Human waste could be the next big weapon in the fight against climate change, a new study suggests.
Research indicates that human waste can not only boost fertility and soil organic structure - but also increase carbon retention in the soil.
"Our research shows that if applied to agricultural soils or re-vegetation projects, bio-solids - as well as increasing soil fertility and boosting plant growth - can lock up carbon," Professor Nanthi Bolan from the University of South Australia said.
"Biosolids contain nitrogen and other nutrients for crop growth, organic matter to improve soil structure, and non-degradable forms of carbon that will stay in the soil for a long time," said Bolan.
"The big issue with bio-solids 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," said Bolan.
Bio-solids contain the major nutrients nitrogen and phosphorus, but also micro-nutrients and trace minerals.
The amount of carbon that can be locked up depends on several variables - how the bio-solids were stabilised at the sewage works, the type of crop they fertilise, and the levels of iron and aluminium in the soils, which combine with, and consequently lock up, the carbon in bio-solids.
Up to 30 per cent of bio-solids can consist of non-degradable carbon - and we need to encourage the use of the right sorts of processes in our sewage works to maximise this, said Bolan.
"If you used bio-solids for tree crops or for landscape re-vegetation it would then lock up more of the mobile carbon for a much longer time than an annual crop like wheat or canola," said Bolan.
Bolan said some people may not like the idea of using human waste in the food system, but in reality we have done this for thousands of years - and modern bio-solids are far cleaner and safer than untreated waste.
At a time when fertilisers are becoming ever more costly and soils degraded, bio-solids offer a major source of low-cost nutrients and a source of better soil quality.
