When we think of recycling it’s usually in terms of manufactured goods being converted back into raw materials for reuse. There are much wider applications, however, and in fact one of the largest and oldest recycling sectors doesn’t deal with manufactured goods at all. Instead it deals with a vital natural resource that’s plentifully available globally but, in a cruel twist of fate, often very scarce at a local level. That resource is water.
Water covers 71 percent of Earth’s surface, and the total volume on the planet is about 321 million cubic miles – an immense quantity. Unfortunately most of it is unusable as a resource. The main uses we put water to are drinking, agriculture and manufacturing, so we need liquid fresh water. Most of Earth’s water – 97.5 percent – is seawater, which is heavily loaded with salt and other minerals, and most of what’s left is frozen or otherwise inaccessible. Only 0.3 percent of the total is fresh surface water, and the demands of the growing population are putting this resource under huge strain. The problem is that most of the water we use is contaminated by that use. Recycling allows us to remove some or all of the contaminants and allow the water to be reused.
In practice all water is “recycled” through the natural water cycle, but deliberate recycling can hugely increase the available supplies. The aim is to allow water to be used more than once before it returns to the water cycle, and there are various ways this can be achieved. One of the simplest and oldest measures is the recovery of rainwater. Towns and cities have elaborate drainage systems to channel rainwater safely away, preventing damage to streets and buildings. This water picks up contaminants however, and is not safe to drink without considerable processing. However it can be used to irrigate fields or, after filtering, for many industrial uses.
Sewage is more of a challenge, as it contains large quantities of potentially hazardous waste. Since the 1920s sewage treatment plants have become increasingly sophisticated at allowing the water content to be reused. The most basic technique is to allow the solid waste to settle out, at which point the water can be released back into rivers; when it is extracted again downstream standard treatment methods can be used. Modern treatments usually process it further, either by chlorination or the use of bacterial cultures, to the point where it can be directly used for purposes other than drinking.
The latest technology can convert waste water directly back into extremely clean water suitable for drinking. Reverse osmosis, where permeable membranes are used to filter out any contamination, and ultraviolet disinfection are capable of turning heavily polluted waste into very high quality drinking water. An extreme example is the ECLSS system on board the International Space Station – this reprocesses all waste water, including urine, into safe potable water.
Many international relations experts predict that future wars could be caused by competition for water supplies. Already droughts can devastate agriculture and threaten millions of lives. If recycling can advance to the point where rivers can provide high quality water to every country they flow through this would go a long way to relieving these issues, so water should be one of the highest priorities for recycling.