Flow Separation

Decentralized solutions, especially at on-site level, would allow for separation of the generated wastewater flows at the source and possibility for reuse of the separate streams or all of them. The separation includes two pipeline systems for gray and black water. It is clear, that the implementation of flow separation in existing buildings will require a total renovation of the plumbing system. Therefore, it is advisable to incorporate the flow separation during the construction process, or in cases of general renovation.

An illustrative video clip is shown below. In the clip, the case of a hybrid system is demonstrated, and also, clean water of drinking water quality is termed "white" water.

Gray water is the wastewater generated from washing and bathing appurtenances. It is of lower level of pollution and requires minimal treatment before it could be reused for different purposes or disposed. As shown in the video clip, it can be combined with rain water from roofs and reused for irrigation or other purposes.

Black water is the water generated by toilets. Wastewater generated by kitchen sinks can be directed to the black water flow due to the oils, fats and particulate materials contained. If it is directed to the gray water flow, a preliminary treatment (sedimentation or screening facility) would be needed. Black water contains more substantial pollution from human waste and requires higher level of treatment to make the water quality suitable for reuse or discharge. In hybrid systems, black water can be directed to an existing sewer and treated together with the municipal wastewater.

Urine separation – in some applications, the flow segregation includes 3 separate plumbing systems – gray water, black water, and urine. This requires the installation of special urine separation toilets, which allow the separation of urine from faeces. The urine is collected in storage tanks and disposed as fertilizer (Fig. 6). The reason behind this scheme is that urine, containing a high concentration of ammonia, inhibits the black water treatment. On the other hand it is a natural fertilizer. This scheme is not applied widely. In many cases it is not accepted well by the public. Its application in urban areas would require a system for collection, storage and treatment of the urine.