Study of the anaerobic membrane bioreactor (AnMBR) technology for urban wastewater treatment

Abstract

Anaerobic membrane bioreactor (AnMBR) technology has arised as an alternative option for wastewater treatment, providing many advantages such as high organic matter removal efficiency (~98%), compact process, energy recovery (biogas) and sludge reduction. It combines the advantages of the use of membranes, already proved in aerobic membrane bioreactors, and the advantages of the anaerobic digestion, widely used since 1900s. The bioreactors can be single or a combination of various reactors, with the membrane either external or immersed. The membrane modules can be multitube (mostly used in external membrane bioreactors), flat sheet or hollow fiber modules (both used mainly in immersed membrane bioreactors). The membrane materials can be polymeric (the mostly used), metallic or ceramic. Also, the biomass can be suspended, granular (widely used in upflow anaerobic sludge blanket reactors) or attached (the most used in anaerobic fluidized-bed reactors). The energy balances confirm that the AnMBR process can be a self-sufficient process, even an energy-producer process, diminishing GHG emissions and reduced carbon footprint. The main limitations of the AnMBRs for urban wastewater treatment are membrane fouling and high quantity of dissolved methane in effluent. Some authors have successfully partially controlled them, but more research is still necessary in this field. In addition, some authors have used AnMBRs for industrial wastewater treatment, with successful results: SRTs up to 230 days with HRTs between 16 h - 5 days, and the COD removal efficiency between 94-99%. However, for urban and high-solid-content wastewaters the applicability is still doubtful: low COD removal efficiency, which does not fulfill with the legislative requirements. The firstly AnMBR commercially used for industrial wastewater treatment in the 1980s were known as Membrane Anaerobic Reactor System (MARS) and Anaerobic Digestion Ultrafiltration (ADUF). In the last decade, Kubota Corporation developed a submerged anaerobic membrane bioreactor process, named KSAMBR process, successfully applied in food and beverages industries, and ADI Systems Inc. developed ADI-AnMBR system, specific for food wastewaters.