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  Abstract: Hydroquinone is one of the most important phenolic compounds, which has a wide application in industries such as rubber, photo developing, cosmetic, and anti-oxidants. Because of its toxic effects, an efficient system should be provided for treating these kinds of wastewater. Therefore in this study, the performance of conventional and packed-cage RBC biological systems in treatment of wastewater containing hydroquinone, and parameters affecting the process were studied. In this study, the removal efficiency of hydroquinone was investigated in two different laboratory scale RBC systems. The first system was a two-stage RBC with rotating discs and the second one was a one-stage packed-cage RBC with bee-cell 2000 biofilm carriers. Each stage of the rotating discs RBC was consisted of 27 parallel plexiglas rotating disks with 15 cm in diameters. The packed-cage RBC had a net drum full of biofilm carriers with specific surface area about 650 m²/m³. Both systems had a total area of 2 m² and were fed by a peristaltic pump. During the startup, the reactors with sludge seed, daily dosage of 200 mg/L COD as glucose and synthetic wastewater was fed to each reactor. After increasing biofilm mass, the acclimation was started with stepwise substitution of glucose with hydroquinone (CODhdroquinone/CODtotal was increased about 10% in each step). After acclimation stage, the amount of COD was being increased stepwise up to 5000 mg/L. Both RBC systems as advanced biological processes had proper COD removal efficiencies for treating hydoquinone synthetic wastewater. Up to the maximum 90, 93 and 88 percent removal efficiencies were obtained in RBCI, RBCII and packed-cage, respectively for COD concentration of 1000 mg/L, hydraulic loading rate of 1.5 L/m³.d and optimum rotation speed of 10 rpm. Also, During the experiments up to 4000 mg/L influent COD, RBC with rotating discs had higher removal efficiencies (about 5%-15%) but at higher loading rates, packed-cage RBC had better results. The effect of hydraulic loading, and the rotational speed of disks in the performance of the both systems were studied. The results proved that the amount of hydroquinone removal increased with raising the rotational speed of the disks up to 10 rpm, and increasing hydraulic loading had a negative effect on the COD removal efficiencies in both conventional and packed-cage RBCs. Also COD concentration increased up to 10000 mg/L in one step whille the hydraulic loading rate and rotational speed were 1.5 L/m².d and 5 rpm, respectively. The results showed that conventional RBC had a better performance for the organic shock. For ensuring of hydroquinone biodegradation in the RBC systems carbon-13 NMR spectroscopy was also studied.

Keywords: RBC, Aromatic, hydroquinone, packed-cage

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