The availability of drinking water is one of the several problems humans face, considering that its availability is reduced to 0.80% of the existing fresh water. Then, coagulation-flocculation is a stage of this treatment. It is a process that agglomerates the suspended particles in a larger (floc) that could be separated by sedimentation and filtration processes to make the water drinkable. So, this work aimed to evaluate the effect of the dose of coagulant of yam starch ( Dioscorea rotundata) and the speed of agitation in the turbid water treatment process. For which the yam starch was extracted by implementing two methods which were NaOH and H2O, using centrifugation at 1500 rpm for 10 min, and adjusting the pH with HCl and NaOH 0.20 M, for later determining the effect of agitation speed (rpm) and coagulant concentration (ppm) on the percentage of turbidity removal, pH, and colour, to be compared with a synthetic coagulant. A yield of 42.60% was found in the wet base. The natural coagulants extracted with NaOH presented better turbidity removal, with a percentage of 92.48% at an agitation speed of 40 rpm and a concentration of 250 ppm. It can be concluded that natural yam coagulant can be recommended for use in the coagulation stage in the raw water treatment process for subsequent conversion to drinking water.

Sedimentation tanks have a vital role in the overall efficiency of solid particles removal in treatment units. Therefore, an in-depth study these tanks is necessary to ensure high quality of water and increasing the system efficiency. In this work, an experimental rectangular sedimentation tank has been operated with and without a baffle to investigate the system behaviour and effectiveness for the reduction of solid particles. Turbid water was prepared using clay, which was collected from the water treatment plant of Al Maqal Port (Iraq), mixed with clear water in a plastic supply tank. Raw and outflow samples were tested against turbidity after plotting a calibration curve between inflow suspended solids versus their corresponding turbidity values. The key objective was to assess the impact of different flow rates, particle concentrations, heights and positions of the baffle on the system efficiency. Findings showed that the tank performance was enhanced significantly (p < 0.05) with the use of a baffle placed at a distance of 0.15 of tank length with height equal to 0.2 of tank depth. Higher removal efficiency (91%) was recorded at a lower flow rate (0.015 dm3∙s–1) and higher concentration (1250 mg∙dm–3), as the treatment efficiency enhanced by 34% compared with the operation without a baffle. Placing the baffle in the middle of the sedimentation tank produced the worst results. System efficiency for solids removal reduced with increasing baffle height. Further research is required to evaluate the efficiency of an inclined baffle.