Composters out there, you know the feeling - when you open your bin or tumbler and an ungodly wave of bad compost smell washes over you.
For non-composters out there - you don’t even want to imagine it.
One of the biggest reasons preventing people from starting composting is the fear of odour. Now it only happens when you haven't been managing it properly but when it does, it can be really bad. Most people don't think of compost as too dangerous but one case in New Zealand saw ten kids hospitalised with nausea!
But where do these smells come from, why do they happen and how can you stop them?
Why does it smell
So what’s the science behind smell, specifically that of a dangerous compost pile? Being such a sophisticated and complex biological process, the reason behind each pile will vary but bad compost smells usually come down to three main phenomena.
The first is hydrogen sulphide (and a whole bunch of “reduced sulphur compounds”) that is appropriately also known as “rotting egg smell”. This pesky organic compound is produced when compost doesn’t have enough oxygen and the aerobic bacteria is overtaken by methane- and sulphur-spewing anaerobic species.
Second reason is ammonia, which is the gas form of nitrogen and hydrogen, which smells kind of like a combination of week-old fish and bathroom cleaning products. This ammonia comes from (no surprises) the nitrogen present in the organic waste. When there’s too much nitrogen-rich material in a pile, the excess amount will turn into that unpleasant ammonia.
Finally is from the waste itself. Different waste types are decomposed by different types of bacteria, whether it’s grass clippings or bananas or teabags, and they all produce various organic compounds we can smell. Unfortunately, through no fault of their own, the bacteria suited to a couple of waste types simply don’t produce the most appealing odours when they’re decomposing. Meat and dairy are the worst offenders you’ll find in your fridge.
Why is it so bad
Okay so apart for the obvious issues of hospitalised children, odours lead to a whole bunch of other serious problems.
If your compost smells like a landfill … it’s because that’s basically what you’ve made. A smelly bin is like a landfill on steroids, meaning that all the methane emissions and leachate that landfills produce are happening there too. Not only will this make for a horrible end-product but none of the environmental benefits of compost are being realised.
When you’ve got an unpleasant pile as well, you’re not going to want to properly maintain it, making the problem worse.
This also impacts other people. Not only does it infringe on the surrounding area and anyone who might live or work near it, but it also creates and reinforces the perception that composting is super gross, deterring them from starting themselves.
How to stop it
If you’ve been feeling a little compost shamed with all this, not to fear! It’s actually super easy to make sure your pile smells like nothing but delicious, nutritious soil food, with three simple steps.
- Make sure there's enough oxygen: Whether it's through a hearty turn or passive aeration system, ensuring your compost is oxygenated means those pesky anaerobes won't be showing up.
- Make sure you've got a good balance: Every time you add to your compost, you're affecting its nitrogen ratio. Too much and that ammonia is just going to seep out so keep the balance by adding the much-needed carbon as well.
- Make sure you're minimising the meat: Look, a little bit of meat or dairy products never hurt a compost pile but emphasis on the little - no giant steaks allowed!
Keep on top of those three things and your compost will be smelling sweet-as in no time!
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