Optimization of lignin removal from synthesized wastewater by iron (III) trimesate

Abstract

Box-Behnken design (BBD) was employed to study an optimal treatment method of synthetic lignin wastewater effluent from pulp and paper wastewater treatment plants using iron (III) trimesate (Fe-BTC) as an alternative coagulant aid. Fe-BTC was prepared by hydrothermal technique using ferric chloride hexahydrate (FeCl3·6H2O) combined with 1,3,5-benzenetricarboxylic acid (trimesic acid, H3BTC) in deionized water and ethanol. X-ray diffractometry and Fourier transform infrared spectroscopy were used to characterize the property of Fe-BTC. Three quadratic models of the four factors including Fe-BTC dosage, pH, initial lignin concentration, and slow mixing time were defined with lignin removal efficiency as a response. Treatment efficiency of lignin removal was 50-80% for experimental data and 60-80% for predicted values. Optimal condition was 1 g/L of Fe-BTC dosage, pH 4, and 50 ppm of initial lignin concentration without slow mixing giving 58.34% lignin removal efficiency. The pH of treated samples was below 3 after all processes. Results showed that Fe-BTC enhanced separation of lignin by coagulation-flocculation. Adsorption-charge neutralization is the main mechanism of this process at acidic pH. Fe-BTC separated the wastewater into three layers with Fe-BTC powder at the bottom, lignin sludge in the middle, and clear supernatant at the top. Lignin sludge can be reused and recycled for use in other applications.