Outcomes of a 2-year investigation on enhanced biological nutrients removal and trace organics elimination in membrane bioreactor (MBR)

Two configurations of membrane bioreactors were identified to achieve enhanced biological phosphorus and nitrogen removal, and assessed over more than two years with two parallel pilot plants of 2m³ each. Both configurations included an anaerobic zone a head of the biological reactor, and differed by the position of the anoxic zone: standard pre-denitrification, or postdenitrification without dosing of carbon source. Both configurations achieved improved phosphorus removal. The goal of 50mgP/L in the effluent could be consistently achieved with two types of municipal waste water, the second site requiring a low dose of ferric salt ferric salt < 3mgFe/L. The full potential of biological phosphorus removal could be demonstrated during phosphate spiking trials, where up to 1mg of phosphorus was biologically eliminated for 10mg BOD5 in the influent. The postdenitrification configuration enabled a very good elimination of nitrogen. Daily nitrate concentration a slow as 1mg N/L could be monitored in the effluent in some periods. The denitrification rates, greater than those expected for endogenous denitrification, could be accounted for by the use of the glycogene pool, internally stored by the denitrifying microorganisms in the anaerobic zone. Pharmaceuticals residues and steroids were regularly monitored on the two parallel MBR pilot plants during the length of the trials, and compared with the performance of the Berlin-Ruhleben WWTP. Although some compounds such as carbamazepine were persistent through all the systems, most of the compounds could be better removed by the MBR plants. The influence of temperature, sludge age and compound concentration could be shown, as well as the significance of biological mechanisms in the removal of trace organic compounds.

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