How OWTSs Using How OWTSs Using Aerobic Treatment WorkAerobic Treatment Work

Texas AgriLife Extension SeviceTexas AgriLife Extension Sevice

OverviewOverview

Treatment ProcessesTreatment Processes Components of an OWTS using Aerobic Components of an OWTS using Aerobic

Treatment, Disinfection and Spray Treatment, Disinfection and Spray DispersalDispersal

What is a Flow Equalization Tank?What is a Flow Equalization Tank?

Aerobic Treatment Unit SystemAerobic Treatment Unit System

Wastewater Treatment Wastewater Treatment ProcessesProcesses

Oxygen stateOxygen state Aerobic vs. AnaerobicAerobic vs. Anaerobic

ProcessesProcesses PhysicalPhysical ChemicalChemical BiologicalBiological

AerobicAerobic Aerobic bacteria require OAerobic bacteria require O22 to live and grow to live and grow Aerobic treatment processes require OAerobic treatment processes require O22 to proceed to proceed Common condition in soil treatment, media filters, MATUsCommon condition in soil treatment, media filters, MATUs

Anaerobic Anaerobic Anaerobic bacteria grow in absence of free oxygen,OAnaerobic bacteria grow in absence of free oxygen,O22

Anaerobic treatment processes do not use oxygen, but Anaerobic treatment processes do not use oxygen, but consumption of items, breaks oxygen bonds Ex. SOconsumption of items, breaks oxygen bonds Ex. SO44, NO, NO33

Common condition in septic tanks, processing tanks, and Common condition in septic tanks, processing tanks, and usually any saturated environment usually any saturated environment

Aerobic vs. Anaerobic Processes Aerobic vs. Anaerobic Processes (???)(???)

Juvenile Rotifers Feeding on Rod-Shaped Bacteria pH 7.04 DO 1.2 ppm

Large Rotifers Attached to Aerobic Treatment Media Feeding on Bacteria & Organic Nutrients pH 6.94, DO 4.54 ppm

Mite on Aerobic Treatment Media pH 6.94, DO 4.54

Aerobic Treatment Unit System Aerobic Treatment Unit System for a Residencefor a Residence

ATU, Disinfection and Spray ATU, Disinfection and Spray Distribution System ComponentsDistribution System Components

Septic/Trash tankSeptic/Trash tank Aerobic Treatment Aerobic Treatment Air SupplyAir Supply ClarificationClarification Sludge ReturnSludge Return DisinfectionDisinfection Pump tank with pump and controlsPump tank with pump and controls Spray fieldSpray field

Septic / Trash TankSeptic / Trash Tank

Septic/Trash TanksSeptic/Trash Tanks Most common treatment system:Most common treatment system:

Water tight tanks.Water tight tanks. Anaerobic Treatment.Anaerobic Treatment. Most common treatment device.Most common treatment device. Septic tank: Minimum of two compartmentsSeptic tank: Minimum of two compartments Trash tank: Typically smaller with one Trash tank: Typically smaller with one

compartmentcompartment Some systems do not have a trash tank.Some systems do not have a trash tank.

Two-Compartment Septic TankTwo-Compartment Septic Tank

Septic Tank Treatment ProcessSeptic Tank Treatment Process Physical separation processes – Physical separation processes –

Settling of heavy materials – sludge layerSettling of heavy materials – sludge layer Floating of lighter materials – scum layerFloating of lighter materials – scum layer Clear zone (clear layer)Clear zone (clear layer) Effluent screen to assist in trapping solids (septic tank)Effluent screen to assist in trapping solids (septic tank)

Time is the main requirement to allow separation to Time is the main requirement to allow separation to occuroccur Detention time:Detention time:

• Septic tank - 2-3 daysSeptic tank - 2-3 days• Trash tank – 1 dayTrash tank – 1 day

Distance between inlet/outlet baffles is criticalDistance between inlet/outlet baffles is critical Calm conditions to prevent mixing in the tank Calm conditions to prevent mixing in the tank Anaerobic digestion and storage of materials until the Anaerobic digestion and storage of materials until the

tank is pumpedtank is pumped

Aerobic TreatmentAerobic Treatment

Aeration ChamberAeration Chamber

Aerobic Treatment ProcessAerobic Treatment Process

Aerobic microbes digest Aerobic microbes digest solidssolids

Organic matter + OOrganic matter + O22 = CO = CO22 + H + H22O + O +

new cellsnew cells

Sludge accumulates in Sludge accumulates in tanktank

Extended aerationExtended aeration High DO, Long detention, Low High DO, Long detention, Low

Food/Microorganisms ratio Food/Microorganisms ratio Organic matter to microbes, Organic matter to microbes,

microbes eat each other, result in microbes eat each other, result in sludgesludge

Suspended Growth Suspended Growth

Aerobic microbes free Aerobic microbes free swimming in the swimming in the aeration chamberaeration chamber

Mixing in the chamber Mixing in the chamber mixes the microbes mixes the microbes and the wastewater and the wastewater contaminants contaminants

Extended aeration to Extended aeration to limit biomass wastinglimit biomass wasting

Submerged Attached Growth/Fixed Submerged Attached Growth/Fixed Film MediaFilm Media

Media is submerged in Media is submerged in the aeration chamberthe aeration chamber

Microbes are attached to Microbes are attached to the mediathe media

Effluent is circulated Effluent is circulated through the media thus through the media thus passing contaminants by passing contaminants by the microbesthe microbes

Extended aeration to Extended aeration to limit biomass wastinglimit biomass wasting

Suspended Growth Suspended Growth ConfigurationsConfigurations

Should be three Should be three chambers/tanks.chambers/tanks.

Single tank with three Single tank with three compartments.compartments.

Multiple tanks.Multiple tanks. May combine aeration May combine aeration

and clarification and clarification chamber with dividerchamber with divider

Attached Growth ConfigurationsAttached Growth Configurations

Most have three Most have three chamberschambers

May be a separate May be a separate media filled insertmedia filled insert

May have media May have media placed in the aeration placed in the aeration chamberchamber

Check manufacturer Check manufacturer literature literature

Air SupplyAir Supply

Aeration of WastewaterAeration of Wastewater

Air is 21% oxygenAir is 21% oxygen Oxygen must transfer Oxygen must transfer

to wastewater for DOto wastewater for DO Quantity of oxygen Quantity of oxygen

transferred directly transferred directly related to BOD related to BOD removalremoval

Mixing of sewageMixing of sewage

DissolvedOxygen

O

Less Transfer

2 O

More Transfer

2

Oxygen Transfer

Aspirator/AeratorAspirator/Aerator

Vacuum pulls air into Vacuum pulls air into the waterthe water

Spinning shaft or Spinning shaft or impeller causes the impeller causes the vacuumvacuum

Limited resistance Limited resistance

CompressorsCompressors Greater pressure Greater pressure Lower air flowLower air flow Two distinct types Two distinct types

of compressorsof compressors RotaryRotary LinearLinear

Air inlet Air inlet Housing - cover Housing - cover

Rotary

Linear

Compressor Air FlowCompressor Air Flow Rotary compressor - Rotary compressor -

Relatively straight Relatively straight increase in flow with a increase in flow with a decrease in pressuredecrease in pressure

Linear compressor – Linear compressor – rapid decrease with rapid decrease with increasing pressureincreasing pressure Flow drops with Flow drops with

resistance to air flowresistance to air flow Must have the correct Must have the correct

compressor to have the compressor to have the correct air flowcorrect air flow

Linear Compressor Curve

0

0.5

1

1.5

2

2.5

3

3.5

4

0 1 2 3 4 5 6 7 8

PSI

CF

M

Model 5078S

Rotary

Linear

BlowersBlowers

Greater air flow Greater air flow Lower pressureLower pressure Air inlet screens/filtersAir inlet screens/filters Air flow discharge Air flow discharge

from unitfrom unit Larger pipeLarger pipe Air flow stops sharplyAir flow stops sharply Cannot operate under Cannot operate under

higher pressurehigher pressure

Air Distribution Lines Minimize friction

loss in the distribution lines:

Proper pipe diameter

Reasonable distance between aerator and aeration chamber

Minimize number of fittings (changes in direction) in the line.

Air DiffusionAir Diffusion

Porous Stone Diffuser

Perforated Pipe

ClarificationClarification

ClarificationClarification

Process occurs in a Process occurs in a “clarifier”“clarifier”

Clarification is the Clarification is the process were the process were the microbes, cell waste microbes, cell waste and biomass settle and biomass settle out of the water.out of the water.

Sludge blanket in the Sludge blanket in the bottom and a clear bottom and a clear zone below the zone below the discharge pointdischarge point

Vertical Settling ChamberVertical Settling Chamber

Calm EnvironmentCalm Environment Particles of Sufficient Particles of Sufficient

size and mass to size and mass to settlesettle

Flow dependentFlow dependent Upward flow rate Upward flow rate

must be less than the must be less than the settling ratesettling rate

ConfigurationsConfigurations Separate chamber with no extra Separate chamber with no extra

filtrationfiltration Cone inserted into aeration Cone inserted into aeration

chamberchamber Many have sloped wallsMany have sloped walls Added tertiary filter or screen in Added tertiary filter or screen in

clarifierclarifier Filtration through socks placed Filtration through socks placed

in the aeration chamberin the aeration chamber Added filtration improves quality Added filtration improves quality

but increases maintenancebut increases maintenance

Flow Equalization TankFlow Equalization Tank

Controlling Flow from a ResidenceControlling Flow from a Residence Owner controls water Owner controls water

usage to match usage to match clarifier capacity clarifier capacity

No large water using No large water using devicesdevices

500 gpd ATU has a 500 gpd ATU has a max of 42 gph without max of 42 gph without flow equalizationflow equalization

Or Install larger Or Install larger capacity systemcapacity system

Flow Equalization/Surge Tank Flow Equalization/Surge Tank ConceptsConcepts

Moderate FlowModerate Flow Daily fluctuationsDaily fluctuations Weekly fluctuationsWeekly fluctuations

Down stream componentsDown stream components Function more effectivelyFunction more effectively May allow decrease size May allow decrease size

Timer controls dosing Timer controls dosing to ATUto ATU

Flow Equalization/Surge TankFlow Equalization/Surge Tank

Incorporating Flow Equalization

Modify the treatment train by adding components Add an additional tank between the trash tank

and aeration chamber Upsize trash tank to full size septic tank, add

pump with timer controls to dose ATU

Sludge ReturnSludge Return

Sludge return Settled solids passing

into a previous treatment chamber

Passive system Settled solids passing

through the bottom opening

Most common method

Active system Settled solids blanket

below the outlet baffle

DisinfectionDisinfection

Disinfection,Disinfection, not Sterilizationnot Sterilization

The goal of disinfection The goal of disinfection is to rid the wastewater stream is to rid the wastewater stream

of organisms capable of causing infectionof organisms capable of causing infection

Sterilization is freeingSterilization is freeingthe wastewater stream of ALL LIFEthe wastewater stream of ALL LIFE..

ChlorineChlorine

Destroys target organisms by chemical Destroys target organisms by chemical oxidation of cellular material.oxidation of cellular material.

Some organisms are resistant to low Some organisms are resistant to low doses of chlorinedoses of chlorine

Oocysts of Chrytosporidium parvumOocysts of Chrytosporidium parvumCysts of Endamoeba histolyticaCysts of Endamoeba histolyticaCysts of Giardia lambliaCysts of Giardia lambliaEggs of parasitic wormsEggs of parasitic worms

Chlorination ConsiderationsChlorination Considerations Chlorine is an oxidizer. Chlorine is an oxidizer. Need clean water (low BOD, low TSS): chlorine Need clean water (low BOD, low TSS): chlorine

is not “stolen” to oxidize organic matter.is not “stolen” to oxidize organic matter. Chlorine reacts with ammonia to form Chlorine reacts with ammonia to form

chloramines. chloramines. Chloramines are not as effective as Chloramines are not as effective as

hypochlorous acid and hypochlorite ion for hypochlorous acid and hypochlorite ion for disinfection.disinfection.

Interferences: BOD, TSS, Humic Materials, Interferences: BOD, TSS, Humic Materials, Nitrite, pH, Iron, manganese and hydrogen Nitrite, pH, Iron, manganese and hydrogen sulfidesulfide

DosingDosing

Dose = Concentration x TimeDose = Concentration x Time Increasing either dosage or contact time, Increasing either dosage or contact time,

while decreasing the other, can achieve while decreasing the other, can achieve the same degree of disinfection. the same degree of disinfection.

Breakpoint-Breakpoint- the process where sufficient the process where sufficient chlorine is added to the system to obtain a chlorine is added to the system to obtain a free chlorine residualfree chlorine residual

CautionCaution People should be People should be

trained to properly trained to properly handle and work with handle and work with chlorine productschlorine products

High riskHigh risk ExposureExposure HandlingHandling

CorrosiveCorrosive UnstableUnstable Be careful where Be careful where

stored!!!!!!stored!!!!!!

Tablet ChlorinationTablet Chlorination

Tablet chlorinators Tablet chlorinators generally have four generally have four components:components:

Chlorine Tablets.Chlorine Tablets. A tube that holds the A tube that holds the

tablets.tablets. A contact device, which A contact device, which

puts the chlorine tablets puts the chlorine tablets into contact with the into contact with the wastewater.wastewater.

A storage reservoir, A storage reservoir, usually a pump tank usually a pump tank where the water is stored where the water is stored before it is distributed.before it is distributed.

Typical Chlorine TabletsTypical Chlorine Tablets Wastewater tablets- Wastewater tablets-

Calcium HypochloriteCalcium Hypochlorite Basic compound – high Basic compound – high

pHpH

Swimming pool – Swimming pool – Trichlorocyanuric acid Trichlorocyanuric acid Acidic compound – low pHAcidic compound – low pH

Hazard to mix acids and Hazard to mix acids and basesbases

Must use products in Must use products in accordance with labelaccordance with label

Residential Liquid Bleach Residential Liquid Bleach ChlorinatorChlorinator

ReservoirReservoir Delivery of Delivery of

chlorinechlorine Vacuum/suctionVacuum/suction PumpPump

Dose volumeDose volume Mixing with Mixing with

effluenteffluent

Residential Liquid ChlorinationResidential Liquid Chlorination Flow passes through Flow passes through

aspirator developing a aspirator developing a vacuum or through a vacuum or through a pump to draw a dose pump to draw a dose of chlorine.of chlorine.

Tubing delivers Tubing delivers chlorine dose to chlorine dose to aspirator or pumpaspirator or pump

Control volume of Control volume of chlorinechlorine

Mixing of chlorine with Mixing of chlorine with effluent in pump tankeffluent in pump tank

Ultraviolet Light Disinfection UnitsUltraviolet Light Disinfection Units

UV light destroys UV light destroys microorganisms by microorganisms by altering their genetic altering their genetic material and / or material and / or retarding their ability retarding their ability to reproduceto reproduce

Ultraviolet Light Disinfection UnitsUltraviolet Light Disinfection Units

Electromagnetic Electromagnetic energy (UV light) energy (UV light) from source lamp from source lamp is emitted into a is emitted into a chamber through chamber through which effluent which effluent passespasses

Other Interferences to Effective UV Disinfection

Dissolved organic compounds (BOD, Dissolved organic compounds (BOD, TOC, COD) TOC, COD)

Organic iron compoundsOrganic iron compounds Humic compounds (tannins)Humic compounds (tannins) Inorganic coatings on protective tubesInorganic coatings on protective tubes

Pump Tank with Pumps Pump Tank with Pumps and Controlsand Controls

Pump Tank & PumpPump Tank & Pump Stores water until time for Stores water until time for

dosing effluentdosing effluent Acts as storage for Acts as storage for

disinfectiondisinfection Storage capacity when Storage capacity when

system breakssystem breaks PumpPump

Type: effluent or sewageType: effluent or sewage Not a grinder or sumpNot a grinder or sump Specific flow & pressure Specific flow & pressure

Panel & Electrical Control CircuitsPanel & Electrical Control Circuits Panel is a housing for Panel is a housing for

components needed to components needed to control a system.control a system.

Record valuable Record valuable operational informationoperational information

Provide a means to collect Provide a means to collect operational data on the operational data on the systemsystem

Timer for night spray Timer for night spray Timer for flow equalizationTimer for flow equalization Audio and visual alarmsAudio and visual alarms Power must be ON!Power must be ON!

Spray FieldSpray Field

Spray FieldSpray Field

Lawn Sprinkler systems? --- NO!!!Lawn Sprinkler systems? --- NO!!! Spray treated wastewater over the surface Spray treated wastewater over the surface

of a yard of a yard Requires greatest level of treatmentRequires greatest level of treatment High risk system!!!!High risk system!!!!

Water QualityWater Quality High potential for human High potential for human

contact with watercontact with water Secondary- Quality EffluentSecondary- Quality Effluent Remove 85-98% of solids and Remove 85-98% of solids and

organic matterorganic matter Remove pathogens?Remove pathogens? Nutrients (nitrogen and Nutrients (nitrogen and

phosphorus) are not required to phosphorus) are not required to be removedbe removed

Soil for Final TreatmentSoil for Final Treatment

Role of vegetative cover in Role of vegetative cover in treatment systemtreatment system

A healthy cover crop is essential for the system A healthy cover crop is essential for the system to function properly. Plants will:to function properly. Plants will: Take up nutrientsTake up nutrients Take up waterTake up water Stabilize the soil and prevent erosionStabilize the soil and prevent erosion Provide food and habitat for beneficial soil Provide food and habitat for beneficial soil

organismsorganisms

Soil microbes are the final treatment!!!!Soil microbes are the final treatment!!!! This is effluent – NOT DRINKING WATER!!!!This is effluent – NOT DRINKING WATER!!!!

Connecting Distribution Heads to Connecting Distribution Heads to LateralsLaterals

SummarySummary

Treatment requirementsTreatment requirements Components of an OWTS using Aerobic Components of an OWTS using Aerobic

Treatment, Disinfection and Spray Treatment, Disinfection and Spray DispersalDispersal

What is a Flow Equalization Tank?What is a Flow Equalization Tank?