Modified eucalyptus bark as a sorbent for simultaneous removal of COD, oil, and Cr(III) from industrial wastewater

This study has investigated the efficiency of eucalyptus bark (EB) to remove COD, oil, and Cr(III) from raw petroleum refinery effluent. Experimental works were conducted to assess the performance of raw and modified EB using chemical impregnation, carbonization, and hybrid pre-treatment. Then modified EB by hybrid H3PO4/carbonization that showed the best performance was further examined under different operating conditions: namely contact time, solution pH, temperature, and sorbent dosage. In general, removal efficiencies of COD, oil, and Cr(III) increased with the increase in contact time and sorbent dosage while acidic pH was favourable for achieving higher removal efficiency for targeted pollutants. The maximum removal efficiencies of COD, oil, and Cr(III) were 80, 91, and 61%, respectively. Meanwhile, the optimum operating conditions were found at contact time 100 min, sorbent dosage 10 g/L, pH 3, and temperature 25 °C. FTIR and SEM were also applied to characterize the sorbent. The Freundlich adsorption isotherm model shows a better correlation coefficient among the other isotherm models including Langmuir and Dubinin-Radushkevich with the R2 value of 0.9758. The adsorption kinetic examined using different kinetic models including pseudo-first order, pseudo-second order, intra-particle diffusion, liquid film diffusion, and double exponential follows intra-particle diffusion model.