In 2012 a trial of emergency compost toilets was conducted by WREMO. The fnding 

Report on a trial of emergency compost toilets, 2013

Report on a trial of emergency compost toilets, 2013 (PDF, 5.2 MB)

This report documents the findings from a trial of emergency compost toilets conducted by WREMO in 2012. The trial demonstrated that households and workplaces could safely and hygienically use a compost toilet exclusively for a month. Compost toilets therefore should be promoted as a viable toilet option in an emergency where sewerage systems are disrupted.

Based on this trial WREMO recommend compost toilets as the best option in 

Find out more about how to build and use an emergency compost toilets