Biogas Production And Potential From U.S. Wastewater Treatment
Figure 2. Percentages of biogas utilization technologies in use at WWTPs producing biogas

An extensive data collection undertaking has yielded an improved picture of wastewater treatment plants in the U.S. with operating anaerobic digesters and if and how the biogas generated is utilized.
Maile Lono-Batura, Yinan Qi and Ned Beecher
BioCycle December 2012, Vol. 53, No. 12, p. 46