vol 7, issue 11

Time for a new design of loo?

19 November 2012
By Jason Goodyer
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A very basic toilet

Many developing countries lack even basic toilet facilities

Nano membrane toilet design

Cranfield University’s nano membrane toilet

The humble flushable toilet has barely changed in almost 200 years: it's a design classic. So why do four out of ten people still have no access to sanitary facilities? It's time to come up with a new loo.

The john, the khazi, the dunny, the can, the bog, the loo; whatever your preferred name for it, the humble toilet is so thoroughly integrated into life in the developed world it barely merits a second thought. When out shopping, in a restaurant or even camping, those looking to spend a penny are rarely more than a short walk away from a clean, sanitary, private place in which to answer the call of nature. Moreover, these eminently convenient public conveniences are often replete with modern accoutrements such as quilted toilet paper, rose-scented handwash and perhaps even a Dyson Airblade or two.

But for millions around the world this brand of lavatorial luxury is by no means the norm. Indeed, many don't even have septic tanks, dug-out latrines or even buckets. The Bill and Melinda Gates Foundation estimates that there are currently 2.6 billion people around the globe, that's a staggering four out of every ten people, without access to sanitary toilet facilities. What's more, one in seven people don't use any form of toilet at all, instead practising open defecation in woods, next to rivers and streams, or even on street corners. With a situation as desperate as this it doesn't take an expert in epidemiology to see how problems can quickly pile up. Every year 1.5 million children die from severe diarrhoea brought on as a direct result of the consumption of food and water tainted with fecal matter – more than die from HIV/AIDS, tuberculosis and malaria combined.

Birth of the modern loo

It's not as if these facts are not well known. Access to toilet facilities is seen as so important that it is often used as a key indicator in quality of life surveys, and in 1925 Indian statesman Mahatma Gandhi declared sanitation to be of more importance than political independence. Of course key to maintaining good hygiene is the storage and treatment of human waste. Since its invention some 300 years ago, the modern toilet has done more to rid the developed world of infectious diseases than practically anything else. Dysentry, cholera and typhus are all largely things of the past in the West thanks to the advent of city-wide sewerage pipes and effective water treatment.

Records show that indoor toilets existed in the Indus Valley more than 4,000 years ago, but it was in Britain in the 18th century that the toilet as we know it was truly born. A flushing system was invented by Elizabethan courtier John Harrington in 1596, but it was Alexander Cummings, a Bond Street watch maker, who was granted the first patent for a flush toilet in 1775. The now familiar siphon design was patented by Albert Giblin, an employee of Thomas Crapper, in 1819. Of course, the oft-quoted fallacy is that Crapper himself invented the flush loo.

Since then, little has changed. Water held in the S-bend prevents the worst of the smells from escaping, and the pulling of a chain or depressing of a handle opens a valve allowing water to gush into the pan from the cistern and wash away the waste.

Upon emptying, the cistern refills with water until a floating ballcock closes the inlet valve and the whole thing is ready to use again.

Toilet of tomorrow

If the developing world is to catch up with the West some serious innovation is needed. The modern flush-toilet requires a level of sewer infrastructure that is completely out of the reach of many countries. What's more. it relies on an abundant supply of clean drinking water, something that is a scarce and treasured resource across many of the poorer parts of the planet. This is where the Bill and Melinda Gates Foundation is hoping to change things.

In the summer of 2011 the foundation launched the 'Reinvent the Toilet' challenge calling on researchers and scientists worldwide to design the loo of the future. The stipulations were simple: the entrants must produce a toilet that is hygienic, sustainable, waterless, does not discharge pollutants and has an operating cost of no more than five US cents a day.

The challenge was initially answered by several universities from across the globe who shared $3m in funding. Among the designs chosen were CalTech's solar-powered hydrogen and electricity generating loo and Loughborough University's toilet that produces biological charcoal, minerals, and clean water. In August this year the foundation announced a second round of grants totalling nearly $3.4m. Among the recipients this time round were the UK's Cranfield University who received $810,000 to produce a prototype of their innovative nano membrane toilet.

"The concept is to develop a low-cost toilet technology for remote locations, or peri-urban environments to use the correct terminology," explains Professor Rob Dorey, chair in nano materials at Cranfield and part of the 13-strong toilet research team. "We have brought together a multidisciplinary team to develop this. The broad concept is that body effluent goes in one end and something nice and copeable with comes out the other end. Drawing across Cranfield's different capabilities we have people who are experts in water treatment, mechanical engineers who know about moving semi-fluid objects around a structure, and designers who can make it look pretty so it's not just a bunch of pipes and ugly looking things stuck together. Of course we also need to figure out how can we go about making it safe by neutralising all the nasties, the pathogens, found inside body effluent, and then finding a way to encapsulate the waste to make it carryable."

Poop and polymers

The solution proposed by the Cranfield team features a number of cutting-edge technologies that are light-years ahead of the acrid blue chemicals and pump flush that come to mind when thinking of a traditional standalone toilet. The titular nano membrane will be constructed from a dense polymeric material that enables the extraction of water from the stools and urine that flow in. The process requires a low vacuum-pressure to be applied via a user-operated handle, thereby thickening the resulting sludge by up to a quarter.

"The nano membrane is made from a polymeric material with a structure that gives it its very fine pore network," says Dorey. "It's basically a collection of tubes all bundled together. When you look at it it looks like the inside of a bungee cord, it's that kind of structure. But obviously there's a degree of nanostructure on the inside that, unlike a bungee cord, allows water vapour to pass through it. It is basically designed to extract'as much liquid as possible. So the nano membrane basically means that anything above a certain size cannot get through it. Water molecules can get through but bacteria and anything larger is too big to fit through so that stays within the solid waste stream. Imagine a membrane with solid waste coming through, water vapour and then condensation on the outside, and then out of the bottom comes a more solid structure which I describe as mildly moist Weetabix in terms of consistency."

Water vapour that is able to cross the polymer membrane is then brought into contact with a series of super hydrophilic beads where it condenses and flows to a distillate store for later use in irrigation or flushing. The resulting sludge briquettes are then enmeshed in a polymer web which is sprayed over the waste via electrohydrodynamic spray atomisation. In this process a high voltage is applied to a liquid supplied through an emitter causing a fine strand of polymer to be sent spraying out. This is then used to coat the waste.

"The moist briquette comes out of the bottom and is then encapsulated with a nanoscale polymer matrix," Dorey continues. "We want to contain said moist briquette in a suitable structure that can be handled safely. At the end of the day you will be able to open a hatch on the back of the toilet and pull out a bag of waste but you only want to touch the bag, not the waste within it. The reason we are using a nano matrix to contain it is because it will still be moist.

"We'd like to get more water vapour out of it. We don't want it to turn into a carrier bag full of squidgy waste. You can imagine what would end up in the bottom of that. We want it to still be able to breathe while still maintaining the strength so you can pick it up and carry it around."

The team also plans to incorporate material with antibacterial properties such as silver or titanium dioxide within this polymer to further lessen the chances of any bacteria passing through the membrane and into the environment outside.

With everything dried out and safely encased in an antibacterial nano polymer bag, the final piece in the picture is to figure out what exactly to do with the waste. Again, the team is not short of ideas.

"We want to make it so that the product that comes out does have a purpose," Dorey explains. "First, you could use it as fertiliser in the local area, or perhaps send it off to a central processing environment which will turn it into fertiliser on a larger scale. But another thing we are looking at is: can we burn it to then power this device so it literally becomes self-sustaining? So literally the only thing you put in is your body effluent, and you burn what comes out to power all of the gubbins inside. That way you don't have this reliance on external sources.

"Obviously, given the environment, a 13A plug socket isn't available just round the corner. Or you could even imagine a situation, given the correct infrastructure, where a representative of the power company would come around, pick up these bags every day and then they burn them for power in a more central facility."

Spend a penny, not hundreds of pounds

Another important consideration for the team is how the toilets will operate on a day-to-day basis in the peri-urban environments for which they are being designed. Key to this is making sure the toilet is as low-maintenance and user-friendly as possible.

"Ideally it's going to be quite basic technology, something that can be repaired in the field. Not something that has to go back to some fancy fabrication plant to be repaired," says Dorey. "The filtration process is carried about by a filter membrane and that has a finite lifetime but you will be able to just pull one out and put another in, almost like changing the toner in a photocopier. Also, the lifetime is predicted to be a number of years not just a few months of use."

Going one step further still, the team is also looking into the possibility of incorporating the recycling of carrier bags into the nano membrane spraying technique, cutting down the need for specialist external supplies even further and making use of an abundant resource.

"Part of the concept is obviously to try to make it entirely self-contained. And that makes it a lot more challenging. In terms of the nano membrane spider-web concept, part of the work is investigating whether or not we can use available resources in the field. One of the things that is readily available is carrier bags. So can we take old carrier bags, put them into the machine and then spin that material down? That's obviously a much more elegant method. Not only does it use waste resources but it also makes it much more self-contained so you don't need to buy in cartridges of the spray material.

"We are always working towards a unit that doesn't have a big dependence on spare parts. For the kind of environment where it is going you don't want to have to say here's our toilet and now you are stuck buying the consumables for it when you earn three pence a day. It's not really practical. We are thinking in broader terms."

The team hope to have a working prototype of the nano membrane toilet ready for testing next year. 

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Timeline: Toilets

2000BC

Archeologists have discovered indoor toilets existed in the Indus Valley 4,000 years ago.

206BC

In 2000 Chinese archeologists announced they had found a toilet in the tomb of a king of the Western Han Dynasty dating back to somewhere between 206BC and 24AD.

c100AD

Ancient Romans built elaborate sewer systems across their cities and linked to simple outhouses that discharged waste into the running waters of the Tiber.

1596

An early example of the flush toilet was invented and built for Queen Elizabeth I by courtier Sir'John Harrington.

1775

The first patent for the flushing s-bend toilet was issued to Alexander Cummings.

1819

Albert Giblin, an employee of the Crapper Company, patented the now familiar siphon toilet.

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