09. BNR-Mehaffey

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S c i e n t i f i c a n d T e c h n i c a l C o n f e r e n c e

Optimizat ion of Wastewater

Faci l i t ies to AddressBiological Nutr ient Reduct ionRequirements

Platinum Sponsor Silver Sponsor

W A T E R S E R V I C E S A N D T H E N E W E N E R G Y C H A L L E N G E S

M i c h a e l J . M e h a f f e y , P . E .

S e n i o r P r o j e c t E n g i n e e rG a n n e t t F l e m i n g , I n c .


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Meeting Regulatory Requirements

Total Nitrogen and Total Phosphorus annual massloading limits for each discharger.

Upgrade existing facilities to ensure compliance. Various nutrient reduction methods available.


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Key Definitions Aerobic Presence of free molecular dissolved oxygen.

Anoxic Presence of chemically bound oxygen (nitrate) inplace of free molecular dissolved oxygen.

Anaerobic Complete absence of both bound and freemolecular dissolved oxygen.


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Key Definitions (cont.) Nitrification Biological process in which ammonia-

nitrogen is converted, under aerobic conditions, to themore stable form nitrate.

Denitrification Biological process in which nitrate isreduced under anoxic conditions to nitrogen gas.


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Nitrification Process

Two-step biological process carried out bymicroorganisms under aerobic conditions Step One: Ammonia converted to Nitrite Step Two: Nitrite converted to Nitrate

Requires 4.6 mg oxygen per mg ammonia oxidized tonitrate denitrification returns 2.9 mg oxygen per mgnitrate denitrified

Nitrification rate slows as temperature decreases -Nitrification stops at T


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Denitrification Process Biological process carried out by microorganisms under

anoxic conditions

Organisms use nitrate in place of dissolved oxygen forrespiration - residual dissolved oxygen will inhibit process

Requires readily biodegradable organic carbonSupplemental source such as methanol

Denitrification rate affected by carbon source andtemperature

Nitrification must precede denitrification


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Phosphorus Removal

Chemical Precipitation process often utilized. A metal ion, such as iron or aluminum, is introduced

to the flowstream.

The metal ions react with soluble ortho-phosphatesto form a metal-phosphate precipitate.

Precipitate settles in the secondary clarifiers and is

then removed with the waste activated sludge.


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Phosphorus Removal

Effluent with a total concentration of 1.0-2.0 mg/Ltotal phosphorus is consistently achievable. Lessthan 1.0 mg/L with tertiary filtration.

FINAL

CLARIFICATION

RAS

WAS

AERATION

METAL ION


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Case Study:Borough of Hanover WWTP

5.6 MGD Average(22,000 m3/day)

Located inPennsylvania, USA

Closed-loopedactivated sludgeprocess (oxidationditches)


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SimultaneousNitrification/Denitrification (SNdN)

Control the residual dissolved oxygen (D.O.)content in the bioreactors, allowing conditionswhere both nitrification and denitrification canoccur at the same time.

Utilizes the principle that floc particles containboth nitrifying and denitrifying microorganisms.


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Borough of Hanover WWTPOxidation Ditches


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Process Control Continuously monitor D.O. through the uses of

a D.O. probe.

D.O. is measured and compared to a set-point

in a process logic controller (PLC). Rate of air supplied to the process is adjusted

to match the set-point.

Brush rotors are manipulated automatically toaccommodate the change in supplied air.


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Post-Denitrification Filters Fixed-film process units in which denitrifying

microorganisms attach themselves to the coarsemedia in the filter.

A supplemental carbon, such as methanol, isadded to the filters to support denitrification.

Denitrification occurs as the nitrified secondary

effluent passes over the media.


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Denitrification Filters


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Improved Performance Total Nitrogen Effluent Average = 2.9 mg/L

Total Phosphorus Effluent Average = 0.8 mg/L


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Final Thoughts

Identify nutrient removal performance levelsnecessary to satisfy annual mass loading limits.

Utilize Best Available Technology to optimizetreatment.

The Borough of Hanover was able to provide arevitalization of the existing facility to exceedregulatory requirements

Questions?? [email protected]

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09. BNR-Mehaffey