A combined treatment of aerobic activated sludge and powdered activated carbon: Pilot-scale study of per/polyfluoroalkyls (PFASs), organic matters, chromium, and color removal from tannery wastewaters

A pilot-scale system of three parallel plug flow reactors was utilized for the treatment of tannery wastewaters with powdered activated carbon (PAC) at different dosage in activated sludge process. The SRT and the carbon replacement (XCI) were set at 35 d and 0 mg PAC/L (R1), 25 d and 100 mg PAC/L (R2), 20 d and 300 mg PAC/L (R3), at fixed HRT (4 days) and temperature (20–22 °C). The removal of per- and polyfluoroalkyls substances (PFASs), organics, chromium and color were assessed. Due to competition phenomena for adsorption between the organics and the PFASs, the highest PAC dosage (R3) was the only one able to decrease the concentration of total PFASs below the limit of 500 ng/L. Soluble COD and chromium removal efficiency up to 92.8 % and 68 % was respectively achieved; in terms of color abatement, the treated wastewaters showed a reduced absorbance up to 56 % compared to condition R1. The mass balance assessment revealed a maximum cost's increase of 0.923 €/m3 of treated water associated to the use of the PAC (R3), highlighting the necessity to adopt sustainable strategies to valorize the generated tannery sludge instead of landfilling, which is still the only disposal practice of this waste.