Emerging Technologies for Louisiana Waste Processing:

Serpentine Plug-flow Reactor (SPFR)

Dr. J. Sansalone, P.E. Civil & Environmental Engineering

Dr. V. SrinivasanBiological Science

Louisiana State UniversityBaton Rouge, Louisiana USA

SPFR originally developed from $12,000 of LA Sea Grant funds

• Waste sludge generally has high concentrations of TSS, VSS and COD and pathogens

• Current designs for completely-mixed anaerobic digesters require large footprints and long hydraulic retention times varying from 30 – 60 days (Metcalf and Eddy 1991)

Problem Statement

Objectives

1. Develop a small-scale anaerobic serpentine plug-flow reactor (SPFR) utilizing a force-fed fast rate digestion process for waste residual treatment

2. Demonstrate the technical feasibility at different organic loading rates and temperatures.

3. Evaluate the potential for methane production of the anaerobic digestion process

Typical bacterial growth curve in terms of numbers

Time

Log

nu

mb

er o

f ce

lls L

ag

ph

ase

Log growth phase

Stationary phase

Death phase

Source: Metcalf & Eddy, 1991

Advantages of Anaerobic Digestion

- High efficiency of organic mass removal

- Effective sludge volume reduction (30-50%)

- Energy is produced as methane

- Pathogens are destroyed

Anaerobic Digestion

Microbiological pathway of anaerobic digestion

GlucoseAmino AcidsFatty Acids

PO

Carbohydrate ProteinsLipids

Phosphorylated Organics

-34

Cells

Stabilized OrganicsAcetic PropionicLactic+Cells

Complex organics

Hydrolysis

Soluble Organics

Organics Acids

Methane CO 2

Acidogenesis Methanogenesis

Low Rate Anaerobic Digester

Standard-rate digesters or conventional anaerobic digestersNo mixing and thus a stratified condition

High rate

With heating, auxiliary mixing, thickening and uniform feeding

Two Stage

Separation of Methanogenesis from the other two phases, Hydrolysis and Acidogensis

Advanced reactors

Up-flow anaerobic sludge blanket (UASB), Anaerobic Filter (AF)Fluidized bed (FB), Anaerobic baffled digester (ABR) Expanded granular sludge bed (EGSB), etc.

Development History of Anaerobic Digester

Low Rate High Rate Two Stage Advanced Reactors

Schematic of Serpentine Plug-flow Reactor (SPFR)

Gas Vent

Effluent to biological treatment

Primary Sludge Influent

Storage Tank

Advantages of Serpentine Plug-flow

o Plug-flow pattern to partially separate the various phases of anaerobic catabolism

o Longer biomass retention time, lower sludge yields

o Resilience to hydraulic and organic shock loading

o Increased resistance against toxic materials

A flow rate of 500 GPD with a corresponding HRT of 48 hours was applied to investigate the feasibility of

the reactor for sludge treatment

Parameters measured: TSS, VSS, Total COD, Dissolved COD, Alkalinity, pH, Temperature

Experimental Design

Results

Statistical Data for Digester Performance

Total COD TSS VSS

Influent [mg/L] 35,478 32,088 18,343

Effluent [mg/L] 9,808 4,482 3,532

Removal Efficiency 67% 84% 80%

pH Alkalinity

[mg/L]

Temperature(0C)

Dissolved COD

(% of Total)

VSS

(% of TSS)

Influent 6.0 986 28.9 10.5 54.6

Effluent 5.5 850 29.1 75.8 75.4

Probability Densities for Total COD

Reactor Influent Reactor Effluent

Total COD [10 3 mg/L]020406080100120

0.0

0.1

0.2

0.3

0.4

Observed

Predicted

Normal Distribution = 35477.9 mg/L = 18328.8 mg/Ln = 632 r = 0.98

Total COD [10 3 mg/L]

05101520

Re

lati

ve

Fre

qu

enc

y

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Observed

Predicted

Normal Distribution= 9808.2 mg/L= 4363.1 mg/Ln = 63r2 = 0.94

Re

lati

ve

Fre

qu

enc

y

Selected Performance Data from other Studies

WastewaterRaw

molassesMolasses

alcohol stillageSwine waste

Whisky distillery

Influent COD (g/l) 990 115.8 58.5 51

HRT (hours) 850 138-636 360 360

Reactor volume 150 150 15 6.3

Temperature (0C) 37 37 35 30

OLR (kg/m3.d) 28 4.3-20 4 2.2-3.46

COD removal (%) 50 70-88 62-69 >90

Biogas production

(v/v/d)>5 >2.3 2.9-3.2 1.2-3.6

Ref.Boopathy and Tilche, 1991

Boopathy and Tilche, 1992

Boopathy and Sievers, 1991

Boopathy et al., 1988

Gas Production

Total Gas Production = C * Q * (VSSIN – VSSEFF)Methane Production = 0.7 Total Gas Production

Where, Q = 500 gal/dayC = 12 to 18 ft3/lb (0.75 to 1.12 m3/kg), Metcalf & Eddy, 1991 70% of the gas is Methane

Average Gas Production = 28.6 m3/d

Average CH4 production = 0.7 * 28.6 = 20 m3/d

Ga

s (

m3/d

ay)

Time (day)

0 50 100 150 200 250 300 350

0

20

40

60

80

100

120516 mg/L 258 mg/L 0 mg/L

Conclusions

1. The anaerobic digester performed well at a relatively low HRT of 48 h without temperature control.

2. The removal efficiency for Total COD, TSS and VSS is 68.9%, 88.5% and 84.7% respectively.

3. The reactor showed great economical prospective for the natural gas production and low construction and operation cost.

Reactor in operation currently near Mobile, AL

Thank you !

QUESTIONS ?

Total COD, TSS, and VSS Profile at Sugar Effect

Influent

Effluent

Removal (%)

Time (day)0 50 100150200250300350

To

tal C

OD

[10

3 m

g/L

]

020406080

100120140

Re

mo

val (%)

0

20

40

60

80

100

120516 mg/L 258 mg/L0 mg/L

Time (day)

Re

mo

val (%)

0 50 100 150 200 250 300 350

TS

S [1

03 m

g/L

]

0

20

40

60

80

100

020406080100120

516 mg/L 258 mg/L0 mg/L

Time (day)0 50 100 150 200250 300 350

VS

S [1

03 m

g/L

]

0102030405060

Re

mo

val (%)

020406080100120

516 mg/L 258 mg/L0 mg/L

Hydraulic Characteristics Study (by Grobicki and Stuckey)

Method - A series of residence time distribution studies by tracking the fate of an inert tracer (Li+) in the effluent

Models - “Dispersion” and “Tanks In Series”

Results

• intermediate between plug-flow and ideally mixed

• Simulated as a series of perfectly-mixed compartments

Comparisons with Other Reactors

ABRAnaerobic

filterCSTRWithout

BiomassWith

Biomass

Dead

Space (%)< 8%

18%

(at 8gVSS/l)50-93% >80%

Ref.Grobicki and Stuckey,

1992 Yong and

Young, 1988 Stuckey,

1983

pH and Alkalinity Profile at Sugar Effect

Influent Effluent

Time (day)

pH

0 50 100 150 200 250 300 3500

2

4

6

8

10516 mg/L 258 mg/L 0 mg/L

Time (day)

50 100 150 200 250 300 350

Alk

alin

ity

0

500

1000

1500

2000

2500516 mg/L 258 mg/L 0 mg/L

Anaerobic Baffled Reactor (ABR)

ABR -- A reactor design, with a series of baffles to force a wastewater to flow under and over (or through) the baffles as it passes from the inlet to the outlet

Two significance of the specific configuration

o Two-phase system with low cost -- Acidogensis and the methanogensis partially separated

o High solids retention capacity, high bacteria activities (increase by a factor of up to four)

WastewaterHRT

(h)

COD

(mg/l) COD

removal (%)

OLR (kg/m3/d)

Gas

Produced

(v/v/d)

Ref.

IN EFF

Greywater 84 438 109 75 0.13 0.025Witthauer and Stuckey,

1982

Greywater 48 492 143 71 0.25 0.05Witthauer and Stuckey,

1982

Greywater 84 445 72 84 0.13 0.025Witthauer and Stuckey,

1982

Sucrose 6.8 473 74 74 1.67 0.49 Orozco, 1988

Sucrose 8 473 66 86 1.42 0.43 Orozco, 1988

Sucrose 11 441 33 93 0.96 0.31 Orozco, 1988

Slaugherhouse 26.4 730 80 89 0.67 0.72 Polprasert et al., 1992

Slaugherhouse 7.2 550 110 80 1.82 0.33 Polprasert et al., 1992

Slaugherhouse 2.5 510 130 75 4.73 0.43 Polprasert et al., 1992

Selected Low Strength Performance Data

Co-substrateInitiationWhen fed two different substrates with high strength, one readily biodegradable and the other refractory, the microbes would utilize the readily biodegradable substrate rapidly, followed by the refractory compound

Related Research ReviewAppropriate dose addition of a readily-degradable co-substrate improved the process performance

1. Pepton (Kobayashi et al., 1989) 2. Glucose (Satsangee and Ghosh, 1996)), 3. Glucose (Joo-Hwa Tay et al., 2001)

Sugar Effect at Digestion Performance

Sugar Concentration (mg/L)

516 (10%) 258 (5%) 0 (0%)

Influent Total COD [mg/L] 36192.2 35927.8 36423.6

Effluent Total COD [mg/L] 8904.4 14783.8 9492.0

Removal of Total COD (%) 68.9 56.6 73.6

Influent TSS [mg/L] 32638.0 33598.5 32020.0

Effluent TSS [mg/L] 2919.8 10207.3 4272.1

Removal of TSS (%) 88.5 68.1 86.5

Influent VSS [mg/L] 19088.3 18946.6 15934.6

Effluent VSS [mg/L] 2276.9 7406.2 2965.6

Removal of VSS (%) 84.7 60.2 81.0

New ChallengeChanges in quantity and quality

Due to - Increase of domestic and industrial activities

- Evolution of more efficient wastewater treatment plants

Public tolerance towards environmental pollutions

Land available for sludge disposal

Inherent limitation of current digesters (10-30 days

HRT)

High cost of advanced anaerobic reactors (i.e. FB)

More cost-efficient technologies are required

Historical Profile of Natural Gas Prices

Source: www.energyonline.com

Date (month)

Pri

ce (

do

llar

s/10

3ft

3)

0

2

4

6

8

10

12

Residential Prices

Commercial Prices Industrial Prices

1998 1999 2000 2001

4 84 8 12 12 4 8 12

Probability Densities for VSS

VSS [103 mg/L]

0510152025303540455055

Re

lati

ve

Fre

qu

enc

y

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Observed

Predicted

Reactor Influent

Normal Distribution

= 18343.2 mg/L= 10104.5 mg/Ln = 56

r2 = 0.97

VSS [103 mg/L]

024681012141618

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Observed

Predicted

Reactor Effluent

Lognormal Distribution

= 3319.1 mg/L = 3532.3 mg/Ln = 56

r 2 = 0.97

Re

lati

ve

Fre

qu

enc

y

Reactor Influent Reactor Effluent

TSS [10 3 mg/L]

0102030405060708090

Re

lati

ve

Fre

qu

enc

y

0.0

0.1

0.2

0.3

0.4

Observed

Predicted

Normal Distribution= 32088.5 mg/L = 18145.1 mg/Ln = 56r2

= 0.93

TSS [10 3 mg/L]

0510152025

Re

lati

ve

Fre

qu

enc

y

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Observed

Predicted

Lognormal Distribution

= 4482.4 mg/L = 5091.4 mg/Ln = 562

r = 0.96

Probability Densities for TSS

Resilience to Organic Loading and Temperature Shocks

Time (d)0 50 100 150 200 250 300T

otal

CO

D [

103 m

g/L

]

020406080

100120140 R

emoval E

fficiency %

0

20

40

6080

100

TS

S [

103 m

g/L

]

Rem

oval Efficiency %

Time (d)0 50 100 150 200 250 300

0

20

40

60

80

100

0

20

40

60

80

100

Influent Effluent % Removal Efficiency

Time (d)0 50 100 150 200 250 300

0102030405060

0

20

4060

80

100

VS

S [

103 m

g/L

]

Rem

oval Efficiency %

Time (d)0 50 100 150 200 250 300

0

10

20

30

40

Influent

Effluent

Air Temperature

Tem

pera

ture

(0 C

)