Behaviour of air diffusers and oxygen transfer efficiencies in the biological treatment of matrices at high alkalinity concentrations: Experimental and full scale application

• Slow pressure growth is evaluated for the elastomeric diffusers in the treatment of high alkalinity matrices.
• These diffusers maintain the original pore shape ensuring oxygen transfer in aerobic phases.
• The preservation of pore shape minimizes the blocking effect and the need for chemical cleanings.
• The precipitate on and inside the pores is mainly composed of calcium and iron deposits.
• The full scale application of elastomeric diffusers increases NH4-N removal and energy saving.

An evaluation of different types of air diffusers applied to the biological landfill leachate treatment was executed. The optimization of performances in the experimental scale was determined evaluating the pressure evolution at different inlet air flows for two types of elastomeric polyethylene diffusers. The microscope analysis permitted the definition of the chemical compounds precipitated on surface of the diffusers and inside the pores. The compounds were mainly composed of calcium and iron deposits. Formic acid solution was identified as the most efficient for the removal of the insoluble salts. During the experimental phase, the elastomeric polyethylene diffuser was found to be the best suited to the biological treatment of matrices at a level of high alkalinity (2900 mgCaCO3l−1). This result determined the replacement of 500 rigid diffusers in the full scale biological reactor. The substitution incremented the standard oxygen transfer efficiency to 16% and the standard aeration efficiency to 5.1 kgO2kWh−1 with an improvement of the ammonia performances and of energy saving.