On-line cake-layer management by trans-membrane pressure steady state assessment in Anaerobic Membrane Bioreactors for wastewater treatment

Membrane bioreactors have been increasingly applied for wastewater treatment during the last two decades. High energy requirements and membrane capital costs remains as their main drawback. A new strategy of operation is presented based on a continuous critical flux determination, preventing excessive cake-layer accumulation on the membrane surface. Reactor operation is divided in cycles of 500 s filtration followed by a short back-flush of 15 s. If cake-layer formation is detected during continuous operation, a decrease in flux or an increase in cross flow velocity is performed. The proposed approach keeps reactor operation oscillating around the critical flux, minimizing reactor maintenance and maximizing performance. An easy to operate statistical steady state determination tool for the trans-membrane pressure was used to detect cake-layer formation. The developed control approach was tested on two Anaerobic MBRs equipped with submerged membranes. Despite the existence of very different critical fluxes and cake-layer formation characteristics, proposed approach was able to keep pressure increase during filtration cycles below 20 mbar. The developed approach is an efficient tool for on-line control of cake-layer formation over the membranes, changing cross flow velocities by manipulating gas sparging in submerged MBRs.