Non-Sewered Sanitation:

Assembling evidence for decision making in a dominant but underrecognised sector

6 Jun 2024 by The Water Diplomat

Non Sewered Sanitation

A new paper published in May in the journal Nature by EAWAG scientist Dr Linda Strande unpacks a promising area of research into non-sewered sanitation, underlining the urgent need to provide scientific evidence in an area which has long suffered relative neglect in the water, sanitation and hygiene (WASH) sector.

In the professional and scientific debates about sanitation there has regularly been a call over the past twenty years for a paradigm shift, in which attention is turned away from an exclusive focus on sewer networks to embrace the great variety of options for non-sewered sanitation. As the author argues, the reality provided to us through global monitoring by UNICEF and the WHO is that nearly half (46%) of the world’s population is not connected to a sewer system. Furthermore, this number is currently increasing at twice the rate of the number of connections to a sewer system.

This is an exciting area of research because these systems are not linked to large scale and long-term infrastructure development and maintenance plans in the way that is true of sewer networks. These systems could be more resilient to extreme weather events, reduce energy consumption and transport distances to treatment, be quicker to deploy in humanitarian settings, and increase the capacity of existing infrastructure. Therefore, scientific research is needed to support choices on a longer and more diverse menu of urban sanitation solutions.

However, there is currently a lack of systematic study of non-sewered sanitation systems that cuts across different technological designs or service delivery models. The reality is that such evidence as there is tends to focus on the analysis of a single solution. Therefore, there is an urgent need for research that is holistic and links together the insights that have already been made in different areas such as the nature of the wastewater collected, what happens to it during storage, the ways in which it is transported and treated, and the monitoring of the process as a whole.  The findings of this research are important first of all to enable acceleration of access to safely managed sanitation (SDG 6.2.) but also more broadly to enable more sustainable solutions which have reduced impact on areas such as (ground)water quality and global emissions of greenhouse gases.

The wastewater stored in on site systems is highly variable compared to sewer-based systems, and again more evidence for decision making is needed. There is information available on urine and its contents such as nitrates and phosphorus, but surprisingly little information on excreta, and some universal lessons need to be drawn about its safe management. For one thing, what is referred to as ‘containment’ in pit latrines and septic tanks is actually a misnomer because, the author states, in urban areas these are “ a chaotic mixture of inappropriately and haphazardly constructed containments, with no level of standardization”.

During storage, it is widely assumed that degradation or natural digestion will occur, but downstream treatment systems to which this sludge is transported  need accurate information on the matter that is being delivered. In fact some decomposition takes place in the fist few weeks, but this rapidly tails off after some time. Microbial activity also declines with time, but more information is needed to determine safe parameters for on site systems.

Within the sewage, water is an important component. The separation of urine, faeces and greywater can result in smaller volumes of less contaminated water, which is an important factor in determining design of systems as this reduces the treatment burden on wastewater. For the remaining solids, there is a general lack of guidelines on how they should be treated safely prior to possible use as a soil conditioner or for other applications.

At the level of monitoring, there is a common misconception that pathogens are made inactive during storage. In reality storage is not the same as treatment, and close monitoring of waste streams is important to enable the production of evidence for ‘safely managed’ sanitation. Similarly greenhouse gas emissions from wastewater in dense urban areas is directly related to the degree to which storage of the waste has enabled its decomposition. However, little evidence has been collected in this important area of work.

In short, the author argues, the global goals for sanitation will not be met with one technology solution alone. A knowledge base of different technological solutions need to be built up, following processes along their respective treatment chains. We need standards methods of analysis so that we can compare different systems with each other and monitor their performance. It is important to be able to collect information on both quantity and quality of the waste collected as well as its degradation or treatment over time. This is important also in the light of efforts to reduce the emissions of greenhouse gases as ell as to ensure that sanitation systems are climate resilient. Already, the rate of failure of existing systems appears to be high, and this is not just due to technology but also to a complex range of governance related issues which themselves also need to be looked at in detail. Ther have been rapid increases in scientific knowledge that is relevant to decision making in the subsector, but the involvement of researchers from across the world in the development of impartial and relevant solutions is essential for a fundamental shift from discourse to reality.