It seems like an environmental no-brainer. As populations increase, cities grow, and water supplies grow ever scarcer in the world’s drier regions, more and more municipalities are tending to recycle wastewater after treatment in sewage works to irrigate parks and other green urban space. What could be wrong with that? Well, quite a lot, actually, according to a new study, which concludes it could increase global warming.
The research, published in the current issue of the Journal of Environmental Quality concludes that the practice emits three times as much nitrous oxide – a greenhouse gas about 300 times more potent than carbon dioxide – as treating the sewage-laden water and discharging it to a river or the sea in the usual way. What is more – the scientists from the Universities of Cincinnati and California, Irvine, calculated the practice is so common in the region around Los Angeles that it emits at least a thousand times as much of the gas in the area than agriculture, the usual source of the pollution.
Yet Prof Amy Townsend-Small, who led the research, still supports the practice – sometimes dubbed “showers to flowers” because of its importance in eking out water supplies in Southern California. She also points out that drinking water has to be brought long distances to the area, which requires energy and thus gives rise to emissions of carbon dioxide.
Add the fact that climate change is likely to reduce rainfall in the area and thus make water in even shorter supply – thus increasing the need for recycling – and it becomes clear just how complicated an apparently straightforward environmental issue can be.
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