trendline, page-22

http://www.fuelcellmarkets.com//news_and_information/3,1,443,1,8162.html

In the above link biomethane is referenced as a fuel alongside ethanol. I dont know if cfu's rig is limited to these fuels or frankly what the difference is between biomethane and HHO/bio digester gas. Biomethane is resultant from waste dumps..pretty thin line between that and a biodigester.

The reliablity of the fuel flow would be paramount as the cell has a long startup and shutdown process. Complimenting another fuel with a biodigester would be the go imho, otherwise having a bulk facility with gas storage would be an option.