overview of wastewater disinfection · disinfection, not sterilization. the goal of disinfection ....

Overview Overview of of

WastewaterWastewaterDisinfectionDisinfection

Mark GrossMark GrossUniversity of ArkansasUniversity of Arkansas

Kitt FarrellKitt Farrell--PoePoeUniversity of ArizonaUniversity of Arizona

University Curriculum Development for University Curriculum Development for Decentralized WastewaterDecentralized Wastewater

ManagementManagement

NDWRCDP DisclaimerNDWRCDP DisclaimerThis work was supported by the National This work was supported by the National Decentralized Water Resources Capacity Decentralized Water Resources Capacity Development Project (NDWRCDP) with Development Project (NDWRCDP) with

funding provided by the U.S. Environmental funding provided by the U.S. Environmental Protection Agency through a Cooperative Protection Agency through a Cooperative

Agreement (EPA No. CR827881Agreement (EPA No. CR827881--0101--0) with 0) with Washington University in St. Louis. These Washington University in St. Louis. These materials have not been reviewed by the materials have not been reviewed by the U.S. Environmental Protection Agency. U.S. Environmental Protection Agency. These materials have been reviewed by These materials have been reviewed by representatives of the NDWRCDP. The representatives of the NDWRCDP. The

contents contents of these materials do not necessarily reflect of these materials do not necessarily reflect the views and policies of the NDWRCDP, the views and policies of the NDWRCDP,

Washington University, or the U.S. Washington University, or the U.S. Environmental Protection Agency, nor does Environmental Protection Agency, nor does the mention of trade names or commercial the mention of trade names or commercial products constitute their endorsement or products constitute their endorsement or

recommendation for use.recommendation for use.

CIDWT/University DisclaimerCIDWT/University Disclaimer

These materials are the collective effort of These materials are the collective effort of individuals from academic, regulatory, and individuals from academic, regulatory, and private sectors of the onsite/decentralized private sectors of the onsite/decentralized

wastewater industry. These materials have been wastewater industry. These materials have been peerpeer--reviewed and represent the current state of reviewed and represent the current state of

knowledge/science in this field. They were knowledge/science in this field. They were developed through a series of writing and review developed through a series of writing and review

meetings with the goal of formulating a meetings with the goal of formulating a consensus on the materials presented. These consensus on the materials presented. These materials do not necessarily reflect the views materials do not necessarily reflect the views and policies of University of Arkansas, and/or and policies of University of Arkansas, and/or the Consortium of Institutes for Decentralized the Consortium of Institutes for Decentralized Wastewater Treatment (CIDWT). The mention Wastewater Treatment (CIDWT). The mention

of trade names or commercial products does not of trade names or commercial products does not constitute an endorsement or recommendation constitute an endorsement or recommendation for use from these individuals or entities, nor for use from these individuals or entities, nor does it constitute criticism for similar ones not does it constitute criticism for similar ones not

mentioned.mentioned.

CitationCitation

Gross, M.A. and K. FarrellGross, M.A. and K. Farrell--Poe. 2005. Poe. 2005. Disinfection Disinfection -- PowerPoint PowerPoint Presentation. Presentation. inin (M.A. Gross and (M.A. Gross and N.E. Deal, eds.) University N.E. Deal, eds.) University Curriculum Development for Curriculum Development for Decentralized Wastewater Decentralized Wastewater Management. National Management. National Decentralized Water Resources Decentralized Water Resources Capacity Development Project. Capacity Development Project. University of Arkansas, Fayetteville, University of Arkansas, Fayetteville, AR.AR.

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..

Human Health Hazards(Diseases)

Pathogenic BacteriaTyphoid feverParatyphoid feverGastroenteritisCholeraBacillary dysentery

Infectious VirusesPoliomyelitisInfectious hepatitisAseptic meningitisEncephalitis

ProtozoaGiardiasisGastroenteritisAmoebic dysenteryCryptosporidiosis

HelminthsGastroenteritisChronic anemia

How does Disinfection Work?

SedimentationSeptic tank/Soil absorption system

PredationBiomat (soil absorption system)

DessicationSoil Adsorption System

Destroy Cell WallChlorineOzone

Affect biochemical processesUV

Commonly Used Disinfection Commonly Used Disinfection Techniques:Techniques:

ChlorinationChlorinationLiquidLiquidGasGasSolid (tablet erosion type)Solid (tablet erosion type)

Ultraviolet LightUltraviolet LightOzonationOzonation

Factors affecting DisinfectionFactors affecting Disinfection

Contact TimeContact TimepHpHConcentration or Intensity of Concentration or Intensity of the disinfectantthe disinfectantConcentration of the Concentration of the organismsorganismsConcentration of interfering Concentration of interfering substances substances

Some Disinfection HistorySome Disinfection History

Chlorine was introduced as a Chlorine was introduced as a deodorizer and disinfectant in deodorizer and disinfectant in hospitals in 1835hospitals in 1835Chlorine was used in water Chlorine was used in water supplies in London during the supplies in London during the cholera outbreak of 1854cholera outbreak of 1854Routine chlorination of public Routine chlorination of public water supplies began in 1904 water supplies began in 1904 in London, and in 1908 in the in London, and in 1908 in the U.S.U.S.In 1909, the courts upheld that In 1909, the courts upheld that chlorination was in the best chlorination was in the best interest of public health. (the interest of public health. (the needs of the many….)needs of the many….)

ChlorinationChlorination

“Clean” Water“Clean” WaterChlorine ChemistryChlorine Chemistry

ClCl22 + H+ H22O O HOClHOCl-- + H+ H++ + + ClCl--

HOClHOCl-- HH++ + + OClOCl-

The pH affects this reaction. Lower pH drives The pH affects this reaction. Lower pH drives the reaction to make the reaction to make HOClHOCl..

HOClHOCl ((hypochloroushypochlorous acid) is a more effective acid) is a more effective disinfectant than disinfectant than OClOCl-- (hypochlorite ion).(hypochlorite ion).

A pH below 7.4 is conducive to A pH below 7.4 is conducive to HOClHOCl formationformation

ChlorineChlorine

Destroys target organisms by Destroys target organisms by oxidation of cellular material.oxidation of cellular material.Some organisms are resistant to Some organisms are resistant to low doses of chlorinelow doses of chlorine

OocystsOocysts of of CrytosporidiumCrytosporidium parvumparvumCysts of Cysts of Entamoeba histolyticaEntamoeba histolyticaCysts of Cysts of GiardiaGiardia lamblialambliaEggs of parasitic wormsEggs of parasitic worms

Forms of ChlorineForms of Chlorine

Free available chlorineFree available chlorine is the is the concentration of chlorine existing in concentration of chlorine existing in the form of the form of hypochloroushypochlorous acid and acid and hypochlorite ions.hypochlorite ions.

Combined ChlorineCombined Chlorine is the is the concentration of chloramines concentration of chloramines formed when nonformed when non--nitrified effluent is nitrified effluent is chlorinatedchlorinated

Some WastewaterSome WastewaterChlorination Chlorination

ConsiderationsConsiderations

Chlorine is an oxidizer. In Chlorine is an oxidizer. In clean water (low BOD) it is clean water (low BOD) it is more effective as a more effective as a disinfectant since it is not disinfectant since it is not “stolen” to oxidize organic “stolen” to oxidize organic matter.matter.

Chlorination Chlorination ConsiderationsConsiderations

Chlorine reacts with Chlorine reacts with ammonia to form ammonia to form chloramines. chloramines. Chloramines are not Chloramines are not as effective as as effective as hypochloroushypochlorous acid acid and hypochlorite ion and hypochlorite ion for disinfection.for disinfection.

Chlorination Interferences

Ammonia•Forms chloramines

•Less effective as disinfection agent

•More persistent or stable than free chlorine

Chlorine and Ammonia

MonochloramineNH3 + HOCl NH2Cl + H2O

DichloramineNH2Cl + HOCl NHCl2 + H2O

TrichloramineNHCl2 + HOCl NCl3 + H2O

Chlorination Chlorination InterferencesInterferences

Biochemical Oxygen Biochemical Oxygen Demand (BOD)Demand (BOD)

Can exert chlorine demandCan exert chlorine demand


Total Suspended Solids (TSS)

Shield organisms


Humic Materials (possibly from peat filtration systems)

Exert chlorine demand


Nitrite

Oxidized by chlorine


pHAffects distribution between hypochlorous and hypochlorite ions

Affects distribution among chloramine species

ChlorinationChlorinationInterferencesInterferences

Chlorine can react with iron, Chlorine can react with iron, manganese and hydrogen manganese and hydrogen sulfide. The oxidized sulfide. The oxidized compounds can precipitate compounds can precipitate downstream from the downstream from the chlorination pointchlorination point

Liquid ChlorineLiquid Chlorine(bleach)(bleach)SolutionSolution MeteringMetering

PumpPump

MixerMixer

Mixing TankMixing Tank

Wastewater FlowWastewater Flow

Typical Liquid Typical Liquid Chlorination SystemChlorination System

Typical Chlorine Tablets

Tablet Chlorinator

Dual Tablet Chlorinator

Tablet Chlorinator

Observation:Observation:

Tablets in chlorinators can Tablets in chlorinators can “bridge” and result in a low “bridge” and result in a low chlorine dose.chlorine dose.Tablets need to be replaced Tablets need to be replaced regularlyregularly

Homeowner management of Homeowner management of disinfection units in general disinfection units in general has proven to be unreliablehas proven to be unreliable

Contact Time and Contact Time and ConcentrationConcentration

The “DOSE” of disinfectantThe “DOSE” of disinfectantcan be considered the can be considered the timetime that the that the water is in contact with the disinfectant water is in contact with the disinfectant multiplied by the multiplied by the concentration or concentration or intensityintensity of the disinfectantof the disinfectant

DOSE = Concentration X TimeDOSE = Concentration X Time(Intensity)(Intensity)

1010--States Standards requires 15 minutes States Standards requires 15 minutes of contact time following the chlorine of contact time following the chlorine injection and mixing (at peak flow)injection and mixing (at peak flow)

Ultraviolet LightUltraviolet Light

UVUV

Disinfection using Disinfection using Ultraviolet LightUltraviolet Light

UV light is in the wavelengthUV light is in the wavelengthrange of about 40nm to 400 nm. range of about 40nm to 400 nm.

The most effective wavelength is The most effective wavelength is 254 nm.254 nm.

UV SpectrumUV Spectrum


The water should be clear soThe water should be clear sothat the light can passthat the light can passthrough the water to thethrough the water to theorganismsorganisms


The UV light is typicallyThe UV light is typicallygenerated by lamps and shinesgenerated by lamps and shinesthrough quartz glass tubes intothrough quartz glass tubes intothe waterthe water

UV Lamp CutawayUV Lamp Cutaway

Disinfection with Disinfection with UV LightUV Light

Dissolved organic compoundsDissolved organic compounds(BOD, TOC, COD) inhibit the(BOD, TOC, COD) inhibit thepassage of UV light to thepassage of UV light to theorganismsorganisms

Disinfection with Disinfection with UV LightUV Light

Organic Iron compounds canOrganic Iron compounds canabsorb UV light, and ironabsorb UV light, and ironprecipitates can coat theprecipitates can coat thequartz glass tubes, inhibitingquartz glass tubes, inhibitingthe passage of UV light intothe passage of UV light intothe water to the organismsthe water to the organisms

UV effects on DNAUV effects on DNA

UV DosageUV Dosage

Dosage (Ct) = Power (intensity) x surface area x time

Dosage often measured asmicrowatt-seconds/cm

UV AssemblyUV Assembly

UV AssembliesUV Assemblies

UV MonitorUV Monitor

UV Lamp MonitorUV Lamp Monitor


UV systems can be UV systems can be expensive to maintain expensive to maintain –– a a new bulb can cost in the new bulb can cost in the range of $40 range of $40 -- $100 and $100 and

should be replaced annually should be replaced annually at a minimumat a minimum


UV and Ozone have less UV and Ozone have less of a residual disinfection of a residual disinfection ability as chlorine. This ability as chlorine. This is favored in wastewater is favored in wastewater

treatmenttreatment

OZONEOZONE

Disinfection with Disinfection with OzoneOzone

OO33

Ozone is an unstable (half life = Ozone is an unstable (half life = 30 min.+/30 min.+/--) colorless gas ) colorless gas produced by discharging produced by discharging electricity in dry air (corona electricity in dry air (corona discharge)discharge)

Ozone is generated at the point Ozone is generated at the point of use (not shipped in in gas of use (not shipped in in gas cylinders)cylinders)

Ozone is the strongest oxidant of Ozone is the strongest oxidant of the commonly used disinfectantsthe commonly used disinfectants

Disinfection with OzoneDisinfection with Ozone

Ozone is produced by Ozone is produced by discharging electricity in discharging electricity in dry air (corona discharge)dry air (corona discharge)Ozone is corrosiveOzone is corrosiveOzone is soluble in water Ozone is soluble in water up to about 5 mg/Lup to about 5 mg/L

Disinfection with Disinfection with OzoneOzone

Ozone disinfects by oxidizing the Ozone disinfects by oxidizing the cell material of organisms..cell material of organisms..

Ozone ConsiderationsOzone Considerations

Ozone is generally not recommended Ozone is generally not recommended for small systems because of for small systems because of

unfavorable economics and operation unfavorable economics and operation and maintenance requirementsand maintenance requirements

Ozone ConsiderationsOzone Considerations

Ozone is an oxidizer, and can Ozone is an oxidizer, and can be expected to react with be expected to react with organic compounds in the organic compounds in the wastewater streamwastewater streamOzone also oxidizes iron, Ozone also oxidizes iron, manganese, and hydrogen manganese, and hydrogen sulfide and cause precipitates sulfide and cause precipitates downstream of the ozone downstream of the ozone injection pointinjection pointOzone is not expected to Ozone is not expected to cause a toxic end product or cause a toxic end product or form disinfectionform disinfection byproductsbyproducts

Ozone generator

Ozone Pocket Detector

Ozone Sensor

What about viruses and What about viruses and protozoa?protozoa?

Disinfection effectiveness is Disinfection effectiveness is generally measured in terms of generally measured in terms of Coliform bacteria (total or fecal). Coliform bacteria (total or fecal). This is an “indicator” organism, This is an “indicator” organism, indicating the possible presence indicating the possible presence of fecal material.of fecal material.Just because no coliform Just because no coliform survived, it doesn’t mean that survived, it doesn’t mean that nothing else survivednothing else survived

So…What about viruses So…What about viruses and protozoa???and protozoa???

Giardia and Cryptosporidium Giardia and Cryptosporidium cysts are more resistant to cysts are more resistant to chlorination than coliformchlorination than coliformViruses apparently are more Viruses apparently are more resistant to chlorination than resistant to chlorination than coliform coliform -- particularly Hepatitis A particularly Hepatitis A virus. virus. Ozonation is fairly effective for Ozonation is fairly effective for Giardia and Giardia and CrytpoCrytpo disinfection, disinfection, but there is some evidence that but there is some evidence that with with ozonationozonation, it’s “all or, it’s “all or none”none”

Conclusions:Conclusions:

Get it clean before you Get it clean before you disinfectdisinfect


Provide some contact timeProvide some contact time


Use enough disinfectantUse enough disinfectant


Experience has shown that Experience has shown that tablet chlorinators are not tablet chlorinators are not

a reliable choice if the a reliable choice if the operation and operation and

maintenance is left up to maintenance is left up to the homeowner.the homeowner.

Conclusions:Conclusions:Ultraviolet disinfection is Ultraviolet disinfection is gaining popularity as the gaining popularity as the disinfectant of choice if disinfectant of choice if pretreatment processes pretreatment processes beyond the septic tank beyond the septic tank

are used.are used.

overview of wastewater disinfection · disinfection, not sterilization. the goal of disinfection ....

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