by Roma Agrawal
As a result, Singapore is busy engineering a solution to its somewhat precarious situation. The Public Utilities Board (PUB) has developed a strategy called ‘Four National Taps’. This refers to the four sources of water it will harness as efficiently as possible to provide a high degree of self-sufficiency for the country.
The first National Tap is rainwater. Singapore’s location and exposure means it receives over 2m of rain every year. To conserve it effectively, engineers have created water catchments: areas of land where rainwater is collected rather than being allowed to drain away into the sea. A network of canals and basins has been built to trap the rain and channel it into dammed streams or reservoirs for storage. This has involved a massive clean-up operation, as over time many of the country’s streams had become polluted by discharge from homes and businesses. So the PUB relocated polluting businesses and set about legally protecting the water stores from contamination. Rainwater is now being collected and stored in two-thirds of the island’s land area. A few streams remain to be dammed – mainly those close to the sea, which have slightly salty water (which wouldn’t be usable without some treatment). But once the engineers have finished, a massive 90 per cent of the land will be used, making Singapore the only place in the world that collects and conserves virtually all of its rainwater.
The second National Tap is water from Malaysia, which Singapore will continue to import until the agreement runs out. The third National Tap is recycled or reclaimed water. Although the practice of recycling waste water is not new – Los Angeles and other parts of California have been doing it since the 1930s – it is still far from commonplace.
Singapore first started thinking about recycling waste water in the 1970s, when the appropriate technology was still too costly and relatively unreliable. Eventually, however, it improved to the point where the project became viable, so now waste water is collected from homes, restaurants and industry and subjected to a three-stage purification process, using the latest in membrane engineering.
The first stage is microfiltration, during which the water is passed through a semi-permeable membrane. This is typically made from synthetic organic polymers such as polyvinylidene fluoride, which allow certain atoms or molecules to pass through but not others, and filter out solids, bacteria, viruses and protozoan cysts. Essentially, the membranes are microscopic versions of a colander, holding onto solids but allowing liquid to drain through. The water that escapes still has dissolved salts and organic molecules in it, so the second stage of recycling is designed to remove these, using a process called reverse osmosis.
Osmosis is the movement of a solvent (a substance that can dissolve others – the most common example is water) from a less concentrated solution to a more concentrated one, until the two concentrations are equal. It is an important part of our natural world – the means by which plant roots absorb water from the soil, for example, and by which our kidneys extract minerals such as urea from our blood. You can see the process in action for yourself, using an egg, vinegar, and treacle or corn syrup. First, soak the egg in vinegar for a couple of days, to dissolve the calcium in the shell and leave what is in effect an osmotic membrane. Then put the egg in treacle or corn oil. Over the next few hours wrinkles will appear in the surface of the egg as water leaves through the membrane, dehydrating the egg in the process. Remove the shrivelled egg and put it in fresh water, and you’ll see the process reverse, as water goes into the egg via the membrane, plumping it back up.
The process of osmosis.
Osmosis happens naturally: fresh water filters through to mix with salty water easily. But if you want to produce more fresh water, you need to use pressure to ‘push’ the salty water through the membrane, which blocks the salt, bacteria and other dissolved matter. The pressure you apply needs to be bigger than the natural osmotic pressure, so you can force fresh water molecules through the semi-permeable membrane. This is reverse osmosis.
The process of reverse osmosis.
Reverse osmosis can remove up to 99 per cent of dissolved salts and other contaminants. So while the water coming out of this process is already of a high quality, there might be a few bacteria or protozoa still in it. As a backup, the water is disinfected using ultraviolet light to kill off any remaining microorganisms, and then it is ready to be distributed.
In 2003, after years of testing, NEWater – which is what the recycled water is called – was introduced to the public. During the parade of Singapore’s 37th National Day, the Prime Minister, Goh Chok Tong, the founding Prime Minister, Lee Kuan Yew, and the thousands of people attending all opened a bottle of NEWater and sipped it while the cameras rolled. No one got ill. In fact, NEWater is used mostly in industrial estates and fabrication plants that require water of an even higher quality than drinking water. NEWater has passed over 100,000 tests and actually surpasses the World Health Organization’s requirements for water that’s fit for human consumption – even if its origins make you squirm.
And finally, the fourth National Tap is seawater. In 2005 Singapore opened its first desalination plant in Tuas, where seawater is first filtered to remove the largest particles, and then put through reverse osmosis in much the same way as for NEWater. The result is pure water, to which the minerals we need to stay healthy are added, before it’s supplied to homes and industries. The Tuas plant can produce 30 million gallons of water (130,000m3) a day. The third and fourth National Taps already produce more than 50 per cent of the country’s needs. By 2060 it’s projected that the scheme will account for about 85 per cent – a spectacular and potentially life-saving transformation brought about by clever planning and engineering.
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That Singapore collects most of its rainwater for reuse and is planning for long-term water sustainability demonstrates how engineering can solve critical, real-world problems. It’s an age-old challenge, involving the most basic and essential of molecules, but one which is now being addressed using some of the most advanced technology available. As time goes on and our global population increases – and with it the demand for water – engineers and scientists across the planet will have to confront the escalating challenges of locating this precious liquid, creating new pathways to channel it, and enhancing the science to purify it.
Otherwise, we will not survive.
CLEAN
My visit to Japan in 2007 was one of the most memorable and inspiring trips I’ve been on. My mum and I wandered the streets of Tokyo marvelling at the vending machines that dispensed eggs, fruit, ramen and even puppies, and we ate at sushi restaurants where enthusiastic chefs and waiters shouted out everyone’s orders in a harmonious chorus.
I was also intrigued by the toilets, which played music, and which featured buttons that lit up, and cleaning sprays that automatically sanitised, making a normally mundane act an exciting affair. In my experimentation, I did press a few buttons and regretted it pretty quickly – but, hey, I felt cleaner afterwards, if a little violated. When we left Tokyo for more remote locations, we encountered much more basic squat toilets: it was a stark contrast – but nothing compared to medieval Japan.
Long before the Tokugawa shogun regime (1603–1868) was established in the country, solid human waste – euphemistically known as ‘night soil’ – was being traded. It was loaded onto ships that sailed all around Japan, distributing it. Unsurprisingly, the ships carried a rancid stench with them, and people complained about these fetid vessels being docked alongside ships carrying tea. Magistrates, however, decided that the trade was vital, and that people would just have to deal with the stench.
Trading human faeces was important because of the particular challenges this small island nation faced. Because of its topography, Japan had little land for growing crops, yet the population was booming and increasing food production was essential. So the land available for agriculture had to be used intensively to produce enough food, with more than one harvest per year. This meant that the natural nutrients of the soil were rapidly becoming depl
eted. Traditionally, the Japanese had turned animal waste into fertiliser to replenish the soil, but there weren’t many animals on the island, so the inhabitants had to look elsewhere for a solution. They found the answer in their own sanitation: the burgeoning population created a lot of waste. So the Tokugawa shoguns decided to make a virtue out of necessity by removing the waste to ships, and then trading it with farmers looking to boost their crops.
The turd trade was soon big business. During the early years of the Tokugawa shogunate, the country began to depend on one of the biggest cities at the time, Osaka, for fertiliser. Boats laden with vegetables and fruits would arrive in the city and exchange their produce for its citizens’ night soil. However, the value of the night soil quickly increased (inflation affects faeces too, apparently) and vegetables were no longer enough to pay for such a valuable commodity: by the early eighteenth century, people were buying it with silver. Laws came into force stating that the rights to faecal matter produced by the occupants of a dwelling belonged to the landlord, though they were generous enough to assign the rights of urine to the tenants themselves. The price of faecal matter from 20 households a year amounted to the same as the cost of grain one person would eat annually. Night soil was by now an integral part of the housing market: the more tenants that landlords had, the more waste they could collect, so the cheaper the rent.
Eventually farmers, villagers and city guilds were all fighting over rights to buy night soil. By the mid-eighteenth century, lawmakers in Osaka assigned ownership and monopoly rights to officially recognised guilds and associations that would determine a fair price. Even then, the high prices crippled the poorer farmers, and people risked harsh jail terms by turning to theft.
Night soil collection may have become a cause of conflict, but it had some unexpected benefits, too. Because waste was collected so obsessively and carefully, the water sources people used to collect drinking water were less likely to be contaminated. Other cultural practices helped: the Japanese drank most of their water in the form of tea – boiling the water got rid of many disease-causing microbes. And those who followed the ritual practices of Shinto, had strong views about sources of uncleanliness – blood, death, illness – and ‘purified’ themselves if they came into contact with anything unclean. All this meant that life in Japan in the mid-seventeenth to mid-nineteenth centuries was more sanitised and hygienic than in many countries in the West, and the Japanese suffered lower mortality rates as a result.
The twentieth century was different. With the constantly growing population and the Second World War causing devastation (not least in economic terms), the good quality of life people had enjoyed deteriorated. In 1985 only about a third of communities had modern sewage systems – a lag caused mainly by the success of the pre-modern methods for dealing with waste. In the 1980s the sewage network was modernised, and nowadays the Japanese are famous for their advanced toilets, in extreme contrast to the night soil trade that flourished not so long ago.
Whether in modern times or the distant past, the way in which a city deals with its waste has been an indicator of how successful and enterprising it is. Almost every home in the cities of Harappa and Mohenjo-daro in the Indus Valley Civilisation (around 2600 BC) was connected to a water supply and had a flushing toilet. In our densely packed post-industrial cities, efficient waste disposal has always been of vital importance. As Florence Nightingale (whose hygiene initiatives revolutionised Victorian hospitals and homes) acknowledged in an 1870 Indian Sanitary Report: ‘The true key to sanitary progress in cities is, water supply and sewerage.’ Those of us lucky enough to have a great sanitation system rarely give a second thought to where our poo goes once the toilet flushes. Those that don’t, on the other hand, are all too aware of the disease and death that festering waste can bring. It might be a subject that makes most of us squeamish, but as the population of our planet rockets, adequate sanitation is becoming increasingly important.
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‘The trouble is,’ said Karl, ‘no one gives a shit about poo.’ He stormed off.
At the time, I was working on the design of a small apartment building near Oxford Street in central London. While I was busy arranging columns around the car-parking bays and the swimming pool in the basement, my drainage-engineer friend Karl was working out how much waste water would be produced by showers, sinks and toilets inside the building, and by rainfall outside. Once he had calculated the amount of flow per hour, he had to make sure there were enough pipes to convey it into London’s sewage system. From historical records, we knew there was a large sewer adjacent to our structure, but we didn’t know exactly how big and full it was, or whether it was in reasonable condition. We wanted to know if we could use it to discharge waste from our structure, but also if digging the basement near this sewer would damage it. Karl had written to a survey company to gather information about the pipe so he could complete his design.
One day, Karl turned up with a DVD and, without much explanation, asked me to feed it into the computer and press play. Almost at once I shrieked and scrambled to turn the thing off. Among my colleagues, in the middle of my office, on my computer screen – which suddenly seemed enormous – were being displayed the results of the sewage survey. I hit the stop button and told Karl I wouldn’t watch it – and that’s when he told me off and strode away.
Chastened, I sat down, took a deep breath and clicked play. The film was shot by a small camera mounted on a robot on wheels being driven through a sewer wirelessly by someone standing safely on the ground. The brick walls were a deep red colour and looked pretty clean despite the unappetising contents that had flowed through them for the past 150 years. The sewer was surprisingly large – I could have walked through it without crouching – and fashioned into a distorted oval a bit like an egg standing on its narrow tip. This shape helps waste to flow easily – in times of low flow, the speed of the effluent is high since it’s in the lowest and narrowest portion of the sewer; at high flows, the larger crown creates space.
The amazement I felt watching this robot moving through a landmark piece of engineering easily overrode any feelings of queasiness I had at seeing what lay at its bottom. Over the next week, Karl and I (having quickly put our faecal fracas behind us) studied the film in detail, and decided that the nearby sewer was intact and in good condition, so waste from the new building could be discharged into it. (We couldn’t simply dump it all in when it suited us because of the risk of overwhelming the sewer. So, like in many buildings in London, we created an ‘attenuation tank’ in the basement where the waste is stored and released into the pipe at an acceptable rate.) It was an exciting moment for me: I was creating a real physical link to the pioneering engineering work done by Joseph Bazalgette more than a century ago, when he envisioned and built a vast network of sewers under the capital. At that time London sorely needed such a system, for in the early nineteenth century, living in London was a very disgusting experience.
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Originally, the plains of London were served by a number of tributaries that provided plentiful water and fish on their path to the River Thames. But as the population of the city increased considerably in the mid-thirteenth century, the quality of the water deteriorated. Things got worse until, eventually, the tributaries were nothing more than open sewers and dumping grounds for animal and even human corpses. By the fifteenth century, ‘water carriers’ made a livelihood for themselves collecting water from wells in two barrels tied to a stick across their shoulders, but the rivers were in such a state that even going upstream didn’t help. The water the citizens of London were drinking was contaminated with their own waste, and dead bodies.
The city also housed 200,000 cesspits – cylindrical pits, often lined on the inside with bricks in an attempt to keep them watertight, about 1m in diameter and twice as deep, with a sealed base and a lid at the top. Their purpose was to store human waste: people would take the chamber-pots they had used to relieve themselves, and empty them into these tanks.
It was then the job of the ‘nightmen’, ‘rakers’ or ‘gong-farmers’ (‘gong’ was apparently a medieval term for a latrine) to periodically clean these out, carrying the waste in buckets to fields. This was better than having the waste in the streets, but it was still decidedly unhygienic, given that the fields weren’t especially far from central London. Cleaning the pits was obviously unpleasant work, but it was also dangerous – spare a thought for Richard the Raker, who in 1326 fell into a cesspit and was asphyxiated and drowned in a putrid mix of urine and faeces.
Attempts by the Commissioner of Sewers to pass Acts to build new sewers in the 1840s remained inadequate. Introducing ‘water closets’ (or the modern-style water-flushed toilets) only made the situation worse: the leaky cesspits had been barely adequate to hold concentrated waste, but now litres of water were being emptied into them, flooding them. In 1850, to try and overcome this, the pits were banned, but as a result the sewers (which were only designed to take away surface water from rain) became completely overwhelmed. All waste – human and other – ended up in the Thames, which was still used by people for washing, cooking, and drinking.
The vile mixture of waste and water in London led to severe and devastating cholera epidemics. They usually struck in late summer or autumn, and half of the people who contracted the disease died. The outbreak in 1831–2 killed more than 6,000 people; it was followed by two more major outbreaks in 1848–9 (just over 14,000 dead) and 1853–4 (another 10,000 fatalities). The common belief at the time was that cholera was airborne and that you contracted it by inhaling a poisonous ‘miasma’. But during the 1854 outbreak Doctor John Snow (1813–1858) monitored the health of people drawing water from a contaminated pump in Soho, and collected evidence that this was not the case: cholera was, in fact, spread by contaminated drinking water.
