Coagulation and adsorption as pretreatments of thin-film composite–forward osmosis (TFC-FO) for ink printing wastewater treatment

Abstract

Abstract This study investigated the performance of coagulation with ferric chloride (FeCl3.6H2O) and adsorption with activated carbon used as pretreatments prior to thin-film composite–forward osmosis (TFC-FO) filtration of ink printing wastewater. Wastewater samples were collected from a printing factory located in Chao Phraya river basin where zero liquid-discharge standards are regulated. The FO filtration unit was operated in co-current mode with the cross-flow velocity of 600 mL/min using 2 M NaCl as draw solution. The FO membrane achieved 83.9–91.0% chemical oxygen demand and 91.2–99.9% color rejections. FO filtration of raw wastewater, coagulation-treated wastewater, and coagulation and adsorption-treated wastewater resulted in 56.3%, 49.0% and 46.1% of flux decline in 150 min. Scanning electron microscopy and Fourier transform infrared spectrometry results revealed that cake formation caused by colloidal particles and pore blocking from precipitation were the major fouling mechanisms. Cake-enhanced concentration polarization also promoted adsorption of color and pigments at the membrane surface. Both fouling mechanisms were successfully mitigated by adsorption following coagulation pretreatment. Overall, the combined pretreatments and FO have potential for the effective treatment and reuse of ink printing wastewater.