Network modelling for road-based Faecal Sludge Management

Improvements in the collection and treatment of sewage are critical to reduce health and environmental hazards in rapidly-urbanising informal settlements. Where sewerage infrastructure is not available, road-based Fecal Sludge Management options are often the only alternative. However, the costs of fecal sludge transportation are often a barrier to their implementation and operation and thus it is desirable to optimise travel time from source to treatment to reduce costs. This paper presents a novel technique, employing spatial network analysis, to optimise the spatio-topological configuration of a road-based fecal sludge transportation network on the basis of travel time. Using crowd-sourced spatial data for the Kibera settlement and the surrounding city, Nairobi, a proof-of-concept network model was created simulating the transport of waste from the 158 public toilets within Kibera. The toilets are serviced by vacuum pump trucks which move fecal sludge to a transfer station from where a tanker transports waste to a treatment plant. The model was used to evaluate the efficiency of different network configurations, based on transportation time. The results show that the location of the transfer station is a critical factor in network optimisation, demonstrating the utility of network analysis as part of the sanitation planning process.