METHANE

CO2

Carbohydrates

Proteins

Lipids

Glucose

PO4-3

Acetic

Propionic

Lactic + Cell

Cells

Hydrolysis

Extracellular

Enzymes

Acid Producers Methanogens

ORGANIC

ACIDS

SOLUBLE

ORGANICS

COMPLEX

ORGANICS

Phosphorylated Organics

Amino Acids

Fatty Acids

Stabilized Organics

MICROBIOLOGICAL PATHWAY OF ANAEROBIC DIGESTION

Figure by MIT OCW.

Adapted from: WEF. "Wastewater Treatment Plant Design. Water Environment Federation." Alexandria,

Virginia, 2003.

Figure by MIT OCW.

Adapted from: Sawyer, C. N., P. L. McCarty, and G. F. Parkin. Chemistry for Environmental Engineering

and Science. 5th ed. Boston, MA: McGraw-Hill, 2003.

25,00010,000500025001000500250

10

20

30

40

50

6.0

pH = 6.2

6.4

6.66.8

7.0 7.2

7.4

7.6

7.8

8.0

8.2

8.4

8.6

8.8

Bicarbonate Concentration as CaCO3, mg/L

0

Relationship between pH, bicarbonate concentration, and carbon dioxide concentration at 35oC and 1 atm.

CO

2 in

Dig

este

r G

as, P

erce

ntag

e

Limits of Normal Anaerobic Treatment

SUBSTANCE MODERATELY INHIBITORY

CONCENTRATION, mg/L

STRONGLY INHIBITORY

CONCENTRATION, mg/L

Na+ 3500 - 5500 8000

K+ 2500 - 4500 12000

Ca++ 2500 - 4500 8000

Mg++ 1000 - 1500 3000

Ammonia-nitrogen (pH dependent) 1500 - 3000 3000

Sulfide (un-ionized gas) 200 200

Copper (Cu) 0.5 (soluble)

50-70 (total)

Chromium VI (Cr) 3.0 (soluble)

200-250 (total)

Chromium III 180-420 (total)

Nickel (Ni) 2.0 (soluble)

30.0 (total)

Zinc (Zn) 1.0 (soluble)

Toxic and Inhibitory Concentrations of Selected Inorganic Materials in Anaerobic Digestion

Figure by MIT OCW.

Adapted from: WEF. Wastewater Treatment Plant Design. Water Environment Federation, Alexandria,

Virginia, 2003.

SCUM

Feed sludge treatment plant

Digester gas

Digested solids

SUPERNATANT

ACTIVE LAYER

STABILIZED SOLIDS

Effluent to

LOW-RATE ANAEROBIC DIGESTION

Figure by MIT OCW.

Adapted from: WEF. Wastewater Treatment Plant Design. Water Environment Federation, Alexandria,

Virginia, 2003.

Figure by MIT OCW.

Adapted from: Reynolds, T. D., and P. A. Richards. Unit Operations and Processes in

Environmental Engineering. 2nd ed. Boston, MA: PWS Publishing Company, 1996, p. 582.

Hatch

Overflow

Gas dome

Roller

Gas line

Composition roof hatch

Ceiling plate (1/4 in.)(6.5 mm)

Sludge inlet pipe

Concrete support

Supernatantwithdrawal

Supernatant gas

Freeboard

16

Sludge in

Sludge in

Gas line

Digested sludge out

Sludge to recycle

Side water depth (swd)

Section Through an Anaerobic Digester with a Floating Cover

Landing bracket

Figure by MIT OCW.

Adapted from: Reynolds, T. D., and P. A. Richards. Unit Operations and Processes in

Environmental Engineering. 2nd ed. Boston, MA: PWS Publishing Company, 1996, p. 584.

Drive

Compressor

B

Gas

Gas

Compressor

A

DC

Gas recycle & draft tube Gas recycle & gas injection

Gas

GasDrive

Impeller & draft tube Impeller

TYPES OF MIXING SYSTEMS FOR ANAEROBIC DIGESTERS

Platform to other

digesters Ele

vat

or

Pip

e ar

ea

Pipes

Platform

Feed

Mixer

Hopper

Supernatant

withdrawal

Scum door

8.8

m21 m

Gas

37o

20 m DIA. Piping to

withdrawal

bottom sludge

spargers

Tower

EGG-SHAPED ANAEROBIC DIGESTER

Figure by MIT OCW.

Gas injection

lines

Gas header

Foam

Separator Scam Breaker

Screw-impeller sludge

mixing pump with

draft-tube assembly

Solids recirculation

header

Digested

biosolids

overflow

Raw sludge

influent

Heat

exchanger

Alternate biosolids

wasting to storage tank

Nozzle for mixing

Unconfined gas mixing Mechanical draft-tube mixing Pumped recirculation mixing

To gas utilization

Mixing Systems For Egg-Shaped Anaerobic Digesters

Figure by MIT OCW.

Adapted from: WEF. Wastewater Treatment Plant Design. Water Environment Federation, Alexandria,

Virginia, 2003.

Figure by MIT OCW.

Adapted from: Hammer, M. J., and M. J. Hammer, Jr. Water and Wastewater Technology.

5th ed. Upper Saddle River, NJ: Prentice-Hall, Inc., 2004. Figure 11-56.

Belt tension roller

Polymer

Sludge feed

Gravity drainage zone Alignment roller

Cake discharge belt conveyor

Belt wash

High pressure zone

Upper beltStatic Box

Wedge zone

Lower belt

A

Filtrate & wash-water collection