Feasibility of thermophilic anaerobic submerged membrane bioreactors (AnSMBR) for wastewater treatment

An anaerobic thermophilic submerged membrane bioreactor was operated for 300 days, with a mixture of volatile fatty acids as substrate. Cake formation was identified as the key factor governing critical flux. Low levels of irreversible fouling were observed. During the first 60 days of operation a rapid decrease in critical flux was observed, due to a reduction in sludge particle size. Critical flux at the end of the reactor operation was only 7 L/m2· h, at a gas superficial velocity of 70 m/h. Based on this flux, membrane costs would be close to 0.5 € per m3 of permeate, assuming a membrane lifetime of 3 years and membrane price of 100 €/m2. Costs calculations show that a side-stream configuration would be more economic if fluxes 3 times higher can be attained.

Results show that cake formation is the limiting factor for the application of AnSMBR. A decrease in particle size observed during AnSMBR operation caused a reduction in critical flux. Initial benefits of high temperature over the critical flux disappeared due to changes in sludge properties, most likely the occurrence of a sludge frac- tion with very low particle size. Low levels of irreversible fouling were observed, even though the reactor was operated for over 200 days with no membrane chemical cleaning. In principle, cake formation can be controlled more effectively by applying a high surface shear. However, sidestream configuration would only be economically convenient if it can attain 3 times higher fluxes. Acknowledgments This research is financially supported by the European Union in the framework of the “Agroiwatech”, project contract nr. ICA2-CT-200210010. Authors acknowledge the personal scholarship from the Chilean Government to David Jeison.