Blackwater Treatment System with Infiltration

This is a water-based system that requires a flush toilet and a Collection & Storage/Treatment Technology that is appropriate for storing large quantities of water.

The inputs to the system can include Faeces, Urine, Flushwater, Anal Cleansing Water, Dry Cleansing Materials and Greywater. There are two User Interface Technologies that could be used for this system: a Pour Flush Toilet or a Cistern Flush Toilet. In the event that Dry Cleansing Materials are collected separately from the flush toilets, they can be directly transferred for Surface Disposal.

The User Interface is directly connected to a Collection and Storage/Treatment Technology for the Blackwater generated: either a Septic Tank, a Anaerobic Baffled Reactor (ABR), or an Anaerobic Filter may be used. The anaerobic processes reduce the organic and pathogen load, but the Effluent is still not suitable for direct use. Greywater should be treated along with Blackwater in the same Collection & Storage/Treatment Technology, but if there is a need for water-recovery, it can be treated separately (not shown on the System Template).

Effluent generated from the Collection and Storage/ Treatment can be diverted directly to the ground for Use and/or Disposal through a Soak Pit or a Leach Field. For these Technologies to work there must be sufficient space available and the soil must have a suitable capacity to absorb the Effluent. If this is not the case, refer to Blackwater Treatment System with Sewerage. Although it is not recommended, the Effluent can also be discharged into the Stormwater Drainage network for Use and/or Water Disposal - Groundwater Recharge. This should only be considered if the quality of the Effluent is high and there is not capacity for onsite infiltration or transportation offsite.

The Faecal Sludge that is generated from the Collection and Storage/Treatment Technology must be removed and transported for further treatment. The Conveyance Technologies that can be used include Human Powered E&T or Motorized E&T. As the Faecal Sludge is highly pathogenic prior to treatment, human contact and direct agricultural applications should be avoided. Faecal Sludge that is removed can be transported to a dedicated Faecal Sludge treatment facility:Sedimentation - Thickening Ponds, Unplanted Drying Beds, Planted Drying Beds, Co-composting, or Anaerobic Biogas Reactor. In the event that the treatment facility is not easily accessible, the Faecal Sludge can be discharged to either a Sewer Discharge Station or a Transfer Station. From the Sewer Discharge Station, the Faecal Sludge is transported by the sewer and is cotreated with the Blackwater flowing in the sewer network (Technologies T1 to T10). The Faecal Sludge from the Sewer Discharge station is released either directly into the sewer or at timed intervals (to optimize the performance of the (Semi-) Centralized Treatment facility).

If sludge is introduced directly into a sewer, there must be enough water to adequately dilute and transport the sludge to the treatment facility. From the Transfer Station, the Faecal Sludge must be transported to a dedicated Faecal Sludge treatment facility by a motorized vehicle (Technologies T11 to T15).

All (Semi-) Centralized Treatment Technologies 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, 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

This system is only appropriate in areas where desludging services are available and affordable and where there is an appropriate way to dispose of the sludge. This system can be adapted for use in colder climates, even where there is ground frost. The system requires a constant source of water. The capital investment for this system is considerable (excavation and installation of an onsite storage Technology), but the costs can be shared by a number of households if the system is designed for a larger number of users.

This water-based system is suitable for Anal Cleansing Water, and since the solids are settled and digested onsite, easily degradable Dry Cleansing Materials can also 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.)