Wastewater Nitrogen - Georgia Environmental … gas and water, as follows NH 4 + + NO 2 ... • After the carbonaceous demand is met in the ... TEST CENTER SUMMARY

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Wastewater Nitrogen Characteristics, Treatment and Removal Options

Bob Smith, Orenco Systems, Inc. GEC 2013

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Nitrogen

Nitrogen (N2) in the environment exists primarily in the earth’s atmosphere as a colorless, tasteless, and generally inert gas

Air, by volume, is composed of about 78.08% nitrogen, with

oxygen (O2) following at about 20.95% Nitrogen is assimilated (absorbed/digested) and/or fixed from the

air in living things


Nitrogen Soil bacteria and ocean algae are primary fixers; nitrogen gas N2 —> Organic-N

Nitrogen is a constituent of DNA and therefore, an essential

element for life. Carbon, Oxygen, Nitrogen, Hydrogen, and Phosphorus, by weight,

compose over 99% of microbial cell structure.


Nitrogen in Urine and Feces

Urine contributes about 75%+ of the nitrogen found in domestic wastewater

Feces contributes about 20% ± of the nitrogen. Source separation can be an effective strategy.


Nitrogen Family

• Organic nitrogen … Organic-N

• Ammonium nitrogen … NH4+

• Ammonia nitrogen … NH3-N

• Nitrite nitrogen … NO2-N

• Nitrate nitrogen … NO3-N


Total Nitrogen (TN)

TN = Organic N + NH3-N + NO2-N + NO3-N

Total Inorganic Nitrogen TIN = NH3-N + NO2-N + NO3-N


Total Kjeldahl Nitrogen (TKN)

TKN = Organic-N + NH3-N Therefore … Organic-N = TKN - NH3-N And … TN = TKN + NO2-N + NO3-N


Ammonification

Ammonification is the transformation of organic nitrogen to ammonium (NH4) and ammonia (NH3) inorganic forms, depending on pH levels.

The initial phase of ammonification occurs in

the septic environment of the primary tankage (70% ±) and about 3/4th of the remaining organic nitrogen is converted to ammonia through the secondary aerobic process.


Ammonification

Urea is transformed to ammonia as follows: CH4N2O + H2O > 2NH3 + CO2


Nitrification

Nitrification is the microbial conversion of ammonium to nitrate.

Nitrification is a two-phase process that

occurs in the highly aerobic environment of secondary and advanced treatment processes


Nitrification In the first phase, ammonium oxidizing autotrophic bacteria

known as nitrosomonas convert ammonia to nitrite in the following manner

2NH4

+ + 302 nitrosomonas > 2NO2- + 4H+ + 2H2O.

In the second phase of nitrification, a nitrite oxidizing

bacteria known as nitrobactor converts nitrite to nitrate as follows:

2NO2

- + 02 nitrobactor > 2NO3-


Denitrification

Denitrification is the microbial utilization of nitrate under anoxic conditions.

Denitrification is a multi-stage process where nitrate

(NO3-) is reduced to nitrogen gas (N2), which is

liberated back into the atmosphere after rising to the liquid surface in tiny bubbles.


Alternate Metabolic Pathways

Anammox is an anaerobic ammonia oxidation process where nitrite and ammonia react and are converted to nitrogen gas and water, as follows

NH4

+ + NO2- ——> N2

gas + 2H2O The nitrite supply must be steady, and can be provide

through partial nitrification or denitrification.


Typical Residential-Strength Influent* From Building Sewer

* Small and Decentralized Wastewater Management Systems, Crites & Tchobanoglous, p. 180, 1998.

17 160 70 500 450 Raw Influent

TP mg/L

G&O mg/L

TN mg/L

TSS mg/L

BOD5 mg/L


Commercial Concentrations Commercial workplace flows typically ranging 6 to 12 gpd/person, or higher

depending on the type of facility. With current practices to utilize water conserving low flow fixtures, commercial

concentrations, after primary treatment, are likely to be in the order of … 400 to 500 mg/L± BOD5 180 to 220 mg/L± TKN 50 to 70 mg/L± TP

These concentrations correlate well with field-measured concentrations from

offices, rest stops, manufacturing and other similar facilities where the primary wastewater flows is primarily from toilets and urinals.


•  Adequate aeration volume for solids retention time (SRT > 8 - 10 days typical of suspended growth)

•  Sufficient aeration capacity for needed dissolved oxygen (DO) concentration (4.57 mg O2/mg NH3-N)

•  Sufficient alkalinity/pH, (7.14 mg alkalinity as CaCO3 per mg NH4-N oxidized – pH >6)

•  No significant toxicity (e.g. trace organics, chlorides, …)

•  Temperature control above 45°F

Nitrification … What’s Needed


Oxygen Availability in Air

≈ 275 mg/L oxygen in free air, which directly interfaces with the biomass ... in contrast to 9 mg/L DO holding capacity of water for oxygen transfer


Nitrification Limiting Factors: • High organic concentrations … BOD, COD, etc

• Lack of sufficient dissolved oxygen … DO greater than 2 mg/L is preferred

• Insufficient alkalinity … filtrate CaCO3 should be around 100 mg/L or greater

• Low pH … maintain greater than 6, with optimum range between 7.2 and 9

• Low Temperature … should be 10°C or higher

• Toxic Inhibitors … e.g., high chloride levels (keep below 180 mg/L)


Ratio of Carbon to Nitrogen

Percentage of Total Population

0.5 35% 2.5 10% 5.5 5% 10 2.5%

Nitrifier Population vs BOD5/TKN ratio


Nitrification Reaction Rate vs BOD/TKN

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Effect of DO on Nitrification DO greater than 2 mg/L is preferred

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Effect of pH on Nitrifiers Filtrate alkalinity (CaCO3 ) should be maintained at 80-100 mg/L or greater for optimum nitrification

Maintain pH above 6, with optimum between 7.2 and 9 for nitrification

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Temperature Effect on Nitrifiers Winter effluent temperature should be 10°C or higher

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Nitrification with Packed Bed Filters

Packed bed filters have demonstrated a strong ability to reduce residential strength ammonia (40 to 55 mg/L) by 98 to 99%

When that expected level appears to degrade by 5% or more,

servicing is likely necessary, as well as an investigation into flow and strength capacities and/or other inhibiting factors (like over use of household cleaners, carpet cleaning, insufficient alkalinity, pH drop, etc.).


Packed Bed Filter Biofilms • At the surface and within the top 6 inches±,

matter is trapped and the greatest biofilm accumulation occurs

• The top zone is mostly responsible for solids and organic reduction

• Heterotrophic bacteria are primarily responsible for reducing organic matter


Packed Bed Filter Biofilms • Oxygen is diffused from the air that fills the

unsaturated voids into the effluent and biofilms.(Oxygen concentration in air ≈ 275 mg/L)

• After the carbonaceous demand is met in the upper levels of the media, inorganic constituents such as ammonia (NH3) is reduced to nitrate (NO3

–) by autotrophic bacteria conversion of ammonia to nitrate) in the lower region of the media


Typical PBF Recirculation Configuration


TEST CENTER SUMMARY AdvanTex Effluent Averages

Total N mg/L

NH3-N mg/L

Total P mg/L

Duration

NSF/ANSI Standard 40 12 (64%) 0.9 (96%) - 7 months

NSF/ANSI Standard 40 Testing with UV 13 (66%) 1.1 - 6 months

Novatec Nitrogen Removal Testing 10 (70%) - - 1 year

Rotorua District Council Approval Testing 14(78%) 0.2 (99%) 8 (36%) 13 months

Rotorua 2010 12.7 (78%) 0.6 (96%)


FIELD TESTING SUMMARY AdvanTex Effluent Averages (no. of SFRs)

Total N mg/L

NH3-N mg/L

Total P mg/L Duration

NSF Pennsylvania Testing Program (11) 17 (68%) 1.7 (96%) - 1-3 years Virginia Approval Testing Program (13) 15 1.8 - 18 months Jefferson County, CO Health Dept Permit Testing (43) 15 - - 2 years 7 months

Skaneateles, NY Demonstration Project (2) 14 0.9 10 2 years 2 months

La Pine, OR Demonstration Project (3) 17 (74%) 1.9 9 (18%) 2 years 7 months Rhode Island Demonstration Project (5) 18 - 9 1 year 4 months Maryland BAT Testing AX20 (12) 17 1 year 5 months Maryland BAT Testing AX20RT (12) 14 1.3 1 year


Typical AdvanTex® Recirc-Filters

• 60 to 70 % total nitrogen reduction without supplemental inputs

∼ To reach concentrations below 10 to 15 mg/L, apply specific engineering practices for nitrogen removal


Two-Stage PBF Configuration


PFB w/ Pre-Anoxic Denite-Recirculation Loop


Denitrification – Key Limiting Factors: • Insufficient organic concentrations [C/N ratio ranges from 4 to 8 g BOD5/ g (NO3-N)]

• Excessive dissolved oxygen (anoxic DO < 1 mg/L … optimum DO < 0.3 mg/L)

• Temperature (keep above 45°F … preferably 50°F)


Effect of DO on Denitrification

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Why Recirculate Treated Effluent? • To optimize wastewater treatment

• To blend and dilute influent concentrations, which promotes more efficient hydrolysis

• To introduce nitrified effluent where there is a free carbon concentration and potential for supporting denitrification.

• To accomplish greater ammonia and total nitrogen removal

• To accomplish greater carbon reduction through denitrification utilization of 4 or more mg BOD5 per mg nitrate removed.


Supplements for Nitrogen Removal

• The effectiveness of nitrification is very dependent upon alkalinity/pH, and the effectiveness of denitrification is very dependent on an organic food source … both of which often requires a chemical feed system designed to consistently dispense appropriate quantities of various buffering and carbon based compounds.

• Chemical feed systems provide a common and effective low cost means for disinfection.


Supplemental Alkalinity Buffering Compounds Compounds Alk-Ratio

ppm/ppm CaCO3

• Soda Ash 1.06 • Acetate 0.82 • Hydrated Lime 0.74 • Quick Lime 0.56 • Bicarbonate 1.68 • Caustic Soda 0.80 • Magnesium Hydroxide 0.50


Supplemental Carbon Sources • Methanol (CH3OH) : 6.6 lb/gal – 1,118,000 mg/L COD

• Ethanol (CH3OH) : 6.8 lb/gallon – 1,650,000 mg/L COD

• MicroC™ (CH3CO2Hxx): 9.56 lb/gal – 600,000 mg/L COD

• Acetic Acid (CH3OOH): 8.8 lb/gal – 1,120,000 mg/L COD


System Description • Multiple Pass, packed bed • Engineered textile • Combines

∼ Textile filter media ∼ Recirculation tank ∼ Discharge tank

Textile Media

Recirculation Side Discharge Side


Applications • Repairs and retrofits • Small sites and poor soils • Sites that require shallow bury • Residential Strength

Wastewater (up to and including 500 gpd)

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Wastewater Nitrogen - Georgia Environmental … gas and water, as follows NH 4 + + NO 2 ... • After the carbonaceous demand is met in the ... TEST CENTER SUMMARY