Discoloration of methylene blue and slaughter house wastewater using maize cob biochar produced using a constructed burning chamber: A comparative study

Abstract

A comparative study on the discoloration of methylene blue (MB) and slaughter house waste water (SHW) using maize cob biochar produced by a laboratory constructed burning chamber was undertaken in this study. Contact time, pH, initial MB and SHW concentrations, mass of biochar and temperature were used to evaluate the efficiency of the biochar in discoloring MB and SHW in batch process. A biochar/sand filtration system was also used to study the discoloration of MB and SHW in continuous filtration. Equilibrium was attained in 15 min with 100% discoloration for SHW and 64% for MB. Maximum discoloration occurred at pH 4 and 0.05 g biochar for SHW and at pH 8 and 0.15 g biochar for MB. MB discoloration decreases with increase initial concentration while SHW discoloration increases with increase initial concentration. Both SHW and MB discoloration decreases with increase in temperature attaining 0% for SHW at 60 °C. Pseudo-second order kinetic model best describe the discoloration of MB and SHW. Langmuir, Freundlich Dubinin-Radushkevich and Temkin isotherm models describe the discoloration of MB but only Langmuir and Temkin isotherm models describe the discoloration of SHW. Slaughter house waste water is easily discolored than methylene blue in batch process as evident from calculated Langmuir equilibrium constant b (1916.71 L/mg for SHW and 0.69 L/mg for MB), Temkin equilibrium constant AT (0.98 L/mg for SHW and 4.1 × 10−9 L/mg for MB) and Langmuir separation factor (RL; 5.2 × 10−5 for SHW against 0.13 for MB). The discoloration process is physical, exothermic and less spontaneous with increasing temperature. A biochar/sand mixture filtration is more efficient in discoloring MB than SHW. Maize cob biochar can effectively be used to remove colour from methylene blue containing waste water and slaughter house waste water using low-cost materials in batch and column processes.