Microbial granules for carbon oxidation and nitrogen removal can also be developed in SBRs operated under alternating aerobic-anaerobic conditions (Qin et al., 2004b, 2005). The microbial granules cultivated under alternating aerobic-anaerobic conditions even exhibited a better settleabil-ity than those developed under pure aerobic conditions. It was found that over 95% of influent COD was removed within the first half hour of aerobic phase. Along with the COD elimination, the NH4+-N concentration decreased slowly to satisfy microbial growth requirement on nitrogen. After depletion of most COD, the NH4+-N concentration declined in a fast way, which was mainly due to nitrification. Ammonia was entirely converted to nitrate at the end of the aerobic phase. The stoichiometric amount of ethanol required for nitrate reduction can be derived from the following equation:
In order to promote denitrification, external carbon source was added according to the above equation in the beginning of the anaerobic phase, and a complete denitrification was achieved in alternating aerobic-anaerobic microbial granular sludge SBRs (Qin et al., 2005).
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