Today, more than 16,000 municipal wastewater treatment facilities (WWTFs) operate in the United States, ranging in capacity from several hundred million gallons per day (MGD) to less than 1 MGD. About 540 of these facilities employ anaerobic digestion to process the wastewater. CHP is a reliable, cost-effective option for wastewater treatment facilities that have, or are planning to install, anaerobic digesters. The biogas flow from the digester is used as "free" fuel to generate electricity and power in a CHP system using a turbine, microturbine, fuel cell, or reciprocating engine.
A report entitled Opportunities for and Benefits of Combined Heat and Power at Wastewater Treatment Facilities provides a guide to basic information for assessing the potential technical fit for CHP at WWTFs that have anaerobic digesters. Assuming only facilities with a flow rate of at least 5 MGD were technically and economically feasible sites for CHP, the report determined that approximately 225 MW of electric capacity could be produced from facilities that have anaerobic digestion but did not currently utilize the biogas produced. An additional 115 MW of electric capacity could be produced assuming facilities with anaerobic digestion and off-gas utilization use the biogas for digester heat loads. Overall, CHP at WWTFs represents an excellent technical fit, with the ability to generate roughly 340 MW of electric capacity that could be used for onsite electricity needs or sold back to the electric grid.
Wastewater treatment facilities are vulnerable to catastrophic events, natural disasters, and other emergencies. Because they provide critical infrastructure for maintaining public health and the environment, they must operate under any of these conditions. The use of CHP as prime power source or as backup can provide critical off-grid reliability to enable wastewater treatment plants to continue operations in the event of a utility failure. Furthermore, in the face of tightening local budgets, cost savings resulting from CHP operations can be redirected to other preparedness priorities. A CHP system also provides the following benefits for a WWTF:
- Produces power at a cost below retail electricity.
- Displaces purchased fuels for thermal needs.
- Qualifies as a renewable fuel for green power programs.
- Enhances power reliability for the plant.
- Offers an opportunity to reduce greenhouse gas and other air emissions.
As of December 2006, wastewater treatment CHP systems were in place at 76 sites in 24 states, representing 220 MW of capacity. The table below shows the number of sites by state, as well as the total CHP capacity in each state. California and Oregon have the largest number of facilities with CHP systems, and Massachusetts has the largest installed capacity. There are no WWTFs in the Gulf Coast Region currently operating CHP systems.
| AR |
1 |
1.7 |
AZ |
1 |
4.2 |
| CA |
23 |
38.1 |
CO |
2 |
7.9 |
| CT |
1 |
0.2 |
FL |
1 |
6.0 |
| IA |
2 |
3.4 |
ID |
2 |
0.5 |
| IL |
2 |
4.3 |
MA |
1 |
76.0 |
| MN |
2 |
5.1 |
MT |
3 |
1.1 |
| NE |
3 |
5.4 |
NH |
1 |
0.4 |
| NJ |
3 |
4.6 |
NY |
5 |
13.3 |
| OH |
1 |
0.1 |
OR |
10 |
5.9 |
| PA |
3 |
22.4 |
UT |
2 |
2.6 |
| VA |
1 |
3.0 |
WA |
3 |
13.6 |
| WI |
2 |
0.5 |
WY |
1 |
0.03 |
| Total: 76 (220.1 MW) |
Case Studies
Future Potential in the Gulf Coast
| LA |
8 |
1,371 |
| OK |
4 |
1,409 |
| TX |
19 |
14,393 |
An additional 1,061 kW of electric capacity could be generated from three facilities in Texas currently utilizing biogas for digester heat loads.
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