Challenge of recycling wastewater | FT Rethink

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We are facing tremendous stresses in our natural water supplies. We've got to be smarter with the water we have.

How realistic is the notion that what's flushed down the toilet could be recycled into water safe enough to drink?

Oh, 100 per cent. 100% per cent.

There's nothing new about the need to conserve water. But more effective ways of using this precious resource more sustainably are emerging.

Water is usable and reusable, and it just requires a set of steps rather than throwing it away into nature.

San Francisco is a world leader in onsite water recycling, where buildings reuse their own water for non-drinkable use. It's a promising water conservation strategy and since 2015 has been mandatory here for any new building over 100,000 sq ft. This large residential and business complex is a typical example. By law, it must have a facility on site to treat and reuse wastewater that would otherwise go down the drain.

Co-developed by the San Francisco Giants baseball club, the $2.5bn Mission Rock complex promises shops, restaurants, and around 1,000 apartments. Their wastewater, including sewage or black water, won't be flushed away, but cleaned and recycled. Recycled water, what is it reused for?

Toilet and urinal flushing, piping within the buildings that need to have water in them at all times to keep odours from getting into places in the building that you don't want them, irrigation of the landscapes, and the lawns around the complex. To protect the public health there will be signage throughout the development.

Yeah, don't drink from the sprinklers.

Correct.

The modern systems that make waste, including sewage, clean and safe enough to use on the lawns are built around a biological process developed in the early 1900s that uses tiny to feed on solids suspended in the wastewater.

These are the bugs that we've grown. And at this point they are fully removing all of the organics that are in the wastewater, as well as all the ammonia. But the whole trick is to separate this out so that you have the bugs stay behind and the water goes out to use.

A multiple filtering process then removes the bacteria and other contaminants to produce water that's clear but, under current rules, not fit for human consumption. Even though it's not allowed yet, would you drink it?

Yes, and I would live to tell the tale.

On average, the manufacturer estimates the systems at Mission Rock could conserve more than 60mn litres of fresh water a year. But for the developers installing it meant additional costs of millions of dollars, with ongoing maintenance and operating fees on top.

It was a considerable cost, but ultimately it was the right thing to do from a long-term perspective. We then had to look at how we could creatively finance this.

But while reuse systems may be expensive up front, the city water authority compelling builders to instal them says they'll also save money, as well as water, in the longer term.

The return on investment for these onsite water treatment systems could be 10 years or less. They use less water. Their water bill and sewer bill will be less.

Ideally, recycled wastewater across the city could eventually be passed as fit for drinking, as well as plumbing, which could make systems even more cost-effective.

We decided to undertake a two-year pilot. We found that it is possible to treat water in a building scale, to take the wastewater and to produce water that's comparable to drinking water.

For many consumers, so-called toilet-to-tap processing may seem unpalatable, to say the least. But on the east side of San Francisco Bay, scientists and engineers are working to refine a process that's already in use hundreds of kilometres above the Earth. As explained in this NASA video, water is too heavy and expensive to be continually launched into orbit. So in the International Space Station, waste, including urine, has to be recycled into drinking water.

Astronauts use these technologies. And so if it's high quality water for somebody on a space station, surely it's good enough for those of us down on Earth. Some of these reused waters are actually cleaner than the drinking water people get out of their taps.

At Peter Fiske's Earthbound Labs, filtration techniques are tested at an atomic level.

We're doing some of our advanced research on one of the most important materials for water treatment, which are membranes. Membranes are used in reverse osmosis and infiltration. One of the most important things this team is doing is understanding the relationships between how you tweak the manufacturing of a membrane and its performance. We can then essentially give better recipes to membrane manufacturers, and that means we can make better membranes.

While cities like San Francisco look to have recycling technology installed in individual buildings, others are employing a different strategy. Around 1,000km to the southeast, water providers are taking a more centralised approach. Recycling sewage, or black water, is no pipe dream here in drought-hit Arizona. We're on our way to a $300mn rejuvenation that aims to do just that.

Mothballed after an economic slowdown in 2009, the Cave Creek treatment plant just outside Phoenix is to be resurrected into a new facility capable of turning waste, including sewage, into enough pure, potable water to supply 25,000 homes a year. Before the builders moved in, I met assistant director Nazario Prieto, who explained why the council moved ahead when regulations around public consumption were yet to be fixed.

Even though we're getting a little ahead of ourselves in terms of advanced purified water because we don't know exactly what the guidelines will be, it's been happening in places across the world already.

While consumers are used to drinking reused water from sources like the Colorado River, Nazario admits that water from sewage will be a big step for many.

We want to talk to those people that are 100per cent against it because we want to understand what they're thinking and why they're against it so that we can show them, no, look at the scientific evidence, right?

Turning wastewater into drinking water isn't new. For example, they've been doing it in Singapore for several decades. But due to consumer resistance, known as the yuck factor, globally, it's far from common. Around 80 per dent of the world's wastewater flows back into the ecosystem without being treated or reused, according to UN estimates.

The city of Phoenix aims to have Cave Creek up and running as early as 2026. Conventional treatment plants like this one at nearby Union Hills could then be used for distribution. But the extra equipment, energy, and maintenance required will come at a much higher cost than the initial $300mn refit.

They could range anywhere from $2bn to $3bn, right? But when you start looking at the cost to purchase water, like let's say on the Colorado River, those costs are going up significantly. One day we're going to look back and say, wow, that was a great deal.

Phoenix is one of many cities across the world with a growing population and growing demand for dwindling resources. While it may cost consumers more in the short term, it's almost certain that as the strain on the water supply increases, processing and reusing what's been drained and flushed away will become less of a choice and more of a necessity.