Automotive Wash Effluent Treatment Using Combined Process of Coagulation/Flocculation/Sedimentation–Adsorption

Abstract

In the treatment of wastewater from vehicle washing, the coagulation/flocculation process using inorganic coagulant is mostly applied; it may or may not be combined with other processes. In literature, few studies use natural coagulants and assess the surfactants’ removal among the physical-chemical parameters, particularly using the adsorption process. In order to fill this knowledge gap, this work aimed to treat the car wash wastewater, applying a combined process of coagulation/flocculation/sedimentation (C/F/S) and adsorption. Process efficiency was evaluated according to the removal of color, turbidity, total solids, volatile solids, total dissolved solids, chemical oxygen demand and surfactants. For primary effluent treatment, C/F/S experiments were performed with Tanfloc SG to investigate the influence of the natural coagulant concentration in color and turbidity removal efficiency. The results showed that 220 mg L−1 was the best coagulant concentration (turbidity = 97.5%; color = 92.5%) (p < 0.05). The supernatant of the C/F/S process was applied to the sequential adsorption process (kinetics and isotherm) with mineral activated carbon. The equilibrium time of the kinetic experiment was established after 2 h of contact, and the Langmuir isotherm model best described the surfactant adsorption behavior (R2 = 0.93; qmax = 5.65 mg g−1). The combined process enhanced the treatment efficiency achieving an overall removal efficiency of 97.3% for color, 98.8% for turbidity, 92.6% for chemical oxygen demand, and 97.2% for surfactants. The combined process proved to be promising for the treatment of car wash wastewater, presenting a reduction surfactant concentration and on the other parameters evaluated, contributing to environmental sustainability.