Development and Optimization of Solar Fecal Sludge Dryer for Promoting Sustainable Urban Sanitation in Ethiopia

Abstract

From those not accessed to improved sanitation, 99% found in developing countries. Fast population growth, high urbanization and on site sanitation dependent with poor or lack of option for fecal sludge treatment are challenges for industrializing countries on the way of achieving improved sanitation. Urbanization without improved sanitation and dramatic fecal sludge reuse(disposal) in developing regions put urban residents and the environment at risk. Resource recovery approaches play a great role in the way of solving sanitation problems. The current study presents design, construction and evaluation of moisture content removal and pathogen inactivation efficiency of mixed mode passive solar fecal sludge dryer in Ethiopia. The drying system has two parts; solar collector and drying cabinet. The solar radiation was absorbed by both solar collector and through roof of drying cabinet simultaneously. The solar collector (air heater) used for absorbing sun light and convert to heat energy was improved by increasing contact of air with absorber and minimizing heat loss from solar collector. Fecal sludge sample was collected from pit latrine top layer to get high Ascaris eggs load and from vacuum truck to get high moisture content and mixed with equal ratio to get representative composite sample. Temperature in solar collector and inside drying cabinet are much higher than the ambient temperature during all the day. The useful heat energy gained from solar collector and drying cabinet was estimated 33% and ~ 4% respectively. The solar collector and system efficiency was also estimated as 34.3% and 26.2%. The drying rate determines as 3.3kg H2O/m2 day and 3kg H2O/m2day of covered and open air sun drying respectively. Pathogen inactivation efficiency of the system revealed thatcomplete inactivation in covered and 63.5% open air sun drying. This indicates that covered dryer is better than open air sun dryer in all parameters. From these, it is possible to reuse dried fecal sludge from covered dryingfor all purposes.