Image credit: Just for Sharing Ideas
I was chatting with a friend who took objection to my post on anaerobic digestion. He had no problem with the concept of finding uses for waste, but cautioned that we often think uncritically about what happens next. After all, once you start using waste, it's no longer waste. And once it's no longer waste, you are creating demand for it. And once you create demand, supply will surely follow. Of course this might be a slight oversimplification. But it is true to say that if you create a use for something, and therefore allow it to generate a revenue stream, you inevitably make it more economically attractive to produce more of the same. On the plus side, looking at anaerobic digestion for example, you are creating an economic incentive to collect and utilize food waste—and you are therefore making measures like San Francisco's mandatory composting laws more economically viable, and politically palatable.
On the downside you are creating demand for biomass. And as this friend pointed out—it would be nice to think that once each waste-to-energy anaerobic digestion plant has used up the readily available stream of waste, the operator will open up another plant elsewhere to use waste there too. But that may not always be the case. Because there's plenty of other types of biomass lying around—much of it locked up in these things we call trees.
Just as incinerators often start out burning forestry waste, and end up using virgin wood once supply of "waste" runs out, so too anaerobic digestion plants may begin by using food waste, and end up utilizing forest products or other 'biofuels' grown deliberately for the purpose. After all, it's often much more economically viable to ramp up capacity at an existing plant than it is to build a new one elsewhere.
I don't believe my friend was saying we shouldn't use waste. But we should retain a critical eye on what the consequences of that use are. And we should plan for ways to avoid unintended (or undeclared) "scope creep" for any waste to energy facility. And of course, while new supply of clean energy must always be part of the puzzle—we desperately need to crack the problem of demand if we are to have any hope of sustainability.
There's no such thing as a free lunch. Even if someone threw it away.