Enrichment of high activity nitrifers to enhance partial nitrification process

abstract Partial nitrification (PN) process is an essential pre-treatment to Anammox process for nitrogen removalfrom ammonium-rich wastewaters. High activity nitrifiers (HANs) are considered as the key to high-ratePN process. The HANs could be successfully enriched at free ammonia (FA) concentrations of 10–20 mg NH 3 –N L 1 , which differed significantly from those enriched at FA concentrations of 1–3mgNH 3 –N L 1 . The maximum specific ammonium conversion rate, half saturation constant, half inhi-bition constant, cell yield and decay rate were 2.87 g N g 1 VSS d , 5.82 mg N L 1 , 8218.8 mg N L 1 ,0.15 g VSS g 1 NH þ4 –N and 0.09 d 1 for HANs at 30 C, respectively, which endowed the PN process a vol-umetric conversion rate (VCR) as high as 2.22 ± 0.33 kg N m 3 d 1 . The cultivation mode of HANs wasworkable and the HANs were promising as inoculum for the PN process. 2010 Elsevier Ltd. All rights reserved. 1. IntroductionPartial nitrification (PN) process plays a key role in the success-ful development of energy-saving nitrogen removal systems (Galiet al., 2007). It oxidizes ammonium to nitrite rather than nitrate,and thus saves 25% oxygen demand. It can be combined with theanaerobic ammonium oxidation (Anammox) process or conven-tional denitrification process via nitrite, resulting in a furtherreduction of energy and carbon dosage (Verstraete and Philips,1998; Fux and Siegrist, 2004).The nitrifiers responsible for the partial nitrification are ammo-nium oxidizing bacteria (AOB) such as Nitrosomonas, but AOB areoften accompanied with the nitrite oxidation bacteria (NOB) suchas Nitrobacter (Sinha and Annachhatre, 2007). So it is very impor-tant to enrich AOB and limit NOB simultaneously for nitrite accu-mulation in the PN process (Blackburne et al., 2008). This objectcan be reached by controlling the operational parameters such aspH, dissolved oxygen (DO), temperature and substrate concentra-tions (Ruiz et al., 2003; Peng and Zhu, 2006; Ciudad et al., 2007;Xue et al., 2009). Since the oxygen saturation coefficients of AOBand NOB are 0.3 and 1.1 mg O