Assessment of the Performance of Mogran Water Treatment Plant During Flood Season

Abstract

The quality of surface water depends upon the character and the area of water shed ,its geology and topography, the extent and nature of the development by man , time of year and weather condition. Blue Nile as a surface water resource; its water quality affected by many of the above factors (the extent and nature of the development by man which include removal of vegetation by cutting forest and unmanaged agriculture)that lead to excessive soil erosion particularly during the flood season so, produced high turbid water .The range of turbidity reached 21400 NTU and TSS 25500 during the flood season of the year 2002 in august .The water quality patter for the Blue Nile had been assessed by using daily recorded data from Mogran w/ws during the flood seasons for the year (1994-2003). To treat such turbid water , plain sedimentation is essential before coagulation and filtration processes. At present Khartoum state water treatment plants have no plain sedimentation units and the treatment used was coagulation followed by filtration. The common coagulant used was Aluminum sulphate (alum), the doses applied exceeding WHO standards which is 150 p.p.m and the applied dose reach 620p.p.m during the flood season of 1990 (august). Using of alum for high turbid water was found impractical. Two effective coagulants were used: organic polymer called poly DADMAC used as coagulant aid with alum, it was effective for high turbidity and color removal and decreasing the amount of sludge resulting from the flocculation process. But it needs exact chemical analysis such as polymer content, monomer content, organic and inorganic contaminants to avoid the health risks associated with residual polymer, monomer and contaminants. The other effective coagulants was inorganic polymer called Poly Aluminum Chloride (PAC), also found effective for high turbidity removal and found less in daily amounts used and cost comparing with alum and polymer with alum. Also the doses should be within the recommended safe dose to avoid the health risks associated with residual aluminum . At all Khartoum water plants , there is no treatment for the sludge and deposits that resulting from flocculation process and they were discarded directly to Nile .