Blackwater Treatment System with Sewerage
This system is characterized by the use of a householdlevel Technology to remove and digest settleable solids from the Blackwater, and a simplified or settled sewer system to transport the Effluent to a (Semi-) Centralized Treatment facility.
The inputs to the system can include Faeces, Urine, Flushwater, Anal Cleansing Water, Dry Cleansing Materials and Greywater. This system is comparable to System 5: Blackwater Treatment System with Infiltration except the management and processing of the Effluent generated during Collection and Storage /Treatment of the Blackwater is different.
There are two transport pathways for the Effluent generated from the Collection and Storage/ Treatment of the Blackwater. Similar to System 5, Effluent can be discharged into the Stormwater Drainage network for Use and/or Disposal as Groundwater Recharge, although this is not the recommended approach. The Effluent should be transported from a Collection and Storage/Treatment facility to a (Semi-) Centralized Treatment facility via a Simplified Sewer network or a Solids-Free Sewer network. An interceptor tank is required before the Effluent enters the sewer, or alter natively, this system can be used as a way of up - grading under-performing onsite Technologies (e.g. septic tanks) by providing improved, (Semi-) Centralized Treatment. Effluent trans ported to a (Semi-) Centralized Treatment facility is treated using one of the Technologies T1 to T10.
All (Semi-) Centralized Treatment Technologies, T1 to T15, produce both Effluent and Faecal Sludge, which require further treatment prior to Use and/or Disposal. Technologies for the Use and/or Disposal of the treated Effluent include Irrigation, Aqua - culture, Macrophyte Pond or Discharge to a water body or Recharge to Groundwater. Technologies for the Use and/or Disposal of the treated Faecal Sludge include Land Application or Surface Disposal.
Considerations
With the offsite transport of the Effluent to a (Semi-) Centralized Treatment facility, the capital investment for this system is moderate to considerable.
Excavation and installation of the onsite storage technology as well as the infrastructure required for the simplified sewer network may be costly (although costs would be considerably less than the design and installation of a conventional sewer network). As well, if there is no pre-existing treatment facility, one must be built to ensure that discharge from the sewer is not directly input to a water body.
The success of this system depends on high user commitment to operation and maintenance of the sewer network; alternatively, 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 interceptor (or septic) tanks since one user’s improperly kept tank could adversely impact the entire community. Also important is a well-functioning and properly managed Centralized Treatment facility; in some cases this will be managed at the municipal /regional level, but in the case of a more local solution (e.g. wetland), there must also be a well-defined structure for operation and maintenance.
This system is especially appropriate for dense, urban settlements where there is little or no space for onsite storage technologies or emptying. Since the sewer network is shallow and (ideally) watertight, it is also applicable for areas with high groundwater tables.
This water-based system is suitable for Anal Cleansing Water inputs, and, since the solids are settled and digested in one of the Collection and Storage/Treatment Technologies, easily degradable Dry Cleansing Materials can also be used. However, durable materials (e.g. leaves, rags) could clog the system and cause problems with emptying and therefore, should not be used.
References
- Elizabeth Tilley et.al (2008). Compendium of Sanitation Systems and Technologies (low res version). Department of Water and Sanitation in Development Countries (Sandec) at the Swiss Federal Institute of Aquatic Science and Technology (Eawag). (Provides a full overview of sanitation systems.)