In-situ drying of faecal sludge in breathable membrane-lined collection containers

Drying of faecal sludge enclosed in a breathable, hydrophobic membrane laminate was investigated for the potential application of breathable membranes in decentralized container-based sanitation systems for developing nations. Moisture loss from the membrane-enclosed faecal sludge was studied using membrane ‘envelopes’ filled with faecal sludge collected from random volunteers. A drying test with a new membrane envelope resulted in 71.2% mass reduction over a period of 7 days with an average moisture flux of 0.73 g/day-cm². Slight decrease in the sludge drying rates was observed over five reuses of the same membrane envelope. A stagnant film model was used to predict drying rates of membrane-enclosed faecal sludge in ten developing countries with high urban populations. Based on a loading rate of 15 L/day into a 200-L (55-gallon) collection container, the predicted drying rates range from 7.1 to 12.4 L/day. The filling time of the membrane-lined container decreased due to in-situ drying, resulting in longer operation time and less frequent emptying of the container.