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ENGINEERING OWTS FOR NUTRIENT REMOVAL

Simon Farrell, PE, REHS

JVA Consulting Engineers

March 27, 2015

CPOW mini conference

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Overview of presentation

• Why focus on nutrient removal?

• Brief review of nitrogen cycle

‒ Definitions

• Traditional OWTS – (single family home)

‒ Basic observations - increase nutrient removal

• Design of OWTS for nitrogen removal

‒ Design fundamentals for nitrogen removal

‒ Conduct your own evaluation

‒ 3 items to focus on

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Why focus on nutrients?

• Transition from ISDS ‘disposal’ to OWTS for ‘treatment’

– Significant progress over the last few years

• OWTS designs are not typically focused on nutrient removal

– Nitrogen and phosphorus

– Why not?

• National and State trend – dischargers focused on nutrient removal

– Start with Municipal WWTF

– Smaller dischargers, OWTS, non-point sources

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Regulatory Considerations - Colorado

• CDPHE Regulation 85 – ‘Nutrients Management Control Regulation’ effective September 2012

– New WWTF: TP 0.7 mg/L, TIN 7 mg/L

• CDPHE Regulation 43 – ‘On-site Wastewater Treatment System Regulation’ effective June 2013

– Treatment Level 2N = >50% TN reduction, TL3 = 40-60 mg/L TN

– TL3N = 20 mg/L TN

• Control Regulations / Watershed Protection Districts

– Control Regulation 74 - Bear Creek Reservoir, TP < 1.0 mg/L

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Chemistry review – Nitrogen Cycle

Organic Nitrogen = CO(NH2)2

• Urea

Ammonium = NH4+

• pKa = 9.25

Nitrite = NO2-

Nitrate = NO3-

Nitrogen gas = N2

• triple bond, inert

• 78% of atmosphere

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Redox Chemistry / Microbiology

Nitrification

NH4+ + O2 NO3

- + H+ + H20

• Aerobic

• Requires Alkalinity

– Stoichiometry: 7.14 mg/L alkalinity as CaCO3 per 1 mg/L NH4

Denitrification:

NO3- + C6H12O6 + H+

N2 (g) + CO2 (g) + H20

• Anoxic

• Requires Carbon Source

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Nitrogen Cycle – Common Terms

• Ammonia – (really NH4+ for most wastewaters)

• Total Nitrogen (TN) – sum of all forms of nitrogen

• Total Inorganic Nitrogen (TIN) – Ammonia, Nitrite,

Nitrate

• Total Kjeldahl Nitrogen (TKN) – Organic plus

Ammonia

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s Organic N

Ammonium NH4+

Vadose zone

Groundwater zone

Capillary

fringe

Nitrification

NH4+ + O2 NO3

- + H+ + H20

Denitrification:

NO-3 + C6H12O6 + H+

N2 (g) + CO2 (g) + H20

0 - 30 cm

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Nitrogen Fate

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Best Practices for Traditional OWTS - septic tank followed by STA

• Open infiltrative surface that allows the transfer of oxygen

– Trenches with chambers

– Reflected in Reg. 43 with incentives

• Keep the infiltrative surface shallow in the soil horizon

– Drip dispersal, NDDS

– Target the rhizosphere – very biologically active

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Best Practices for Traditional OWTS

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Advanced Treatment

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• OWTS design specifically for nitrogen removal

• Numerous technologies are available

– Orenco Advantex• AX-100, AX MAX, AX-RT

– Biomicrobics• MicroFAST, BioBarrier, ABC-N

– HOOT Systems• H-series, Hoot-NR, Hoot ANR

– All based on the same fundamentals

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Fundamentals of N removal in OWTS

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1. Have realistic expectations on influent nitrogen concentrations

- Particularly important for onsite systems

2. Focus on nitrification first

- Requires oxygen and alkalinity

3. Denitrification

- Requires anoxic conditions and carbon

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Influent Levels of Nitrogen

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Untreated Domestic WastewaterSource: MetCalf and Eddy 5th Edition

Total Nitrogen (low strength) 23 mg/L

Total Nitrogen (medium strength) 35 mg/L

Total Nitrogen (high strength) 69 mg/L

Application TypesSource: Orenco Design Criteria

TKN (Type 1 – residential) 50-80 mg/L

TKN (Type 2 – commercial) 90-200 mg/L

What is the objective?

• 50% nitrogen removal (NSF 245 standard)

• 10 mg/L TIN at end of pipe

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• Nitrification: NH4+ to NO3

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– Requires aerobic conditions• Methods?

– Requires alkalinity• Average Alkalinity: 50 – 200 mg/L (Civil Engineering reference manual – Michael Lindeburg)

Focus on nitrification first

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Municipal Application

Influent TKN 35 mg/L

Alkalinity required 250 mg/L

School

Influent TKN 100 mg/L

Alkalinity required 714 mg/L

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• Denitrification: NO3- to N2 (g)

– Requires anoxic conditions

– Requires carbon source• Methods?

Denitrification

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Summary - nutrient removal in OWTS is coming….

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1. Have realistic expectations on influent nitrogen concentrations

- Particularly important for onsite systems

- Determine the end goal – 50% reduction or 10 mg/L

2. Focus on nitrification first

- Requires oxygen and alkalinity

3. Denitrification

- Requires anoxic conditions and carbon

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JVA Consulting Engineers

• Thank you JVA!

• Mid-size Engineering Firm (approx. 90 people)

• Offices in Boulder, Ft. Collins, Winter Park, Glenwood Springs and soon to be Denver

• Focused on small to mid-size water and wastewater systems (1,000 gpd to 2 MGD)

• Team of engineers focused on decentralized and onsite wastewater treatment

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Questions