Sanitation technologies

In the last steps, we have looked at water sources and water treatment, and why they are important for achieving sustainable development in SDG 6. But another crucial element to this SDG, is how we can achieve improved sanitation for all. This is key to last week’s discussion on good health and well-being.

What is the aim of sanitation?

Sanitation aims to protect humans from contact with waste (particularly faeces) in order to protect public health from the spread of waterborne diseases. It also needs to protect the environment (surface water, groundwater etc.), as well as provide security and dignity for users. If we recall Step 3.2, which described the four generic ways that waterborne diseases can be transmitted, it is clear that the safe disposal and treatment of faecal excreta should break the life cycle of most vectors of such diseases.

How can effective and appropriate sanitation be achieved?

Effective sanitation needs to be considered as a linked system of processes – aka the sanitation chain – starting with the experience of the user, excreta and wastewater collection methods, conveyance of waste, treatment, and disposal or reuse.

Ultimately, the treatment of the waste can be achieved by facilitating the natural breakdown processes in a safe environment which is mainly driven by complex communities of microorganisms. This can be at a local level as in the case of a pit latrine, or in a more intensified manner in large-scale treatment plants through the addition of a continuous supply of additional energy. Pathogenic organisms and other contaminants are thus rendered harmless and ultimately broken down into constituent organics and nutrients which will then be naturally recycled back through the ecosystem.

There are many different approaches; from large-scale centralised sewer networks and treatment plants, which rely on significant quantities of water to move the waste, to more decentralised approaches (see Step 3.13 for an example) through to small-scale on-site systems using soil-based treatment, as discussed in Step 3.11 and shown in the figure below.

^{Percolation area being constructed for septic tank effluent in Ireland (left) and urine diversion toilet in South Africa (right). © Laurence Gill}

The “ecosan” approach

The sustainability of the overall sanitation chain can be improved if systems are designed to recycle as much of the water and material resources as possible.

This is the philosophy behind so-called ecological sanitation (or ecosan) for example, which is an approach that aims to “close the loop” (mainly for the nutrients and organic matter) between sanitation and agriculture in a safe manner.

This thinking includes interesting concepts whereby different waste streams are separated at source in order to aid in the re-use of effluent. Waste water can be separated into black water (faeces related), yellow water (urine related), and grey water (washing related). Most of the phosphorus we excrete, for example, is contained in our urine, and so the separation of this fraction enables this vital nutrient, which is predicted to be heading towards a global shortage (see article on The Story of Phosphorus below), to be more easily recovered.

The example of a VIP latrine

A VIP (or ventilated improved pit) latrine nicely illustrates some principles of appropriate sanitation, particularly in areas where open defecation may be the established norm.

First of all, the latrine, as illustrated below, enables users to deposit excreta below the ground, and not at the surface where children or animals can make contact with it or where it may get spread by heavy rain events. A flow of air down into the pit and then up the ventilation pipe is created by the draw across the extended ventilation pipe which removes any odours from the latrine, thus providing a pleasant facility which should encourage users. The superstructure building allows people to have security and dignity. The ventilation also means that any flies that might enter the pit attracted by the faeces will be drawn up the pipe and get trapped in a screen at the top of the pipe, thus preventing any further spread. Finally, the pit needs to be sited on adequate depth of free draining soil and also provide access for periodic desludging.

^{Schematic of VIP latrine (left) and photo in Democratic Republic of Congo (right). © Laurence Gill Click to expand.}

How can the aims of SDG 6 be achieved?

The first priority must be to ensure that the 2.4 billion people in the world who lack access to appropriate sanitation are able to access such facilities in an affordable and socially acceptable manner.

The cessation of open defecation is critical for ensuring public health, particularly in crowded urban environments.

As discussed, appropriate sanitation may initially involve getting excreta below the ground. The implementation of such practices and facilities requires a participatory approach with the target local communities, in addition to hygiene promotion activities (see Step 3.9). A sustainable financial model for the provision of such facilities is often more challenging to implement compared to the provision of a water supply where people feel that they are getting something tangible for their money. Hence, in many countries waste water treatment/sanitation systems are often linked to the payments made for the supply of safe water.

With respect to the sustainable development of more structured sanitation chains, factors such as energy and associated maintenance requirements in waste water treatment processes need to be evaluated, as well as what happens to any byproducts. A particularly challenging aspect here is faecal sludge management – see Strande, Ronteltap and Brdjanovic (2014) – for example, how to desludge and then deal with the waste from pit latrines.

The lack of large-scale sanitation infrastructure in many parts of the world today gives us many opportunities to develop more appropriate and sustainable systems for the future. This needs strategic thinking, taking into account lessons learnt from the past and more contemporary concepts of sustainability, in order achieve the goals of SDG 6.