Tag Archives: compost

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


  • 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.


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.

Steps on a carbon-neutral journey

How will I know that my home is carbon neutral? How will others believe me? The first steps are working out what to measure, and how to measure it. This post explains how that’s done.  It’s a little bit dry, so to keep you interested, here’s a snapshot of the next step which was the waste audit, described by the household 13yo as ‘totally gross’.

Myrle pouring rubbish for waste audit

The National Carbon Off-set Standard (NCOS) tells us to do a life cycle analysis (LCA) of the greenhouse gas emissions associated with home. That means working out a ‘cradle to grave’ assessment of all greenhouse gas emissions involved in running a household. The NCOS points us to the International Standard for Environmental Management – Life cycle assessment – Principles and Framework IS014040 identifies four phases for an LCA. Here’s how it looks for my house.

flow diagram for carbon LCA

There are some general standards, and some choices about the scope of a greenhouse gas inventory. These are well established for businesses and products, and they can also be applied to a home. For instance, the Scope 1 emissions from my diagram are really a must. Those are the direct emissions from gas heating and fires, and anything else burned or decomposing at a site. Strangely, human breathing is not included in inventories, even though animal farts may be.

pre-winter solstice bonfire 2015

Emissions from electricity used in a building are also a must in the inventory. But you don’t have to include the full fuel cycle emissions from electricity, like transmission losses from the poles, wires, and the times when high voltage loads are transformed to lower voltages. I’ve chosen to include the full fuel cycle. The interpretation stage gives me a chance to change my mind about this if it’s not working out. Similarly, I’d love to include the emissions associated with the stuff we buy for my home. I would, but the data gathering and calculations are way too complex.

The reason that we can exclude these ‘scope 3’ emissions is that they are all included in the inventories being done by other people or businesses. For instance, I’ll be counting emissions from air travel, even though airlines are required to record and report all of those emissions under Australia’s National Greenhouse and Energy Reporting Scheme.

Keep your eye out for the next post, on my home waste audit. That’s when we’ll start to see how my emissions stack up, and what I can do to reduce them.

Towards a carbon neutral home

In Paris, 2015, the Council of Parties reached international agreement that urgent action is needed to prevent climate change. Then February 2016 broke all the records for breaking global warming records. More needs to be done and I can do some of it myself, starting at home.

New Commitment for 2016: Make my home carbon-neutral.

I’ll aim for my home-life to be healthy, comfortable and affordable, but not to contribute to global warming. I’ll also record the details in this blog, and encourage other households to join in.

The plan is to systematically:

  • measure my carbon footprint,
  • look for ways to reduce emissions,
  • off-set whatever remains,
  • continue assessing and reporting so I can continue the journey, and maybe even become carbon negative.

The Australian National Carbon Offset Standard shows these steps together like this.

So what does it mean to be carbon neutral?

We humans are emitting greenhouse gases into the atmosphere faster than they can be absorbed back into the earth. As a result, more heat is trapped within the atmosphere than previously, and global temperatures are rising. This is happening even though some people don’t understand, or disagree with the science.

(If you are one of those climate change denialists, there’s no point me arguing with you, and you won’t be interested in this blog, so kindly head off and put your head in the sand somewhere else).

People who measure and reduce the greenhouse effect have worked out an accounting system to keep track of emissions. The basic idea is to get all of the emissions in the same units. Lots of different gases contribute to global warming. Each gas has a different impact, or global warming potential. A tonne of methane (CH4) for instance, causes about 25 times as much global warming as a tonne of carbon dioxide (CO2). And a tonne of sulphur hexafluoride (SF6) has about 23,900 times as great an impact. Because CO2 is both the most common greenhouse gas, and also has the smallest impact per unit, we simplify things, by using CO2 as the reference point. All we have to do is to convert all emissions to their carbon dioxide equivalent (CO2e), and we can sum the totals together.

Carbon Neutral Standard diagram

Being carbon neutral means minimising your emissions, then balancing any that remain with an equal amount sequestered or off-set. Basically, you absorb as much as you emit.

In the next few blogs, I’m going to measure the emissions my household has from:

  • waste,
  • electricity,
  • other energy sources,
  • transport,
  • other sources.

Wish me luck and come along for the ride.

The hot dirt on compost

By Su Wild-River

It’s well known that compost generates heat. Clever people even heat their houses, run cookstoves and cars off compost. Here’s a little look at a humble backyard compost system through the lense of a thermal imaging camera.

A thermal imaging camera is really a heat sensor, not a camera which shows what you see with your eyes. In these photos, the hottest areas are shown in white, and a rainbow spectrum going through red, to yellow, green and finally blue, show colder areas.

The photographs were taken on a cool autumn morning, with an ambient temperature around 14 degrees Celsius (about 57 Fahrenheit). The yellow glowing thing is a ‘compost dalek’, or plastic drum with air vents at the top, and compost inside.

Its interesting to see in the first pair of photos, that the water-filled pot at the front, and the two ceramic pieces behind are the coolest spots around. These are the high thermal mass areas of the photographs, and I was surprised at first to see that they were so cold, as I usually think of thermal mass as warm. Of course the main feature of thermal mass is not that it stays warm, but that it moderates temperature changes. Large thermal mass elements, like water tanks insulated slabs change temperature so slowly that they stay around the long-term average ambient temperature.

Compost by Kath McCann. Photos by Su Wild-River

Compost by Kath McCann. Photos by Su Wild-River

The outside of the compost dalek registers a temperature of around 16.5 degrees Celsius. It is much warmer than everything around it, and only the vents are colder.

Looking inside without turning the compost gives us a look at even higher temperatures. The hottest parts here are about 20 degrees Celsius. They are the deeper parts of the compost, so we dug a bit further.

Compost by Kath McCann, Photos by Su Wild-River

Compost by Kath McCann, Photos by Su Wild-River

Only an inch or so down, the hottest temperature was 26.4 degrees Celsius. This is more than 10 degrees above the background temperature.

Compost by Kath McCann, Photos by Su Wild-River

Compost by Kath McCann, Photos by Su Wild-River

Now this compost is owned by Kath McCann, a keen gardener, and a good composter, but not someone who is using the stuff to heat her house. It seems as if even humble compost could make enough heat to warm us up, if only we plan and use it wisely.

So there you go. Compost really is warm. How could you be using yours?

Writing plain English science into legislation; or Compost Eats Methane

By Su Wild-River

This post was first published at: http://nofunnybusiness.net/2013/12/writing-plain-english-science-into-legislation-or-compost-eats-methane/

Both legislators and scientists can struggle to communicate our work effectively in plain English. How much harder is it when we try to encapsulate science in a law? I’m facing this challenge at the moment, drafting a Carbon Farming Initiative methodology which if accepted, will form a regulation under the Carbon Credits (Carbon Farming Initiative) Act 2011.

The Carbon Farming Initiative (CFI) was introduced by Australia’s previous Labor Government, and is one element of Australia’s climate change mitigation framework that issupported by the current Coalition government. The program allows farmers and land managers to earn carbon credits for reducing or avoiding greenhouse gas emissions. CFI methodologies establish the rules for calculating credits confirming that they are genuine, permanent and additional to business as usual. To achieve this, the methodologies must beclear, unambiguous, complete and precise.

The methodology I’m working on is called Passive Landfill Gas Drainage and Biofiltration. In plain English, this means putting compost on landfills, because compost eats methane.

This methodology is in part a eulogy to much-loved environmental professional Mark Ricketts who died suddenly in 2011. Shortly before his death, Mark was advising me and my students on a project to estimate the carbon emissions and reductions from landfills when he told me to consider compost, and then earned giggles with stories of the insatiable hunger of compost greeblies and the yumminess of smelly gas.

I had previously worked alongside Mark while he was drafting the Queensland Environmental Protection Act 1994. I watched his optimistic daily trips to the parliamentary draftsman and his exasperated return to our office as he tirelessly negotiated for each sentence to be as simple and readable as possible. The result of his work is a plain English law that encapsulates the precautionary principle, ecologically sustainable development and other complex concepts based in science.

Drawing inspiration from Mark, my team’s CFI proposal was to design a simple, practical method which used robust science, while being easily understood by the hundreds of operators of small local landfills across Australia. Many of these good folk lack the time and capacity to read complicated laws, engineering equations or to establish scientific procedures for their monitoring and evaluation. But they can pick a winner and follow procedures.

Our methodology needs to be consistent with all related national and international methods, so I have read and reviewed hundreds of scientific papers on compost and landfills and the calculation of carbon emission reductions. Most emission reduction methodologies explain themselves through symbols and equations with the most relevant one having five solid pages of such equations, interspersed by just a few sentences for those of us without maths as a first language (pp2-6). Here’s an example:

Excerpt from CDMIIIAX

In contrast, our equations look like this:

 Net greenhouse gas abatement = quantity of methane that is oxidised by the biofilter – baseline emissions – project emissions.

Other strategies for keeping it simple include minimising the number of measurements and using simple, cheap and readily available equipment.

So far progress is good, and our focus on practicality and clarity is well received by the government and stakeholders alike. It was hugely satisfying when the non-technical member of our Technical Working Group smiled saying he found our draft methodology very readable.

Assuming the methodology gets approved, the next step will be to find project proponents. Unfortunately, this step is less likely to succeed. Australia’s initial carbon credit value of $23 per tonne meant that projects could have pay-backs in under seven years, and reap annual profits thereafter. A direct action approach delivering a carbon price of – say $8 would take over 50 years to pay back. The most likely outlook is an elegant methodology that will fail to feed any compost.

Am I the only one disappointed?