Sewage Water Quality and its Dilution in the Coastal Waters of South Corniche, Jeddah, Red Sea

Abstract. The water quality of an outfall discharging domestic andindustrial effluents and their dilution were assessed. The water samplesshow that concentrations of NO2-N, NO3-N, NH4-N and PO4-Pwere 3.56, 25.38, 21.30 and 56.85 µmole/l, respectively. The CODand BOD limits were higher than normal and were 1030 and 325 mg/l, respectively. The mean concentrations of Cd, Cr, Cu, Ni, Pb and Zn(0.58, 49.60, 29.63, 74.05, 6.82 and 89.59 µg/l, respectively) werealso higher than the normal permissible limits. Aerobic heterotrophicbacteria, coliform and faecal coliform were 9.3 × 109/ml, 8.3 × 108and 6 × 107/100ml, respectively. The higher number of bacteria couldbe partly due to the relatively large and varied industrial activity fromwhich the sewage was derived and probably as a result of poor managementof the effluents. The water column during February andMarch 2000 was fairly uniform and the average density was 1.0267kg/m3. The currents during this time were in a southeast directionwith a speed of 0.5 m/sec. The dilution factor was evaluated based onthe density of the sewage, the density of the receiving water and theamount and depth of discharge. For a discharge of 2 × 105 m3/day, theminimum dilution of about 100 can be achieved with a diffuser lengthof 200 m in a 30 m depth level.