Enhancement of oxygen mass transfer coefficients in a hybrid membrane bioreactor

Background Oxygen mass transfer is a key parameter for processing aerobic bioreactors in terms of operational costs and efficiency. In membrane bioreactors, a reduction of the aeration capacity is often observed at high solid ratios, caused by the presence of solids and the non‐Newtonian properties of activated sludge. Results The aim of this work is to study how oxygen transfer is impacted when a high porosity packing material is added (free bacteria plus fixed bio‐films). Measurements are performed on a pilot scale ‘hybrid membrane bioReactor’ (HMBR), using clear water, a Newtonian solid suspension and a non‐Newtonian solution. The influence on the oxygen transfer coefficient (kLa) of non‐Newtonian properties, the presence of solids, the presence of a packing material and of the air flowrate, are presented. It is observed that the type of fluid used and the presence of a packing material both have a strong influence. Conclusion An important drop in kLa (respectively 53% and 31%) is obtained with the non‐Newtonian solution and the physico‐chemical suspension, compared with water. On the contrary, an enhancement in kLa, up to 46% is observed in the presence of a packing material. The air flow rate has little influence in the range of parameters investigated here. © 2013 Society of Chemical Industry