Nitrogen removal in a four-step feed alternating anoxic-oxic sequencing batch reactor

The aim of the present study was to determine the nitrogen removal efficiency that can be achieved in four-step SBR and to investigate the morphology of the activated sludge in an SBR operated with such an operational strategy. In the present work a four-step SBR with step ratio of 1.5 was used to treat a synthetic wastewater containing a COD and N of respectively 1000 mg/l and 107 mg/l. The study was conducted in two phases with different time distribution between anoxic and oxic stages in SBR cycle. The same COD and nitrogen removal efficiencies, of respectively 92% and 96%, were obtained for both phases. This was a higher performance compared to previous reports of three-step SBRs employing similar conditions. In both phases SVI initially decreased but after one month of operation sludge bulking occurred. Filamentous bacteria responsible for sludge bulking problem were identified as M. parvicella and the reason for its proliferation was attributed to low substrate concentrations and the consequent incomplete denitrification obtained in the final stages of the four-step SBR cycle.

Keywords:

M. Parvicella , Nitrogen Removal , SBR , Sludge Bulking , Step-Feed