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Biological, physical, and chemical processes for nutrient removal

CEE484Decentralized and Onsite Wastewater Management

April 20, 2007

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Nitrogen and Phosphorus in Onsite Wastewater (50 gal/capita-day)

173.3Total P7213.3TKN305.5Organic N427.8NH4-N

50095TSS1050200COD45085BOD5

mg/Lg/capita-dayConstituent

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Topics• Forms of nitrogen• Nitrogen Transformations• Biological Nitrification and Denitrification• Fate of Nitrogen• Forms of phosphorus• Chemical, physical and biological

processes for phosphorus removal

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Oxidation states of nitrogen

+4Nitrogen dioxideNO2

+5NitrateNO3-

+3NitriteNO2-

+2Nitric oxideNO+1Nitrous oxideN2O0Nitrogen gasN2

-3-3

AmmoniaAmmonium

NH3

NH4+

N ValenceNameCompound

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Nitrogen compound measurements in wastewater

Reported as N to follow nitrogen in various forms

TKN – NH4-NOrganic Nitrogen

TKN + NO2-N + NO3-NTotal Nitrogen (TN)

Digestion, distillation, wet chemistry

Organic N + NH4-N

Total Kjeldhal Nitrogen

TKN

NH4-N + NO2-N + NO3-N

Total Inorganic Nitrogen (TIN)

wet chemistry, UV spec

NO3-NNitrate

wet chemistry, UV spec

NO2-NNitrite

wet chemistry, probeNH4-NAmmonium ion

Common methodsAbbrev.Compound

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Terms used to describe nitrogen transformations in the environment

N2NO2-, NO3

-Denitrification

NH3NH3Volatilization

NO2-, NO3

-NH3, NO2-Nitrification

Biomass~10% N on dry wgt basis

NH3, NO3-Synthesis

NH3Organic NAmmonification(deamination)

Organic NN2Fixation

ProductCompound(s)Transformation

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Biological processes involve growing living microbes

• What do they need?– Growth substrate – carbon source

• Organic substances – heterotrophs• Inorganic carbon – CO2- autotrophs

– Energy• Oxidation-reduction reactions

– i.e. use oxygen to oxidized glucose to CO2 and H20– Nutrients

• All living things need N and P– Trace minerals

• Iron, sulfur, etc– Acceptable pH and temperature– Acceptable dissolved solids level

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Nitrification is an Aerobic Process

NH4+ + 1.83 O2 + 1.98 HCO3

- = 0.98 NO3

- + 0.021 C5H7O2N + 1.88 H2CO3 + 1.04 H2O

• Autotrophic Growth - Energy From Oxidation of NH4

+ and Cell Carbon From HCO3

-

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NH O NO H H O4 2 2 22 3 2 4 2+ − ++ → + +

Nitro-bacteria (nitrobacter)

− −+ →NO O NO2 2 32 2

NH O NO H H O4 2 3 22 2+ − ++ → + +

Nitroso-bacteria (nitrosomonas)

Nitrification to NO3 Involves 2 types of Autotrophic Bacteria

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Effective Nitrification• Sufficient time for microbes (slower growers)

– Affected by Temperature– Water contact time with aerobic soil– Time in decentralized treatment biological reactors

• Adequate Dissolved Oxygen (DO) Concentration– Aerobic soil– Sufficient air supply in treatment reactors

• Adequate pH– Sufficient alkalinity,– reaction uses 7.1 mg alkalinity (as CaCO3) per mg

NH4-N oxidized• No Significant Toxicity

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Biological Denitrification

• Heterotrophic bacteria• Use Nitrate or Nitrite to oxidize organics in

absence of oxygen– Reduce oxidized nitrogen to nitrogen gasNO-

3 NO -2 NO N2O N2

• Facultative organisms• Wide range of carbon sources can be used• Produce alkalinity

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Reactions And Stoichiometry - Methanol and Wastewater for Carbon Source

Example with methanol consumption:5 CH3OH + 6 NO3

- = 3 N2 + 5 CO2 + 7 H2O + 6 OH-

M = 2.47 No + 1.53 Ni + 0.87 DOWhere M = methanol dose, mg/L

No = NO3-N concentration, mg/LNi = NO2-N concentration, mg/LDO = Dissolved oxygen concentration, mg/L

ALKALINITY PRODUCED: -3.57 g as CaCO3 / g NO3-NAnd 2.86 g of equivalent Oxygen is supplied per g of NO3-

N used

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• How much nitrogen removal would you expect to occur across a septic tank?

• What is fate of NH4-N when dispersed into soil?

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Nitrogen Removal• Soils

– Nitrification-denitrification– Volatilization is generally very low– Short term

• Plant growth• Biomass synthesis

– Capture and storage• Sorption/ion exchange of NH4

+

• Treatment Reactors– Nitrification-denitrification– Biomass synthesis and sludge wasting– Volatilization is very very low

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Forms of Phosphorus

2-3 mg/LOrganic Phosphorus

4-6 mg/LPolyphosphates

(Tripolyphosphate, pyrophosphates,

trimetaphosphates)

6-9 mg/LOrthophosphate

Approx. concentration at50 gal/cap-d

Phosphate Form

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Household Sources

0.6 Human Waste

0.1Other Household Cleaners

0.3Laundry Detergent

Amount(kg/capita-year

Origin

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Phosphorus Removal Mechanisms in Soil

• Uptake but no long term removal without harvesting– Plant uptake and plant growth– Biomass synthesis

• Captured and stored – depends on soil characterisitcs– Sorption/precipitation at high concentration (>5.0 mg/L)

• example phosphate precipitates– FePO4(2H2O)-strengite, AlPO4(2H2O)-variscite, Ca10(PO4)6(OH2)-

hydroxyaptite– Sorption/precipitation at low concentration (< 5.0 mg/L)

• Surfaces of iron and aluminum minerals in strongly acid to neutral pH.

• On calcium minerals in neutral to alkaline pH

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Phosphorus Removal in Wastewater Treatment Systems

• Biomass synthesis and sludge wasting– 1.0 to 1.5 % of cell dry weight is P

• Enhanced biological phosphorus removal• Chemical addition and precipitation• Filtration with chemical addition• Filtration on surface active media –

– Activated alumina filter material– Iron coated sand material

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Precipitation with aluminum or iron

Al2(SO4)3(14H2O)+ 2H3(PO4) = 2Al(PO4) + 3H2SO4 + 14H2O

FeCl3 + H3(PO4) = Fe(PO4) + 3HCl3

Chemical addition uses alkalinityBest at pH = 6.5 to 7.2

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Dose is concentration dependent

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0.0 1.0 2.0 3.0 4.0 5.0

Mol

ar A

l/P ra

tio

Soluble P, mg/L

Al mg/L dose = (Al/P ratio)(mg/L P to be removed)

Chemical PrecipitationDose Ratio Increases at Lower P Concentration

For P = 1.0 mg/L Molar ratio = 1.0 -1.5 M Al/M PFor P = 2.0 mg/L Molar ratio = 1.0 – 1.2 M Al/M PFor P < 0.5 mg/L Molar ratio = 2.0 – 4 M Al/M P

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Chemicals can be added at a number of locations and at more than one place in treatment

PrimaryTrt Aeration

Secondary clar.

Alum or Fe Alum or Fe Alum or Fe

FilterPossible

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Enhanced Biological Phosphorus Removal Incorporates an Anaerobic Contact zone Prior to Aerobic Zone in Activated

Sludge Treatment

ANAEROBIC

AEROBICEFFL.INFL.

WASRAS

Time=45 to 60 min

Tme=6 to 12 hours

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What are the process steps and mechanisms of EBPR?

P is removed by phosphorusaccumulating organisms (PAOs) and exits system in waste sludge

P release

Acetate

InfluentBOD

Anaerobic Anoxic and/orAerobic

P uptake

-Carbon storage-PHB-poly P storage

Waste sludgeNO3

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Nutrients Key Points

• Forms of N and P• Biological reactions for removal of N and P• Chemical precipitation reactions• Methods for removal in soil• Methods for removal in treatment systems

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Anammox Process• Developed at Delft University - Netherlands• Unique autotrophic bacteria• Nitrite oxidizes ammonia to nitrogen gas• NH4

+ + 1.3 NO2- + 0.042 CO2 =

• 0.042 Biomass + N2 + 0.22 NO3- + 0.08 OH-

+ 1.82 H2O• Prefer fixed film media for growth • Slow growing bacteria• Prefer high temperature, 25-300C