Biodigester in Households for Sludge Treatment

How can a ​biodigester ​be successfully ​implemented in ​a household to ​generate energy ​and treat ​faecal sludge? ​Which type of ​biodigester is ​the most ​convenient for ​a household and ​why?  ​ What are the ​challenges of ​using a ​biodigester at ​homes or even ​IDP camps? ​ I would ​appreciate ​examples of ​where this ​technology has ​been successfully ​used.  ​