Novel nitritation process using heat-shocked nitrifying bacteria entrapped in gel carriers

Kazuichi Isaka*, Tatsuo Sumino, Satoshi Tsuneda

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

32 Citations (Scopus)


Nitritation (ammonium being oxidized to nitrite) is a cost-effective method for treating wastewater having high ammonium concentrations or low C/N ratios. We developed a novel nitritation process based on the observation that nitrite-oxidizing bacteria (NOB) in sewage sludge can be killed by heat shock, but ammonium-oxidizing bacteria (AOB) may survive. The effects of maximum heat-shock temperature and heat-shock duration on populations of AOB and NOB in gel carriers were measured. No NOB were detected after a heat-shock treatment higher than 60 °C for 20 min. However, the population of AOB continued to exist at above 108 MPN/mL-carrier even after heat shock at 80 °C for 1 h. To evaluate the nitritation performance, continuous feeding tests were conducted using heat-shocked gel carriers treated at three temperatures. Stable nitritation was observed for 49 days when gel carriers were heat shocked at 60-90 °C for 1 h. However, because nitrate production, i.e., nitratation, was observed after 77 days, the gel carriers were heat shocked again. Consequently, nitratation stopped immediately and nitritation restarted after 14 days. These results clearly show that this technique is effective for suppressing nitratation.

Original languageEnglish
Pages (from-to)265-270
Number of pages6
JournalProcess Biochemistry
Issue number3
Publication statusPublished - 2008 Mar


  • Heat shock
  • Immobilization
  • Inhibition
  • Nitrification
  • Nitritation
  • Nitrite

ASJC Scopus subject areas

  • Bioengineering
  • Biochemistry
  • Applied Microbiology and Biotechnology


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