Based on the problems associated with the existing techniques for treating Blackwater, an innovative Solid-Liquid separation device for toilet interface has been  designed and developed for separating soiled water and faeces in the present invention. The developed device involves a unique engineering approach to reduce the  organic and nutrients loadings on sewage/wastewater and hydraulic loading on sewerage system. The device can be adjoined after flush passage so that it can be used as  a retrofittable attachment in the existing user interface (toilet seat) or in the new toilet closet. The invented Solid - Liquid separation device is compact, closed,  detachable and retrofittable.