattached growth attached growth bioreactorsbioreactors

Combination systemsCombination systemsutilize the best of suspended and attached growthutilize the best of suspended and attached growth

Aerobic Treatment UnitsAerobic Treatment UnitsSupplies dissolved oxygen to aerobic microbesSupplies dissolved oxygen to aerobic microbes

Aerobic Treatment UnitAerobic Treatment UnitBiological reactorBiological reactor

DO, microorganisms and food must be in contactDO, microorganisms and food must be in contactThe effluent is aerated via one of several means.The effluent is aerated via one of several means.Aerobic organisms digest foodAerobic organisms digest foodGenerates high quality effluents with variety of oxidized Generates high quality effluents with variety of oxidized end products end products -- little odor, stable effluent not requiring little odor, stable effluent not requiring further breakdownfurther breakdown10 10 -- 20 times faster than anaerobic20 times faster than anaerobic

Aerobic Treatment UnitAerobic Treatment UnitTypical componentsTypical components

Purdue University

Aerobic Treatment UnitAerobic Treatment UnitSequencing batch reactors or Periodic Sequencing batch reactors or Periodic processesprocesses

Intermittent inflow Continuous inflow

USEPA Manual, 2002USEPA Manual, 1980

PackedPacked--Bed Media FiltersBed Media FiltersAttached growth Attached growth bioreactorsbioreactors

similar to trickling rock filterssimilar to trickling rock filters

PackedPacked--Bed Media FiltersBed Media FiltersWhat is it?What is it?

A container or lined A container or lined excavation containing a excavation containing a specific media through specific media through which wastewater flowswhich wastewater flowsAn aerobic, fixedAn aerobic, fixed--film film bioreactorbioreactor

PackedPacked--Bed Media FiltersBed Media FiltersOpenOpen--Cell Foam CubesCell Foam Cubes

wastewater is sprayed over cubeswastewater is sprayed over cubeswater trickles through mediawater trickles through mediacollected at bottom of containercollected at bottom of container

PackedPacked--Bed Media FiltersBed Media FiltersNonNon--Woven Textile SheetsWoven Textile Sheets

PackedPacked--Bed Media FiltersBed Media Filters

PeatPeatNSFCNSFC

PackedPacked--Bed Media FiltersBed Media FiltersOther MediaOther Media

PackedPacked--Bed Media FiltersBed Media FiltersSingleSingle--pass optionpass option

PackedPacked--Bed Media FiltersBed Media Filters

MultipleMultiple--passpass

NSFC

Final Treatment and DispersalFinal Treatment and Dispersal

Final Treatment by the physical, chemical and Final Treatment by the physical, chemical and biological processes in the soilbiological processes in the soilDispersal of the treated water back into the Dispersal of the treated water back into the hydrologic cyclehydrologic cycle

Final Treatment & Dispersal OptionsFinal Treatment & Dispersal Options

PurposePurposeMay provide further treatmentMay provide further treatmentTo assimilate the treated effluent To assimilate the treated effluent into the into the receiving environmentreceiving environment in in such a way that neither public such a way that neither public health nor environmental quality health nor environmental quality are adversely impacted.are adversely impacted.

Subsurface DispersalSubsurface DispersalDrainfieldDrainfield

InfiltrativeInfiltrative surface (point of application) surface (point of application) -- bottom bottom surfacesurface

USEPA Manual, 1980

SoilSoil--Based System SelectionBased System Selection

Restrictive layer

Soil depth

Application & Distribution of Application & Distribution of Effluent to SoilEffluent to Soil

Two general options available:Two general options available:GravityGravity--flowflowDosedDosed--flowflow

Application & Distribution OptionsApplication & Distribution Options

GravityGravity--flow distribution flow distribution -- DescriptionDescriptionEffluent flows out of one component to the next Effluent flows out of one component to the next downstream component and on to an infiltrative downstream component and on to an infiltrative surface by gravity.surface by gravity.Flow will be dependent on when flow occurs.Flow will be dependent on when flow occurs.Considered to be nonConsidered to be non--uniform over infiltrative uniform over infiltrative surface.surface.Unless properly managed, the biomat may become Unless properly managed, the biomat may become too restrictive.too restrictive.

GravityGravity--Flow DistributionFlow DistributionParallel distributionParallel distribution

Network of equal length lateralsNetwork of equal length laterals•• Receive flow by gravityReceive flow by gravity•• Distribute flow by gravityDistribute flow by gravity

Typically 4Typically 4--inch pipeinch pipeNeeds flowNeeds flow--splitting devicesplitting device

GravityGravity--Flow DistributionFlow Distribution

Parallel distributionParallel distributionFlowFlow--splitting devicessplitting devices

•• distribution boxdistribution box•• tees/wyes/headertees/wyes/header

GravityGravity--Flow DistributionFlow Distribution

Parallel distributionParallel distributionEach lateral should be parallel to slope contourEach lateral should be parallel to slope contourBottom of each lateral should be flatBottom of each lateral should be flatEven if there are equal flows to each lateral, flows Even if there are equal flows to each lateral, flows will will notnot be uniform down length of lateralsbe uniform down length of lateralsBecause of nonBecause of non--uniform distribution, use of this uniform distribution, use of this option is limited in some jurisdictionsoption is limited in some jurisdictions

GravityGravity--Flow DistributionFlow DistributionSerial distributionSerial distribution

Receives flow by gravityReceives flow by gravityDistributes flow by gravityDistributes flow by gravitySequentiallySequentially loads laterals, forcing one to fully loads laterals, forcing one to fully pond before a gravity flow to the next lateralpond before a gravity flow to the next lateralTypically uses 4 inch pipeTypically uses 4 inch pipeNeeds device to force ponding and allow Needs device to force ponding and allow sequential loading of lateralssequential loading of laterals

GravityGravity--Flow DistributionFlow DistributionSerial distributionSerial distribution

Relief lineRelief line•• Simple overflow line from one trench to the next Simple overflow line from one trench to the next

downslope trench downslope trench

GravityGravity--Flow DistributionFlow DistributionSerial distribution Serial distribution -- Relief lineRelief line

Forces liquid to pond to predetermined level in Forces liquid to pond to predetermined level in upslope lateral before flowing to the next one upslope lateral before flowing to the next one

USEPA Manual, 1980

Subsurface DispersalSubsurface DispersalDrainfieldDrainfield

Gravel or gravelless product fills trench/bedGravel or gravelless product fills trench/bed

Subsurface DispersalSubsurface DispersalDrainfieldDrainfield

with aggregatewith aggregate

Subsurface DispersalSubsurface DispersalDrainfieldDrainfield

Design considerationsDesign considerations•• Sized by soil and design flow (gallons/ftSized by soil and design flow (gallons/ft22/day)/day)

BottomBottomSidewallSidewall

•• Need aerated soil belowNeed aerated soil below•• Many configurationsMany configurations•• Maximum slopes typically of 20% Maximum slopes typically of 20% -- 45%45%

Subsurface DispersalSubsurface Dispersal

DrainfieldDrainfieldDesign considerationsDesign considerations

•• Long & narrow as possibleLong & narrow as possible•• Follow the contoursFollow the contours

NSFC

Subsurface DispersalSubsurface DispersalAtAt--grade systemgrade system

Subsurface DispersalSubsurface DispersalAtAt--grade systemgrade system

Uses native, original soilsUses native, original soilsThere’s insufficient soil depth for a typical subsurface system There’s insufficient soil depth for a typical subsurface system but enough so a mound isn’t required.but enough so a mound isn’t required.Used with gravity or pressure distribution. A pressure Used with gravity or pressure distribution. A pressure distribution or dripline network are recommended.distribution or dripline network are recommended.Low linear loading rateLow linear loading rate––long & narrowlong & narrowProper preparation of surface is criticalProper preparation of surface is critical

Subsurface DispersalSubsurface Dispersal

Mound systemMound system

NSFC

Subsurface DispersalSubsurface Dispersal

Mound systemMound systemUsed where soil too shallow for other subsurface Used where soil too shallow for other subsurface dispersal technologies or where soils are too coarse.dispersal technologies or where soils are too coarse.Typically, 12Typically, 12--24 inches of original soil are 24 inches of original soil are required.required.Treatment provided in sand with more polishing Treatment provided in sand with more polishing provided by original soil.provided by original soil.Pressure distribution or dripline networks are Pressure distribution or dripline networks are strongly recommended.strongly recommended.

Application & Distribution OptionsApplication & Distribution Options

DosedDosed--flow distributionflow distributionPredetermined volumes of effluent are held in a Predetermined volumes of effluent are held in a chamber and dosed to the next component.chamber and dosed to the next component.This provides:This provides:

•• More uniform loading to next componentMore uniform loading to next component•• Resting times between dosesResting times between doses

To next To next componentcomponent

Pretreatment Pretreatment unitunit

Holding chamber & Holding chamber & dosing devicedosing device

DosedDosed--Flow DistributionFlow DistributionOther pertinent informationOther pertinent information

Can be used to distribute effluent in almost any Can be used to distribute effluent in almost any situationsituationCosts more and is more complex than gravity flowCosts more and is more complex than gravity flowFor many has become the method of choiceFor many has become the method of choiceOnOn--going monitoring & maintenance are importantgoing monitoring & maintenance are importantControl panels with AlarmsControl panels with Alarms

DosedDosed--Flow DistributionFlow DistributionDosing methods Dosing methods -- DemandDemand

Dose occurs when sufficient volume of Dose occurs when sufficient volume of effluent has been collected.effluent has been collected.Dosing frequency depends on how much Dosing frequency depends on how much wastewater is being generated.wastewater is being generated.There is no control on how much effluent is There is no control on how much effluent is being dosed daily.being dosed daily.

DosedDosed--Flow DistributionFlow DistributionDosing methods Dosing methods -- TimedTimed

A timer controls the number of doses per day and A timer controls the number of doses per day and the dose volume.the dose volume.Will allow only a certain amount of effluent to be Will allow only a certain amount of effluent to be dosed daily.dosed daily.Is more costly and complicated.Is more costly and complicated.Protects downstream components from Protects downstream components from overloading.overloading.Useful for controlling surges or bigUseful for controlling surges or big--flow days.flow days.

DosedDosed--Flow DistributionFlow Distribution

Dosing devices Dosing devices –– PumpPumpIn pump tankIn pump tank

NSFCNSFC

DosedDosed--Flow DistributionFlow DistributionDosing devices Dosing devices –– SiphonSiphon

Passive device, part of a demand systemPassive device, part of a demand systemPower is not requiredPower is not requiredProper installation is criticalProper installation is critical

DosedDosed--Flow DistributionFlow Distribution

Options Options –– Dose to gravityDose to gravityWhen drainfield is at higher elevation than septic When drainfield is at higher elevation than septic tanktank

NSFCNSFC

DosedDosed--Flow DistributionFlow DistributionOptions Options –– Pressure distributionPressure distribution

Designed to distribute effluent uniformly over Designed to distribute effluent uniformly over infiltrative surface of receiving component.infiltrative surface of receiving component.

Pressure DistributionPressure DistributionObjectives:Objectives:

Quickly pressurize networkQuickly pressurize networkBe fully pressurized for most of doseBe fully pressurized for most of doseMinimize draining into lower lateralsMinimize draining into lower lateralsHave about the same amount of effluent reach each Have about the same amount of effluent reach each square foot of infiltrative surfacesquare foot of infiltrative surface

Pressure DistributionPressure DistributionLow Pressure Pipe System (LPP)Low Pressure Pipe System (LPP)

Pressure DistributionPressure Distribution

Low Pressure Pipe System (LPP)Low Pressure Pipe System (LPP)Laterals are typically 1Laterals are typically 1--2 inches in diameter2 inches in diameterOrifices are typically 1/8 to 3/16 inches in diameterOrifices are typically 1/8 to 3/16 inches in diameterDepending on specific site, there is usually one Depending on specific site, there is usually one orifice every 4orifice every 4--15 square feet15 square feetOrifices can face 6 o’clock or 12 o’clockOrifices can face 6 o’clock or 12 o’clockLow pressures in network Low pressures in network -- typically between 2 and typically between 2 and 5 feet of head (maximum differences exist)5 feet of head (maximum differences exist)

Pressure DistributionPressure Distribution

How it worksHow it worksPredetermined quantity of effluent collectedPredetermined quantity of effluent collectedAt predetermined volume or time, dosing device At predetermined volume or time, dosing device discharges effluent to distribution networkdischarges effluent to distribution networkBecause of small pipe and orifices, distribution Because of small pipe and orifices, distribution network pressurizes quicklynetwork pressurizes quicklyCurrent design objectives want equal amounts of Current design objectives want equal amounts of effluent from each orificeeffluent from each orifice

Pressure DistributionPressure Distribution

Drip distributionDrip distributionA small diameter pressurized distribution A small diameter pressurized distribution network that delivers small, precise volumes of network that delivers small, precise volumes of pretreated effluent at slow controlled rates.pretreated effluent at slow controlled rates.

Drip DistributionDrip Distribution

Like miniature version of pressure distributionLike miniature version of pressure distributionEmitters instead of orificesEmitters instead of orifices

Geoflow

Drip DistributionDrip DistributionContentsContents

Drip dispersal componentsDrip dispersal components

Drip DistributionDrip DistributionHow it worksHow it works

On a timed cycle, effluent discharged by pumpOn a timed cycle, effluent discharged by pumpEffluent filtered (Effluent filtered (≤≤ 100 microns)100 microns)Supply line feeds manifold and drip linesSupply line feeds manifold and drip linesEffluent flows out of emitters into soil or mediaEffluent flows out of emitters into soil or mediaPeriodically, a solenoid valve (or manual valve) opens Periodically, a solenoid valve (or manual valve) opens and dripline is flushedand dripline is flushedFilters are periodically flushedFilters are periodically flushed

Drip DistributionDrip DistributionHow it worksHow it works

Drip DistributionDrip DistributionInstallation considerationsInstallation considerations

Trencher

Static Plow Vibratory Plow

Application & Dispersal OptionsApplication & Dispersal Options

Surface dispersalSurface dispersalNot the preferred option if soil and site conditions Not the preferred option if soil and site conditions are suitable for subsurface dispersalare suitable for subsurface dispersalOptions:Options:

•• To the surface of the groundTo the surface of the ground•• To surface waterTo surface water

Increased exposure to public and animalsIncreased exposure to public and animalsDischarge permits may be requiredDischarge permits may be requiredNot permitted in many states & provincesNot permitted in many states & provinces

Surface DispersalSurface Dispersal

To the surface of the groundTo the surface of the groundUniform application needed to prevent pondingUniform application needed to prevent pondingSufficient area neededSufficient area neededFencing may be requiredFencing may be requiredMost jurisdictions require pretreatment by an ATU Most jurisdictions require pretreatment by an ATU or media filter, followed by disinfectionor media filter, followed by disinfectionOnOn--going monitoring & maintenance are criticalgoing monitoring & maintenance are critical

Surface DispersalSurface Dispersal

To the surface of the To the surface of the ground ground –– spray spray irrigationirrigation

Proper nozzle Proper nozzle selection is criticalselection is criticalWant to minimize Want to minimize aerosolsaerosols

Texas A&M University

Surface DispersalSurface DispersalTo the surface of the ground To the surface of the ground –– spray spray irrigationirrigation

Surface DispersalSurface Dispersal

To surface waterTo surface water•• Significant pretreatment requiredSignificant pretreatment required•• In U.S. requirements of NPDES permit must be metIn U.S. requirements of NPDES permit must be met•• Strongly discouraged, not permitted in most jurisdictionsStrongly discouraged, not permitted in most jurisdictions

QuestionsQuestions