We produce over 2 billion tons of waste per year, a number that's expected to grow by 70% by 2050. We've long sought ways to turn all this waste into energy, but this has usually meant incineration - that is, burning our trash - a method that many environmentalists say is far too polluting.

A better solution may lie in gasification, an old technology that advocates are trying to repurpose as a way to deal with our waste. Gasification companies don't burn trash, instead they turn into a synthetic gas, in a process they say is both economical and eco-friendly.

This synthetic gas can then be converted into a wide variety of end products like electricity, diesel fuel, hydrogen fuel, or ethanol, depending on whats most valuable in any given market.

While in the past, gasification companies have struggled to scale-up and meet their energy production targets, now companies like Sierra Energy, Enerkem and Plasco say they're ready to commercialize and expand.