One-third of the global population relies on non-sewered sanitation. In urban areas of low-and-middle income countries, treatment of faecal sludge is often insufficient. On-site sanitation technologies can provide sustainable and more affordable sanitation solutions for urban areas, but only if functioning faecal sludge management is in place. As a first step for treatment, faecal sludge is dewatered, resulting in a solid stream and liquid stream. There are many existing technologies to treat the solid fraction. However, treatment technologies for the liquid are often insufficient and land-intensive. This liquid after dewatering of faecal sludge is called ‘supernatant’. The reason why treatment of this supernatant is difficult, is because the composition is prone to variability.

In conventional sewer-based wastewater treatment, attached growth processes have proven to be robust to influent variability. Those technologies do not take a lot of space, which is an advantage in urban areas. Attached growth processes are aerobic treatment processes in which the biomass responsible for treatment is attached to some type of medium. This research is a proof of concept whether an attached growth system, in this case an MBBR process, could be an alternative for existing supernatant treatment technologies in non-sewered sanitation. A 5000 people urban community-scale scenario is considered, covering variability in influent composition and intermittency in faecal sludge supply.

To prove this concept, there is looked whether COD and N removals can be achieved to certain discharge standards.
First there is assessed whether the MBBR is able to run on one type of supernatant. After this, the variability in influent composition regarding COD/N ratio, salt ratio, and pH is tested by spiking the baseline supernatant. Intermittency in influent supply to the reactor is also tested. After these separate experiments, a realistic scenario is tested with supernatants from different types of sources, and intermittent supply over the weekend.

As a conclusion, the concept of using an MBBR for treatment of supernatant after dewatering of faecal sludge is proven for a community-scale scenario of 5000 people, and further research has to determine new outcomes like the possibility of pathogen reduction and phosphorous removal. After this, field tests need to determine the actual feasibility full-scale in non-sewered sanitation setting.