Actually, it has been used in the past, and quite frankly from an energy standpoint, it's not all that efficient -- at least the way it was done before this new TDP process. The prime example I'm aware of is the Hyperion Wastewater treatment plant in Los Angeles. It has large digesters where the sewage "stews" in bacteria and methane gas is drawn off. The methane is used to fire gas turbines that supply some of the electricity to run the facility. The turbines also exhaust heat which is used to super dry the compost (what's left at the bottom of all the settling ponds). The dried compost is burned in a fluidized bed boiler which is used to produce more electricity to run the plant.
The concept behind the plant, (which was funded by the EPA) was to have a zero discharge facility (no sludge to landfill) and to have it be energy self-sufficient. From what I understand, it never reached either of those goals. The biggest problem was the BTU content of the methane was not only very low, but also highly variable. To keep the gas turbine running at any kind of efficiency, they had to supplement the methane with with natural gas. The same was true with the dried compost --- the BTUs were all over the place.
But it does sound like this TDP process could be a good solution for municipal sewage. Instead of fighting the water, they use it as part of a molecular process as opposed to a physical process.