S. Gabarrón

Towards integrated operation of membrane bioreactors: effects of aeration on biological and filtration performance.

Two experimental studies evaluated the effect of aerobic and membrane aeration changes on sludge properties, biological nutrient removal and filtration processes in a pilot plant membrane bioreactor. The optimal operating conditions were found at an aerobic dissolved oxygen set-point (DO) of 0.5 mg O2 L(-1) and a membrane specific aeration demand (SADm) of 1 m h(-1), where membrane aeration can be used for nitrification. Under these conditions, a total flow reduction of 42% was achieved (75% energy reduction) without compromising nutrient removal efficiencies, maintaining sludge characteristics and controlled filtration. Below these optimal operating conditions, the nutrient removal efficiency was reduced, increasing 20% for soluble microbial products, 14% for capillarity suction time and reducing a 15% for filterability. Below this DO set-point, fouling increased with a transmembrane pressure 75% higher. SADm below 1 m h(-1) doubled the values of transmembrane pressure, without recovery after achieving the initial conditions.

Ragging in MBR: Effects of Operational Conditions, Chemical Cleaning, and Pre-Treatment Improvements

The fouling behavior in MBR affected by the ragging phenomenon was characterized by the fast increase of the TMP values. It was caused by the rags attached to the membranes which were not removed through the backwashing or recovery cleanings. However, the modification of operational conditions, such as the reduction of the operational flux or the MLSS concentration, achieved improvements on the fouling rates profile. On the contrary, the increase of filamentous bacteria in the activated sludge negatively affected the fouling behavior. Finally, a strategy based on an optimized mechanical pre-treatment with flocculants addition showed promising results for ragging prevention.

Development of an algorithm for air-scour optimization in membrane bioreactors

Abstract Membrane Bioreactors are used in an increasing number of wastewater treatment facilities because of their compactness and efficiency in solid-liquid separation. In this paper the development of an air-scour control algorithm based upon short term and long term membranes permeability evolution is presented. An open loop calibration and partial validation was carried out in a semi-industrial scale pilot plant where manual changes in air-scour flow had been previously carried out. The control system was successfully tested in closed loop in an industrial scale pilot plant, defining a maximum daily air-scour decrease or increase of 6% of the air-scour recommended by membranes suppliers. A maximum air-scour saving of 20%, calculated in terms of air flow saved, was achieved without interfering with the biological nutrient removal and without any apparent long term effect.