Wonders of waste

Our bodies are fantastic recyclers. We take what we need from food and excrete the rest. Our urine and faeces are replete in nutrients, including nitrogen and phosphorus, the staples of most chemical fertilisers. Profligate application of fertilisers should be more tightly regulated, especially because the excesses that run into rivers and oceans stimulate algal blooms that deoxygenate water, killing local ecosystems.

But farmers in impoverished regions have long known the benefits of spreading their own "night soil" on the land. Yet one disadvantage of human manure is that often it carries nasty microbes.

Enter the "peepoo" - a biodegradable, urea-laced plastic bag, marketed as a single-use personal toilet in places where sanitation is scarce. Over
a few weeks, ammonia released from the urea kills the germs, leaving the mineral-rich biomass, including extra nitrogen from the urea. There is enough phosphorus in the global human excrement-count to cover one-fifth of the world's fertiliser needs. Animal manure would
add twice as much again.

Micro-entrepreneurs in Africa are selling peepoos to individuals, who can then collect a refund by selling their product on as fertiliser. Nearly half of the world's population lacks a toilet and millions of people die from bugs in unsanitised faeces. "Stools-for-sustainable development" sounds good to me.