Seeking the Optimum Approach to Generate VFA/rbCOD to Ensure Reliable EBPR at the Robert W. Hite Treatment Facility

Kim Cowan, Lab Support Specialist

Kurt Carson, O&M Engineer

RMWEA JTAC

December 17th, 2015

Outline

• RWHTF facility

• EBPR upgrades

• Calculated VFA deficit

• SCVFA definition

• VFA/rbCOD: Five options overview

• Bench testing & process modeling results

• Pilot testing

• Conclusions

Robert W. Hite Treatment Facility

Robert W. Hite Treatment Facility

Robert W. Hite Treatment Facility

Split Secondary Treatment – Different configurations

South Secondary is conventional A2O Process

North Secondary is a Modified Ludzak-Ettinger retrofitted with a sidestream EBPR Process

South Secondary uses VFA/rbCOD in the Primary Effluent

North Secondary utilizes VFA/rbCOD in the Gravity Thickener Overflow

RWHTF Plan – South Plant

• Mainstream A2O • PE is carbon source

RWHTF Plan – North Plant Gravity Thickener Overflow is the carbon source

EBPR Upgrade 1.0 mg-P/L

2018 Tertiary Treatment planned $377M in the CES

VFA deficit 2-3 tpd (1,800 to 2,700 kg/day)

Our SCVFA (short-chain volatile-fatty acids) definition: Rossle and Pretorius (2001) SCVFA unit: mg-COD/L

SCVFA = sum of acetic, propionic, valeric & caproic COD equivalents; normalized as acetic

SCVFA – What is it?

SCVFA = One usable data point

Acetic Acid Butyric Acid

Iso-butyric Acid Caproic Acid Iso-caproic Acid Propionic Acid N-valeric Acid

Iso-valeric Acid

SCVFA = Σ(Each SCVFA

analyte, converted to COD

equivalents, then weighted

as acetic)

Units = mg/L(acetic)COD

SCVFA – What is it?

Wow, 300 lbs of dogs! That’s

a lot of dogs!

…it WOULD be a lot of

chihuahuas, but not a lot of

mastiffs… let’s get these dogs

on an equivalent standard dog

unit. Standard Canine Volume

Factor A…

…ok going too far with the

metaphor…

SCVFA – What is it?

VFA analyte VFA analyte (mg/L) COD equivalent ratio VFA analyte COD equivalent Acetic COD equivalent VFA analyte Acetic COD equivalent SCVFA

Acetic Acid 558 1.067 595.386 1.067 595.386

1642.689

Butyric Acid 231 1.818 419.958 1.067 393.5876289

Iso-butyric Acid 0 1.818 0 1.067 0

Caproic Acid 0 2.207 0 1.067 0

Iso-caproic Acid 0 2.207 0 1.067 0

N-valeric Acid 28 2.039 57.092 1.067 53.50702905

Iso-valeric Acid 0 2.039 0 1.067 0

Propionic Acid 423 1.514 640.422 1.067 600.20806

SCVFA – Where does it come from?

RWHTF Design – Tertiary Polishing

The more effective EBPR is in the Secondary

Processes, the more aggressive we can get in our

design assumptions for tertiary treatment

MAJOR potential cost savings if we can optimize

reliable Bio-P. $377M currently budgeted.

Calculating VFA deficit

RWHTF influent 3.4 tons/day PO4

Centrate return 1.5 tons/day PO4

Available VFA and rbCOD in the Primary Effluent and Gravity Thickener Overflow

VFA:P ratio Source

SSEC 8:1 WEF, 2010

NSEC 5:1 PAR 1171 field data

units average

Influent flow mgd 130 inputs

Influent PO4 mg-P/L 4.2 calcs

flow split to south % 40 output

flow mgd 1

PO4 concentration mg-P/L 400

P-sequestration efficiency % reduction of recycle P 85

flow split of recycle stream to south % 50

assumed South VFA/PO4 ratio mg-VFA/mg-P 7.5

VFA in Primary Effluent mg-COD/L 25

assumed North VFA/PO4 ratio mg-VFA/mg-P 5

VFA in GTO mg-COD/L 175

GTO flow to SAR mgd 6.9

North calcs

flow split to north % 60

influent PO4 mass to north lbs-P/day 2732

flow split to north % 50

recycle PO4 mass to north lbs-P/day 30

pre-fermenter mass VFA in north lbs-VFA/day 10071

total North PO4 lb-P/day 2762

estimated required VFA - PAR 1171 observed lb-VFA/day 13810.92

total North VFA lb-VFA/day 10071

South Calcs

influent PO4 mass to south lbs-P/day 1821

recycle PO4 mass to south lbs-P/day 30

pre-fermenter mass VFA in south lbs-VFA/day 10842

total South PO4 lb-P/day 1851

estimated required VFA - literature value lb-VFA/day 13886

total South VFA lb-VFA/day 10842

Total VFA deficit for North and South lb-VFA/day 6784

North VFA deficit lb-VFA/day 3740

South VFA deficit lb-VFA/day 3044

Pre-fermenter available carbon

recycle load PO4

Influent PO4

VFA/RBCOD: 5 Options 1. Acetic Acid

2. APD

3. Local Recycle

Stream

4. Elutration and/or

SML addition

5. Repurposed

fermenter

Option 1 - Acetic Acid

• Benefits – Operational ease – Consistency/purity

• Drawbacks – $870K – $1.3M

– Lack of propionic & other SCVFA compounds

Option 2 - Acid Phase Digester Effluent

• Characterization

– SCVFA = 10,564 mg-COD/L

• 25% acetic, 38% propionic

– 442 mg-P/L

– 569 mg-N/L of total ammonia

nitrogen -

• Net gain 7,470 mg-COD/L

• 90,000 to 130,000 gallons per day

• 16 dry tpd or 19% increase in

solids loading

Option 3 - Locally Generated Recycle Stream

• 4,000 – 6,000 gallons per day

• >90% Packaged beer (off-spec, expired, etc.)

o <10% Soft drinks & water

• Direct dose vs. additional fermentation

• Characterization of the recycle stream

Option 4 - Elutriation and/or

Settled Mixed Liquor Addition

• Dual purposing for solids separation and

fermentation

• Hydrolysis is rate limiting

• Practical limitation on return streams

Option 5 - Repurposed Fermenter

• Existing

tank

• GTU vs GTI

• ex-situ

fermentation

Process Modeling Approach

• Technical merit of settled mixed liquor

inoculation (Option 4)

– Determine relative settled mixed liquor

volume ratios

• Fermentation of GTI and GTU (Option 5)

• Determine the APD characterization

(Option 2)

– SCVFA and nutrients

Process Modeling Results Option 4

Option 5

Bench Scale Prescreening

Bench Scale Prescreening

Bench Scale Method: Fermentation

Bench Scale Method: Fermentation

Method Application

Option 3: Locally Generated Waste Stream • LGWS addition to GVT Underflow at 30%, 60% & 90%

• Compare against control (distilled water)

• Compare against EtOH

Option 4: SML Addition to GVT Underflow • SML addition to GVT Underflow at 1:100, 1:1,000 & 1:10,000

• Compare against control (Secondary Effluent)

Option 5: GVT standalone fermentation • GVT Underflow compared to GVT Influent

Locally Generated Recycle Stream (Beer)

Initial Stream Characterization Data • High COD

• Low solids

• Low nutrient load (COD:N, COD:P)

• ~4% EtOH

Locally Generated Recycle Stream (Beer)

Locally Generated Recycle Stream

0

200

400

600

800

1,000

1,200

1,400

1,600

Start 1 day 2 days 3 days

SC

VF

A P

rod

uce

d,

lb/d

ay

30% Locally Generated Recycle Stream

60% locally Generated Recycle Stream

90% Locally Generated Recycle Stream

Locally Generated Recycle Stream

• Lower concentrations, higher yield • Inhibitory substances? • Test <30% in future

• 24 Hour SRT sufficient

• Test shorter SRT in future

Elutriation/Settled Mixed Liquor

Elutriation/Settled Mixed Liquor

• 100:1 and 1,000:1 dilution ratios

• Settled mixed liquor effectiveness: 12%

increase in SCVFA

SCVFA: 3716 mg-COD/L 4168 mg-COD/L

• Return flow: 0.23 MG to 0.258 MG

• Return solids load: 53.8 tpd 48.0 tpd

Fermented Primary Sludge

Fermented Primary Sludge

Fermented Primary Sludge

• Bench testing results confirm traditional

fermenter production ranges

• 17% - 25% increase in solids

• Fermenter capacity limitations allow for GVT

Underflow, not GVT influent

Future Testing: Bench Scale (locally generated recycle stream)

• Direct-dose – Phosphorus release & uptake testing

– Test dosing site options (PE vs. RAS)

• HRT optimization – Initial testing of micro-aerobic 24-hr HRT promising

– 48-hr fully aerated HRT = massive increase in acetic acid

– SCVFA = 422% increase (438 2290 mg-COD/L)

– But, only 12% as propionic (ratio <0.2 Propionic:Acetic)

Pilot Scale Carbon Augmentation Study (CAS)

• 6 Month Pilot with Waste Management (WM) • Logistical and Technical considerations

– December 2015, CDPHE pilot authorization approved

– Use existing acetic acid dosing point

• 2 tanks, parallel testing

– QC parameters & performance evaluation

– ~4000-6000 gpd

Carbon Augmentation Study

Characterization of the Beer Waste

Bench-scale: Evaluate the Beer Waste as a carbon Source

In-situ – P-release and uptake profiles

In-situ – specific process rates

Ex-situ - can we make it better, ferment it more

Full-scale: Demonstrate a full-scale P release in the anaerobic zones

Microbial population shifts; more or less stability

RAMEN, DAPI, DNA, FISH analysis

Assess the efficacy of a long-term relationship with WM.

Baseline versus Acetic Acid Dosing Pre-Testing

Preliminary CAS results

CAS Considerations The logistical considerations are just as important as

the technical

Full-scale profiling is critical to understand the process dynamic of alternative carbon sources

Conclusions of Various Options

• Acetic Acid (Option 1) – Costly – Lack of propionic & other SCVFA – Availability lends to possible backup carbon source

• Acid Phase Digester (Option 2)

– High recycle nutrient load

– Steals carbon from methanogens in meso-phase digesters

– Odor concerns

• Locally Generated Recycle Stream (Option 3)

– Promising results, more study needed for dosing parameters

– Inhibition noted at higher concentrations

– Logistic considerations (QC, M&E, contractual agreements, etc.)

– Pilot to run from December 2015 - June 2016.

Conclusions of Various Options, cont.

• Elutriation & Settled Mixed Liquor (Option 4) – May be undesirable to dual purpose gravity thickeners

– Modest yield of SCVFA

• Fermentation (Option 5)

– GTI more productive while GTU more concentrated

– Intensive O&M nature may prove undesirable

References

• Carson K. 2012 Evaluation of Performance for a Novel Sidestream Enhanced Biological Phosphorus Removal Configuration at a Full-scale Wastewater Treatment Plant. Master of Science Thesis, University of Colorado, Boulder, Colorado.

• Cavanaugh L., Carson K., Lynch C., Philips H., Barnard J. and McQuarrie J. (2012) A Small Footprint

Approach for Enhanced Biological Phosphorus Removal: Results from a 106 mgd Full-scale Demonstration. Proceedings of the 85th Annual Water Environment Federation Technical Exhibition and Conference [CD-ROM], New Orleans, Louisiana, Sep 29 – Oct 3; Water Environment Federation: Alexandria, Virginia.

• Lopez-Vazquez CM, Oehman A, Hooijmans CM, Brdjanovic D, Gijzen HJ, Yuan Z, van Loosdrecht

MC. (2009) Modeling the PAO-GAO Competition: Effects of Carbon Source, pH and Temperature. Water Res. 2009 Feb; 43(2): 450-62. (Epub 2008 Nov 1).

• Metcalf and Eddy. Wastewater Engineering Treatment and Resource Recovery. McGraw Hill

Education, 2014. Print. • Oehmen A, Lemos PC, Carvalho G, Yuan Z, Keller J, Blackall LL, Reis MAM. Advances in enhanced

biological phosphorus removal: from micro to macro scale. Water Res. 2007; 41(11): 2271-2300. • Rossle WH, Pretorius WA. (2001) A Review of Characterisation Requirements for In-line

Prefermenters, Paper 1: Wastewater Characterization. Water SA Vol. 27 No. 3 July 2001, ISSN 0378-4738.

Thank you

Questions?

Kimberly Cowan, CWP Kurt Carson, CWP, EIT Laboratory Support Specialist O&M Engineer Associate

kcowan@mwrd.dst.co.us kcarson@mwrd.dst.co.us

(303) 286-3079 (303) 286-3227

Metro Wastewater Reclamation District

6450 York St., Denver CO 80229