Mixing Intensity Effects of Attached Growth on Enriched Anammox Cultures

Anaerobic ammonium oxidation (anammox) is a promising new technology for the treatment of wastewater with high ammonium and low carbon concentrations. Earlier work suggests that optimal processing would be realized within a sequencing batch reactor (SBR). However, the relatively slow growth of anammox bacteria inhibits the rates of nitrogen removal and biomass yielding. Improved anammox performance has been demonstrated when the bacteria are in granular form or attached to a growth medium. Little has been reported concerning the effect of mixing rate on nitrogen (N) removal with attached anammox bacteria. This work subjected anammox bacteria attached to polystyrene sponge in SBR to various intensities of impeller mixing and studied the effect on NH4+ and NO2- removal. Nitrogen processing was virtually the same with velocity gradient values between 13.5 and 222 s-1. More vigorous mixing at 407 and 666 s-1 values significantly inhibited N removal, likely due to detachment of bacteria from the growth medium. Following the poor N removal at the two higher mixing intensities, agitation was reduced to 24.8 s-1 velocity gradient value. Recovery of N removal rates required 2-3 weeks, the slow time attributed to slow reattachment to the growth medium. Denaturing gradient gel electrophoresis (DGGE) analysis identified the prominent anammox species in the experimental study as Candidatus Brocadia anammoxidans and Candidatus Kuenenia stuttgartiensis