Breathable membrane enclosures for faecal sludge stabilization : a paper presented at the second conference on developments in faecal sludge managem...

Breathable membranes are used in the process of membrane distillation to desalinate water. They are made of a hydrophobic material with pore spaces that only allow vapour transport. The objective of this research was to evaluate them for drying and stabilization of faecal and other sludges. A central feature of the membrane is that water vapour can be expelled due to a moderate temperature gradient. Other constituents, including both particulate and dissolved, are retained. In applying this principle to sludge, the heat from intrinsic biodegradation or from solar heat will gradually expel water vapour, to dry the sludge while preventing groundwater contamination. In order to utilize this concept with sanitation methods in rural areas, it was necessary to quantify the membrane's capability to pass water, as a specific flux rate which is dependent on temperature gradient and membrane type. Test methods were therefore developed to obtain the flux rates with either a vapour or aqueous phase across the membrane from the sludge. Flux measurements are reported with controlled temperature gradients between 0°C and 10°C. Applying only a 2°C sludge-air difference across the membrane gives low moisture content (over 90% solid matter) and 99% removal of faecal coliform within 6 days. With the sludge separated from water by the membrane, and a 2°C sludge-water difference, the removal of water is slower, but 99% faecal coliform die-off was attained within 21 days while 2/3 of the moisture is removed [authors abstract]