Bio-gas, or methane, produced by digesters at wastewater treatment plants can be utilized in several ways to defray energy costs. At a minimum, the methane can be used to fire a dual-fuel boiler that could heat the digesters and possibly supplement space heating in the building(s). Natural gas can be supplied to the boiler during periods that methane production is too low to meet demands. This is a very common practice at wastewater treatment plants.

In facilities where a substantial amount of power is consumed and thermal energy can be utilized, like most wastewater treatment plants, cogeneration (also known as combined heat and power or CHP) can be another effective energy cost savings measure. In simple terms, electric power is produced onsite through a prime mover, which can be a methane-fired turbine, microturbine or reciprocating engine-driven generator. The process produces a significant amount of heat that can be recovered for other uses like heating the digesters and providing supplemental space heating for the buildings.

A major factor for either dual-fuel boilers or CHP technologies to perform properly is the quality of the bio-gas being produced by the digesters. The bio-gas will need to be analyzed first and digester output calculated. A scrubbing system to clean the methane will also be necessary to prepare the gas for combustion. Since heat recovery can be somewhat simple or very complex to utilize… each situation needs to be evaluated individually for CHP opportunities.