The oldest recorded joke may have been semi-scatological, but as Brad pointed out last week, the problem of shit disposal is hardly something to laugh about. It's a particularly big problem for the world's poor, 2.6 billion of whom lack access to any sort of toilet—flush or composting. This is an environmental problem with a huge public-health toll. According to the WHO, diarrheal diseases—which spread considerably faster in the absence of toilets—kill 1.8 million people each year, 90 percent of them children under five. And diarrhea is just one of a veritable shit-ton of diseases that spread via the oral-fecal route, helped along by inadequate sanitation.

But what if there were a way to use human excrement to improve public health and prevent deforestation in the process? That's the idea behind the household biogas digester, an invention that sounds too good to be true until you realize that there are 16 million already in operation, mostly in China and India. A biogas digester takes a family's sludge and turns it into methane, which they can then use as a cooking fuel (right). A family of four can generate enough methane to meet their own cooking needs, though, if they need help, they can also put animal dung in the digester. Cooking with methane saves the household from having to cook with wood or other biomass, which goes a long way towards preventing deforestation. And because methane is clean-burning, it also eliminates indoor air pollution from smoke, which leads to lower respiratory infections in children and chronic lung disease in adults, killing an estimated 1.6 million people annually.

Not too shabby for a technology that gets rid of something that nobody wants in the first place. So why doesn't everyone—or at least everyone in the developing world—have a biogas digester? Mostly because of the upfront expense. They cost a few hundred dollars, and even though they might eventually pay for themselves—especially if they help save on fuel costs—it's hard for a poor family to get a loan to buy one. It will become even harder if microlenders, who have so far been fairly insulated from the credit crunch, start feeling the effects of a global economic slowdown. Just one more way in which a recession might not be so great for the planet.

--Rob Inglis, High Country News