Outcomes of a 2-year investigation of Membrane Bioreactor Process configurations for biological advanced nutrients removal from municipal wastewater
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 2 m3 each. Both configurations included an anaerobic zone ahead 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 50µgP/L in the effluent could be consistently achieved with two types of municipal wastewater, the second site requiring in addition 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 post-denitrification configuration enabled a very good elimination of nitrogen. Daily nitrate concentration as low as 1 mgN/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.