(Semi-) Centralized Treatment System
This is a water-based sewer system in which Blackwater is transported to a centralized treatment facility. The important characteristic of this system is that there is no Collection and Storage/Treatment.
The inputs to the system include Faeces, Urine, Flush - water, Anal Cleansing Water, Dry Cleansing Materials, Stormwater, and Greywater.
There are two User Interface Technologies that can be used for this system, a Pour Flush Toilet or a Cistern Flush Toilet. Dry Cleansing Materials can be handled by the system or they can be collected separately and directly transferred for Surface Disposal.
The Blackwater generated at the User Interface is directly connected to a (Semi-) Centralized Treatment facility by a Simplified Sewer network or a Gravity Sewer network. Greywater is co-treated with the Black water. Stormwater collected within the Storm - water drains can be input to the Gravity Sewer network, al though Stormwater overflows are required.
As there is no Collection and Storage/Treatment, all of the Blackwater is transported to a (Semi-) Centralized Treatment facility. The inclusion of Greywater in the Conveyance Technology helps to prevent solids from accumulating in the sewers. One of the Technologies T1 to T10 is required for the treatment of the transported Blackwater. The Faecal Sludge generated from the treatment of the Technologies T1 to T10 must be further treated in a dedicated Faecal Sludge treatment facility (Technologies T11 to T15) prior to Use and/ or Disposal.
All (Semi-) Centralized Treatment Technologies, produce both Effluent and Faecal Sludge. Technologies for the Use and/or Disposal of the treated Effluent include Irrigation, Aquaculture, 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
The capital investment for this system can be high; gravity sewers require extensive excavation and installation can be expensive, whereas Simplified Sewers are generally less expensive if the site conditions permit a condominial design. This system is only appropriate when there is a high willingness to pay for the capital investment and maintenance costs and where there is a pre-existing treatment facility that has the capacity to accept additional flow. Depending on the type of sewers used, this system can be adapted for both dense urban and peri-urban areas. It is not well-suited to rural areas. There must be a constant supply of water to ensure that the sewers do not become blocked. Users may be required to pay user fees to pay for the centralized treatment and maintenance. Depending on the sewer type and management structure (simplified vs gravity, city-run vs community operated) there are varying degrees of operation or maintenance responsibilities for the homeowner.
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.)