Abstract: An in-vessel composting system wherein the exhaust gas from aerated compost feed material is pretreated by scrubbers and then by a chiller/condenser. A small portion of this cool, relatively dry, ammonia-free gas is passed through an activated carbon column and discharged to the atmosphere. The remaining portion of the exhaust gas is supplemented by ambient air to make-up for the volume of air vented and recirculated through the composting system until such time as the system requires a fresh supply of oxygen. The system is then recharged by blowing in ambient air and venting the spent recirculating air.

Abstract: A method is provided for the control of nitrogen oxide and carbon monoxide emissions from a digester gas engine by the injection of air immediately upstream of the intake valve to form a gradient charge in the combustion chamber having an incombustible portion adjacent the piston and a more concentrated combustible portion adjacent the spark plug, and by the calibration of the spark advance curve of the engine.

Abstract: A method is provided for the control of nitrogen oxide and carbon monoxide emissions from a digester gas engine by the injection of air immediately upstream of the intake valve to form a gradient charge in the combustion chamber having an incombustible portion adjacent the piston and a more concentrated combustible portion adjacent the spark plug, and by the calibration of the spark advance curve of the engine.