Treatment of photographic processing wastewater using anaerobic-aerobic biofilm reactor

Two types of anaerobic-aerobic biofilm processes were applied to the treatment of the photographic processing wastewater. Two-phase fixed bed reactor packed with sponge cubic media and completely mixing three-phase fluidized bed reactor, respectively, were used as an anaerobic and aerobic biofilm reactors. One of the aerobic biofilm reactors was packed with cement balls (CB) made by crushed cement particles, and another packed with biological activated carbon (BAC). The fivefold diluted photographic processing wastewater, from which Ag had been removed previously, was used as an influent (BOD 5700 g/m³, COD(cr) 17,000 g/m³, T-N 2600 g/m³). During long-term continuous biological treatment, BOD values in effluent decreased gradually and reached 280 g/m³, which could fulfill the sewage discharge control value in Japan (BOD < 600 g/m³). It took more than one year to acclimatize the sludge and to get the effective microorganisms for degrading the compounds in the photographic processing wastewater. However, pH values in the aerobic biofilm reactors fell down to 3~4. This was possibly because thiosulfate (5700 g/m³) in the photographic processing wastewater was almost oxidized to sulfate by sulfur-oxidizing bacteria. For the purpose of obtaining higher BOD removal efficiency, pH in the aerobic biofilm reactor was adjusted to 7 using pH controller. As a result, BOD removal ratio was gradually improved, and the sewage discharge control value was steadily achieved after 181 days. The number of bacteria in the anaerobic biofilm reactor and the aerobic biofilm reactor with pH controller were 6.0 x 10⁹ N/mL and 1.1 x 10⁸ N/mL, respectively.