Electricity | Natural Gas | Water | Wastewater Adding Whey for Denitrification Dale Adams, P.E Managing Engineer, Colorado Springs Utilities September

Electricity | Natural Gas | Water | Wastewater

Adding Whey for Denitrification

Dale Adams, P.EManaging Engineer, Colorado Springs Utilities

September 8, 2015

Slide 21/16/2015 Electricity | Natural Gas | Water | Wastewater

BackgroundNitrogen RemovalPhosphorous RemovalBenchtop fermentation of wheyFull scale designProblems with start-up


Agenda


• Whey is a by-product of cottage cheese production• A Dairy approached Colorado Springs Utilities to say they

would find a way to dispose of whey to avoid BOD surcharge

• Utilities analyzed the whey – thought to be a good source of carbon

• JDPWRRF was limited on carbon for its biological treatment processes

• Plant effluent pH was too low – had to add sodium hydroxide to raise effluent pH - $100K per year


Background


• Temporary tanks were installed in 2009 and the dairy trucked cottage cheese whey to fill the tanks

• During the pilot project whey was dosed to the inlet of the primary sedimentation tanks

• As winter approached, the decision was made to move the whey operation into a spare grit tank to keep the whey from freezing and use the grit tank pump to dose the whey

• This allowed a larger inventory to be maintained and some fermentation occurred


Background


• Ammonia conversion to nitrogen gas is a multi-step biologically driven process

• One set of bacteria (nitrifiers) takes ammonia to nitrite then to nitrate under aerobic conditions (lots of air is blown into the basins to give the bacteria oxygen)

• Another set of bacteria (denitrifiers) take nitrate to nitrite under anoxic conditions (very low oxygen) and then to nitrogen gas which goes to the atmosphere; requires CARBON for this step

• The conversion of nitrate to nitrogen gas adds alkalinity back into the wastewater – raising the plant’s effluent pH


Nitrogen Removal



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ASE

Nitr

ate

(mg/

L)

Date

JDPWRF - Activated Sludge Effleunt (ASE) Nitrate Concentrations (mg/L)

AS Effluent Nitrate (mg/L)

Whey Addition

Aged Whey Ef fect



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Fina

l Eff

luen

t Alk

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ity (m

g/L)

Date

JDPWRF - Final Effluent Alkalinity (mg/L)

Final Effluent Alkalinity (mg/L)

Whey Addition


• Was not occurring at JDPWRRF very much prior to whey addition

• Biological P removal requires several things:• First an anaerobic zone is needed (no oxygen)• Second, volatile fatty acids need to be present• Under these conditions bacteria dump phosphorous and store

the VFA as energy• Under subsequent aerobic conditions, bacteria take up twice as

much phosphorous


Phosphorus Removal



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Fina

l Eff

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t Ort

ho-p

hosp

hate

(mg/

L)

Date

JDPWRF - Final Effluent Ortho-phosphate Concentrations (mg/L)

Final Effluent Ortho-phosphate (mg/L)

Whey Addition

Aged Whey Ef fect


• Set up a reactor• Fed it fresh whey at a rate that controlled the hydraulic

residence time• Temperature was maintained at 94 F – the temp that we

receive cottage cheese whey from the dairy• pH was maintained at 5.7-6.0• VFAs were analyzed to see what was happening with

fermentation


Benchtop Fermentation Experiments




• Adding Whey for Denitrification


• Whey is very a very dilute source of carbon


Design of Full-scale Carbon Facilities


• Dairy may not stay in the cottage cheese business • Need to design for flexibility• Tanks were designed to handle whey, primary sludge,

and acetic acid (could not make them compatible for methanol)


Design of Full-scale Carbon Facilities


Design for Handling Whey

• Two tanks, each 35,000 gallons

• Telescoping valves for scum removal

• Mixer in main chamber under fermentation mode

• Connection from tank headspace to odor control ductwork in existing PSTs

• Special coatings systems to withstand a variety of chemical action

• Waterproofing membrane on outside

Slide 161/16/2015

Process Schematic

Mixers

Future Mixers

Future PS Screens

pH Control Pumps

Feed Pumps

Tank Drain/Future PS Recirc. Pumps Pumps

Telescoping Valves

Control Valves and Flow Meters


Primary sludge fermentation

• Up to two more tanks, each 35,000 gallons

• Combination submersible tank drain/future PS recirculation pumps to be used

• Additional mixers will be installed

• FRP baffles will be installed


Start-up Problems

• Started up the whey tanks with pH control set at 5• Shortly after start-up ground settlement broke the

feed piping – 20 foot deep excavation and repair was completed

• After the repair bio-P and nitrogen removal have not responded like we saw during the pilot project

• The dose location is different than during the pilot project

• We have not had time yet to do a deep dive into why the system is not performing as expected

Documents

Electricity | Natural Gas | Water | Wastewater Adding Whey for Denitrification Dale Adams, P.E Managing Engineer, Colorado Springs Utilities September