Biological, physical, and chemical processes for nutrient...
Transcript of Biological, physical, and chemical processes for nutrient...
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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