Evaluation of operating parameters affecting the two-stage nitritatin/anammox process in mainstream flows: From...

Operating parameters for the two-stage nitritation/anammox (PN/A) process in mainstream flows from lab-scale to pilot-scale were investigated. In the batch experiment, the specific activities of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) were fitted with a Monod model, and the oxygen affinity of NOB was higher than that of AOB. Nevertheless, dissolved oxygen concentrations higher than 2.0 mgO₂/L were effectively applied for selective inhibition of NOB. In addition, organic matter was evaluated as the operating parameter that inhibited the activity of NOB more selectively than AOB under mainstream conditions. The operating parameters determined in the batch experiment were verified in a continuous experiment, and it was shown that the shortening of hydraulic retention time with increasing aeration time in the sequencing batch reactor cycle has the potential to selectively enhance the activity of AOB over NOB. The effect on the C/N ratio and temperature in a lab-scale anammox reactor was investigated. The denitrification with the addition of organic matter contributed to the improvement of nitrogen removal efficiency, but a C/N ratio of more than 1.0 severely deteriorated the sludge settleability. The operating factors for the mainstream PN/A determined in the lab scale were applied to the pilot plant. As a result, a nitrogen removal efficiency of 79 ± 11% was stably achieved with effluent total nitrogen of 2.6 ± 1.5 mg/L. However, unpredictable fluctuations in environmental factors revealed that residual ammonium was another critical factor affecting mainstream PN/A.