Investigation and optimization of COD, color, total dissolved solids, and turbidity removal from surface water using natural and synthetic coagulants

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