HARNESSING BIOENERGY AT WASTEWATER TREATMENT PLANTS

This paper addresses harnessing bioenergy at wastewater treatment plants by focusing on
supply-side management: biogas production and use. Successful case studies are compared
and contrasted in terms of economic, environmental, social, and operational objectives. Rules of
thumb for determining when a project is economically viable are discussed. Air emissions and
permitting considerations are covered for equipment and overall installations. These case
studies include biogas used for process and space heating using steam or hot water boilers, and
for combined heat and power projects using cogeneration equipment, such as internal
combustion engines, gas turbines (conventional and mini), several types of fuel cells, and
Stirling engines. Examples of where carbon dioxide is removed from the biogas and
“biomethane” is fed to a natural gas pipeline or further compressed and used as a vehicle fuel
are also included.
Several wastewater treatment plants are also taking advantage of the opportunity to
supplement wastewater solids fed to digesters with organic waste from food processing or
other sources (restaurant waste, etc.). This approach—known as codigestion—has several
advantages: it increases biogas production, decreases solid waste at landfills, and decreases
greenhouse gases by capturing and beneficially using methane that otherwise could be emitted
to the atmosphere at the landfill. Successful case studies of plants practicing codigestion are
described.
Harnessing bioenergy at wastewater treatment plants has the potential to produce enough
electricity for more than 4 million people, while also reducing greenhouse gases. Diverting the
organic fraction of municipal solid waste to anaerobic digesters would further reduce
greenhouse gas emissions and could generate enough electricity to serve more than 10 million
additional people. This potential is based on just the wastewater treatment plants and organic
fraction of municipal solid waste generated in the United States alone. With worldwide
application and using agricultural organic wastes, the potential is immense. This paper on
harnessing bioenergy at wastewater treatment plants brings together the collective experience
of numerous bioenergy projects in the United States and Canada. Those involved in the
planning of biosolids and biogas facilities will benefit from the lessons learned, rules of thumb,
and insights obtained from these case studies.