Using poo to combat climate change

One of my many early memories of farming practices was going with Mum and Dad to the sludge plant. I was young enough then that I only have fragments of the memory left. Driving up and around the hill to get there. Big fences. The cold sea breeze on my face. A ute. Grey, wet-looking, slightly sandy-textured sludge. The sound of shovels. I remember that going was a big adventure – everything was a big adventure back then. Still is. I remember asking several times when we were going again, and eventually Mum or Dad trying to explain to me that we weren’t. I think it was no longer permitted, but as I say it was long enough ago that I have no idea what regulatory or social changes had or hadn’t happened.

I remember this every so often, and always wondered what they did with the sludge instead if nobody came and bought it. Kids’ perspectives can be funny. A few years back, the town in question asked its ratepayers if they would pay extra to send the ex-sewage, now “biosolids”, to use on tree plantations instead of dumping it into the local ocean. There was a resounding “YES”. But from my work with composting toilet systems I know there are still a lot of regulatory barriers to reusing biosolids or the reclaimed and cleaned water from “blackwater” – the laws in W.A. say “once sewage, always sewage”.

So it’s interesting to read a recent media release from the Clean Up Conference and CRC-CARE, titled “Using poo to combat climate change“. CRC-CARE is the Cooperative Research Centre for Contamination Assessment and Remediation of the Environment,  their director just won a Banksia Award, and they ran the Clean Up Conference in Melbourne in September.

Basically,  Australia stockpiles about 70,000 tonnes of biosolids – the solid waste left over after sewage treatment – a year. We could be using that not just to build more fertile soils and boost plant growth, as I believe was my parents’ intent so long ago, and not just to recycle increasingly scarce nutrients such as phosphorus and some trace minerals back into our country’s often very poor soils, as is one of the stated aims of many modern eco composting toilet systems, but to lock up carbon in the soil system.

Professor Nanthi Bolan of CRC-CARE told the conference that because Australian biosolids are generally low in toxic heavy metals – compared with some other countries round the world – they are particularly suitable to be incorporated into agricultural soils.

“The big issue with biosolids is the cost of transporting them to where they will be used and spreading them on the soil. Our research indicates this can be offset not only by the boost to fertility and soil organic structure – but also by its ability to increase carbon retention in the soil.

“In other words you could earn carbon credits by using treated human waste as a soil improver – which would pay for part of the cost of transporting and distributing it.”

She goes into more details about how it could work and the factors involved here.

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