seeking the optimum approach to generate vfa/rbcod to ensure … · 2015. 12. 21. · kim cowan,...
TRANSCRIPT
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
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
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
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
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
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
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
• 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
• 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.
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
[email protected] [email protected]
(303) 286-3079 (303) 286-3227
Metro Wastewater Reclamation District
6450 York St., Denver CO 80229