الفهرس 
Introduction
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Abstract
In this study, the use of an innovative system namely down-flow hanging sponge (DHS) system for treatment of grey water for reuse are extensively examined. The system was operated at an HRT’s of 11.7, 5.8 and 2.9 hr, and organic loading rates (OLR’s) of 1.9, 3.6 and 6.8 kgCOD/m3 .d. Physico-chemical characteristics of grey wastewater were carried out. COD, TKN, NH4-N, NO2-N, NO3-N, oil & grease, total coliform, TSS and VSS were determined as described by Standard Methods (APHA, 2005). A total of 82 samples of the influent and the effluent of DHS system were collected and analyzed. During the study period (one year) the quality of the raw grey water was monitored regularly and exhibited quite high variability. Based on the results obtained in this study, it is concluded that, decreasing the total HRT applied to DHS system from 11.7 to 2.9 h for treating grey wastewater (GWW) affecting negatively the overall removal efficiency of the treatment system. So, it is recommended to operate such a system at a hydraulic retention time (HRT) of 5.8 h for producing an effluent quality suitable for reuse in agriculture purposes. The proposed aerobic DHS is a sustainable and promising treatment system for treatment of grey water because of the Low investment and running costs, operational simplicity, minimum mechanization along with sustainability of the system as a whole and at the same time fulfilling the discharge standard of the region. It can treat grey wastewater at the lowest possible use of energy. Cost is reduced as there is no need for aeration, cutting down the expenses associated with aerating devices, their operation, maintenance or replacement. Very less excess sludge produced, cost associated with sludge handling is also minimized. uses polyurethane sponge as a growth and support medium for biomass. Small area occupied as a result of its small size compared with other traditional treatment unites. Grey wastewater Reuse has great benefits of Reduces the demand on fresh potable water sources. Reduce the volume of wastewater to be discharged, resulting in a positive impact on the aquatic environment. And provision of nutrient-rich wastewaters can increase agricultural production and decrease the use of chemical fertilizers.