Urine grows better fish food
Human waste could be an alternative to chemical fertilizers.
Human urine could nourish the plankton used as food on fish farms. Plankton grown in diluted urine do better than those given other nitrogen-rich materials, ecological engineers have found.
Bara Bihari Jana and his colleagues at the University of Kalyani, India, mixed ground water with human urine from the university's urinals and added the zooplankton Moina micrura, which is often fed to hatchling fish in commercial fisheries.
They also tried rearing the plankton in various cocktails of cow urine, vermin compost, poultry droppings and cow dung, all of which are commonly used in fish farming in poor regions where chemical fertilizers are not available. All treatments used half a litre of urine, or half a kilo of dung, to every 4,500 litres of water.
Young plankton in human urine began reproducing at least four days earlier than those in other tanks, lived longer and produced more offspring, the researchers found. The study is published in Ecological Engineering1.
"Human urine is a stable liquid and contains valuable nutrients. I see no reason why it couldn't be used for this purpose if it provides a suitable chemical environment for the zooplankton to grow," says Stephen Smith, an environmental biochemist at Imperial College London.
The Indian team suggests that human urine contains high concentrations of nitrogen compounds that degrade rapidly to release amino acids and minerals, fertilizing the growth of algae, which the plankton then feeds on. "We believe this quick release of nutrients induced the fast reproduction in the plankton," says Jana.
Worldwide, culturing planktonic fish food is a multi-billion dollar industry that uses millions of tonnes of chemical fertilizer.
Human urine is cheaper and more environmentally friendly than chemical fertilizers. Its use would reduce eutrophication — the process where fertilizers washed off the land cause damaging blooms of plankton in rivers, lakes and the sea.
"New and alternative uses for wastes and wastewater like this need to be identified," says Smith. "My only potential concern would be that the urine is from healthy individuals not taking medication or antibiotics as these could be excreted in the urine."
"We have not yet encountered any diseases or abnormalities in the zooplankton grown in tanks with human urine, but we are looking for hormone residues and antibiotics, just to be sure" says Jana.
Human urine also has potential as an agricultural fertilizer. Studies into its feasibility and safety usually suggest that it is an acceptable alternative to chemical fertilizers, but concerns about disease transfer and recycling of antibiotics and hormones in the human food cycle have hampered progress.
- Golder, D. et al. Ecological Engineering 30, 326-332 (2007).