US EPA Reports Steadily Rising Growth in Anaerobic Digestion in US

The following is an extract from the Agstar report published in November 2007:-

Construction of anaerobic digestion systems for livestock manure stabilization
and energy production has accelerated substantialy in the past several years.

The EPA estimates that there are currently about 111 digesters operating at commercial livestock facilities in the United States.

In 2007, farm digester systems produced an estimated 215 million kilowatt
hours equivalent of useable energy.

Besides generating electricity (170 million kWh), some operations use the gas as a boiler fuel, some upgrade the gas for injection
into the natural gas pipeline, and some flare gas for odor control.

Many of the projects that generate electricity also capture waste heat
for various on‐farm thermal uses.

The majority of commercially operating systems (Figure 2) are plug flow
and complete mix reactors (both tanks and covered lagoons) operating
at mesophilic temperatures
(95° ‐ 105°F).

The remainder of the systems include covered lagoons operating at a
mbient temperature, and attached growth and induced blanket reactors.

European‐style complete mix systems are also emerging in the U.S. market.

Although the majority of systems are still farm owned and operated,
using only livestock manure, other approaches are emerging.

These include the commingling of high strength organic wastes
(e.g., food waste, ag waste, cheese whey) to increase gas
production per unit volume of reactor; third party owned/operated
systems; centralized systems handling manure from multiple farms;
and direct gas sales to customers or gas utilities.

Most digester systems (80 percent) currently are found in the dairy industry in the Midwest, West, and Northeast. More here..