Powdered activated carbon and membrane bioreactors (MBR-PAC) for tannery wastewater treatment: long term effect on biological and filtration process performances

This paper describes the findings of an experimental investigation carried out on a pilot scale membrane bioreactor (MBR) with the addition of powdered activated carbon (PAC) to analyze improvements in effluent quality and in the filtration process. The results refer to a pilot plant monitoring stretched over a period of 594 days: 380 without PAC, 123 with a PAC concentration of 1.5 g/L and 91 with 3 g/L. The sludge residence time and hydraulic retention time were maintained between 30 and 90 days and 50 and 100 hours respectively. Improvements in COD removal were found to be low, but not negligible, and greater than the PAC adsorption effect alone. COD removal stability appeared to increase as PAC concentration increased. No effects were observed on the nitrification processes. The filtration process was evaluated in terms of sludge filterability, fouling rate and fouling reversibility. The fouling rate decreased with an increasing PAC concentration and showed complete reversibility both in presence and in absence of PAC.