Anaerobic treatment of fibreboard manufacturing wastewaters in a pilot scale hybrid usbf reactor

The treatment of fibreboard manufacturing (FBM) wastewaters was carried out in an industrial pilot plant, which consisted of a hybrid upflow sludge bed filter (USBF) anaerobic reactor and a coagulation–flocculation unit as a pre-treatment. COD removal efficiencies of 90–93% were attained in the anaerobic reactor operating at 37°C at organic loading rates (OLR) of 6.5–8.5 kg COD/m3 d. Flocculant sludges were used as inoculum, and granulation was observed in the USBF reactor after 120 days of operation. The overall linear upward velocity (result of liquid and gas flow) was the key factor controlling biomass retention and, therefore, a stable operation at high OLR. According to ecotoxicity values (measured by means of bioluminescence assays), the wastewaters were partially detoxified, being EC50 values for the liquid effluent 25 times lower than those corresponding to the influent. Besides, phenolic compounds removal efficiencies of 90% were attained. The hybrid reactor configuration is an interesting alternative to treat these wastewaters since it is less sensitive to biomass clogging or floatation.