Impact of greywater reuse on black water quality

Greywater recycling is viewed as a promising option to help bridge the enlarging gap between supply and demand in water stress areas. However, greywater recycling may negatively impact the strength and flow of the black water, which may complicate its treatment. In this paper, the impact of greywater recycling on the black water strength and flow have been investigated for three different wastewaters from Greece, Jordan and Oman, which exemplifies three different socioeconomic cases. Seven scenarios have been investigated for the Greece case, while four scenarios have been investigated for each of the Jordan and the Oman cases. The number of scenarios for each case is mainly dependent on the number of possible independent combinations of all greywater streams that can be recycled. The results showed that the black water strength and flow are slightly impacted by greywater recycling for toilet flushing. However, when greywater is recycled for irrigation, the impact on the black water strength and flow varied considerably among the scenarios, in response to the wastewater and greywater characteristics; flow and concentration. Furthermore, significant differences have been observed among the three socioeconomic cases, considered in this paper, in terms of the black water characteristics, and greywater recycling options.