Fun for the whole family with a household waste audit

The waste audit on our path to an zero-emissions home revealed a grand total of 50kg of annual emissions and some ways to reduce it. Here’s how to do a waste audit, and what we found.

Why waste?

The average Australian generates about 1,200 kg of waste each year. The average emissions from municipal (household) waste, is approximately 1.4 times the weight of the waste, meaning that average Australians emit about 1,680 kg of CO2e  each year. Total emissions from Australian solid waste are about 23,000,ooo tonnes per year, or  3.8% of Australia’s total emissions footprint in 2014-5. So emissions from waste are worth worrying about.

Emissions from waste are mainly the result of organic substances, like food scraps and paper, breaking down in landfills. When this happens underground in a landfill, it forms methane, which has about 25 times the global warming potential of carbon dioxide.

Most rubbish bins contain lots of organic waste. Organics are about 65% of household waste when councils do not collect garden and park waste, and about 60% when they do.

My council does collect garden and park waste, but I don’t use the service. Instead I give (nearly) all of my food scraps to the chooks and compost (most of) the rest. We make very good use of the council recycling bin, so our landfill waste is significantly less than would be without that service. So I was expecting my waste emissions to be lower than the average. I did a waste audit to check.

Here’s how to do a waste audit, and what we found.

My household waste audit

Equipment

  • A unit of waste – we used one average week’s waste, collected from all household bins.
  • A tarp, or enclosed area to sort the waste – we used a kids play-pen.
  • A set of scales for weighing the waste.
  • Buckets to hold waste.
  • Tongs, so you don’t have to touch it.
  • Gloves, for the bits you do have to touch.

Method

Decide on your categories.

If you are trying to work out whether the waste is going in the right bins, your categories need to match the bins, eg:

  • landfill waste,
  • recycling,
  • organic.

If you are working on a carbon footprint, then your categories need to match the groups of wastes with different emissions factors, or global warming potentials. This only applies to the organic component and according to the Australian National Greenhouse Accounts Factors (Table 41), includes:

  • food,
  • paper and cardboard,
  • garden and green,
  • wood,
  • textiles,
  • sludge,
  • nappies,
  • rubber and leather, and
  • inert waste.

I was interested both in whether householders were using the right bins, and also in calculating the greenhouse emissions. So I used every relevant organic waste category, plus ‘landfill waste’, which is essentially the waste that should have been in the rubbish bin, because there wasn’t another option. I also added two other categories of interest. They were:

  • paper towels – which I use quite a bit to mop up organic kitchen waste which I don’t want to flush down the sink, as it fills up my septic tank with sludge, and
  • monstrous hybrids – which are an infuriatingly difficult category made up of things that could be recycled, if only they weren’t joined together with things that can’t be.

Sort your waste

Tip the waste into the sorting area, and get to work with the tongs. Put all of the waste into its waste category.

Then, fill a bucket with waste from just one category and weigh it. First you’ll need to zero the scales so that you weight the waste, not the bucket. If you are thinking about bin sizes, you need to estimate the volume, or size of the waste, but for carbon accounting, just the weight will do.

Record the results

Here are the results from my household’s weekly waste audit.

 Category kg
hand towels 0.21
Co-mingled recyclables 0.1
Inert waste 0.58
Monstrous hybrids 0.05
Food 0.19
 Total 1.13

Multiply by 52 to get an annual total.

  Weekly Annually
 Category kg  kg
hand towels 0.21 10.92
Co-mingled recyclables 0.1 5.2
Inert waste 0.58 30.16
Monstrous hybrids 0.05 2.6
Food 0.19 9.88
 Total 1.13 58.76

Calculate the greenhouse gas emissions

To calculate the emissions, you need the emissions factors for each type of waste. These are in table 41 of the Australian National Greenhouse Accounts Factors, which is regularly updated, so get the current version. This gives a multiplier for the weight of each type of waste. To work out emissions, all you have to do is multiply the weight of each organic waste type by the relevant factor, like this.

Weekly Annually Factor Emissions
Category kg kg Multiply by weight kg CO2e
hand towels 0.21 10.9 2.9 31.7
Co-mingled recyclables 0.1 5.2 0 0
Inert waste 0.58 30.2 0 0
Monstrous hybrids 0.05 2.6 0 0
Food 0.19 9.9 1.9 18.78
Total 1.13 58.76   50.44

How did we go?

This gives me a total of just over 50 kg of emissions from waste each year. My household is about 3 people, so that’s only about one per cent of the emissions of an average three-person household (3 x 1680= 5,040).

Frankly, I’m amazed it could be so low, and so I’ll use some other blog posts to look into how I’m keeping it down. Most of it seems to be the chooks, and the aerobic composting, but we’ll see.

Can we improve?

Despite the emissions being so low, there are several things I could do to reduce even further. I could:

  • either stop using hand towel or put it in the council’s green bin. This would take out 31.7kg per year of CO2e emissions.
  • be more rigorous about composting all organic waste or giving it to the chooks. The food waste still in the mix was generally uneaten cat food, or meat bones. These are tough wastes to get rid of, since bones don’t break down, and I don’t like to feed cat food to the chooks, because who knows what’s really in it. However if I could solve this, it would cut out the other 18.8 kg of organic waste. Again, some of it could go in the council green bin.

Why not check your own waste

Inspired? Have a go at doing your own waste audit. Its fun for the whole family. Or perhaps not. As I said in another post, the household 13yo found it totally gross (there were some maggots on the food waste).

Myrle pouring rubbish for waste audit

If you do a waste audit, tell us what you found.

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