> It seems like a pretty a clear, unmitigated win vs plastic

Did you use hot water to wash them?

Probably yes. Last time I did the math making them out of plastic saved energy vs heating water to wash glass (it was a close call, it depended on if you used a dishwasher vs sink washing).

So it might seem environmental friendly, but if you run the numbers it's not necessarily so.

Energy usage for creation is only one axis of "environmentally friendly", though. It's starting to seem like small bits of plastic permeating everything might not be ideal.

Did your calculations include things like the extraction and distillation of the petroleum?

Beyond the environmental impact, there's also just the stupid, wasted effort that goes into pointlessly recreating the same thing over and over when you don't have to. In this case, the bottle goes back on the return trip from delivering new milk, which had to happen anyway. The milk ends up being the only thing delivered, on net. It's just strikingly elegant in its lack of wasted effort and material. It's not clear if it's a net win, though, given the delivery part, unless there are others on the same street signed up for the same day.

If anyone's in the Bay Area and is interested in delivery sort of like this, which also tries to set up regular delivery routes to minimize the marginal impact of a customer, I recommend checking out Farmstead (https://www.farmsteadapp.com/). They provide a similar milk delivery service by picking up Straus milk bottles and refunding the deposit. They also solved my biggest issue with most of the delivery services by picking up their reusable bags and having minimal packaging inside, but COVID put a stop to the bag pickup, at least temporarily.

That’s honestly one of the most interesting parts of nuclear for me, along with large scale renewables (eg hydro): when you can break the energy = CO2 connection by using energy sources that don’t release extra CO2 per kWh, a lot of the math starts to change. Things that didn’t help before (washing glass bottles with water heated by natural gas) actually become a net benefit. Likewise making the glass in the first place.

People are cleaning the plastic with hot water to put it into the recycling. The only difference being that the glass actually gets used again and isn't dangerous to the environment and us as it breaks down. Plastic has turned into an unmitigated man made nature disaster.

Commercial glass washers can use very little energy; the rinse is done with a small amount of near boiling water which goes into the wash tank, where it's then used for washing.

Doesn't that depend on where the electricity for the hot water comes from?

I'm inclined to say "no", unless you're using a renewable energy source that would otherwise go unused. So excess locally produced power that can't be sold to the grid, essentially.

Power markets are very liquid, so I tend to favour calculating your personal footprint based on the average co2 output of the grid, not the particular energy production method you've chosen. This makes it clear that even if you're paying for wind power, it's still better not to waste electricity.

Some of that energy may become greener over time. There's also the final output of unrecyclable, possibly toxic (if heated in the sun) plastic vs glass which naturally degrades to ... sand?

Reusing washed glass bottles for perishables like milk can be a public health risk. It's hard to get the cleaning process to the point where when the stars align for that 1 out of 100,000 bottles it still gets sterilized.

Until I see statistics proving the opposite I don't believe that. Washing bottles hot enough to kill germs really is not hard and we used to reuse lots of glass bottles.

Getting glass hot enough to kill microbes isn't hard, but it does take a lot of energy. Microbes will attach to the glass and use that as a heat sink, so just hot water isn't enough, you have to use enough to heat the glass.

It's actually tremendously hard to do that on an industrial scale. We still get listeria outbreaks even with pasteurized milk and new bottles. Adding in a source of contaimination is going to make it that much harder.

The issue isn't getting bottles hot enough to kill germs. It's doing so in a way that doesn't aerosolize the bacteria and preventing all the other ways cross contaimination can occur.

If you pour a glass of milk at home, do you throw the glass away afterwards?

That's not the risk. The risk is introducing harmful bacteria into a bottle and then having it reproduce for some days before someone drinks it. Since you're not storing milk in the glass it's not an issue if it isn't completely sanitized.