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Overall, Washi in India has undertaken some interesting research into the application of membranes in extracting the water element out of pit latrine whilst leaving the sludge and pathogens in situ within the pit.
A single membrane was found to clog with organic matter very quickly so a one stage process was not possible within the cost and design constraints. Their solution involves a three stage process, which has an impact on the devices design and how it can become a commercially viable scalable product.

First stage, a form of roughing filter to separate the highly contaminated effluent from the liquid. Washi tried a sand filter, a 800 µ cloth filter and a porous concrete filter. The sand filter clogged, the porous concrete gave poor results and the cloth filter worked best.

Second stage, activated carbon filters to remove the odour. No coliform reduction.

Third stage, a 5µ micro filter together with UV or a batch chlorination process to remove coliforms. The chlorination result were good but it required a long settling time and is fail to danger ie people will not buy the chlorine and discharge highly contaminated effluent.

Experiments were also carried out using aeration to increase treatment around the cloth filter.

The net result is a prototype continuous filtration process which can take effluent straight from the pit and discharge water which complies with India discharge standards. The prototype can has a discharge rate of 1.2 litres per minute.

For more info see https://waterforpeople.box.com/s/lz64ni9hqvkbe3x3j9taq2z6qpa0mnls