Few urban infrastructure decisions cast as long a shadow as designing a sewerage network. Once laid, it is virtually impossible to replace or re-engineer. How a city plans for sanitation can have a major influence on public health, quality of life, environmental health, disaster resilience, climate footprint, budgets and much more for decades, even centuries, to come.
Despite this, sanitation systems often get little discussion or innovative thinking. A few cities, though, are demonstrating how sanitation planning can lead to far-reaching benefits for a city’s economy and long-term sustainability.
Ahead of Wednesday’s session on Citywide Inclusive Sanitation at the World Urban Forum in Abu Dhabi, here are some principles for sanitation planning in expanding urban centres, drawn from experiences in sustainable urban sanitation.
Plan for long-term functioning
It’s not uncommon that new urban sanitation systems – both conventional and innovative ones – fail within a few years. Perhaps the hardware was not a good match for the geophysical or climatic conditions. Perhaps it was overtaken by a growing population or changing land use. Equally it could be that, locally, no-one knew how to operate and maintain system; or that no agency had a clear mandate, and resources, to do the job.
The problem could also be in the households, who expected a different type of toilet, or found the operation and maintenance requirements too onerous or expensive. In the case of systems designed to recycle nutrients in excreta as agricultural inputs, perhaps farmers were not convinced about the safety, effectiveness or desirability of the reuse products.
These kinds of obstacle can usually be anticipated and avoided. An important part of the solution is to involve users and other stakeholders and experts in the planning and design process. Another is to pay at least as much attention to the legal, financial, environmental and socio-cultural aspects of sanitation as to health and hardware.
Part of the Jenfelder Au development, Hamburg. Photo:
Don’t lock out future sustainability upgrades
Sustainability ambitions change. Circular economy thinking is catching on, and human waste is increasingly being seen as a source of clean, cheap energy and agricultural inputs, boosting health, food security, livelihoods, livability, disaster resilience, nutrition . . . in short, contributing to most of the Sustainable Development Goals (SDGs).
But just like solid waste recycling, resource recovery from wastewater and excreta is far more economical and far more practical when the different streams are kept separate.
The most conventional, typical “off-the-peg” model for urban sanitation remains huge networks of wide-bore, underground pipes collecting household, commercial and industrial wastewater, along with stormwater, and channeling the resulting mix to a central municipal treatment plant. It is particularly unsuited to safe resource recovery, and almost impossible to retrofit for source-separation. Far better and more cost-effective to build in source-separation from the start.
A good example here is the new Jenfelder Au neighbourhood in Hamburg, Germany. The residential buildings are plumbed to allow greywater (from laundry, showers, kitchens etc.) and blackwater (only from toilets) to be collected and treated separately in decentralized treatment plants. Blackwater is mixed with other organic waste to produce biogas fuel for a combined heat and power plant. Stormwater, meanwhile, is treated in a water-cascade and pond system, meaning it is returned to the natural environment, while also buffering against floods. Treated greywater may in the future be returned to houses for flushing toilets and similar uses.
Also worth noting is the REVAMP tool developed by SEI, soon to be officially launched. REVAMP helps cities calculate the potential resources they could recover and reuse from sanitation and other organic waste streams and is designed to support multi-stakeholder collaboration on sanitation planning.
The conventional centralized, waterborne system isn’t always best
Centralized sewer systems connecting to flush toilets in every house and business have long been seen as the gold standard of urban sanitation. True, they often have economies and efficiencies of scale on their side, but not always. But other models may be more appropriate, easier and cheaper to manage.
One downside of centralized system is the huge capital outlay required, which has to be heavily subsidized – especially when the new residents are too poor to pay high services fees.
Another is their relative inflexibility, once they are in place. In fast-growing cities, change is a constant. Population structures and densities, land use, competing demand for water resources are all potentially in flux. Investment in a conventional, centralized system can be quite a gamble. Where periurban areas are urbanizing organically and unpredictably, there is a risk that new demand will either overload the central wastewater treatment plant – meaning waste is not effectively sanitized before it is released – or require building another centralized treatment plant.
Waterborne systems also rely on a plentiful, reliable supply of clean water. Not every city can afford to be pouring so much treated down the drain for decades to come.
An interesting response to these challenges is Montero municipality in Bolivia, where the utility has opted for a mix of sanitation solutions and plans to continue investing in both centralized wastewater management and different off-grid sanitation systems depending on what is technically feasible, in order to achieve access for all in the city by 2030.
Don’t make sanitation services a source of inequality
Context should be allowed to dictate what mix of centralized, decentralized and off-grid sanitation is best for a growing city or neighbourhood. But service provision should be equal and fair. For example, a 2012 study in Dakar, Senegal, found that off-grid households (who were provided with faecal sludge collection services) were paying five times more per capita for sanitation than were sewer-connected households. At the same time, around 96% of costs of providing sewer-connected services were subsidized by the utility, compared to only 13% for off-grid customers (who tend to be poorer).
All users, whether off-grid or sewer-connected, have a right to expect clean toilets with hand-washing facilities and provision for menstrual hygiene that don’t smell and don’t put them at risk of disease. Similarly, operation and maintenance staff along the service chain – including in resource recovery – staff, such as pit latrine and septic tank emptiers or anyone involved the service, should have all the necessary safety equipment and decent pay.
When it comes to public and institutional toilets, they have a right to privacy, cleanliness and to being able to use the facilities without risking physical or sexual abuse.
All of these are matters of design, of funding, of effective governance – along the whole sanitation service chain