They’re not subjects that most people like to think about, let alone talk about, but poo and pee – human waste or excreta, if you’d rather – are facts of life, and how we as a society choose to manage them affects us all, whether or not we’d like to chitchat about it in polite society.

There’s good reason to carefully manage our poo, of course, as there are plenty of startling statistics demonstrating the danger it poses. The World Health Organization (WHO) claims that one gramme of faeces can contain 100 worm eggs, 1,000 parasite cysts, one million viruses and 10 million bacteria, which together can cause diseases including cholera, dysentery, typhoid, hepatitis A and diarrhoea. The latter, on its own, is responsible for 1.5 million deaths each year, mostly of young children in ‘developing’ countries.

It is for these reasons that, as part of its Millennium Development Goals (MDGs), the United Nations (UN) is aiming for 75 per cent global sanitation cover by 2015. Currently, around 2.5 billion people lack access to ‘adequate sanitation’ and in sub-Saharan Africa, fewer than a third of people are covered by basic sanitation. The figure is not much higher in southern Asia (36 per cent), where 1.1 million litres of raw sewage are dumped into the Ganges every minute.

In setting out the MDGs, the WHO estimated that achieving 75 per cent global sanitation cover would cost a hefty US$14 billion (£9 billion) annually between 2000 and 2015. Step forward Bill and Melinda Gates, who have, through their foundation, offered US$42 million (£27.4 million – not $14 billion, granted, but it’s a start) in ‘sanitation grants’ as part of their Reinvent the Toilet project. The foundation issued a challenge to researchers around the world in ‘an effort to develop “next-generation” toilets… that can capture and process human waste without piped water, sewer or electrical connections, and transform human waste into useful resources, such as energy and water, at an affordable price’.

While the funding has entered a second round, the winner of the first round of the Reinvent the Toilet Challenge was the California Institute of Technology for the development of a solar-powered, self-contained flush toilet that generates hydrogen, which can be stored in fuel cells to supply electricity, and sterilises human waste so it can be used as fertiliser.

The ‘winning’ toilet is surprisingly complex, given the stated aim of reaching billions at a low cost, and has received criticism from some quarters. Writing on TreeHugger, for instance, green design commentator Lloyd Alter notes: ‘By adding water you lose the valuable urine and you create a need to dry the poop… Also, it is hugely complicated. The idea that this could be maintained and operated in some of the poorest countries in the world is a serious stretch.’ The search for the ‘toilet of tomorrow’ continues.

Reinvent the Toilet winning design from the California Institute of Technology

When launching the Reinvent the Toilet project, Sylvia Mathews Burwell, president of the Gates Foundation’s Global Development Program, noted: “No innovation in the past 200 years has done more to save lives and improve health than the sanitation revolution triggered by invention of the toilet.” The received wisdom here is that having flush toilets connected to a centralised sewerage system marks an advanced state of affairs, but how does this ‘conventional sanitation’ fare when it comes to economics and the environment? The folly of using vast quantities of potable water to flush our wastes down the toilet is largely recognised, but it turns out modern sewerage systems could damage the environment (and our pockets) in other ways, too.

Forgetting early Roman counterparts, sewers are relatively new to the Western world – and finding this ‘safe’ way to manage wastes hasn’t come easy. Displaying an ignorance to the potential uses and harms of human faeces (but a real aptitude for naming things), for example, our medieval forbears would simply dump human wastes in the Thames (from Dung Pier) or pile it in huge mounds (one of which, covering 7.5 acres, was called Mount Pleasant). Urine, however, was a different matter, and this sterile, nutrient-rich substance was frequently used in the tanning, gunpowder, textile and cleaning industries.

Pre-industrial Eastern civilisations had complicated systems designed to keep human wastes away from water supplies and use ‘night soil’ as fertiliser; as Susan B Hanley writes in ‘Urban Sanitation in Preindustrial Japan’: ‘The most important difference between waste disposal in Japan and in the West was that human excreta were not regarded as something that one paid to have removed, but rather as a product with a positive economic value. The night soil of Japanese cities – and Chinese as well – was long used as fertilizer. With the growth of Japan’s population, the limitation of the amount of arable land and the increasingly intensified use of land to feed the growing population, combined with the relative scarcity of animal wastes and other fertilizers, meant that human waste had a value as fertilizer that far exceeded its value in the West.’

An 18th-century night soil carter's calling card

Looking back much, much further, we can discover the evolutionary reason why human wastes would make good fertiliser: prehistoric humans, like other land animals, would have simply deposited their wastes wherever nature called as they went on their nomadic way – forming part of the cycle that sanitation campaigner Abby Rockefeller has described as: ‘soil-to-bacteria-to-plants-to-animals-to-soil’.

The trouble was, once humans gave up the nomadic lifestyle (and vastly increased in number), such behaviour was no longer viable, and so the West moved from pit latrines or outhouses, to cesspools and vault privies. This system, in turn, caused further trouble: in addition to losing the nutrients in human waste, leaky cesspools could pollute drinking water. Thus, to avoid spreading disease through contaminated water, European and American cities began pumping fresh drinking water into homes, starting in the early 1800s.

This allowed people to use flush toilets, but also led to further complications; Rockefeller explains in ‘Civilization and Sludge’: “Of course, once water was in great quantities piped into homes, it had to be piped out again, and the first ‘logical’ place to pipe it, including the flush water from water closets, was backyard cesspools. These cesspools, which hitherto had received the contents of chamber pots – urine and faeces – now regularly overflowed with faecally polluted water, and a new level of horrendous odours and the spread of water-borne diseases was the immediate result.”

Epidemics of cholera actually increased when the temporary solution of connecting cesspits to open sewers was implemented, and so engineers eventually started creating systems of closed sewers to transport waste. Again, Rockefeller explains: “The engineers [in Europe and the United States] were divided again between those who believed in the value of human excreta to agriculture and those who did not. The believers argued in favour of ‘sewage farming’, the practice of irrigating neighbouring farms with municipal sewerage. The second group, arguing that ‘running water purifies itself’ (the more current slogan among sanitary engineers: ‘the solution to pollution is dilution’), argued for piping sewage into lakes, rivers and oceans. In the United States, the engineers who argued for direct disposal into water had, by the turn of the nineteenth century, won this debate. By 1909, untold miles of rivers had been turned functionally into open sewers and 25,000 miles of sewer pipes had been laid to take the sewage to those rivers.”

These days, 95 per cent of the UK population is connected to wastewater treatment works (there are 9,000 in the country), served by around 200,000 miles of sewers, according to Water UK, the representative organisation for all of the UK’s water and wastewater utilities. The impressive infrastructural feat doesn’t come cheap, though, and London, at least, is in need of an upgrade (or an alternative). London’s Victorian sewer system, designed by Joseph Bazalgette when residents of the capital numbered two million, is now struggling to cope with more than eight million users: the sewer’s 57 overflow points annually deposit 16 million tonnes of waste into the Thames. The contentious solution put forward by Thames Water is to build a 20-mile long ‘super sewer’ to collect 39 million tonnes of sewage a year from the 34 worst overflow points. The Thames Tideway Tunnel is expected to cost more than £4 billion – up from £2.5 billion when it was first announced, and almost twice the original operating budget of the Olympics – and is facing fierce opposition from residents near the proposed construction sites, who are angered by the prospect of three years of building works.

Modern sewers require complex infrastructure

And money’s not the only problem; Boston Globe writer Rebecca Tuhus-Dubrow outlines some other concerns with modern sewerage systems: “Annually, each of us produces about 13 gallons of faeces and 130 gallons of urine, which is instantly diluted into the 4,000 gallons we use to flush it. This large quantity of contaminated liquid further mixes with ‘grey water’, the water from the laundry, shower and sink, tripling or quadrupling the amount of water that must be treated as sewage in energy-intensive plants. In effect, the system takes a relatively small amount of pathogenic material – primarily the faeces – and taints enormous amounts of water with it.” Household wastewater is also mixed with discharges from industry so that by the time it reaches sewage plants in this country, less than 0.1 per cent of the mixture is actually something that requires treatment, according to Water UK.

We eventually realised that running water does not necessarily purify itself, and now we have quite complicated treatment systems that wastewater must go through before being released back into nature. Preliminary treatment involves screening to remove large articles, as well as settlement to remove grit and dirt. Then, primary treatment is also accomplished through settlement, which Water UK explains: ‘[T]he sewage flows into large round or rectangular tanks. In these the heavier organic material sinks to the tank floor and is swept by a scraper blade to a submerged outlet. From here it is pumped as slurry to a storage tank for subsequent treatment.’ Most of the biosolids thus removed, the remaining wastewater goes through secondary, or biological treatment. Biological filtration involves the sewage being distributed into two-metre deep circular or rectangular beds of stones, which provide an ideal environment for bacteria and other microorganisms to digest the remaining organic material in the water. Alternatively, ‘activated sludge’, a blend of microorganisms that again reduce the organic content, is added to the wastewater – this time in aerated tanks. Some plants also employ membrane separation, and some add extra steps to remove nitrogen and phosphorus, macro nutrients required by plants, but harmful to water life as, through ‘eutrophication’, they encourage excessive weed growth and algal blooms. Where ‘high quality effluents’ are required, tertiary treatments like sand or gravel filters, wetland filtering or ultraviolet disinfection might be used.

And the treatment doesn’t stop there. The solid sludge removed in the first process must also be treated. The vast majority of sewage sludge in the UK – 75 per cent – is now treated through anaerobic digestion (AD), while a significant proportion of the remainder is dried and incinerated. Following treatment, around 80 per cent of the UK’s sewage sludge is spread to land; Water UK says it ‘is a valuable product of the wastewater treatment works’, and an Environment Agency (EA) spokesperson assures me it’s safe. The EA’s website explains: ‘Approximately 3-4 million tonnes of sewage sludge is applied to land each year. Sewage sludge has been used as a fertiliser on farmland for many years and is not waste when tested, supplied and used in accordance with the Sludge (Use in Agriculture) Regulations.’ The regulations require that the sludge is tested for pH values and elements including phosphorus, nitrogen, zinc, copper, cadmium, lead and mercury. They also carry certain restrictions on the use of land to which sludge has been applied, including: not grazing animals or harvesting forage crops for at least three weeks; and not harvesting for at least 10 months any fruit or vegetable crops that are grown in direct contact with the soil, and which are normally eaten raw.

At first glance, this might seem like a great bit of recycling, especially as the AD process also generates biogas, but some are worried about the content of the sludge, as the human wastes have been mixed with household chemicals as well as industrial discharge before they head back to the land. The EA spokesperson explains: “There are both domestic and industrial inputs [mixed together in the sewers], with the industrial inputs being controlled and managed via Trade Effluent Discharge Consents that are issued and charged for by the Water Company that operates that sewer system… The input of hazardous substances is limited at source through the use of the Trade Effluent Consents.” Resource asked for more information about how often monitoring takes place, but did not receive a response.

And, despite assurances, some are still concerned. Laura Orlando, Adjunct Assistant Professor at the Boston University School of Public Health and Executive Director of the US-based Resource Institute for Low Entropy Systems (RILES), tells me why: “Once the hazardous materials partition into sludge, those that are hydrophobic will find the solids – they are essentially there to stay unless volatile. There is no way, unfortunately, to ‘treat’ sewage sludge to make it safe for use as a soil amendment or fertilizer…

“That which goes down the drain ends up in the sewer. More industrialised nations… will have greater amounts of hazardous materials in their wastewater. That is not to say sewerage in less industrialised places is free of toxins. Just go through the phone book, or drive through the capital and see what is dumping into the sewer. Shops that fix cars are dumping radiator fluid, photo processing places, the chemicals from their work, dry cleaners have their toxic load, etc. It doesn’t take heavy industry to make the wastewater poisonous…

“Bottom line, the pollution sink is the sewer. And the ‘treatment’ of this pollution is a public relations term, little else. (Sewage treatment has always been, and remains today, focused on reducing the nutrient loads, not on impacting organic chemical constituents).”

Orlando is calling for “honesty about the terrible pollution problems caused by sewers and its by-products: wastewater and sludge, [and] ecological infrastructure that is based in a prevention, life-positive framework”. Her organisation, RILES, advocates ‘ecological sanitation’, a concept which sees human wastes as resources to be used, ideally in closed-loop systems. The idea is to retain the nutrients in organic waste while preventing overuse of water (and unnecessary infrastructure), avoidingthe introduction of hazardous materials to the water systems, and simultaneously agricultural output.

A 'do-it-youself' compost toilet at Dial House, Essex

Orlando explains: “Ecological sanitation infrastructure starts with a prevention orientation, with health and ecosystem protection as its fundamental tenet. Sewers and sewerage are counter to this orientation.

“Source separation is a key mantra of ecological systems. There is no one system for urban environments, but a matrix of ecological systems, based on input, maintenance, and desirable outputs. Composting toilets are certainly part of that matrix, but do not stand alone in an urban environment.”

Urine diversion is often a key part of ecological sanitation, as it is urine that is rich in nitrogen, potassium and phosphorus (the main ingredients in common artificial fertilisers, which are increasingly difficult to come by through mining, and are valuable on land, but dangerous in water; their removal is the most energy-intensive part in wastewater treatment). Indeed, studies at the Swedish University of Agricultural Sciences have found that using urine on its own or combining it with wood ash is even more effective than using mineral fertilizer on plants. ‘Separating toilets’, in which urine and faeces go down independent pipes in a single bowl, are catching on in Sweden. (Sweden has also long had a ban on spreading sewage sludge to land, after brominated flame retardants were found in sewage sludge, and then also in food and breast milk.)

Other European countries are trialling ‘vacuum toilets’, which function like the loos on planes and require very little water. In Holland and Germany, projects have tested transferring the vacuumed-away waste to local biogas plants for immediate energy generation. Here in the UK, a company called Loowatt has designed an ‘off-grid’ toilet that mechanically seals human waste in a cartridge (with an ‘odour-inhibiting system’) for periodic emptying directly to anaerobic digestion plants. And perhaps the simplest of human waste technologies, which Orlando mentions, is the composting toilet, which sees wastes drop into a hole which is ventilated to prevent odour. In some versions, the liquid waste separates at the bottom of the hole and can be used immediately. Solids, meanwhile, need to be left to compost for at least a year before they turn into safe, ready-to-use fertiliser.

No one of these technologies will provide an answer to the human waste conundrum on its own, but Bill Gates and the other powers that be might want to take note of these and other already available options.