Shipworms eat with their gills?

A recent study on shipworms, sea-dwelling clams that look like worms has found that their digestive process actually starts in their gills! This is quite unusual because pretty much all animals ingest the food through some sort of mouth-like orifice and then proceeds to be digested in a gut of some sort with the aid of digestive enzymes that get secreted by symbiotic bacteria that live there. In the case of the shipworm however, those bacteria have taken residence in their gills, and the enzymes they produce somehow survive the journey down to the gut. Scientists are hoping to find out exactly how the enzymes survive and what makes the bacteria so good and breaking down cellulose into ethanol, because there is a hope that ethanol could be a potential biofuel.

Some questions I still have about this is how helpful would these bacteria really be in producing ethanol? And would we just use the bacteria or the shipworm as well, and if we did would they be treated humanely?