Optimization of Coagulation-flocculation Process for Pre-treatment of Artisanal Tannery Wastewater Using Response Surface Methodology

Abstract

There is a dearth in knowledge on artisanal tannery wastewater treatment as most studies are focused on treatment of wastewater generated from modern-day leather manufacturing industries. The extensive use of plant materials in artisanal tanneries introduces high loads of polyphenolic compounds in the wastewater rendering biological treatment of the wastewater ineffective. This study, therefore, employed coagulation-flocculation process to pre-treat artisanal tannery wastewater with the aim of applying the central composite design, a statistical approach in Response Surface Methodology (RSM) to model and optimize the removal of Chemical Oxygen Demand (COD), Total Suspended Solids (TSS) and turbidity and to minimize Sludge Volume Index (SVI). Optimization process focused on the two most important influencing parameters: dosage of aluminium sulphate and initial pH of wastewater. Results revealed that optimal pH and aluminium sulphate dosage of 6.09 and 11.6g/L respectively could yield maximum removal efficiencies of 38.51% of COD, 76.05% of TSS and 79.64% of turbidity from the wastewater with a minimum SVI of 29.57mL/g. Further experiments conducted to validate these results showed a good agreement between the experimental and predicted results signifying the suitability of RSM for optimization of the coagulation treatment process. This is the first reported study on optimization of coagulation-flocculation treatment of artisanal tannery wastewater. Results of this study can be used practically for efficient pre-treatment of artisanal tannery wastewater.

Performance Optimization of Chemical and Green Coagulants in Tannery Wastewater Treatment: A Response Surface Methodology Approach

“…Te surface morphology of cassava starch and powdered orange peels illustrated in Figure 2 is obtained from the SEM micrographs. Cassava starch was observed to have granules which were smooth, spherical, and tightly packed together [30]. Tis observation is in agreement with that described by Xia et al [41].…”

“…R 2 values greater than 75% [43] and also very close to the adjusted R 2 values are usually considered satisfactory [44]. Te R 2 values obtained for COD and TSS removal efciencies as well as for SVI were 89.75%, 87.83%, and 98.04%, respectively, for cassava starch; 91.73%, 92.55%, and 98.89%, respectively, for orange peel powder; and 97.92%, 96%, and 98.69% respectively, for alum (Figures 3-5) which were all greater than 75% signifying good predictive models [30].…”

“…Te concentration of total nitrogen (36.70 mg/L) may be due to the presence of vegetal matter as well as the small pieces of fesh and adipose tissues released from the animal skins into the wastewater [33]. Te chloride ions (722 mg/L) in the wastewater could be resulting from the salts used in preserving the animal skins [30].…”

“…where Y denotes the predicted response; β O , β i , and β ij are collectively referred to as model coefcients; β O represents the constant coefcient; and β i , β ii , and β ij are the linear, quadratic, and interaction coefcients, respectively. Te error associated with the model is represented by ε. X i and X j are the codes given to the two independent variables-coagulant dosage and pH, respectively [30]. Statistical signifcance of the regression models was evaluated through the analysis of variance (ANOVA) test.…”

“…Te efect of process parameters, coagulant dosage and initial pH of wastewater, on SVI, removal of COD, and TSS from the tannery wastewater are illustrated in the 2D contour and 3D response surface plots (Figures 6-11) [30]. In addition, the statistical signifcance of each of the model coefcients (linear, quadratic, and interaction terms) using the F-test and p values is presented in Table 5.…”