The British company Clean Air Power offers a technology which can mix biomethane with commercial natural gas or diesel which is is claimed to reduce by 26 percent CO2 emissions for heavy duty vehicles. As a side effect, this means less cost in fuel, about 17,000 GBP per year (numbers provided by Clean Air Power). They have already installed this system, called Dual-Fuel (TM) in about 1600 vehicles around the world, claiming to have reduced CO2 emissions in 50,000 tons.
This company also affirms that biomethane is fairly more productive than liquid biofuels, yielding more energy per hectare of land. Usually, this gas is just released to the atmosphere as a result of waste fermentation. There's even a Swiss company, called Active Compost, that affirms that the most effective way of generating biogas is with Anaerobic Digestion (read: bacteria) - and besides gas you obtain fertiliser. It seems a win-win idea, don't you think?