Effects of biofilm in improvement of activated sludge efficiency for treatment of industrial effluents containing formaldehyde

  Introduction: Formaldehyde is used in many industrial applications as raw material and therefore high concentrations are found in their effluents. Activated sludge processes based on biofilm growth are increasingly used because of appreciate abilities in controlling of high organic load industrial effluents. The main objective of this study was to determine the effect of biofilm in improvement of activated sludge efficiency for treatment of industrial effluents containing formaldehyde.   Materials and Methods: Two lab scale activated sludge reactors (with and without fixed bed for biofilm growth) were investigated in organic loading rate of 0.7 – 10.5 kgCOD/m3.d, aerobic condition and the room temperature. In this study, the effects of organic and hydraulic loads were investigated for the mentioned two processes.   Results: The most COD removal efficiency for biofilm activated sludge was 98.86%. The reactor containing biofilm had removal efficiency of more than 64% up to the organic loading rate of 10.5 kgCOD/m3.d, while the conventional activated sludge reactor collapsed in organic loading rate of 7.5 kgCOD/m3.d.   Conclusion: Findings of this study indicate that activated sludge reactor containing fixed bed for biofilm growth is significantly more efficient than the conventional activated sludge one.