In early December, I zeroed off my waste measurement as I began to weigh all the different streams. It’s been fun and I’ve taken some satisfaction in seeing our diversion number stay high. By weight, nearly 2/3 of our garbage is divertable compost whether that goes in the backyard or to the curb for treatment by the municipality. Overall, our diversion rate is above 90% right now. But in the back of my mind I’ve been bothered by something. Our compost numbers are high, but compost is a lot of water. A couple of times a week I throw bags that weigh 2 or 3 kilograms into the bin, but I know that come spring those will rot down to a fraction of their current volume.
If the need for diversion is in large part driven in many jurisdictions by the need to preserve landfill capacity, shouldn’t I be tracking volume, not weight? (There are other reasons to stress diversion, but capacity is a key one).
Weighing garbage at set-out is easy: tracking its volume? Not so much.
Thankfully, there is an entire literature on measuring the volume of consumer waste. I’ve picked conversion factors that I found in a document posted in the archives of the Environmental Protection Agency. Find that here. I’m sure that there are controversies and updates and evolving science in the world of waste, but the numbers they’ve posted pass at least my gut check for each category related to the other. So how does our household waste stack up?
Different types of waste have been assumed to have different volumes and I’ve performed a few conversions and calculations as follows:
The numbers for each category are very different when presented as volume, not weight. Of the cumulative waste we’ve set out since I started tracking:
- by weight, the black box is 20.2% of our waste and 24.2% by volume
- by weight, the blue box is just 11.3%, but a much larger 32.8% by volume
- by weight, our compost (municipal and backyard) is 61%; it’s just 23.% of the total by volume
- finally, waste going to landfill is just 7.6% of our waste to date by weight, but it’s 19.5% by volume.
I know some people who likely have updated assumptions about how to calculate the weight-to-volume conversion who I can ask about the most recent industry assumptions, but it’s been a bit of an eye-opening exercise even just pursing it this far.