Wastewater Treatment Wastewater Treatment in Soilsin SoilsJames L. Anderson, PhD

David GustafsonAziz Amoozegar, PhD

David Lindbo, PhD

Model Decentralized Wastewater Practitioner Curriculum

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CitationCitationGustafson, D., J. Anderson, A. Amoozegar, and Gustafson, D., J. Anderson, A. Amoozegar, and

D.L. Lindbo. 2005. Wastewater Treatment in D.L. Lindbo. 2005. Wastewater Treatment in Soils Soils –– Power Point Presentation. Power Point Presentation. inin (D.L. (D.L. Lindbo and N.E. Deal eds.) Model Decentralized Lindbo and N.E. Deal eds.) Model Decentralized Wastewater Practitioner Curriculum. National Wastewater Practitioner Curriculum. National Decentralized Water Resources Capacity Decentralized Water Resources Capacity Development Project. North Carolina State Development Project. North Carolina State University, Raleigh, NC.University, Raleigh, NC.

OverviewOverview

What is Sewage?What is Sewage?What kinds of Systems?What kinds of Systems?What is Soil?What is Soil?How do Soils & Sewage interact?How do Soils & Sewage interact?

Biomat and the treatment environmentBiomat and the treatment environmentConcernsConcerns

SewageSewageWhat is it?What is it?

WaterWaterBacteria foodBacteria food

•• BODBOD•• NutrientsNutrients

TSSTSS•• SolidsSolids

PathogensPathogensSolutes Solutes OthersOthers

The BIG PictureThe BIG Picture

Impermeable Layer

Ground Water

Slow Moving

Lateral Flow

Deep Percolation

Slowly Permeable layer

Stream

Water Table

Ground WaterMounding

Vadose Zone

Septic System

WastewaterInput Runoff

Infiltration

Precipitation

Evapotranspiration

Well

SystemsSystems

High O2 flow to infiltrative surface – good treatment

Low O2 flow to infiltrative surface –poor treatment

Protection methodsProtection methods

Separation Separation VerticalVerticalCovered Covered

SetbacksSetbacks

What is Soil?What is Soil?Particles Particles –– TextureTexture

% Sand % Sand -- % Silt % Silt -- % Clay% ClayStructureStructure

Minerals & Nutrients Minerals & Nutrients Organic matterOrganic matter

Pores: Air & WaterPores: Air & WaterSurface AreaSurface AreaSoil OrganismsSoil Organisms

How wastewater is treated?How wastewater is treated?

Inside the trench the conditions are Inside the trench the conditions are AnaerobicAnaerobicAerobic environmentAerobic environmentBacteriaBacteriaUnsaturatedUnsaturatedFlow Flow

Depth & TreatmentDepth & TreatmentSeparation distance allows for interactions Separation distance allows for interactions with particles and bacteriawith particles and bacteriaOxygen is critical for aerobic environmentOxygen is critical for aerobic environmentShallower systems have more:Shallower systems have more:

ReRe--aeration potentialaeration potentialSeparationSeparationEvapotranspirationEvapotranspiration

Soil DevelopmentSoil Development

Parent MaterialParent MaterialSoil profileSoil profile

Environmental ChangesEnvironmental ChangesLandscape PositionLandscape Position

Parent MaterialParent Material

TillTillOutwashOutwashLoessLoessLacustrineLacustrineBedrockBedrock

Weather bedrockWeather bedrockOrganicOrganic

Environmental ChangesEnvironmental ChangesCompactionCompactionTemperatureTemperatureWaterWaterWindWindVegetationVegetation

Landscape PositionLandscape Position

ErosionErosionTransferTransferWetnessWetness

Soil Profile and HorizonsSoil Profile and Horizons

Understanding these Understanding these ideas will help in ideas will help in create a better create a better system designsystem design

Unsaturated SoilUnsaturated SoilSoil color is important in identifying the Soil color is important in identifying the Aerobic state of the soilAerobic state of the soilBright colors are Bright colors are well aerated or drainedwell aerated or drainedGrays Grays ((redoxredox features)features)are wetare wet

Color & SaturationColor & Saturation

Well Drained Moderately Well Drained

Poorly Drained

Munsell ColorbookMunsell Colorbook

Other visual keys Other visual keys determination to saturated determination to saturated

conditionsconditions

TextureTextureCoarser soils:Coarser soils:

Faster movementFaster movementLess surface areaLess surface areaLess removal sitesLess removal sites

Finer soils:Finer soils:Slower movementSlower movementMore surface areaMore surface areaMore removal sitesMore removal sites

TextureTexture

How big a system should I installHow big a system should I installSandSand-------- Loam Loam -------- ClayClay

StructureStructure

Soil Structure impactsSoil Structure impacts

# PoresWater

MovementMany High

Few Low

Major TypesGranularPrismaticBlockyPlatyMassive

Granular Soil StructureGranular Soil Structure

Photo by M. Stolt

Columnar Soil StructureColumnar Soil Structure

Photos by G. Loomis

Sandy Textured Structureless –

Single Grain Soil

Sandy Textured Structureless –

Single Grain Soil

High potential for poor wastewater treatment High potential for poor wastewater treatment

Soil Structure

Easily altered or destroyedDynamic, changed by:

• Moisture content• Chemistry of soil water• Biological activity• Construction/ management practices• Clay mineralogy

What happens when you put What happens when you put wastewater in the soil?wastewater in the soil?

BiomatBiomat formsformsCreating Creating unsaturated flowunsaturated flow

This means:This means:More contact with the soil particlesMore contact with the soil particlesAerobic organisms treat the wastewaterAerobic organisms treat the wastewater

A cross section of BiomatA cross section of Biomat

Biomat Biomat

How do pathogens get How do pathogens get treated?treated?

They are physically filteredThey are physically filteredThey are attached to the soil particlesThey are attached to the soil particlesThey die due to environmental conditionsThey die due to environmental conditionsThey are attacked by soil organismsThey are attacked by soil organisms

Given time the soil is a very effective Given time the soil is a very effective treatment mediumtreatment medium

Pathogen retentionPathogen retention

Pathogen removalPathogen removal

What Nutrients?What Nutrients?

Nutrients of concern Nutrients of concern Nitrogen & PhosphorusNitrogen & PhosphorusN N -- groundwater troublegroundwater troubleP P -- Surface water troubleSurface water trouble

Points of impactPoints of impact

PhosphorusPhosphorus

P complexes with other minerals in the soil P complexes with other minerals in the soil The complexes are insolubleThe complexes are insolubleP will move if the soil moves (erosion)P will move if the soil moves (erosion)Some of the P is used by the vegetationSome of the P is used by the vegetationSoils have finite capacities to sorbs Soils have finite capacities to sorbs PhosphorusPhosphorus

Very slowly solubleCa-P minerals

P retained by clay& iron & aluminum oxides

Soil solut ion

People

Animals

Fert ilizers

Readily solubleCa-P minerals

P occluded in iron& aluminum minerals

extremely insoluble

Loss in runoff

Loss on erodedsoil particles

Soil organisms biomass

P in active soil organic matter

P in slow & passivesoil organic mat ter

Plant residues,manure,biosolids

Root uptake

Desorption

Adsorption

Immobilization

Minerialization

Inorganic forms of P

Organic forms of P

Dominantforms of Pin high pH

&calcareous soils

Phosphorus Removal in Phosphorus Removal in Conventional Septic SystemsConventional Septic Systems

• Phosphorus adsorbed to iron, aluminum, calcium, and magnesium in soils

• P removal depends on soil surface area

• Sands have less surface area than finersoil particles

• Wet soils have potentially less iron in them, so less P removal potential

Nitrogen Removal in Conventional Septic System

Less than 15 percent removal in septic tank

Septic tank effluent composed of organic-Nand ammonium-N

Conversion to nitrate-N in drainfield

Nitrate-N very mobile

10 ppm EPA nitrate-N drinking water standard

NitrogenNitrogen

N starts as AmmoniaN starts as AmmoniaIn an aerobic environment it is transformed In an aerobic environment it is transformed to Nitrateto NitrateNitrate moves with the water unless Nitrate moves with the water unless additional treatment steps are takenadditional treatment steps are taken

NH4+

NO3-O2

N Cycle in Septic SystemsN Cycle in Septic Systems

Nitrification and SorptionNitrification and Sorption

Denitrification ?Denitrification ?

Min

erM

iner

ImmobilizationImmobilization

aliza

tion

aliza

tion

Nitrogen Removal in Nitrogen Removal in Conventional Septic SystemConventional Septic System

Less than 15 percent removal in septic tankLess than 15 percent removal in septic tank

Septic tank effluent composed of organicSeptic tank effluent composed of organic--NNand ammoniumand ammonium--N N

Conversion to nitrateConversion to nitrate--N in drainfield N in drainfield

NitrateNitrate--N very mobile and conservative N very mobile and conservative

10 ppm EPA nitrate10 ppm EPA nitrate--N drinking water standardN drinking water standard

VOC and HCsVOC and HCs

SourceSourcecleaning fluids, solventscleaning fluids, solvents

Variable amountsVariable amounts

VOC and HCs: ConcernsVOC and HCs: Concerns

CarcinogensCarcinogensToxinsToxins

VOC and HCs: ReactionsVOC and HCs: Reactions

SorptionSorptionMicrobial transformationMicrobial transformationVolatilizationVolatilization

Additives have been Additives have been shown to assist in a shown to assist in a

system stressed by VOCs system stressed by VOCs and HCsand HCs

Pollutant attenuation potentialPollutant attenuation potential

+ = promotes attenuation- = discourages attenuation

Pollutant

Phosphorus

Nitrogen

Pathogens

AerobicSoils

+

-

+

W etSoils

-

+

-

SandySoils

-

-

-

Non- SandySoils

+

+

+

Treatment ChallengesTreatment Challenges

Shallow bedrockShallow bedrockKarstKarst bedrockbedrockSaturated soilsSaturated soilsSlowly permeable soilsSlowly permeable soilsRapidly permeable soilsRapidly permeable soilsFill soilsFill soilsSeasonally used systemsSeasonally used systems

N Cycle in Septic SystemsN Cycle in Septic Systems

Nitrification and SorptionNitrification and Sorption

Denitrification ?Denitrification ?

Min

erM

iner

ImmobilizationImmobilization

aliza

tion

aliza

tion

Nitrogen Removal in Nitrogen Removal in Conventional Septic SystemConventional Septic System

Less than 15 percent removal in septic tankLess than 15 percent removal in septic tank

Septic tank effluent composed of organicSeptic tank effluent composed of organic--NNand ammoniumand ammonium--N N

Conversion to nitrateConversion to nitrate--N in drainfield N in drainfield

NitrateNitrate--N very mobile and conservative N very mobile and conservative

10 ppm EPA nitrate10 ppm EPA nitrate--N drinking water standardN drinking water standard

Soils are a Soils are a very effectivevery effectivetreatment media & treatment media &

TreatmentTreatment is the goalis the goal

Photo: Photo: Inspection Inspection

neededneeded