If architecture is 'design for living', one of its greatest challenges is how to live with the masses of waste we excrete. Four pioneers in green sanitation design outline solutions to a dilemma too often shunted down the pan.
Every year, on average, each of us excretes 50 litres of faeces, rife with pathogens and heavy metals. Multiplied by Earth's population of 7 billion — and rising — that constitutes not so much an elephant in the room as a herd of mammoths. Sustainable solutions are urgently needed, particularly for the 2.6 billion people who lack adequate sanitation and the 1.1 billion practising open defecation. Rich countries, meanwhile, often have hidden sanitation issues of their own.
There is no single design solution to sanitation. But there are universal principles for systematically and safely detoxifying human excreta, without contaminating, wasting or even using water. Ecological sanitation design — which is focused on sustainability through reuse and recycling — offers workable solutions that are gaining footholds around the world, as Nature explores on the following pages through the work of Peter Morgan in Zimbabwe, Ralf Otterpohl and his team in Germany, Shunmuga Paramasivan in India, and Ed Harrington and his colleagues in California.
In compost-based ecosanitation, excreta is reframed as a resource: fertilizer. Much of the research on this has focused on upping nutrient levels and finding faster, more effective ways of removing heavy metals and pathogens such as viruses. Meanwhile, research-based, ecological processing of waste water is vastly improving water-based systems, bringing them closer to the ecosanitation ideal.
Environmental sustainability is only part of ecosanitation, however. Defecation is as culture-laden as other behaviours, so the designs must also be socially sustainable — tailored to local customs and strictures, whether in Malawi or Manhattan.
The developed world may think it has cracked the problem, but trouble is gurgling away underground. 'Flush and forget' sanitation systems constitute one of the more bizarre hangovers from the Victorian age. In older toilets, up to 25 litres of drinking water go down the pan per flush, although 'low-flow' toilet designs are coming into their own and, in 1995, the US federal government set a 7-litre-per-flush limit.
Aside from wasted water, the faeces-laden 'black water' from flush toilets is not always treated. Many older US and UK sewage systems, for instance, mix toilet waste water with storm water in so-called combined sewage outflows, which can overflow after heavy rain. The US Environmental Protection Agency estimated in a 2004 report to Congress that 850 billion gallons of untreated water were entering US waterways every year.
Sewage sludge — the semi-solid mush left after wastewater treatment in sewage works — can be as problematic. Although it can contain significant traces of pharmaceuticals and heavy metals even after treatment, it is widely used in the West as a soil conditioner and fertilizer on cropland, with uncertain effects on human health.
In the packed cities and scattered villages of the developing world, the challenge is even more daunting. Thousands of children die every day from a lack of basic sanitation or clean water. Open defecation contaminates soils with the eggs and larvae of soil-borne intestinal worms, or helminths, as well as other pathogens. More than one billion people are infected with these helminths, which cause, among other problems, weakness and malnutrition.
So a toilet can be transformative. A clean environment means better health — and that, in turn, is a springboard to development. As governments debate the finer points of global development challenges at Rio+20 next week, they might find it worth asking why sanitation falls to the bottom of most policy agendas.
Peter Morgan: Inspired by ant turrets and the flight paths of flies
Environmental scientist and designer of the Blair VIP toilet, Harare
“The designer knows he has reached perfection, not when there is no longer anything to add, but when there is no longer anything to take away.” I recalled this anonymous quote when, as a young biologist in Rhodesia (now Zimbabwe) in the 1970s, I was working for the health ministry's Blair Research Laboratory — named after former health secretary Dyson Blair. Blair had persuaded me to change fields, from schistosomiasis control to technological solutions for public health, and tasked me with designing new toilet systems for use in rural areas.
Open defecation was then common, and the existing pit toilets bred blowflies of the genus Chrysomyia, as well as other fly species that carry enteric disease. In a survey conducted between March 1974 and April 1975, we counted more than 20,000 flies emerging from a single pit toilet.
It had long seemed to me that simplicity could be related to elegance of design. My first innovation, called the Blair toilet after Dyson (and later dubbed the Blair ventilated improved pit, or BVIP toilet), is simple: a pit, lined with bricks for stability; a concrete sanitary slab with one hole for squatting, and another fitted with a vent pipe stretching from the slab to above roof level; and a spiral superstructure that obviates the need for a door but guarantees semi-darkness (see 'Air traffic control').
The design harnesses natural principles. The turrets of ant nests — the most elegant of nature's chimneys — inspired the vent. The natural behaviour of flies, which are attracted by odour and light, determined the other design features. When air passes over the top of the vent, suction draws more air through the squatting hole into the pit, then sends the odours up through the vent. Some flies are drawn to those odours; others, entering the pit through the squat hole, are drawn to the light from the bottom of the vent. Either way, the flies are trapped and die, because the vent is fitted with a non-corrodable screen, usually made of aluminium.
The concept is simple and it works. From October to December 1975, weekly counts of fly output were taken from two Blair toilets and two unventilated pit toilets: a total of 13,953 flies were trapped from the unventilated toilets and only 146 from the ventilated toilets (P. R. Morgan Cent. Afr. J. Med. 23, 1–4; 1977). A family BVIP will last 10–15 years, and once it is abandoned, the superstructure materials can be recycled. The excreta gradually dries, and can be used as compost.
The BVIP is now the backbone of Zimbabwe's sanitation programme, with half a million family toilets built so far, and is widespread in other African countries. A multicompartment unit was designed for schools. More recently, I have drawn up a cheaper, upgradeable family unit, which can be built in stages — allowing them to ascend the 'sanitation ladder'.
I devised other toilets to speed up the composting process. The Arborloo is an unlined pit 1 metre deep, which is fitted with a circular brick or concrete rim and a sanitary slab. As it fills, soil, ash and leaves are added to accelerate composting and control flies and odour. After a year, the toilet superstructure is moved to a new pit, and a tree is planted in a layer of soil on top of the old pit, to provide shade, fuel or fruit. Thousands of these have been built in Malawi and about 70,000 in Ethiopia.
The Fossa Alterna is another variation: two shallow pits are dug and used alternately, swapping at annual intervals. By the time one pit has filled, the compost in the other will be mature and ready for use.
Perhaps working in an area for which I have not received formal training has given me freedom of expression in observing, exploring and researching. I had to use instinct and plain logic. And it pays to adapt natural principles honed over millions of years.
Ralf Otterpohl: Boosting compost with biochar and bacteria
Environmental engineer and director, Institute of Wastewater Management and Water Protection, Hamburg University of Technology, Germany
With my team in Hamburg, I have studied resource-oriented sanitation — in which waste is seen as reusable — for 15 years. I was drawn towards this path having started out mathematically modelling mass flows at large-scale wastewater treatment plants — a process I found frustratingly inefficient.
In 2010, I began to focus on a practice originating in Brazilian Amazonia more than 1,000 years ago that could, paradoxically, kick-start a modern revolution in composting sanitation. The pre-Columbian Indians created 'black' soils known in Portuguese as terra preta. Found in patches throughout the Amazon, they are composed of charcoal (biochar), composted excreta and other bio-waste. They are absorptive and high in nitrogen, phosphorus, potassium and calcium. At Hamburg, we are adapting this mixture for use in ecosanitation systems.
Systems using terra preta technology can help to solve two problems that plague many developing countries: poor soils and a lack of sanitation. The technology offers the efficient creation of well-structured, humus-rich compost, which is important for food security, resistance to soil erosion, water retention in soil and the growth of local agricultural economies. And it is cost-effective. A basic terra preta sanitation toilet costs about US$50, inputs are cheap, and it is not hooked up to sewage systems.
Terra preta sanitation is a three-step process. First, lactic-acid bacteria are added after each defecation: the anaerobic fermentation sanitizes and deodorizes. We have used cultures ranging from sauerkraut liquor to strains scientifically selected not to produce gas, such as Lactobacillus plantarum, Lactobacillus casei and Pediococcus acidilactici. At the same time, a waste-sugar source such as molasses or vegetable scraps is added as bacterial feed. This process continues while the excreta collect and for at least another week after collection ceases.
Second, about 50 grams of powdered charcoal — preferably 'clean', from wood-gas stoves — is added with each bacterial application to absorb odour and bind nutrients. This biochar also creates microporous space for the lactic-acid bacteria to inoculate the faeces and lower their pH value.
Finally, earthworms (vermiculture) compost the collected and treated material aerobically, further sanitizing the mixture over a period of three months to a year. The resulting compost is safe for use with non-food 'industrial' crops or forest trees. Two years of further processing creates compost that can be used on food crops.
Terra preta sanitation systems can be modified to suit rural or urban sites, but it must be possible to seal collection and transport receptacles for the fermentation to work. Rural versions can be simple bucket toilets fitted with a urine diversion, so that faeces drop into one bucket and urine is piped into another. Urine can be lacto-fermented separately with the bacterial mix for a month or more to avoid nitrogen losses and odours, then used as fertilizer, preferably on non-food crops. Alternatively, the urine can be used immediately after collection, mixed with at least five parts water.
For urban settings we are designing a new family toilet flushed with very small amounts of water, sprayed either manually with a bottle or through a nozzle attached to sink pipes. This toilet mixes faeces and urine. Because moisture impedes composting and the high nitrogen content must be compensated for with a carbon source, half a kilogram of woody waste must be added later at the composting site. This unit has a tank big enough for at least a week's worth of waste. The treated waste can then be collected and made into terra preta at a professional communal composting site.
Our research shows that these toilet systems and variations on the basic terra preta processes could work even in densely populated cities — a revolution indeed.
Ed Harrington: Building a coastal wetland in the heart of a city
General manager, San Francisco Public Utilities Commission, California, and former chair of the Water Utility Climate Alliance.
From the earliest planning stages, in 2009, for the new 13-storey headquarters of the San Francisco Public Utilities Commission, I knew the building would need to demonstrate the commission's ambitious sustainability goals — we needed to 'walk the talk'.
Water reuse was a central concern, but we quickly discovered that many decentralized water-reuse technologies were too energy-intensive for our building's energy budget. My team proposed that we pursue ecological sanitation methods inspired by wetlands, and challenge ourselves to defy conventional wisdom that the space such methods demand is too big for dense urban areas.
In our low-energy solution, wastewater treatment, which is usually buried in the basement, is visible — in the atrium and from the pavements where thousands walk every day. And we've done it in one of the highest-density neighbourhoods in one of the highest-density cities in the United States.
The building, which is expected to receive a leadership in energy and environmental design (LEED) platinum certification from the US Green Building Council in Washington DC, contains a sustainable, integrated water-management system that will serve more than 1,000 staff and visitors daily. The Living Machine system treats all waste water in the building for reuse in flushing toilets (see 'Water management wetlands style'). Rainwater is harvested from the roof and the child-care centre's play area for landscape irrigation. By treating and reusing all waste water on site in a self-contained system, we avoid discharging usable water.
Our system reduces total water use by about 65%, saving 3 million litres of drinking water per year. We anticipate eventually producing a surplus of 2.6 million litres of treated water for non-potable uses such as toilet flushing or park irrigation nearby.
The process begins and ends with low-flow toilets. After flushing, black water from the toilets is combined with grey water, from the sinks and showers, in plumbing pipes. The mixed waste water is then directed to tanks beneath the pavement for filtration; filtered solids such as faeces are pumped periodically to the municipal sewage system. From the tanks, the water is pumped into tidal-flow wetland 'cells', set next to the pavement and in the lobby, and disinfected using ultraviolet light and trace amounts of chlorine.
The cells are filled with gravel, bacteria and flowering grasses and plants — including Japanese sweet flag (Acorus gramineus) and western bleeding heart (Dicentra formosa). The plants were chosen for their root structure, which supports the establishment of treatment bacteria, and for resiliency in San Francisco's climate and urban environment.
The cells mimic the ecology and natural water-treatment processes of coastal wetlands, and are alternately flooded and drained to create multiple tidal cycles per day, speeding up the natural water-treatment processes by increasing the influx of oxygen. The system is responsible for recycling some 19,000 litres of water per weekday, but all people see is lush, vibrant plantings. It is a blend of function and aesthetics, as well as a demonstration of the ecological sanitation processes at work.
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