onsite nitrogen removal ppt

8/13/2019 Onsite Nitrogen Removal Ppt

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Onsite Nitrogen RemovalOnsite Nitrogen Removal

Stewart OakleyStewart Oakley

Department of Civil EngineeringDepartment of Civil Engineering

California State University, ChicoCalifornia State University, Chico

University Curriculum DevelopmentUniversity Curriculum Development

forforDecentralizedDecentralized WastewaterWastewaterManagementManagement


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NDWRCDP DisclaimerNDWRCDP DisclaimerThis work was supported by the National Decentralized WaterThis work was supported by the National Decentralized Water

Resources Capacity Development Project (NDWRCDP) withResources Capacity Development Project (NDWRCDP) withfunding provided by the U.S. Environmental Protection Agencyfunding provided by the U.S. Environmental Protection Agency

through a Cooperative Agreement (EPA No. CR827881through a Cooperative Agreement (EPA No. CR827881--0101--0)0)

with Washington University in St. Louis. These materials havewith Washington University in St. Louis. These materials havenot been reviewed by the U.S. Environmental Protectionnot been reviewed by the U.S. Environmental Protection

Agency. These materials have been reviewed byAgency. These materials have been reviewed by

representatives of the NDWRCDP. The contentsrepresentatives of the NDWRCDP. The contentsof these materials do not necessarily reflect the views andof these materials do not necessarily reflect the views and

policies of the NDWRCDP, Washington University, or the U.S.policies of the NDWRCDP, Washington University, or the U.S.

Environmental Protection Agency, nor does the mention of tradeEnvironmental Protection Agency, nor does the mention of trade

names or commercial products constitute their endorsement ornames or commercial products constitute their endorsement orrecommendation for use.recommendation for use.


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CIDWT/University DisclaimerCIDWT/University Disclaimer

These materials are the collective effort of individuals fromThese materials are the collective effort of individuals fromacademic, regulatory, and private sectors of theacademic, regulatory, and private sectors of the

onsite/decentralized wastewater industry. These materials haveonsite/decentralized wastewater industry. These materials havebeen peerbeen peer--reviewed and represent the current state ofreviewed and represent the current state of

knowledge/science in this field. They were developed through aknowledge/science in this field. They were developed through aseries of writing and review meetings with the goal of formulatiseries of writing and review meetings with the goal of formulatingnga consensus on the materials presented. These materials do nota consensus on the materials presented. These materials do not

necessarily reflect the views and policies of University ofnecessarily reflect the views and policies of University ofArkansas, and/or the Consortium of Institutes for DecentralizedArkansas, and/or the Consortium of Institutes for Decentralized

Wastewater Treatment (CIDWT). The mention of trade names orWastewater Treatment (CIDWT). The mention of trade names orcommercial products does not constitute an endorsement orcommercial products does not constitute an endorsement or

recommendation for use from these individuals or entities, norrecommendation for use from these individuals or entities, nordoes it constitute criticism for similar ones not mentioned.does it constitute criticism for similar ones not mentioned.


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CitationCitation

Oakley, S. 2005. Onsite Nitrogen RemovalOakley, S. 2005. Onsite Nitrogen Removal --

PowerPoint Presentation.PowerPoint Presentation. inin (M.A. Gross and(M.A. Gross andN.E. Deal, eds.) University CurriculumN.E. Deal, eds.) University Curriculum

Development for Decentralized WastewaterDevelopment for Decentralized Wastewater

Management. National Decentralized WaterManagement. National Decentralized WaterResources Capacity Development Project.Resources Capacity Development Project.

University of Arkansas, Fayetteville, AR.University of Arkansas, Fayetteville, AR.


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Chemistry of NitrogenChemistry of Nitrogen

Nitrogen can exist in nine various forms in the environmentNitrogen can exist in nine various forms in the environment

due to seven possible oxidation states:due to seven possible oxidation states:

Nitrogen CompoundNitrogen Compound FormulaFormula Oxidation StateOxidation State

Organic nitrogenOrganic nitrogen OrganicOrganic--NN --33

AmmoniaAmmonia NHNH33 --33

Ammonium ionAmmonium ion NHNH44++ --33

Nitrogen gasNitrogen gas NN22 00

Nitrous oxideNitrous oxide NN22OO +1+1

Nitric oxideNitric oxide NONO +2+2

Nitrite ionNitrite ion NONO22-- +3+3

Nitrogen dioxideNitrogen dioxide NONO22 +4+4

Nitrate ionNitrate ion NONO33--

+5+5


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Chemistry of NitrogenChemistry of Nitrogen

Because of the various oxidation states that can change in theBecause of the various oxidation states that can change in the

environment, it is customary to express the forms of nitrogenenvironment, it is customary to express the forms of nitrogen

in terms of nitrogen rather than the specific chemicalin terms of nitrogen rather than the specific chemicalcompound: (compound: (egeg., Organic., Organic--N, NHN, NH33--N, NHN, NH44

++--N, NN, N22--N, NON, NO22----N, andN, and

NONO33----N.)N.)

Thus, for example, 10 mg/L of NOThus, for example, 10 mg/L of NO33----N is equivalent to 45 mg/LN is equivalent to 45 mg/L

of NOof NO33-- ion.ion.


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The Nitrogen Cycle in SoilThe Nitrogen Cycle in Soil--GroundwaterGroundwater

SystemsSystems

As shown in Figure 1, transformation of the principal nitrogenAs shown in Figure 1, transformation of the principal nitrogen

compounds in soilcompounds in soil--groundwater systems (Organicgroundwater systems (Organic--N, NHN, NH33--N,N,NHNH44

++--N, NN, N22--N, NON, NO22----N, and NON, and NO33

----N) can occur through five keyN) can occur through five key

mechanisms in the environment:mechanisms in the environment:

FixationFixation

AmmonificationAmmonification

SynthesisSynthesis

NitrificationNitrification

DenitrificationDenitrification


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Nitrogen FixationNitrogen Fixation

Nitrogen fixation is the conversion of nitrogen gas into nitrogeNitrogen fixation is the conversion of nitrogen gas into nitrogenn

compounds that can be assimilated by plants. Biologicalcompounds that can be assimilated by plants. Biological

fixation is the most common, but fixation can also occur byfixation is the most common, but fixation can also occur bylightning, and through industrial processes:lightning, and through industrial processes:

Biological:Biological: NN22 OrganicOrganic--NN

Lightning:Lightning: NN22 NONO33--

Industrial:Industrial: NN22 NONO33-- or NHor NH33/ NH/ NH44++


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AmmonificationAmmonification

Ammonification is the biochemical degradation ofAmmonification is the biochemical degradation of

OrganicOrganic--N into NHN into NH33

or NHor NH44

++ by heterotrophic bacteriaby heterotrophic bacteria

under aerobic or anaerobic conditions.under aerobic or anaerobic conditions.

OrganicOrganic--N + MicroorganismsN + Microorganisms NHNH33/ NH/ NH

44

++

Some OrganicSome Organic--N cannot be degraded and becomesN cannot be degraded and becomes

part of the humus in soils.part of the humus in soils.


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SynthesisSynthesis

Synthesis is the biochemical mechanism in whichSynthesis is the biochemical mechanism in which

NHNH44

++--N or NON or NO33

----N is converted into plant OrganicN is converted into plant Organic--N:N:

NHNH44++ + CO+ CO22 + green plants + sunlight+ green plants + sunlight OrganicOrganic--NN

NONO33-- + CO+ CO22 + green plants + sunlight+ green plants + sunlight OrganicOrganic--NN


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SynthesisSynthesis

Nitrogen fixation is also a unique form of synthesis that can onNitrogen fixation is also a unique form of synthesis that can onlyly

be performed by nitrogenbe performed by nitrogen--fixing bacteria and algae:fixing bacteria and algae:

NN--FixingFixing

Bacteria/AlgaeBacteria/Algae

NN22 OrganicOrganic--NN


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Nitrification is the biological oxidation of NHNitrification is the biological oxidation of NH44++ to NOto NO33

-- through athrough a

twotwo--step autotrophic process by the bacteriastep autotrophic process by the bacteria NitrosomonasNitrosomonas

andand NitrobacterNitrobacter::

NitrosomonasNitrosomonas

Step 1:Step 1: NHNH44++ + 3/2O+ 3/2O22 NONO22---- + 2H+ 2H++ + H+ H22OO

NitrobacterNitrobacter

Step 2:Step 2: NONO22-- + 1/2O+ 1/2O22 NONO33--


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The twoThe two--step reactions are usually very rapid and hence it isstep reactions are usually very rapid and hence it is

rare to find nitrite levels higher than 1.0 mg/L in water.rare to find nitrite levels higher than 1.0 mg/L in water.

The nitrate formed by nitrification is, in the nitrogen cycle, uThe nitrate formed by nitrification is, in the nitrogen cycle, usedsed

by plants as a nitrogen source (synthesis) or reduced to Nby plants as a nitrogen source (synthesis) or reduced to N22 gasgas

through the process of denitrification.through the process of denitrification.

Nitrate can, however, contaminate groundwater if it is not usedNitrate can, however, contaminate groundwater if it is not used

for synthesis or reduced through denitrification as shown infor synthesis or reduced through denitrification as shown in

Figure 1.Figure 1.


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NONO33-- can be reduced, under anoxic conditions, to Ncan be reduced, under anoxic conditions, to N22 gasgas

through heterotrophic biological denitrification as shown in thethrough heterotrophic biological denitrification as shown in the

following unbalanced equation:following unbalanced equation:

HeterotrophicHeterotrophic

BacteriaBacteria NONO33

-- + Organic Matter+ Organic Matter NN22 + CO+ CO22 + OH+ OH-- + H+ H22OO


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Autotrophic denitrification is also possible with eitherAutotrophic denitrification is also possible with either

elemental sulfur or hydrogen gas used as the electron donor byelemental sulfur or hydrogen gas used as the electron donor by

autotrophic bacteria as shown in the following unbalancedautotrophic bacteria as shown in the following unbalancedequation:equation:

AutotrophicAutotrophic

BacteriaBacteria

NONO33-- + CO+ CO22 + Inorganic Electron Donor+ Inorganic Electron Donor NN22 + Oxidized Electron+ Oxidized Electron

(Sulfur or H(Sulfur or H22 gas)gas) DonorDonor


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Sources of Nitrogen Discharges toSources of Nitrogen Discharges to

GroundwaterGroundwaterAgricultural Activities:Agricultural Activities:

A significant source of nitrate in groundwater.A significant source of nitrate in groundwater.

Nitrate can enter groundwater at elevated levels by:Nitrate can enter groundwater at elevated levels by:

Excessive or inappropriate use of nitrogenExcessive or inappropriate use of nitrogen--based nutrientbased nutrientsources:sources:

Commercial fertilizersCommercial fertilizers

Animal manuresAnimal manures

Types of crops utilizedTypes of crops utilized

Crop irrigation that leads to nitrate leachingCrop irrigation that leads to nitrate leaching

Inappropriate livestock manure storageInappropriate livestock manure storage


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GroundwaterGroundwater

Septic TankSeptic Tank--Soil Absorption Systems:Soil Absorption Systems:

Contamination of groundwater with nitrates from septic tankContamination of groundwater with nitrates from septic tank--soil absorption systems is a problem in many parts of the US.soil absorption systems is a problem in many parts of the US.

The buildThe build--up of nitrate in groundwater is one of the mostup of nitrate in groundwater is one of the most

significant longsignificant long--term consequences of onsite wastewaterterm consequences of onsite wastewaterdisposal.disposal.

As an example, the annual nitrogen contribution for a family ofAs an example, the annual nitrogen contribution for a family of

four from a septicfour from a septic--tank soil absorption system on a quartertank soil absorption system on a quarteracre lot could be as high as 50 lbs. per year.acre lot could be as high as 50 lbs. per year.


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GroundwaterGroundwater

Septic TankSeptic Tank--Soil Absorption Systems:Soil Absorption Systems: The annual nitrogen requirement for a quarter acre of BermudaThe annual nitrogen requirement for a quarter acre of Bermuda

grass is also about 50 lbs. per year, which could also be closegrass is also about 50 lbs. per year, which could also be closeto the annual nitrogen production of a family of four.to the annual nitrogen production of a family of four.

The nitrogen from the septic tankThe nitrogen from the septic tank--soil absorption system,soil absorption system,

however, is not uniformly distributed throughout a lawn and ishowever, is not uniformly distributed throughout a lawn and istypically discharged at a depth below which plants can utilize itypically discharged at a depth below which plants can utilize it.t.

Nitrogen exists as OrganicNitrogen exists as Organic--N and NHN and NH33--N/NHN/NH44++--N in septic tankN in septic tank

effluent, and is usually transformed into nitrate as theeffluent, and is usually transformed into nitrate as thewastewater percolates through the soil column. Also, thewastewater percolates through the soil column. Also, thenitrogen loading from high housing densities can greatlynitrogen loading from high housing densities can greatlyexceed any potential plant uptake of nitrogen even if theexceed any potential plant uptake of nitrogen even if the

effluent was uniformly distributed for plant uptake.effluent was uniformly distributed for plant uptake.


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Control of Nitrogen Discharges from OnsiteControl of Nitrogen Discharges from Onsite

SystemsSystems

Public health and water pollution control agencies have tried toPublic health and water pollution control agencies have tried to

limit the number of onsite systems in a given area by:limit the number of onsite systems in a given area by:

Quantifying nitrogen loadingsQuantifying nitrogen loadings

Examining alternative onsite technologies that provideExamining alternative onsite technologies that provide

nitrogen removalnitrogen removal


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Quantifying Nitrogen Loading RatesQuantifying Nitrogen Loading Rates

HantzscheHantzsche--Finnemore Mass Balance Equation:Finnemore Mass Balance Equation:

The HantzscheThe Hantzsche--Finnemore Equation estimates nitrate loadingsFinnemore Equation estimates nitrate loadingsto groundwater based upon the measured factors of rainfall,to groundwater based upon the measured factors of rainfall,

aquifer recharge, septic system nitrogen loadings, andaquifer recharge, septic system nitrogen loadings, and

denitrification.denitrification.


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nnrr == IInnww(1(1--d) +d) + RRnnbb(I + R)(I + R)

nnrr == NONO33--

--N concentration in groundwater, mg/LN concentration in groundwater, mg/L

II == volume of wastewater entering the soil averagedvolume of wastewater entering the soil averagedover the gross developed area, in/yrover the gross developed area, in/yr

nnww == TotalTotal--N concentration of wastewater, mg/LN concentration of wastewater, mg/L

dd == fraction of NOfraction of NO33--

--N lost to denitrificationN lost to denitrification

RR == average recharge rate of rainfall, in/yraverage recharge rate of rainfall, in/yr

nnbb == background NObackground NO33--

--N concentration, mg/LN concentration, mg/L


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The number of gross acres per dwelling unit to ensure thatThe number of gross acres per dwelling unit to ensure thatgroundwater NOgroundwater NO33--N will not exceed 10 mg/L can be calculatedN will not exceed 10 mg/L can be calculatedfrom the following equation:from the following equation:

A =A = 0.01344W[n0.01344W[nww ddnnww 10]10]R(10R(10 -- nnbb))

AA = gross acres/dwelling unit= gross acres/dwelling unit

WW = average daily wastewater flow per dwelling unit,= average daily wastewater flow per dwelling unit,gallonsgallons


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Nitrogen Dynamics in Septic TankNitrogen Dynamics in Septic Tank--

Soil Absorption SystemsSoil Absorption Systems

Because the carbon to nitrogen ratio of wastewater is typicallyBecause the carbon to nitrogen ratio of wastewater is typically

on the order of 4:1 to 6:1, there will be excess nitrogen afteron the order of 4:1 to 6:1, there will be excess nitrogen aftersecondary biological treatment (BOD removal) that cannot besecondary biological treatment (BOD removal) that cannot be

assimilated by microorganisms as shown in the followingassimilated by microorganisms as shown in the following

unbalanced equation:unbalanced equation:

bacteriabacteria

COHNS + OCOHNS + O22 + Nutrients+ Nutrients COCO22 + NH+ NH44++ + C+ C55HH77NONO22 + end products+ end products

OrganicOrganic new bacterialnew bacterial

MatterMatter cellscells


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Septic Tanks:Septic Tanks:

The removal of TotalThe removal of Total--N within septic tanks is on the order of 10N within septic tanks is on the order of 10

to 30%, with the majority being removed as particulate matterto 30%, with the majority being removed as particulate matter

through sedimentation or flotation processes.through sedimentation or flotation processes.

Because of the septic tank's anaerobic environment, nitrogenBecause of the septic tank's anaerobic environment, nitrogen

exists principally as Organicexists principally as Organic--N and NHN and NH33--N/NHN/NH44++--N (TKN).N (TKN).


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Subsurface Absorption Trenches:Subsurface Absorption Trenches:

Nitrogen can undergo several transformations within and belowNitrogen can undergo several transformations within and below

subsurface absorption trenches:subsurface absorption trenches:

Adsorption of NHAdsorption of NH44++--N in the soilN in the soil

Volatilization of NHVolatilization of NH33--N in alkaline soils at a pH above 8.0N in alkaline soils at a pH above 8.0

Nitrification and subsequent movement of NONitrification and subsequent movement of NO33-- --N towards theN towards the

groundwatergroundwater Biological uptake of both NHBiological uptake of both NH33

--N/NHN/NH44++--N and NON and NO33

-- --NN

Denitrification if the environmental conditions are appropriateDenitrification if the environmental conditions are appropriate

T P f


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Treatment Processes forTreatment Processes for


Sequential Nitrification/Denitrification Processes (Figure 2):Sequential Nitrification/Denitrification Processes (Figure 2):

Sequential nitrification/denitrification processes form the basiSequential nitrification/denitrification processes form the basissof all biological nitrogen removal technologies that have beenof all biological nitrogen removal technologies that have been

used or proposed for onsite wastewater treatment.used or proposed for onsite wastewater treatment.

Aerobic processes are first used to remove BOD and nitrifyAerobic processes are first used to remove BOD and nitrify

organic and NHorganic and NH44++--N.N.

Anoxic processes are then used to reduce NOAnoxic processes are then used to reduce NO33-- --N to NN to N22 gas,gas,either using the wastewater as a carbon source or an externaleither using the wastewater as a carbon source or an external

carbon source.carbon source.


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T t t P fT t t P f


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Treatment Processes forTreatment Processes for


Table 1Table 1

Examples of Onsite Biological Nitrogen Removal from the LiteratuExamples of Onsite Biological Nitrogen Removal from the Literaturere

TotalTotal--N Removal Effluent TotalN Removal Effluent Total--NNTechnology ExamplesTechnology Examples Efficiency, %Efficiency, % mg/Lmg/L

Suspended Growth:Suspended Growth:

Aerobic units w/pulse aerationAerobic units w/pulse aeration 2525--6161 3737--6060

Sequencing batch reactorSequencing batch reactor 6060 15.515.5

Attached Growth:Attached Growth:

Single Pass Sand Filters (SPSF)Single Pass Sand Filters (SPSF) 88--5050 3030--6565

Recirculating Sand/Gravel Filters (RSF)Recirculating Sand/Gravel Filters (RSF) 1515--8484 1010--4747

MultiMulti--Pass Textile FiltersPass Textile Filters 1414--3131 1414--1717

RSF w/Anoxic FilterRSF w/Anoxic Filter 4040--9090 77--2323

RSF w/Anoxic Filter w/External Carbon SourceRSF w/Anoxic Filter w/External Carbon Source 7474--8080 1010--1313

RUCK SystemRUCK System 2929--5454 1818--5353


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Biological NitrificationBiological Nitrification

Process Chemistry:Process Chemistry:

Nitrification is a twoNitrification is a two--step autotrophic process (nitrifiers usestep autotrophic process (nitrifiers useCOCO22 instead of organic carbon as their carbon source for cellinstead of organic carbon as their carbon source for cell

synthesis) for the conversion of NHsynthesis) for the conversion of NH44++ to NOto NO33

----N. During thisN. During this

energy yielding reaction some of the NHenergy yielding reaction some of the NH44++ is synthesized intois synthesized into

cell tissue giving the following overall oxidation and synthesiscell tissue giving the following overall oxidation and synthesisreaction:reaction:

AutotrophicAutotrophic

1.00NH1.00NH44++ + 1.89O+ 1.89O22 + 0.08CO+ 0.08CO22 0.98NO0.98NO33-- ++ 0.016C0.016C55HH77OO22N + 0.95HN + 0.95H22O + 1.98HO + 1.98H++

Bacteria new bacterial cellsBacteria new bacterial cells


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Process Chemistry:Process Chemistry:

The previous balanced equation shows that:The previous balanced equation shows that: For each mole of NHFor each mole of NH44

++ oxidized, 1.89 moles of oxygen are required andoxidized, 1.89 moles of oxygen are required and

1.98 moles of hydrogen ions will be produced.1.98 moles of hydrogen ions will be produced.

In mass terms, 4.32 mg of OIn mass terms, 4.32 mg of O22 are required for each mg of NHare required for each mg of NH44++--NNoxidized, with the subsequent loss of 7.1 mg of alkalinity as Caoxidized, with the subsequent loss of 7.1 mg of alkalinity as CaCOCO33 inin

the wastewater, and the synthesis of 0.1 mg of new bacterial celthe wastewater, and the synthesis of 0.1 mg of new bacterial cells.ls.

Sources:Sources: US EPA, Manual:US EPA, Manual: NitrogenNitrogen Control, EPA/625/RControl, EPA/625/R--93/010, Office93/010, Office ofofWaterWater, Washington,, Washington, D.CD.C.,., SeptemberSeptember, 1993, 1993, p.88., p.88.

MetcalfMetcalf&& EddyEddy,, WastewaterWastewaterEngineeringEngineering:: TreatmentTreatment,, DisposalDisposal,,

andandReuseReuse,, 3rd.3rd. EditionEdition,, McGrawMcGraw--Hill,Hill, NewNewYorkYork, 1991, 1991, p.696., p.696.


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Process Microbiology:Process Microbiology:

Nitrifying organisms exhibit growth rates that are much lowerNitrifying organisms exhibit growth rates that are much lower

than those for heterotrophic bacteria.than those for heterotrophic bacteria. As a result, the rate of nitrification is controlled first byAs a result, the rate of nitrification is controlled first by

concurrent heterotrophic oxidation of CBOD; as long as thereconcurrent heterotrophic oxidation of CBOD; as long as there

is a high organic (CBOD) loading to the system, theis a high organic (CBOD) loading to the system, the

heterotrophic bacteria will dominate. (See Figure 3.)heterotrophic bacteria will dominate. (See Figure 3.)

Nitrification systems must thus be designed to allow sufficientNitrification systems must thus be designed to allow sufficient

detention time within the system for nitrifying bacteria to growdetention time within the system for nitrifying bacteria to grow..

After competition withAfter competition with heterotrophsheterotrophs, the rate of nitrification will, the rate of nitrification willbe limited by the concentration of available NHbe limited by the concentration of available NH44++--N in theN in the

system.system.


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Dissolved Oxygen Requirements and Organic Loading Rates:Dissolved Oxygen Requirements and Organic Loading Rates:

Suspended Growth SystemsSuspended Growth Systems

The concentration of DO has a significant effect on nitrificatioThe concentration of DO has a significant effect on nitrification inn in

wastewater treatment.wastewater treatment.

Although much research has been performed, practical experienceAlthough much research has been performed, practical experience

has shown that DO levels must be maintained at approximately 2.0has shown that DO levels must be maintained at approximately 2.0

mg/L in suspendedmg/L in suspended--growth (aerobic) systems, especially whengrowth (aerobic) systems, especially when

NHNH44++--N loadings are expected to fluctuate widely; this is likely toN loadings are expected to fluctuate widely; this is likely to

be the case in domestic onsite wastewater systems.be the case in domestic onsite wastewater systems.


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Bi l i l Ni ifi iBi l i l Nit ifi ti


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Table 2 shows design organic loading rates for variousTable 2 shows design organic loading rates for various

attachedattached--growth systems to achieve nitrification.growth systems to achieve nitrification.

Unfortunately, organic loading rates for onsite attachedUnfortunately, organic loading rates for onsite attached--growthgrowthsystems are not well defined even for CBOD removal, let alonesystems are not well defined even for CBOD removal, let alone

nitrification.nitrification.

The more commonly used hydraulic loading rates show mixedThe more commonly used hydraulic loading rates show mixed

results for nitrification as cited in the literature.results for nitrification as cited in the literature. This is no doubt due, at least in part, to varying organic loadiThis is no doubt due, at least in part, to varying organic loadingng

rates that were not taken into consideration since the CBODrates that were not taken into consideration since the CBOD55 ofof

septic tank effluent can vary greatly, ranging from less than 10septic tank effluent can vary greatly, ranging from less than 1000

to 480 mg/L.to 480 mg/L.

Bi l i l Nit ifi tiBi l i l Nit ifi ti


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Table 2Table 2

Design Loading Rates for Attached Growth Systems to Achieve >85%Design Loading Rates for Attached Growth Systems to Achieve >85% NitrificationNitrification

Hydraulic Loading OrganiHydraulic Loading Organic Loadingc Loading State of KnowledgeState of Knowledge

Process Rate, gpd/ftProcess Rate, gpd/ft22 Rate, lbs. BOD/ftRate, lbs. BOD/ft22--dayday for Designfor Design

Trickling FiltersTrickling Filters

Rock MediaRock Media 3030--900900 0.040.04--0.120.12 Well KnownWell Known

Plastic MediaPlastic Media 288288--17001700 0.100.10--0.250.25 Well KnownWell Known

Sand FiltersSand Filters

Single PassSingle Pass 0.40.4--1.21.2 0.0001350.000135--0.0020.002 Lesser KnownLesser Known

RecirculatingRecirculating 33--55 0.0020.002--0.0080.008 Lesser KnownLesser Known

Bi l i l Nit ifi tiBi l i l Nit ifi ti


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pH and Alkalinity Effects:pH and Alkalinity Effects:

The optimum pH range for nitrification is 6.5 to 8.0.The optimum pH range for nitrification is 6.5 to 8.0.

Nitrification consumes about 7.1 mg of alkalinity (as CaCONitrification consumes about 7.1 mg of alkalinity (as CaCO33) for) for

every mg of NHevery mg of NH44

++--N oxidized.N oxidized.

In low alkalinity wastewaters there is a risk that nitrificationIn low alkalinity wastewaters there is a risk that nitrification willwill

lower the pH to inhibitory levels.lower the pH to inhibitory levels.

Bi l i l Nit ifi tiBiological Nitrification


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pH and Alkalinity Effects:pH and Alkalinity Effects:

Figures 6 and 7 graphically show the loss of alkalinity with nitFigures 6 and 7 graphically show the loss of alkalinity with nitrificationrificationfor septic tank effluent that percolated through the soil columnfor septic tank effluent that percolated through the soil column andandwas measured at a twowas measured at a two--foot depth with suctionfoot depth with suction lysimeterslysimeters..

In this particular example, the alkalinity decreased from an aveIn this particular example, the alkalinity decreased from an average ofrage of

approximately 400 mg/L to 100 mg/L as CaCOapproximately 400 mg/L to 100 mg/L as CaCO33 in order to nitrify anin order to nitrify anaverage of about 40 mg/L organicaverage of about 40 mg/L organic--N and NHN and NH44

++--N.N.

Figure 8 shows the theoretical relationship of the fraction of TFigure 8 shows the theoretical relationship of the fraction of TKN thatKN that

can be nitrified as a function of initial TKN and alkalinity incan be nitrified as a function of initial TKN and alkalinity in thethewastewater.wastewater.


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Figure 6: Alkalinity Concentrations in Septic Tank Effluent and

Vadose Zone Receiving Nitrified Effluents

0

100

200

300

400

500

600

700

Jun-96 Jul-96 Aug-96 Se p-96 Oc t-96 Nov-96 De c -96 Ja n-97 Fe b-97

Date

Alkalinity,mg

/LasCalciumC

arbo

nate Se ptic Tank Efflue nt

Vado se Zone Be ne ath Tre nch


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Figure 8: Nitrification as a Function of Initial TKN and Alkalinity

1 0


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0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 10 20 30 40 50 60 70 80 90 100

TKN, mg/L as N

FractionofTKNNitrifie

Alkalinity = 100 mg/L as CaCO3


Alkalinity = 300 mg/L

as CaCO3




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Temperature Effects:Temperature Effects:

Temperature has a significant effect on nitrification that mustTemperature has a significant effect on nitrification that mustbe taken into consideration for design.be taken into consideration for design.

In general, colder temperatures require longer cell residenceIn general, colder temperatures require longer cell residence

times in suspendedtimes in suspended--growth systems and lower hydraulicgrowth systems and lower hydraulic

loading rates in attachedloading rates in attached--growth systems due to slower growthgrowth systems due to slower growth

rates of nitrifying bacteria.rates of nitrifying bacteria.



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Inhibitors:Inhibitors:

Nitrifying bacteria are much more sensitive than heterotrophicNitrifying bacteria are much more sensitive than heterotrophic

bacteria and are susceptible to a wide range of organic and inorbacteria and are susceptible to a wide range of organic and inorganicganicinhibitors as shown in Table 3.inhibitors as shown in Table 3.

There is a need to establish a methodology for onsite wastewaterThere is a need to establish a methodology for onsite wastewater

systems for assessing the potential for, and occurrence of,systems for assessing the potential for, and occurrence of,nitrification inhibition.nitrification inhibition.

Figure 9 illustrates the effect of an inhibitor on nitrificationFigure 9 illustrates the effect of an inhibitor on nitrification in a septicin a septictank/recirculating trickling filter system; in this particular ctank/recirculating trickling filter system; in this particular case a carpetase a carpetcleaning solvent that was flushed down the toilet contaminated tcleaning solvent that was flushed down the toilet contaminated theheseptic tank and destroyed the nitrifying bacterial population inseptic tank and destroyed the nitrifying bacterial population in thetheattachedattached--growth media. If this system had not been continuouslygrowth media. If this system had not been continuouslymonitored, the effects of the inhibitor on nitrification would hmonitored, the effects of the inhibitor on nitrification would haveave

passed unnoticed.passed unnoticed.



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Table 3: Examples of Nitrification InhibitorsTable 3: Examples of Nitrification Inhibitors

Inorganic CompoundsInorganic Compounds Organic CompoundsOrganic Compounds

ZincZinc CadmiumCadmium AcetoneAcetone

Free CyanideFree Cyanide ArsenicArsenic Carbon DisulfideCarbon Disulfide

PerchloratePerchlorate FluorideFluoride ChloroformChloroform

CopperCopper LeadLead EthanolEthanol

MercuryMercury Free ammoniaFree ammonia PhenolPhenol

ChromiumChromium Free nitrous acidFree nitrous acid EthylenediamineEthylenediamine

NickelNickel Hexamethylene diamineHexamethylene diamine

SilverSilver AnilineAniline

CobaltCobalt MonoethanolamineMonoethanolamine

ThiocyanateThiocyanate

Sodium cyanideSodium cyanide

Sodium azideSodium azide

HydrazineHydrazine

Sodium cyanateSodium cyanate

Potassium chromatePotassium chromate

Figure 9 Nitrogen Removal in a Septic Tank Recirculating Trickling Filter System

After Oakley, et al. (1996).


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After Oakley, et al. (1996).

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360

Days in Operation

NitrogenConcentration,mg/Las

TKN

NO3-N

A carpet cleaning

solvent was introducedinto the system after

120 days in operation.

Nitrification Inhibition


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56/100

Biological DenitrificationBiological Denitrification


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Process Description:Process Description:

For heterotrophic denitrification, the carbon source can comeFor heterotrophic denitrification, the carbon source can comefrom the original wastewater, bacterial cell material, or anfrom the original wastewater, bacterial cell material, or an

external source such as methanol or acetate.external source such as methanol or acetate.

For autotrophic denitrification, which is common in waterFor autotrophic denitrification, which is common in water

treatment but not wastewater treatment, the electron donor cantreatment but not wastewater treatment, the electron donor can

come from elemental sulfur or hydrogen gas.come from elemental sulfur or hydrogen gas.

The possible process configurations for heterotrophicThe possible process configurations for heterotrophic

denitrification are shown in Figure 10.denitrification are shown in Figure 10.


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gg

Heterotrophic Denitrification: Wastewater as the Carbon SourceHeterotrophic Denitrification: Wastewater as the Carbon Source

The following unbalanced equation illustrates the processThe following unbalanced equation illustrates the processwhen wastewater or bacterial cell material is used as thewhen wastewater or bacterial cell material is used as the

carbon source:carbon source:


aCOHNSaCOHNS + bNO+ bNO33-- cNcN22 + dCO+ dCO22 + eC+ eC55HH77OO22N + f OHN + f OH-- + gH+ gH22O + end productsO + end products

organic Bacteriaorganic Bacteria bacterialbacterial

mattermatter cellscells



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gg


The reduction of 1 mg of NOThe reduction of 1 mg of NO33--

is equivalent to 2.86 mg of Ois equivalent to 2.86 mg of O22..

Thus, for example, a wastewater with an ultimate BOD (BODThus, for example, a wastewater with an ultimate BOD (BODLL))of 200 mg/L could potentially reduce almost 70 mg/L of NOof 200 mg/L could potentially reduce almost 70 mg/L of NO33

----NN

if the wastewater were used as the carbon source.if the wastewater were used as the carbon source.

This does not happen in practice, however, because a portionThis does not happen in practice, however, because a portionof the organic carbon in the wastewater must be used for cellof the organic carbon in the wastewater must be used for cell

synthesis and not nitrate reduction.synthesis and not nitrate reduction.



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gg


For complex organic matter such as wastewater, theFor complex organic matter such as wastewater, thestoichiometric equivalency can range from 3.46stoichiometric equivalency can range from 3.46--5.07 mg5.07 mg

BODBODLL/mg NO/mg NO33-- --N, with 4.0 mg BODN, with 4.0 mg BODLL/ mg NO/ mg NO33

----N used as a ruleN used as a rule

of thumb.of thumb.

In terms of BODIn terms of BOD55, this amounts to 2.72 mg BOD, this amounts to 2.72 mg BOD55/ mg NO/ mg NO33-- --N forN for

kk (base e) = 0.23 d(base e) = 0.23 d--11..



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gg


Figure 11, which assumes the "rule of thumb" stoichiometricFigure 11, which assumes the "rule of thumb" stoichiometricequivalency of 4.0 mg BODequivalency of 4.0 mg BODLL/mg NO/mg NO33

-- N (2.72 mg BODN (2.72 mg BOD55/mg NO/mg NO33--

N), shows total nitrogen removal as a function of initial TKNN), shows total nitrogen removal as a function of initial TKNand wastewater BODand wastewater BOD55..

In this figure it is assumed there is sufficient alkalinity forIn this figure it is assumed there is sufficient alkalinity fornitrification, and thatnitrification, and that kk = 0.23 d= 0.23 d--11. It is obvious from Figure 11. It is obvious from Figure 11that nitrogen removal by denitrification using wastewater as thethat nitrogen removal by denitrification using wastewater as thecarbon source is highly feasible for an initial TKN of 40 mg/L ocarbon source is highly feasible for an initial TKN of 40 mg/L orr

less, but becomes more problematic as the initial TKNless, but becomes more problematic as the initial TKNincreases in relation to BODincreases in relation to BOD55..

Figure 11: Nitrogen Removal as a Function of Initial TKN and Wastewater BOD5 When Wastewater is

Used as Carbon Source.


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0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250

Wastewater BOD5, mg/L

Effluent

TN,mg/Las

TKN = 20 mg/L

TKN = 40 mg/L

TKN = 60 mg/L

TKN = 80 mg/L

TKN = 100 mg/L

(It is assumed there is sufficient alkalinity, the initial TKN is nitrified, and that the stoichiometric equivalency is 4.0 mg BODL/ mg

NO3-

-N = 2.72 mg BOD5/mg NO3-

-N for k = 0.23 d-1

.)



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Heterotrophic Denitrification: External Carbon SourceHeterotrophic Denitrification: External Carbon Source

Where there is insufficient CBOD left in the wastewater to serveWhere there is insufficient CBOD left in the wastewater to serveas an electron donor for denitrification, an external carbonas an electron donor for denitrification, an external carbon

source must be supplied.source must be supplied.

Although there are many possibilities, methanol and acetateAlthough there are many possibilities, methanol and acetatehave been studied the most and their stoichiometry is wellhave been studied the most and their stoichiometry is well

known.known.



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Heterotrophic Denitrification: External Carbon SourceHeterotrophic Denitrification: External Carbon Source

Methanol:Methanol:


NONO33-- + 1.08CH+ 1.08CH33OH + 0.24HOH + 0.24H22COCO33 0.47N0.47N22 ++ 0.056C0.056C55HH77OO22N + HCON + HCO33-- + 1.68H+ 1.68H22OO

methanol Bacteriamethanol Bacteria bacterial cellsbacterial cells

Acetate:Acetate:


NONO33--

+ 0.87CH+ 0.87CH33COOCOO--

+ H+ H++

0.46N0.46N22 ++ 0.08C0.08C55HH77OO22N + 0.87HCON + 0.87HCO33--

+ H+ H22O + 0.44COO + 0.44CO22acetate Bacteria bacacetate Bacteria bacterial cellsterial cells



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Heterotrophic Denitrification: Process MicrobiologyHeterotrophic Denitrification: Process Microbiology

The heterotrophic denitrifying bacteria are facultativeThe heterotrophic denitrifying bacteria are facultative

aerobes that can use either oxygen or nitrate (under anoxicaerobes that can use either oxygen or nitrate (under anoxic

conditions) as an electron acceptor for the oxidation ofconditions) as an electron acceptor for the oxidation of

organic matter.organic matter.

Denitrifiers are commonly found in nature and areDenitrifiers are commonly found in nature and are

ubiquitous in wastewater.ubiquitous in wastewater.

Generally, denitrification processes perform similarly toGenerally, denitrification processes perform similarly to

aerobic processes designed for CBOD removal.aerobic processes designed for CBOD removal.



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Heterotrophic Denitrification: Process MicrobiologyHeterotrophic Denitrification: Process Microbiology

When an adequate carbon source is available, the principalWhen an adequate carbon source is available, the principalproblem associated with denitrification is the achievement ofproblem associated with denitrification is the achievement of

anoxic conditions.anoxic conditions.

The dissolved oxygen concentration controls whether or notThe dissolved oxygen concentration controls whether or not

the denitrifying bacteria use NOthe denitrifying bacteria use NO33-- or Oor O22 as the electronas the electronacceptor.acceptor.

Dissolved oxygen must not be present above certain maximumDissolved oxygen must not be present above certain maximum

levels or the denitrifying bacteria will preferentially use it flevels or the denitrifying bacteria will preferentially use it foror

oxidation of organic matter rather than NOoxidation of organic matter rather than NO33--..

As a result, the design of anoxic zones is one of the mostAs a result, the design of anoxic zones is one of the most

important factors in denitrification processes.important factors in denitrification processes.



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Heterotrophic Denitrification: pH and Alkalinity EffectsHeterotrophic Denitrification: pH and Alkalinity Effects

Theoretically, 3.57 mg of alkalinity as CaCOTheoretically, 3.57 mg of alkalinity as CaCO33 is produced foris produced foreach mg of NOeach mg of NO33

----N reduced to NN reduced to N22 gas when the wastewater isgas when the wastewater is

used as the carbon source.used as the carbon source.

Thus denitrification can recover approximately half of theThus denitrification can recover approximately half of thealkalinity lost in nitrification and can help overcome pH dropsalkalinity lost in nitrification and can help overcome pH drops

in low alkalinity waters. Because denitrifying organisms arein low alkalinity waters. Because denitrifying organisms are

heterotrophic, they normally will be affected by pH changes inheterotrophic, they normally will be affected by pH changes in

the same way heterotrophic bacteria are affected.the same way heterotrophic bacteria are affected.



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Heterotrophic Denitrification: Temperature EffectsHeterotrophic Denitrification: Temperature Effects

The data from the literature suggest that denitrification ratesThe data from the literature suggest that denitrification ratescan be significantly affected by temperature drops below 20can be significantly affected by temperature drops below 20 C,C,

with the denitrification rate at 10with the denitrification rate at 10 C ranging from 20% to 40% ofC ranging from 20% to 40% of

the rate at 20the rate at 20C.C.

It can be expected that this decrease is similar to thatIt can be expected that this decrease is similar to that

encountered for heterotrophic organisms removing CBOD andencountered for heterotrophic organisms removing CBOD and

should be taken into consideration for designs in cold climatesshould be taken into consideration for designs in cold climates


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Autotrophic Denitrification:Autotrophic Denitrification:

Autotrophic denitrification, while somewhat common inAutotrophic denitrification, while somewhat common indrinking water treatment, is not commonly used indrinking water treatment, is not commonly used in

conventional wastewater treatment, let alone onsite wastewaterconventional wastewater treatment, let alone onsite wastewater

treatment.treatment.

There is one example of elemental sulfur being tried inThere is one example of elemental sulfur being tried in

autotrophic denitrification for onsite systems in Suffolk Countyautotrophic denitrification for onsite systems in Suffolk County,,

New York, but this attempt ended in failure.New York, but this attempt ended in failure.



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Summary of Heterotrophic Denitrification Processes:Summary of Heterotrophic Denitrification Processes:

Table 5 summarizes the three processes for heterotrophicTable 5 summarizes the three processes for heterotrophic

denitrification (which are shown in Figure 10) with their advantdenitrification (which are shown in Figure 10) with their advantagesagesand disadvantages for onsite nitrogen removal.and disadvantages for onsite nitrogen removal.

In summary, organic carbon can be provided in the following waysIn summary, organic carbon can be provided in the following ways::

As an external carbon source to an anoxic reactor after nitrificAs an external carbon source to an anoxic reactor after nitrification;ation; As an internal source in the form of bacterial cells through a sAs an internal source in the form of bacterial cells through a sequentialequential

process of aerobic and anoxic zones;process of aerobic and anoxic zones;

The influent wastewater can be used as the carbon source by recyThe influent wastewater can be used as the carbon source by recyclingclingnitrified effluent to an anoxic reactor that precedes the aerobinitrified effluent to an anoxic reactor that precedes the aerobic nitrificationc nitrification

reactor, operating alternating aerobic/anoxic zones on one reactreactor, operating alternating aerobic/anoxic zones on one reactoror(sequencing batch reactor), or conveying the flow sequentially t(sequencing batch reactor), or conveying the flow sequentially throughhroughalternating aerobic/anoxic zones. Denitrification reactors can balternating aerobic/anoxic zones. Denitrification reactors can be designede designedas suspendedas suspended--growth or attachedgrowth or attached--growth processes.growth processes.



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Table 5:Table 5: Onsite Processes for Heterotrophic DenitrificationOnsite Processes for Heterotrophic Denitrification

ProcessProcess AdvantagesAdvantages DisadvantagesDisadvantages

External Carbon SourceExternal Carbon Source High removal rates.High removal rates. Insufficient performance data forInsufficient performance data forDenitrification easilyDenitrification easily onsite systems. Operation andonsite systems. Operation andcontrolled.controlled. maintenance data lacking. Routinemaintenance data lacking. Routine

monitoring required. Alkalinity lostmonitoring required. Alkalinity lost

through nitrification may or maythrough nitrification may or maynot be recovered, depending onnot be recovered, depending onthe carbon source used.the carbon source used.

Wastewater as CarbonWastewater as Carbon Lower energy andLower energy and Insufficient performance data.Insufficient performance data.SourceSource chemical requirements.chemical requirements. Process difficult to control. RoutineProcess difficult to control. Routine

Fifty percent recoveryFifty percent recovery monitoring required. Operation andmonitoring required. Operation and

of alkalinity lost throughof alkalinity lost through maintenance data lacking.maintenance data lacking.nitrification. Fifty percentnitrification. Fifty percent

reduction in Oreduction in O22 requirerequire--

ments for CBOD removal.ments for CBOD removal.

Bacterial Cells as CarbonBacterial Cells as Carbon Lower energy andLower energy and Insufficient performance dataInsufficient performance data

SourceSource chemical requirements.chemical requirements. Process difficult to control. RoutineProcess difficult to control. Routine

monitoring required. Operation andmonitoring required. Operation and

maintenance data lacking.maintenance data lacking.



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Denitrification reactors can be designed as suspendedDenitrification reactors can be designed as suspended--growthgrowth

or attachedor attached--growth processes.growth processes.

The lack of reliable performance data precludes a sound designThe lack of reliable performance data precludes a sound design

strategy for onsite denitrification, although much valuablestrategy for onsite denitrification, although much valuable

information exists for centralized treatment systems.information exists for centralized treatment systems.

In general, using wastewater as the carbon source has manyIn general, using wastewater as the carbon source has many

potential advantages, such as recovery of alkalinity (potential advantages, such as recovery of alkalinity ( 50%) and50%) anddiminished oxygen requirements for CBOD removal since NOdiminished oxygen requirements for CBOD removal since NO33

--

is used as the electron acceptor.is used as the electron acceptor.

Process Design for Onsite Nitrogen RemovalProcess Design for Onsite Nitrogen Removal


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Centralized Wastewater Treatment:Centralized Wastewater Treatment:

Nitrogen removal through biological nitrification/denitrificatioNitrogen removal through biological nitrification/denitrification,n,as practiced in centralized wastewater treatment, is generallyas practiced in centralized wastewater treatment, is generallyclassified as an advanced treatment process.classified as an advanced treatment process.

Detailed information on wastewater flows and characteristics isDetailed information on wastewater flows and characteristics isrequired for successful design, operation, and troublerequired for successful design, operation, and trouble--shootingshooting

if nitrogen removal is to be successful.if nitrogen removal is to be successful. As a result, design and operational parameters, such asAs a result, design and operational parameters, such as

alkalinity requirements, organic loading rates necessary toalkalinity requirements, organic loading rates necessary toachieve nitrification, and stoichiometric equivalencies forachieve nitrification, and stoichiometric equivalencies for

various reactions have been widely published in order tovarious reactions have been widely published in order toadvance knowledge and improve design and operation.advance knowledge and improve design and operation.



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Onsite Wastewater Treatment SystemsOnsite Wastewater Treatment Systems

Much of the published literature does not report data in termsMuch of the published literature does not report data in termsof parameters that can be used to rigorously assess systems,of parameters that can be used to rigorously assess systems,

compare them to other sites, and improve design andcompare them to other sites, and improve design and

operation.operation.

As an example, the loading rates on single pass sand filter (ISFAs an example, the loading rates on single pass sand filter (ISF))systems have been almost exclusively expressed in terms ofsystems have been almost exclusively expressed in terms of

hydraulic loading rates; the most useful information in terms ofhydraulic loading rates; the most useful information in terms of

nitrification, however, would be organic loading rates.nitrification, however, would be organic loading rates.

Alkalinity concentrations are also very rarely monitored inAlkalinity concentrations are also very rarely monitored inonsite wastewater treatment studies, but are fundamental inonsite wastewater treatment studies, but are fundamental in

assessing the limits on nitrification.assessing the limits on nitrification.



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Onsite Wastewater Treatment Systems: Key Design FactorsOnsite Wastewater Treatment Systems: Key Design Factors

Wastewater FlowsWastewater Flows

Range of FlowratesRange of Flowrates

Diurnal Variability of FlowratesDiurnal Variability of Flowrates

Wastewater CharacteristicsWastewater CharacteristicsOrganic Loadings (BODOrganic Loadings (BOD55))

Alkalinity and pHAlkalinity and pH

BODBOD55/TKN/TKN

Presence of InhibitorsPresence of Inhibitors



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Technological Assessment and Design Considerations.Technological Assessment and Design Considerations.

Figures 12 and 13, which show nitrogen removal as a functionFigures 12 and 13, which show nitrogen removal as a functionof initial TKN, alkalinity, and BODof initial TKN, alkalinity, and BOD55, have been developed for the, have been developed for the

range of BODrange of BOD55 values (100values (100--140 mg/L) reported for septic tank140 mg/L) reported for septic tank

effluents with an effluent filter.effluents with an effluent filter.

These figures can be used for an initial technical assessment ofThese figures can be used for an initial technical assessment of

possible removal efficiencies and design considerations for apossible removal efficiencies and design considerations for a

given wastewater.given wastewater.

Figure 12 Nitrogen Removal Using Wastewater as Carbon Source as a Function of TKN and Alkalinity

(It is assumed the BOD5= 120 mg/L, that 50%of the alkalinity lost by nitrification is recovered in denitrification,

and that the stoichiometric equivalency is 4.0 mg BODL/mg NO

3--N = 2.72 mg BOD

5//mg NO

3--N for k = 0.23 d-1.)


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0.0

10.0

20.0

30.0

40.0

0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0

Initial TKN, mg/L

EffluentTN,mg/L

Increasing Alkalinity

Alkalinity > 200 mg/L as CaCO3

BOD5= 120 mg/L

and that the stoichiometric equivalency is 4.0 mg BODL/mg NO

3N 2.72 mg BOD

5//mg NO

3N for k 0.23 d .)


as CaCO3


as CaCO3

BOD5 LIMITS

N REMOVAL


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Examples of Onsite Nitrogen RemovalExamples of Onsite Nitrogen Removal

TechnologiesTechnologies


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Suspended Growth:Suspended Growth:

Aerobic units w/pulse aerationAerobic units w/pulse aeration

Sequencing batch reactorSequencing batch reactor

Attached Growth:Attached Growth:

Single Pass Sand Filters (SPSF)Single Pass Sand Filters (SPSF)

Recirculating Sand/Gravel Filters (RSF)Recirculating Sand/Gravel Filters (RSF)

Recirculating Textile FiltersRecirculating Textile Filters

RSF w/Anoxic FilterRSF w/Anoxic Filter

RSF w/Anoxic Filter w/external carbon sourceRSF w/Anoxic Filter w/external carbon source

RUCK systemRUCK system




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SuspendedSuspended--Growth Systems (Figure 14)Growth Systems (Figure 14)

Aerobic Units with Pulse Aeration.Aerobic Units with Pulse Aeration. These units are, in principal,These units are, in principal,

extended aeration activated sludge systems in which aeration isextended aeration activated sludge systems in which aeration isperiodically stopped or pulsed to promote denitrification. Operaperiodically stopped or pulsed to promote denitrification. Operational datational dataon these systems is lacking although nitrogen removal efficiencion these systems is lacking although nitrogen removal efficiencies havees havebeen reported to be in the range of 25been reported to be in the range of 25--61 percent.61 percent.

Sequencing Batch Reactor (SBR).Sequencing Batch Reactor (SBR). The SBR differs generally fromThe SBR differs generally fromaerobic units in that fillaerobic units in that fill--andand--draw, and alternating aerobic and anoxicdraw, and alternating aerobic and anoxiccycles, are created within a single reactor; during the anoxic pcycles, are created within a single reactor; during the anoxic phasehasesedimentation takes place and thesedimentation takes place and the supernatnantsupernatnant is pumped from theis pumped from thereactor. Both endogenous phase bacteria and influent wastewaterreactor. Both endogenous phase bacteria and influent wastewater serve asserve asthe carbon source. SBR technology has been demonstrated to be anthe carbon source. SBR technology has been demonstrated to be anexcellent nitrogen control technology for largeexcellent nitrogen control technology for large--scale systems, but there isscale systems, but there isa paucity of information for onsite systems.a paucity of information for onsite systems.


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AttachedAttached--Growth Systems (Figure 15)Growth Systems (Figure 15)

Single Pass Sand Filters (SPSF).Single Pass Sand Filters (SPSF). SPSF technology is the mostSPSF technology is the moststudied of all proposed nitrogen removal technologies. Thestudied of all proposed nitrogen removal technologies. Themechanism of nitrogen removal includes a combination of CBODmechanism of nitrogen removal includes a combination of CBODremoval and nitrification within the sand medium at low organicremoval and nitrification within the sand medium at low organicloadings (low BODloadings (low BOD55/TKN ratio), and subsequent denitrification/TKN ratio), and subsequent denitrificationwithin anoxic microenvironments in the sand.within anoxic microenvironments in the sand.

TotalTotal--N removal rates with SPSFs have been quoted in theN removal rates with SPSFs have been quoted in theliterature as ranging from 8% to 50%.literature as ranging from 8% to 50%. The greatest advantage ofThe greatest advantage ofISF technology is in the achievement of nitrification. TheISF technology is in the achievement of nitrification. The

percentage of TKN nitrification in SPSF systems has been reportepercentage of TKN nitrification in SPSF systems has been reporteddto range between 75% to 96%.to range between 75% to 96%.


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Single Pass Sand Filters, Continued.Single Pass Sand Filters, Continued. Unfortunately, there is aUnfortunately, there is apaucity of sound design data for nitrification based on organicpaucity of sound design data for nitrification based on organicloading rates. Most of the loading rates have been reported inloading rates. Most of the loading rates have been reported in

terms of hydraulic loading rather than organic loading. Also,terms of hydraulic loading rather than organic loading. Also,

accurate data on measured loadings per unit area based on theaccurate data on measured loadings per unit area based on the

type of distribution system used as opposed to calculatedtype of distribution system used as opposed to calculatedloadings are difficult to come by.loadings are difficult to come by.

Assuming there is sufficient alkalinity for nitrification, it caAssuming there is sufficient alkalinity for nitrification, it can ben be

expected that SPSF systems will always be denitrificationexpected that SPSF systems will always be denitrification--limitedlimiteddue to the lack of availability of both a carbon source and anoxdue to the lack of availability of both a carbon source and anoxicic

conditions.conditions.




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Recirculating Sand/Gravel Filters (RSF).Recirculating Sand/Gravel Filters (RSF). RSF technology isRSF technology is

also very well studied in the literature. Totalalso very well studied in the literature. Total--N reduction has beenN reduction has beenreported to range from 15% to 84%. RSFs can achieve highreported to range from 15% to 84%. RSFs can achieve highnitrification rates and consistently higher denitrification ratenitrification rates and consistently higher denitrification rates thans thanISFs because the nitrified effluent can be recycled back to aISFs because the nitrified effluent can be recycled back to arecirculation tank where it mixes with wastewater from the septirecirculation tank where it mixes with wastewater from the septicctank, thus using the incoming wastewater as a carbon source.tank, thus using the incoming wastewater as a carbon source.

As with SPSF systems, the organic loading rates for RSF systemsAs with SPSF systems, the organic loading rates for RSF systemsare poorly defined in the literature. The available data suggestare poorly defined in the literature. The available data suggest thatthat

organic loading rates that promote nitrification typically are iorganic loading rates that promote nitrification typically are in then therange of 0.002range of 0.002--0.008 lbs. BOD0.008 lbs. BOD55/ft/ft

22--day. The extent of denitrificationday. The extent of denitrificationcan be expected to vary widely since RSF systems have notcan be expected to vary widely since RSF systems have nottypically been designed and operated specifically for nitrogentypically been designed and operated specifically for nitrogenremoval.removal.




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Recirculating Sand/Gravel Filters, Continued.Recirculating Sand/Gravel Filters, Continued.

There is no doubt RSF performance could be significantlyThere is no doubt RSF performance could be significantlyimproved for nitrogen removal with design and operationalimproved for nitrogen removal with design and operational

changes.changes.

The recirculation tank is not generally configured toThe recirculation tank is not generally configured tomaximize the mixing of septic tank effluent with RSFmaximize the mixing of septic tank effluent with RSF

effluent or to optimize the formation of anoxic conditions foreffluent or to optimize the formation of anoxic conditions fordenitrification.denitrification.




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Recirculating Sand/Gravel Filters, Continued.Recirculating Sand/Gravel Filters, Continued. A better designA better design

to enhance denitrification recycles the filter effluent to the ito enhance denitrification recycles the filter effluent to the inletnletside of an anoxic recirculation tank, or an anoxic rock filter,side of an anoxic recirculation tank, or an anoxic rock filter, wherewhereit mixes with septic tank effluent; the final effluent for dischit mixes with septic tank effluent; the final effluent for discharge isarge isthen taken from the filter. This type of system has been termedthen taken from the filter. This type of system has been termed"classical predenitrification"classical predenitrification. The rock filter fosters anoxic. The rock filter fosters anoxicconditions by preventing hydraulic shortconditions by preventing hydraulic short--circuiting and allowscircuiting and allowsdenitrifying organisms to grow on the rock surfaces, althoughdenitrifying organisms to grow on the rock surfaces, althoughthere could be serious problems with maintenance due to sludgethere could be serious problems with maintenance due to sludgeaccumulation.accumulation.

Systems using this type of design have been reported in theSystems using this type of design have been reported in theliterature. While one system exhibited a mean Totalliterature. While one system exhibited a mean Total--N removal ofN removal of40% with a mean effluent concentration of 23 mg/L, another study40% with a mean effluent concentration of 23 mg/L, another studyreported Totalreported Total--N removals of 80 to 90% and effluent TotalN removals of 80 to 90% and effluent Total--NN

concentrations ranging from 7concentrations ranging from 7--10 mg/L.10 mg/L.




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Recirculating Sand/Gravel Filters, Continued.Recirculating Sand/Gravel Filters, Continued. OperationalOperational

changes that could improve nitrogen removal include optimizingchanges that could improve nitrogen removal include optimizingthe recirculation ratio in order to i) minimize dissolved oxygenthe recirculation ratio in order to i) minimize dissolved oxygen ininthe recirculation tank and ii) maximize denitrification.the recirculation tank and ii) maximize denitrification.

The recirculation ratio forThe recirculation ratio for dentrificationdentrification must be at least 4:1 ormust be at least 4:1 orgreater in order to remove at minimum 80% of the NOgreater in order to remove at minimum 80% of the NO33-- --N. ManyN. Many

RSFs in operation may be below this minimum since the range ofRSFs in operation may be below this minimum since the range ofrecommended recirculation ratios is often 3:1 to 5:1. Also, veryrecommended recirculation ratios is often 3:1 to 5:1. Also, veryhigh recirculation ratios used to prevent filter drying during lhigh recirculation ratios used to prevent filter drying during lowow--

flow periods can inhibit denitrification because they cause highflow periods can inhibit denitrification because they cause highdissolved oxygen concentrations in the recirculation tank. Thedissolved oxygen concentrations in the recirculation tank. Theoptimization of the recirculation ratio for Totaloptimization of the recirculation ratio for Total--N removal has to beN removal has to bedone on a sitedone on a site--specific basis.specific basis.




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Single Pass (ITF) and MultiSingle Pass (ITF) and Multi--Pass Textile Filters (RTF).Pass Textile Filters (RTF). TextileTextilefilters are a relatively new technology. The design configuratiofilters are a relatively new technology. The design configurationsns

and operational characteristics of single pass and multipleand operational characteristics of single pass and multiple--passpass

textile filters are essentially the same as for sand/gravel filttextile filters are essentially the same as for sand/gravel filters withers with

one important exception that has been reported in a refereedone important exception that has been reported in a refereedjournal article: hydraulic and organic surface loading rates arejournal article: hydraulic and organic surface loading rates are

much higher due to the specific surface area of the textile medimuch higher due to the specific surface area of the textile medium.um.

((LeverenzLeverenz, H.,, H., et al.,et al., EvaluationEvaluation ofofHighHigh--PorosityPorosity MediumMedium inin

IntermittentlyIntermittently DosedDosed,, MultiMulti--PassPass PackedPacked BedBed FiltersFilters forfor thetheTreatmentTreatment ofofWastewaterWastewater,, SmallSmallFlowsFlows QuarterlyQuarterly, Vol. 2, No., Vol. 2, No.

2, pp. 282, pp. 28--35, 200135, 2001))


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Peat Filters.Peat Filters. Peat filters have been used in a manner similar toPeat filters have been used in a manner similar to

intermittent sand filters, with similar hydraulic and organic lointermittent sand filters, with similar hydraulic and organic loadingadingrates. The results of a very few studies show a potential for hirates. The results of a very few studies show a potential for highghTotalTotal--N removal, but there is very little known about theN removal, but there is very little known about themechanisms for adequate design.mechanisms for adequate design.

It can be assumed that the peat would serve as a carbon source fIt can be assumed that the peat would serve as a carbon source fororreduction of NOreduction of NO33

----N after nitrification has occurred in the filter.N after nitrification has occurred in the filter.Unfortunately, few detailed design and operational data areUnfortunately, few detailed design and operational data areavailable to adequately characterize the various peat media inavailable to adequately characterize the various peat media in

terms of design and operational parameters for both nitrificatioterms of design and operational parameters for both nitrificationnand Totaland Total--N removal.N removal.




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Recirculating Sand/Gravel Filters with Anoxic Filter andRecirculating Sand/Gravel Filters with Anoxic Filter andExternal Carbon Source.External Carbon Source. This system is similar to the RSFThis system is similar to the RSFabove with an anoxic rock filter except the anoxic rock filter nabove with an anoxic rock filter except the anoxic rock filter nowow

follows the RSF and an external carbon source is added as shownfollows the RSF and an external carbon source is added as shown

in Figure 15. Part of the RSF effluent is recycled to thein Figure 15. Part of the RSF effluent is recycled to therecirculation tank, and another part is discharged to the anoxicrecirculation tank, and another part is discharged to the anoxic

rock filter where the external carbon source is added. Totalrock filter where the external carbon source is added. Total--NN

removal in this type of system has been reported to be very highremoval in this type of system has been reported to be very high..

One detailed study on pilot scale systems showed TotalOne detailed study on pilot scale systems showed Total--NN

removals of from 74 to 80% with Totalremovals of from 74 to 80% with Total--N effluent concentrationsN effluent concentrations

ranging from 10ranging from 10--13mg/L.13mg/L.




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AttachedAttached--Growth Systems (Figure 15 Continued)Growth Systems (Figure 15 Continued)

RUCK System.RUCK System. The RUCK system, which is shown in Figure 15,The RUCK system, which is shown in Figure 15,is a proprietary system that uses source separation for nitrificis a proprietary system that uses source separation for nitrificationation

and denitrification. Separate collection systems are designed foand denitrification. Separate collection systems are designed forr

greywater and blackwater, with each having its own septic tank.greywater and blackwater, with each having its own septic tank.

The blackwater, which is comprised of wastewater from toilets,The blackwater, which is comprised of wastewater from toilets,showers and baths, is discharged to an SPSF for nitrification anshowers and baths, is discharged to an SPSF for nitrification andd

then passes to an anoxic rock filter; the greywater, comprised othen passes to an anoxic rock filter; the greywater, comprised off

kitchen and laundry wastewater, passes from its septic tankkitchen and laundry wastewater, passes from its septic tank

directly to the anoxic rock filter, where it serves as the carbodirectly to the anoxic rock filter, where it serves as the carbonn

source.source.


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AttachedAttached--Growth Systems (Figure 15 Continued)Growth Systems (Figure 15 Continued)

RUCK System, Continued.RUCK System, Continued. While the RUCK system hasWhile the RUCK system hasoften been cited in the literature as a potential technology foroften been cited in the literature as a potential technology fornitrogen removal, there is a paucity of performance data that hanitrogen removal, there is a paucity of performance data that havevebeen published. While the process is intended to provide at leasbeen published. While the process is intended to provide at leastt80% Total80% Total--N removal, results from a few studies have shown muchN removal, results from a few studies have shown much

poorer removal rates of from 29poorer removal rates of from 29--54% Total54% Total--N removal.N removal.

The variability in nitrogen removal efficiency is no doubt due tThe variability in nitrogen removal efficiency is no doubt due to theo thecomplexity of the system, the variability of the quality of greycomplexity of the system, the variability of the quality of greywater,water,

and the need to adjust the operation to siteand the need to adjust the operation to site--specific conditions.specific conditions.The RUCK system likely requires significant adjustment toThe RUCK system likely requires significant adjustment toblackwater and greywater characteristics and site conditions toblackwater and greywater characteristics and site conditions tooperate effectively.operate effectively.



Sh ll T h d S b f D i I i i S


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Shallow Trench and Subsurface Drip Irrigation Systems.Shallow Trench and Subsurface Drip Irrigation Systems.

The use of either shallow trench or subsurface drip irrigation (The use of either shallow trench or subsurface drip irrigation (SDI)SDI)

systems has been proposed as an alternative means to removesystems has been proposed as an alternative means to removeTotalTotal--N in the soil column. Both systems have the potential toN in the soil column. Both systems have the potential topromote nitrogen uptake by plant roots if effluent was dischargepromote nitrogen uptake by plant roots if effluent was dischargedddirectly within the root zone.directly within the root zone.

There is also a potential that both systems within the 'A' horizThere is also a potential that both systems within the 'A' horizon ofon ofthe soil could promote denitrification of nitrified effluents ifthe soil could promote denitrification of nitrified effluents if theretherewas sufficient organic matter present, either naturally or addedwas sufficient organic matter present, either naturally or added,,and if the conditions were conducive for denitrification (and if the conditions were conducive for denitrification (ieie.,.,

anoxic). This type of denitrification has been demonstrated withanoxic). This type of denitrification has been demonstrated withthe use of a reactive porous media barrier using sawdust as athe use of a reactive porous media barrier using sawdust as acarbon source, which was used to denitrify nitrified septic tankcarbon source, which was used to denitrify nitrified septic tankeffluents percolating through the soil column.effluents percolating through the soil column.



Sh ll T h d S b f D i I i ti S tSh ll T h d S b f D i I i ti S t


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Shallow Trench and Subsurface Drip Irrigation Systems.Shallow Trench and Subsurface Drip Irrigation Systems.

To date, the results on the use of shallow trenches or SDI systeTo date, the results on the use of shallow trenches or SDI systemsms

for onsite nitrogen removal is mixed at best, with removalfor onsite nitrogen removal is mixed at best, with removalefficiencies of Totalefficiencies of Total--N ranging from 0 to 40%.N ranging from 0 to 40%.

Coupling nitrogen loadings with plant uptake requires significanCoupling nitrogen loadings with plant uptake requires significanttoperational monitoring and adjustment.operational monitoring and adjustment.

Denitrification, if it is desired, cannot be easily controlled wDenitrification, if it is desired, cannot be easily controlled within aithin atrench system or the soil column as it can within a treatmenttrench system or the soil column as it can within a treatmentreactor above ground.reactor above ground.

Monitoring of nitrogen removal in the soil column is also aMonitoring of nitrogen removal in the soil column is also asignificant problem since lysimeter systems have to be used, andsignificant problem since lysimeter systems have to be used, andthey require some degree of sophistication in installation andthey require some degree of sophistication in installation and

sample collection.sample collection.

onsite nitrogen removal ppt

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