Abstract
Anaerobic ammonia oxidation (anammox) bacteria are inhibited by heavy metals at high concentrations but require trace amounts of some heavy-metal elements for growth and activity maintenance. The present study evaluates the long-term limitation effects of Se(VI), Zn(II), and Ni(II) on the start-up period of an anammox reactor. To strictly limit the levels of heavy metals in the reactor, all tests used ultrapure water as the influent synthetic wastewater and all reactors were installed in a clean booth. The anammox biomass was maintained through the gel entrapment technique. In the absence of Se(VI) and Ni(II), the anammox reactor start-up was 18.9 kg-N (m3-carrier d)−1 (nitrogen conversion rate (NCR) per gel carriers), indicating that Se(VI) and Ni(II) are not required or need not be continuously added to maintain the anammox process. Under Zn(II) limitation, the anammox process failed to start-up and the NCR tended to decrease rapidly. After readdition of 0.005 mg L−1 of Zn(II), the NCR did not decline further and instead partially recovered at a very slow rate. The NCR was completely recovered after adding 0.020 mg L−1 of Zn(II). These results reveal that Zn(II) limitation seriously affects the start-up of the anammox process while Se(VI) and Ni(II) are not required or need not be continuously added to the anammox process.
Highlights
Anaerobic ammonium oxidation is a novel biochemical reaction and anammox processes are currently employed in cost-effective wastewater treatments (Mulder et al, 1995; Strous et al, 1999; Strous et al, 2006; van der Star et al, 2007)
For the immobilization of anammox gel carriers, the anammox bacteria in the seed sludge were enriched from sewage sludge and grown in a 50-L fixed-bed reactor filled with porous polyester nonwoven fabric carriers at 35°C (Fujii et al, 2002)
(Li et al, 2018). reported that Zn(II) increased the activities of anammox bacteria and the total population of the sludge in an anammox system in an sequencing batch reactor (SBR). These results suggest that the change in the anammox activity owing to the limited concentration of trace elements (TEs) may be caused by the change in the number of anammox bacteria
Summary
Anaerobic ammonium oxidation (anammox) is a novel biochemical reaction and anammox processes are currently employed in cost-effective wastewater treatments (Mulder et al, 1995; Strous et al, 1999; Strous et al, 2006; van der Star et al, 2007). The anammox process is mainly used in the digester supernatant treatment of municipal wastewater (van der Star et al, 2007; Lackner et al, 2014). The anammox bacteria require trace amounts of heavy metals for metabolism and growth. Such trace elements (TEs) mainly act as coenzymes and the cofactors of enzymes (Fermoso et al, 2009; Glass and Orphan, 2012). Anammox activity is reportedly increased by adding heavy metals. Zhang et al (2019) reported that a long-term exposure to 1 mg L−1 of Fe(II) enhanced the anammox activity, and Sindhu et al (2021) reported an increase in the nitrogen removal performance of a sequencing batch reactor (SBR) after adding 55.8 mg L−1 of Fe(II).
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