Abstract:
Water is essential to our existence and is needed by all organisms. As time goes on and human
needs grow, the quality of the water has an adverse effect. Surface water is contaminated with
pointed and non-pointed sources. Many of the impacts of contaminated surface water were
against affecting the environment and public health. The aim of the study was to investigate and
optimize the effectiveness of linseed, alum, and a blended form of coagulant in removing COD,
turbidity, color, and TDS from surface water. The study was conducted in Jimma town in 2023
by applying an experimental study design. The study designed a 2:1 linseed-alum ratio for
blending coagulants. Surface water samples were taken from the Awetu river using grab
sampling techniques. Design Expert 13.0.5.0 and Minitab 16 statistical software were used for
the experimental design and data analysis. The relationship between the process variable and
the response was examined using analysis of variance (ANOVA). The best conditions and
responses from the numerical and experimental optimization processes for pH, dose, and stirring
times were investigated within the framework of CCD using RSM (CCD-RSM). A jar test was
performed to assess coagulation ability by varying design parameters: pH (5.0, 7.0, 9.0), dosage
(1, 1.75, 2.5 g), stirring speed (40, 60, 80 rpm), and settling time (30, 40, 50 min). A comparison
of the results with the accepted international standard was carried out. Results for
physicochemical parameters were in the range of pH (3.0-9.0), color (0.004-0.028 Abs),
turbidity (1.4-4.6 NTU), COD (15-62 mg/L), and TDS (112.6-308.8 mg/L) for blended; color
(0.016-0.035 Abs), turbidity (2.5-5.13 NTU), COD (38.8-76.96 mg/L), and TDS (210-433 mg/L)
for using linseed; and color (0.008-0.034 Abs), turbidity (2.20-5.14), COD (25.6-68 mg/L), and
TDS (173-391 mg/L) for analyzed using alum. The maximum removal for color, turbidity, COD,
and TDS were 99.02%, 97.02%, 95.80%, and 94% for blended; 96.20%, 95.10%, 88.60%, and
89.20% for linseed; and 98.50%, 95.3%, 92.47%, and 91.25% using alum, respectively. This was
achieved at a fixed pH value of 3.02, 3.03 and 3.5, a dosage of 1.5, 1.75, and 1.75 g/L, and a
stirring time of 38.9, 37.4, and 47.4 min, respectively. The concentrations of all responses in the
sample were below the maximum limits recommended by the WHO and USEPA. The finding
indicated that the use of blended coagulants has a high potential for treating water
