Pre-treatment of domestic wastewater with pre-composting tanks: evaluation of existing systems.

A relatively new technology called pre-composting tank or Rottebehaelter, retaining solid material and draining water to a certain extent, has been found to be an interesting component of decentralised systems to replace the usual septic tank. Results of the investigation revealed that solid material which has been retained in the pre-composting tanks still contained a high percentage of water. However, there was no odour problem at and near the tanks. The pre-composted materials have to be further composted together with household and garden wastes for a year prior to their use as soil conditioner. The filtrate is further treated in a constructed wetland. One of the major advantages of this system compared to other systems, such as septic tanks, is that it does not deprive agriculture of the valuable nutrients and soil conditioner from human excreta and does not require an expensive tanker truck. It can be the most appropriate system for application in regions where there is a demand for local reuse of the end product. It has to be stated that maintenance is a crucial factor.