Primary Sludge Fermentation for Reliable Biological ... PNCWA- Session 5-1... · Primary Sludge Fermentation for Reliable Biological Phosphorus Removal Li Lei, Barry Rabinowitz, Bill

Primary Sludge Fermentation for Reliable Biological Phosphorus

Removal

Li Lei, Barry Rabinowitz, Bill Leaf, Rick Bishop, Bob Kresge

1PNCWA 2009 – Boise, ID 9/16/2009

Outline

• Introduction• Common Primary Sludge Fermentation

Processes• Comparisons of Non-economic Factors• Implemented Fermentation System Examples

2PNCWA 2009 – Boise, ID 9/16/2009

• Implemented Fermentation System Examples• Performance and Key Considerations• Design Parameters• Cost Estimates• Summary and Conclusions

Introduction – West Boise WWTF

Raw Sewage Plant EffluentPrimary Clarifiers

WAS Thickener

South JHB Basin & Secondary Clarifiers

North JHB Basin & Secondary Clarifiers

Primary Sludge

Thickener

14 mgd, 200 mg/L BOD, 7.5 mg/L TP

(13 mgd

3PNCWA 2009 – Boise, ID 9/16/2009

Biosolidsto Land Application

Dewatering

AnaerobicDigester

Anaerobically Digested Sludge from other WWTP

• largest facility in ID; sized for 24 mgd; currently ∼14 mgd; • Biological: can operate in JHB & provide a level of P removal• Potential more stringent TP limits (1, 0.5, 0.2, 0.07 mg/L)

(13 mgd Lander Street WWTF)

And eval. done for TP removal

Introduction - Enhanced Biological Phosphorus Removal (EBPR)

• Encourages PAOs to grow and incorporate phosphorus into cell biomass, which subsequently is removed through sludge wasting

• PAOs have – higher phosphorus (P) content (0.3 vs. 0.02 g P/VSS)– a selective advantage in an anaerobic/aerobic

4PNCWA 2009 – Boise, ID 9/16/2009

– a selective advantage in an anaerobic/aerobic environment

– require VFAs to grow in anaerobic environment

• Sources of VFAs – Key Parameter For EBPR Success– rbCOD in wastewater → VFAs in anaerobic zones– external sources, e.g. acetic acid– generated on-site through PS fermentation (moderate to

cold climate)

Some basics about BPR. BPR is achieved through The PAOs have, and get their selective…

Introduction – JHB Process For EBPR

Waste Activated

SludgeAnoxic Aerobic

Mixer

Return Activated Sludge

Influent

Secondary

Clarifier

Effluent

AnaerobicAnoxic

Nitrate Recycle

VFA

5PNCWA 2009 – Boise, ID 9/16/2009

Influent Clarifier• Anoxic zone for the RAS reduces the amount of nitrate-N

entering the anaerobic zone • Subsequent anaerobic zones receive the primary effluent,

along with the denitrified RAS stream• Identified as an important component for TP removal for its

low O&M costs, vs. chemical P removal• Reliability need to be improved for stricter P limit• Inadequate influent rbCOD/VFA for full biological N and P

removal; compounded by external P load

A key hurdle to overcome is the

Introduction – Primary Sludge Fermentation

• PS Fermentation: – likely to have lower operational costs than

supplementing external sources– provides required retention time & mixing for

VFA production not likely in Anaerobic Zones

6PNCWA 2009 – Boise, ID 9/16/2009

• Hydrolysis: particulates to soluble monomers– Lipids → fatty acids– Carbohydrates → monosaccharides– Proteins → amino acids

• Fermentation (acidogenesis): hydrolysis products → mixed VFAs

Common PS Fermentation Processes

• Activated primary clarifier • Complete-mix fermenter • Single-stage fermenter/thickener• Two-stage complete- mix fermenter/thickener• Unified Fermentation and Thickening (UFAT)

7PNCWA 2009 – Boise, ID 9/16/2009

• Unified Fermentation and Thickening (UFAT)

Common Processes - Activated Primary Clarifier (APC)

Primary Clarifier

Fermented Sludge to solids handling

Primary Effluentto Bioreactor

RawInfluent

8PNCWA 2009 – Boise, ID 9/16/2009

to solids handling

Sludge Recycle

•PSD recycle to 1) inoculate Inf., 2) provide longer SRT than HRT, 3) elutriate VFAs formed. •Typical SRT = 2 to 3 days •SRT control by adjusting sludge wasting•Sludge blanket monitoring required for determine solids inventory and solids in PE for accurate SRT calcs

This slide show the PFD of APT Similar to regular PCs with one exception: PSD reclyce is provided to

Common Processes - Complete-Mix Fermenter (CMF)

Primary Clarifier

Primary Effluent

Fermenter

Fermented Sludge

RawInfluent

Primary

9PNCWA 2009 – Boise, ID 9/16/2009

Sludge Recycle

Primary Sludge

•CMF in side-stream•A portion of the fermenter mixed liquor is returned to PC•The VFAs formed is elutriated in primary effluent to bioreactors•Independent HRT & SRT; HRT: PS Volume; SRT: Fermented sludge waste•No thickening→ higher recycle and wasting flows

Common Processes - Single-Stage Fermenter/Thickener

Primary ClarifierPrimary Effluent

Primary

Fermenter/ThickenerRawInfluent

Fermented

Supernatant

10PNCWA 2009 – Boise, ID 9/16/2009

Primary Sludge

Fermented Sludge

•Static fermenter for fermentation and thickening•No sludge recycle; independent PCs and fermenter/thickener•SRT: target sludge blanket height and sludge inventory + accounting for solids in supernatant•Frequent measurements of the sludge blanket depth and solids concentrations.

Common Processes - Two-Stage Fermenter/Thickener

Primary Clarifier

Primary Effluent

Primary Sludge

Fermenter/Thickener

Supernatant

Waste Sludge

Fermenter

Sludge Recycle

RawInfluent

11PNCWA 2009 – Boise, ID 9/16/2009

Sludge Recycle

•Complete-mix fermenter + gravity thickener •Thickened sludge is recycled back to fermenter•Excess sludge is wasted•Independent PC and fermentation; no recycle to pcs•SRT: control sludge wasting; easier determination of solids inventory

Common Processes - Unified Fermentation And Thickening (UFAT) Process

Waste Sludge

Primary Clarifier

Primary Sludge

Fermenter/Thickener Fermenter/ThickenerRawInfluent

12PNCWA 2009 – Boise, ID 9/16/2009

•Static fermenter/thickener + gravity thickener •Similar to single-stage, with an additional thickener/fermenter•underflow and overflow of 1st fermenter/thicener are remixed to help elutriate the VFAs•Higher sludge blanket could be kept in 1st tank to achieve SRT•Independent PCs and fermentation; no recycle to PCs•Difficult to control SRT, similar to single-stage system

Comparisons of Non-economic Factors (1)Advantages Disadvantages

APC •Lower capital cost•Lower space requirements

•Difficult to control SRT•Requires deep primary clarifiers (10 ft SWD available)•Mixed successes

13PNCWA 2009 – Boise, ID 9/16/2009

•Mixed successes

CMF •Simplest in operations and controls •Independent HRT & SRT for fermentation

•Higher sludge wasting and recycle flows•Higher hydraulic loading to solids handling units•Higher hydraulic & solids loading to PCs

due to these limitations of APC and CMF and mixed performance reported for the APC , there two processes screened out from further considerations.

Comparisons of Non-economic Factors (2)

Advantages disadvantages

1-Stage •Independent PCs & fermenter/thickener

•Difficult to control SRT accurately•Relies on frequently measuring sludge blanket

14PNCWA 2009 – Boise, ID 9/16/2009

measuring sludge blanket depth and solids concentrations

2-Stage •Independent PCs & no recycle to PCs•Simple control of fermentation process

•Requires more tanks and associated equipment.

Comparisons of Non-economic Factors (3)

Advantages disadvantages

UFAT •Independent PCs & no recycle to PCs•Easy to retrofit into existing gravity

•Difficult to control SRT accurately•Relies on frequently measuring sludge blanket

15PNCWA 2009 – Boise, ID 9/16/2009

existing gravity thickeners, potentially reducing cost

measuring sludge blanket depth and solids concentrations• Stratification of sludge and VFAs occurs in fermenters; more prone to inhibition caused by pH and localized high VFA concentrations

Implemented Examples (1)

1-Stage 2-Stage UFAT

Facilities Kelowna, BC Kalispell, MT Durham, OR

Capacity, mgd 10.6 3.1 25

EBPR Process A2O Modified UCT A2O

Eff. TP, mg/L 0.11 0.4 <0.07

16PNCWA 2009 – Boise, ID 9/16/2009

Fermenters •150-250 mg/L VFA in supernatant, ∼ 17 mg/L increase to influent•3.6 to 5.9 ft sludge blanket in a 10.7 SWD

•200 – 500 mg/L VFA in supernatant @ 5 day SRT•1% PS; 1.2% solids in fermenters; 2% in sludge recycle

•0.081 lb VFA/lb VSS with 47% elutriation•Ave. 2.8 d-SRT @ 19 °C; 1 – 3 d-SRT @ 14 to 24 °C

Implemented Examples (2)

1-Stage 2-Stage UFAT

Facilities Kelowna, BC Kalispell, MT Durham, OR

Thickening •6% Solids•TPS + WAS → 20% solids dewatered sludge

2% TPS 1 d-SRT

17PNCWA 2009 – Boise, ID 9/16/2009

sludge

Special Issues/features

•Automatically reversing rake in fermenters•Scrubber/biofilter for odor Control

•Mechanical mixer + scum buster external pumping in fermeters•corrosion to concrete: plastic coating/S.S.

•Floating scum and grease layer due to reduced primary capacity•upset due to methane production @ 5.5 SRT @ 22 °C

6 to 7 percent, comparable to the 4 to 10

Performance and Key Considerations (1)

• Performance in VFA Augmentation– production: 0.1 to 0.2 g VFA/g VSS applied – recovery/ elutriation:

• 20% to 50% for static fermentaer• up to 90% for complete-mix

– VFA Increase in the influent: 10 to 20 mg/L

18PNCWA 2009 – Boise, ID 9/16/2009

– VFA Increase in the influent: 10 to 20 mg/L • SRT

– ≥ SRTmin to prevent fermenting microorganisms being washed out

– ≤ SRTmax to prevent methanogenic activity – 3 to 5 days generally– 2 to 3 days for T≥ 20 °C

• Temperature – Tanks usually not heated → varying temp.– Higher T increases fermentation rate– Critical to maintain a proper SRT at higher

temperatures• pH: VFA production lowers pH


19PNCWA 2009 – Boise, ID 9/16/2009

• pH: VFA production lowers pH– Acidogen/acetogen (ADM1, IWA)

• not inhibited at pH ≥ 5.5• completely inhibited at pH ≤4• significant inhibition at 5 ≤ pH ≤ 5.5

(Veeken, et. al.)– ensure sufficient alkalinity and prevent high

sludge concentrations

• Mixing– increases the VFA yield– help elutriate the generated VFA into the

fermenter overflows– Prevent localized high VFA concentrations and

potential pH inhibition


20PNCWA 2009 – Boise, ID 9/16/2009

potential pH inhibition– increase odor generation

• Sludge characteristics– COD fractionation, seasonal variation– Fermentation in upstream system

• Degree depending on retention time, temperature, and aeration

• lowers the VFA yield in the fermentation system

Design Parameters Performance •0.1 g VFA/g VSS applied

•10 mg/L VFA Increase to the influent •25% Primary sludge VSS reduction

SRT & Temp. •5-day SRT at 12ºC to size various fermentation systems•3.5-day SRT at 18ºC to optimize cost for warmer temperature

Temperature Higher T increases fermentation rate; Critical to

21PNCWA 2009 – Boise, ID 9/16/2009

Temperature Higher T increases fermentation rate; Critical to maintain a proper SRT at higher temperatures

Mixing Mechanical mixing for the complete mix fermenter

Static fermenter /thickener

20 to 30 lb/day/sf; 400 to 800 gpd/sfDilution water: elutriation; aerobic cleansing

Odor Control Yes. Likely more intensive odor than GTsLonger SRT, higher turbulenceBiofilter recommended; likely taping into existing

Since the P removal season will be in warmer period of May to Sep., conceptual cost was also developed with a reduced SRT of 3.5-day to identify the extent of impact on system sizing and cost. The corresponding design temp is 18 deg C, the lowest monthly ave. temp during the period.

Cost Estimates - Basis

• Order-of-magnitude, Class 5 (AACE)• Accuracy: +100% to -50%• January 2008 Dollars• Cost estimates are based on

– equipment vendor supplied budgetary quotes– bid costs for comparable projects

22PNCWA 2009 – Boise, ID 9/16/2009

– bid costs for comparable projects – 29% for demo., sitework, SCADA, yard piping

& elec.– contractor mark ups

• 30% contingency• 20% overhead, profit, mobilization,

demobilization, bonds, and insurance – 23% non-construction costs (permitting,

engineering, SDC, commissioning/start up)

Cost Estimates - 5-d SRT (1)

Fermentation Systems Single Stage Two-Stage UFAT

Fermenters Number of units - 2 (new) 2 (new)

Type - Complete-Mix fermenters in series

Static fermenters in series

Dimensions, ea - 60' (L) x 43' (W) x 18' (D), 350,000 gallons each

40’ diameter, 20’ deep

Thickeners Number of units 2 (existing)

Type Static, fermenter/thickener

23PNCWA 2009 – Boise, ID 9/16/2009

Dimensions, ea 30’ diameter, 10’ deep

Number of units 2 (new) 1 (new) 1 (new)


Dimensions, ea 65’ dia, 16’ deep 40’ dia, 16’ deep 40’ dia, 16’ deep

Total Project Cost $9,010,000 $9,010,000 $8,540,000

New Biofilter Cost $550,000 $560,000 $440,000

Total Project Cost (less New Biofilter)

$8,460,000 $8,450,000 $8,100,000

slide shows major structures and cost for 3 fermentation systems. For all alternatives, 2 exit. gravity thickeners of 30’ dia, and 10’ depth will continue to serve as thickeners with dual function of fermenter. For single stage, 2 new Static, fermenter/thickener will be added in parallel to the existing ones, with 65’ dia. and 16’ depth each. For 2 stage, just 1 new smaller size Static, fermenter/thickener needed, it has 40’ dia. and 16’ depth. The 2-stage sys. also need 2-new CMF, 350 K MG each. For UFAT sys, a same size fermenter/thickener will be needed as the 2nd fermenter/thickener. 2 new primary fermenter of 40’ dia., 20’ SWD will be needed in series. The resulting cost for various fermentation sys. will cost from 8.1 M to 8.5 M. In addition, about 0.5 M will be needed if new odor control is added.

Cost Estimates - 5-d SRT (2)

• $ 8.1 M to $ 8.5 M depending on configuration• Odor control with a new biofilter: ∼ $ 0.5 M• The costs of three fermentation systems are

estimated approximately the same and are within about 6% of each other

• UFAT process has the lowest overall cost, but

24PNCWA 2009 – Boise, ID 9/16/2009

• UFAT process has the lowest overall cost, but the difference in cost is not significant

• Based on non-economic and economic analyses, 2-stage fermentation system offers simpler and more effective SRT control without incurring significantly higher cost

To summarize, not significant, especially consider the accuracy of this level cost estimate

25PNCWA 2009 – Boise, ID 9/16/2009

Cost Estimates – 3.5-d SRT (1)

• Objectives– further optimize and explore possible cost

reduction– 2-stage fermentation was selected for the

optimization

• Approaches

26PNCWA 2009 – Boise, ID 9/16/2009

• Approaches– Reducing SRT for fermentation in warmer, P

removal season only– In winter, operate with reduced VFA or as

regular thickener to save operational cost– Different PS solids concentrations

• 1% PS as currently allowable by PS degritting• 1.5% PS if new grit removal in liquids stream

In winter, w/ shorter SRT and reduced VFA production; or, to save operational cost, can bypass the CMF and just use the fer/thic. as regular gravity thic. 1.5% to see if saving can be achived by feeding thickner PSD and thus reducing the sizes for ferm. and thicke.

Cost Estimates – 3.5-d SRT (2)Fermentation Systems 1% PS 1.5% PS

Fermenters Number of units 2 (new) 2 (new)

Type Complete-Mix Tanks in series

Complete-Mix Tanks in series

Dimensions, each 60' (L) x 28' (W) x 18' (D), 225,000 gallons each

60' (L) x 28' (W) x 18' (D), 225,000 gallons each

Thickeners Number of units 2 (existing)


27PNCWA 2009 – Boise, ID 9/16/2009

Dimensions, each 30’ diameter, 10’ deep

Number of units 1 (new)


Dimensions, each 35’ dia, 16’ deep 30’ dia, 16’ deep

Total Project Cost $7,720,000 $7,510,000

New Biofilter Cost $470,000 $470,000

Total Project Cost (less New Biofilter)

$7,250,000 $7,040,000

Fermenter sizes are the same for both, with total volume of 450 K MG, compared to 700K MG required at 5-d SRT. for thick.sizes will also be reduced from the 40’ dia requi. at 5-d SRT to 35’ dia at 3.5 d SRT. The dia is further red. to 30’ dia. The resulting project cost is 7.7 M at 3.5 d SRT, the cost will be about 7.5 M if thicker PS is fed to the ferm. sys. the cost for a new biofilter will be slightly less than 0.5 M.

Cost Estimates – 3.5-d SRT (3)

• Approximately 14% or $1.3 M cost saving would be realized by reducing SRT

• $ 7.5 M for 1.5% PSD and $ 7.7 M for 1% PSD, including about $0.5 M for a new biofilter

28PNCWA 2009 – Boise, ID 9/16/2009

biofilter• Feeding thicker primary sludge to the

fermentation system would achieve about $ 0.2 M additional cost saving, which is unlikely to cover the cost for the new grit removal system

To summarize,

Summary and Conclusions

• Primary sludge fermentation is proven to improve EBPR reliability by VFA supplementation

• 2-stage fermentation system– offers simpler and more effective SRT control without

incurring significantly higher cost– cost estimate for warmer season fermentation ≈ $7.3 M

29PNCWA 2009 – Boise, ID 9/16/2009

– cost estimate for warmer season fermentation ≈ $7.3 M

• UFAT process offers a good compromise between the single-stage and two-stage systems in terms of performance, costs and operability

• Odor control using biofilters is recommended for the fermentation system due to its high potential for odor generation. A new biofilter will cost ∼$0.5M. But potential exists to tap into existing under-loaded biofilters.

To conclude the finding in the ferm. sys. evalut.,

Documents

Primary Sludge Fermentation for Reliable Biological ... PNCWA- Session 5-1... · Primary Sludge Fermentation for Reliable Biological Phosphorus Removal Li Lei, Barry Rabinowitz, Bill