Evaluating the Potentials of Local Soil Samples and Alum in Removing Color from Slaughterhouse Wastewater by Coagulation and Filtration

Abstract

A large quantity of slaughterhouse wastewater (SWW), containing many pollutants, is generated during the slaughtering and cleaning process and needs to be treated before discharge to protect the environment. Slaughterhouse effluent treatment by filtration using soil/sand media, which is cheaper and more affordable than most advanced technologies that are not affordable in developing countries, is scarce in the literature. In this study, coagulation and filtration, carried out independently, were used to remove the color from SWW. Local alum (coagulant), gravel, sand, and soil were used for treating the wastewater. The physico-chemical parameters of raw SWW and treated SWW were determined. SWW concentration, reactor volume, and coagulant dose were used to evaluate the batch coagulation process, while soil type, soil/sand mixtures at different bed heights, SWW initial pH, SWW concentration, and backwashing of the column were used to evaluate the filtration process. The local alum used is mainly composed of SiO₂ (2.17%) and Al₂O₃ (67.12%). At the end of this study, 0.2 g of local alum was chosen as the optimum dosage, and it was concluded that local alum is as good as commercial alum in the treatment of SWW. Results also show that coagulation efficiency increases with an increase in the volume of SWW (maximum value 87.61%) and the concentration of SWW (maximum value 86.79%). The % of soil/sand mixture, bed height, pH, concentration, and backwashing have an effect on filtration efficiency. A bed height of 30 cm, having 25% soil and 75% sand, gave the best color removal (with a mean filtration efficiency of 74.22 ± 7.78%) in SWW. Filtration efficiency increases as pH increases, decreases as wastewater concentration increases, and increases with backwashing. Combined coagulation and filtration using local soils and sand produced improved SWW with properties close to the World Health Organization drinking water standards, reducing biological oxygen demand (BOD) by 98.26% and chemical oxygen demand (COD) by 98.89%.