Can we recycle our used water?

08 May 2018

Interview with

Jonathan Bridge, Sheffield Hallam University

Reed filtration

Reed filtration

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Whilst the water treatment process is thorough, it’s also expensive. What if we could re-use some of our waste water without this huge amount of treatment? Like the water we’ve used for our morning shower or our washing up, - otherwise known as grey water. Izzie Clarke spoke to Jonathan Bridge from Sheffield Hallam University.

Jonathan - The sewage treatment process is able to be recreated quite nicely in a natural reed bed. By constructing a wetland environment where you allow your waste water to pass over some gravelly sandy zone and the settle out in a reed bed, you’re actually mimicking the exact processes which were used in an industrial scale. But, in principle, you could take the water that has come through your reed bed filtration system and put it back into your washing machine, into your washing up water, into these other uses which don’t require that very highest standard.

Izzie - Say this reed filtration system, in a big city say like Cambridge or London or elsewhere, that would probably be quite hard to handle?

Jonathan - It takes up potentially a lot of area, yeah. When we’re living cheek by jowl in high density urban environments or in apartment blocks, there simply isn’t the space to have that traditional extensive filtration system.

Izzie - Is there any way around that though?

Jonathan - Well yeah. People have been designing sort of green infrastructure, so green buildings which do incorporate these facilities. You may have seen buildings with green walls where you have plants planted all the way up the side of a building. Now that can be for several different purposes. It also has a cooling effect, and so it can be used for the building’s energy usage. But there are systems which have been essentially designed to do that same treatment train that we saw in the reed bed filtration system but vertically. You pump the grey water in at the top and it trickles down through the green wall being treated by these natural plant and microbial systems as it goes, so at the bottom of the wall you’d come out with that water that you can treat or directly recycle.

The technology and the ideas are there and people have designed entire skyscrapers built around this sort of technology which also incorporates food production and self-sufficiency on a large scale.

Izzie - So why aren’t we all doing this? It sounds amazing.

Jonathan - A problem with these vertical systems is what would happen if it went wrong? Because they’re new technologies we’re not sure what their limits and constraints are to things like overflow from a very heavy rainstorm or something else going wrong. And the problem there is the building, which relies on that treatment, suddenly doesn’t have a water supply for that type of water any more, so it’s potentially less robust or less guaranteed supply than are existing centralised water supply systems.

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