System 7: Blackwater Treatment System with Effluent Transport

This system is especially appropriate for urban settlements where there is little space for onsite storage technologies and where the soil is not suitable for the infiltration of Effluent. Since the sewer network is shallow and (ideally) watertight, it is also applicable for areas with high groundwater tables. This system can be used as a way of upgrading existing, under-performing Collection and Storage/Treatment technologies (e.g. Septic Tanks) by providing improved, (Semi-) Centralized Treatment.

The success of this system depends on high user commitment concerning the operation and maintenance of the sewer network. A person or organization can be made responsible on behalf of the users. There must be an accessible, affordable and systematic method for desludging the interceptors since one user’s improperly maintained tank could adversely impact the entire sewer network. Also important is a well-functioning and properly maintained treatment facility. In some cases this will be managed at the municipal or regional level. In the case of a more local, small-scale solution (e.g., constructed wetlands), operation and maintenance responsibilities could also be organized on the community-level.

This water-based system is suitable for Anal Cleansing Water inputs, and, since the solids are settled and digested onsite, easily degradable Dry Cleansing Materials can be used. However, rigid or non-degradable materials (e.g., leaves, rags) could clog the system and cause problems with emptying and, therefore, should not be used. In cases when Dry Cleansing Materials are separately collected from the flush toilets, they should be disposed of in an appropriate way (e.g. (Surface Disposal (Solids)).

With the offsite transport of the Effluent to a (Semi-) Centralized Treatment facility, the capital investment for this system is considerable. Installation of an onsite Collection and Storage/Treatment technology may be costly, but the infrastructure required for Simplified and Condominal Sewers or the Solids-free Sewer network will be considerably less expensive than the design and installation of Conventional Sewers (Combined Sewers). The offsite treatment plant itself is also an important cost factor, particularly, if there is no pre-existing facility to which the sewer can be connected.

Guidelines for the safe use of of Sludge and Effluent have been published by the World Health Organization (WHO) and are referenced on the relevant technology information sheets.