Anaerobic Digestion Terms

Front 1

Hydrolysis

Back 1

Complex organic matter (i.e. VS) is broken down to soluble organic matter; carbohydrates are broken down into sugars, fats are broken down into fatty acids, and proteins are broken down into amino acids.

Front 2

Acetogenesis

Back 2

Fermentation reactions result in the formation of acetic and other volatile acids (e.g. proprionic and butyric acids) , CO2, NH3, and H2

Front 3

Methanogenesis

Back 3

Acetic acid is converted to methane and CO2

Front 4

Buffer basic definition

Back 4

A chemical equilibrium system that prevents rapid changes in pH

Front 5

Safety equipment on a digester

Back 5

Pressure relief/vacuum valves, flame arrester, drip trap, sediment trap, thermal valve, pressure regulators, waste gas burner.

Front 6

BTU

Back 6

The amount of energy it takes to raise 1 lb of water by 1 degree Fahrenheit.

Front 7

Pressure/Vacuum relief valve ad typical setting.

Back 7

A valve that opens to relieve excess pressure under the dome and prevent blowing out of the water seal in a floating cover digester. Occupy a common housing with the flame arrester. Typical pressure in a digester dome is 6 to 8 inches of water column.

Front 8

Vacuum relief valve and typical setting.

Back 8

This is similar to the pressure relief valve but relieves negative pressure to prevent possible collapse of the digester cover. Typical setting is 2 inches of water column.

Front 9

How often should the pressure relief valves and vacuum relief valves be checked?

Back 9

At least once every six months and daily under freezing conditions

Front 10

Flame Arrester

Back 10

Rectangular box containing approximately 50 to 100 corrugated, stamped aluminum sheets called baffles. The baffles cool any flame that develops in a gas line to below ignition temperature.

Front 11

Where should the flame arresters be installed?

Back 11

a) as part of the pressure/vacuum relief valve

b) after a sedimentation trap

c) at a waste gas burner

d) before every boiler, furnace, or other flame

Front 12

Drip Trap

Back 12

Since digester gas is so moist the moisture needs to be collected before it settles in an inopportune spot and impedes gas flow. Traps are dome-shaped devices containing 1 to 2 quarts of water and located at low points on gas lines. Drain once per day.

Front 13

Sediment trap

Back 13

Large cylindrical containers holding approximately 12 gallons and affixed with a sight glass. Located on top near the gas dome. Also may be attached to gas lines. Removes sediment from digester gas by a combination of centrifugal force and a drop in velocity of the gas as it enters the trap. Drain 2x/day.

Front 14

Thermal valve

Back 14

A fusible element which melts at 260 F. Causes a thermal valve to close shutting off the flow of gas. May be attached to a flame arrester. Requires an annual check to ensure proper operation.

Front 15

Pressure regulators

Back 15

Often installed next to and before the Waste Gas Burner. Control the gas pressure in the entire digester gas system, normally set at 8 inches of water column. Thermal valves are typically installed between the pressure regulator and the WGB.

Front 16

Manometer

Back 16

Measures pressure in a gas line

Front 17

Difference between a thief hole and a sludge sampling manifold

Back 17

.

Front 18

Function of an overflow pipe

Back 18

.

Front 19

LEL/UEL of methane

Back 19

4.4%/15%

Front 20

BTU in 1 cubic foot of digester gas

Back 20

~600 BTU

Front 21

BTU in 1 cubic foot of methane

Back 21

~932 BTU

Front 22

How % is measured for digester gas

Back 22

In cubic feet. 64% methane = 64 cu ft methane/100 cu ft of gas