A random call from a reporter piqued my interest: Does recycling glass really save energy? That is, after you take into consideration all the energy spent to collect glass from people’s homes, truck the collected glass to a distribution center, route it to a glass manufacturer, and then melt it down for reuse, does glass recycling really save anything, compared with using virgin materials?

I was actually fearing the worst here. Obviously, given all the energy costs of recycling glass, it’s conceivable that it isn’t a very good deal for the environment. Plus the reporter was asking specifically because he’d heard some mention that the benefits of glass recycling were overblown.

As it turns out, though, I shouldn’t have worried. From just about every serious analysis I dug up, it seems that glass recycling really does save energy, compared with using virgin material. Some handy citations: here, here, here, and this extensive lit. review (PDF).

But as with most things, there is a bit of a twist.

As several of the studies point out, glass recycling saves energy — but much less energy per ton of glass than, say, recycling newspaper, steel, and aluminum. (See, e.g., page 31 of the lit. review.) And because the theoretical energy savings of glass recycling appear to be relatively slim, it could mean that actual savings depend on lots of devilish details — how far the glass is shipped, how dispersed are the neighborhoods from which glass is collected, whether people make special car trips to recycling centers, etc.

One of those devilish details — covered here, about 3/4 of the way down the page — is the type of furnace used to melt the recycled glass. From the article:

[C]leaner-operating electric furnaces … use less energy and thus create less emissions than natural gas-powered furnaces, [but] cannot use as much recycled glass, so they are not as efficient.

That is, by using an efficient, low-emissions furnace, you can actually decrease the overall energy efficiency of your glass recycling operation. Darn.

And then there’s this: Even though using recycled glass does appear to have a lower environmental cost than using virgin materials, the environmental cost is not zero. Obviously — from an energy standpoint at least — it’s better to drink water from the tap than water shipped in glass bottles, even if the bottles are made from recycled glass.

But more to the point, it may be that buying a drink in a lightweight plastic bottle uses less energy than buying a beverage in container made from recycled glass — even if the glass bottle is re-recycled, and the plastic bottle just gets thrown away after a single use. This study from Israel (PDF) suggests as much — though it points out that this is only true for certain types of plastics, and may only be true for the specific circumstances in Israel’s recycling system. And in the same vein, this analysis from the Institute for Lifecycle Environmental Analysis suggests that paperboard cartons have a lower environmental cost than bottles made from recycled glass.

Of course, I’m no expert here. All the information I have on the subject comes from a bit of googling — and much of it seems to be at least a decade old. But it looks like glass recycling really is worthwhile … and, simultaneously, that the gradual trend among beverage bottlers to replace glass with plastic may not, on balance, be such a terrible development.