Changes of nitrogen-removal performance and that of the bacterial community in a mixed culture comprising freshwater and marine anammox bacteria under averaged environmental condition
Graphical abstract
Introduction
Anammox is a nitrogen-metabolic pathway that was first reported in 1995 (Mulder et al., 1995). In the anammox reaction, ammonium (NH4+) is oxidized by nitrite (NO2−), and a small amount of nitrate (NO3−) is produced under anoxic conditions. Strous et al. proposed the following Eq. (1) as a typical stoichiometric formula for the anammox reaction obtained in sequencing batch reactors (Strous et al., 1998):
The anammox reaction is catalyzed by anammox bacteria, which were discovered in 1997 (Strous et al., 1997). Anammox bacteria are anaerobic and autotrophic bacteria that derive energy through the redox reaction with NH4+ and NO2− without an organic-carbon source (Strous et al., 1998). So far, anammox bacteria have been broadly divided into five candidate genera: “Candidatus Brocadia,” “Candidatus Kuenenia,” “Candidatus Jettenid,” “Candidatus Scalindua,” and “Candidatus Anammoxoglobus” (van Niftrik and Jetten, 2012). The species in the genus of “Candidatus Scalindua” have been discovered in marine environments and exhibit a high tolerance for salt (Awata et al., 2012). In addition, the optimal temperatures for the growth of the species within “Candidatus Scalindua” were reported to be typically lower (around 25 °C) than those for the species in other anammox genera (over 30 °C) (Awata et al., 2012; Kawagoshi et al., 2012).
In recent years, numerous studies have been conducted on the application of anammox for nitrogen removal from nitrogen-rich wastewater (van der Star et al., 2007) because of great advantages such as economical and fast nitrogen removal (Jetten et al., 2005). However, anammox processes still have unfavorable characteristics that must be solved prior to practical application. For example, anammox bacteria exhibit quite low growth rates (doubling time is over 10 days) (Strous et al., 1998) and widespread inhibitory factors for their activities have been revealed (Fernandez et al., 2012; Dapena-Mora et al., 2010; Dosta et al., 2008; Guven et al., 2005). Additionally, anammox bacteria are susceptible to damage by rapid changes of environmental conditions, and their recovery from such damage is sometimes difficult for the bacteria (van Niftrik and Jetten, 2012). Such a weakness of anammox bacteria may be improved via adaptation to environmental change (Fernandez et al., 2008; Collins et al., 2005; Toh and Ashbolt, 2002). Although the mechanism of adaptation is not well understood, it is possible that a shift of bacterial flora can contribute to the adaptation process. Kartal et al. successfully acclimatized freshwater-anammox cultures to a high-salinity condition (salt concentration: 30 g/L) and reported that the abundance ratio of halotolerant anammox bacteria and another anammox bacteria varied according to salinity change (Kartal et al., 2006). These results indicate a possibility that different anammox bacteria could live in a reactor and their population may vary according to changes in environmental conditions. On the other hand, Liu et al. reported that freshwater anammox bacteria can live in a high-salinity medium (30 g/L salt) by adapting to the high-salinity condition and can reasonably perform nitrogen removal; however, its nitrogen removal performance abruptly declined at a salt concentration of >30 g/L (Liu et al., 2009).
In consideration of these previous studies and findings, it is expected that a mixed anammox culture comprising different kinds of anammox bacteria could achieve stable nitrogen-removal performance by shifting the dominant bacterial species according to the change in the environmental condition. Therefore, we conceived the construction of a mixed anammox culture by combining marine-anammox bacteria (MAB) and freshwater-anammox bacteria (FAB) to establish the robust anammox culture that can appropriately respond to the changes in salinity and temperature to maintain stable nitrogen-removal performance. Furthermore, changes in the bacterial community of the mixed anammox culture with the environmental condition is very noteworthy information. In this study, we constructed the mixed anammox culture in a continuously stirred tank reactor (CSTR), which can rapidly change the bacterial population in the reactor and revealed its nitrogen-removal performance and the population shift in the bacterial community under the averaged environmental conditions between the culture conditions required for MAB and FAB.
Section snippets
Inoculation of biomass
In our laboratory, biomasses of freshwater anammox bacteria (FAB) and marine anammox bacteria (MAB) were maintained in packed-bed-type reactors with a nonwoven fabric as the biomass carrier (Kawagoshi et al., 2009). The reactors were both operated at a nitrogen-loading rate (NLR) of 0.3 kg N/m3/d for more than six months and showed a stable nitrogen-removal performance: more than 85% of the nitrogen in the influent (medium) had been converted to nitrogen gas. Next, 2.0 g (wet weight) of anammox
First period (0–22 d)
Fig. 2(a–d) show the time course of the setting values of operation condition and measurement results throughout the experimental period: pH values of the medium and effluent are shown in Fig. 2(a); the molar ratios of consumed NO2− to consumed NH4+ (NO2−/NH4+) and produced NO3− to consumed NH4+ (NO3−/NH4+) are shown in Fig. 2(b); HRT, NLR, NRR, and NRE are shown in Fig. 2(c); the total nitrogen (TN) concentration in the medium and the nitrogen concentrations of NH4+, NO2−, and NO3− in the
Nitrogen-removal performance in the mixed culture with suspended marine- and freshwater-anammox biomass under averaged condition
In this study, startup of mixed anammox-bacterial culture inoculated with both the freshwater and marine-anammox biomasses was conducted under an averaged cultivation condition, and the change of bacterial composition was investigated during the culture period. In our previous studies on the startup of anammox cultures (Kawagoshi et al., 2009, 2010), we used a packed-bed reactor with a nonwoven fabric as the biomass carrier and promoted the biomass to make biofilm to reduce the amount of
Acknowledgments
This study was financially supported by Grants-in-Aid for Scientific Research (No. 23560647) from the Japan Society for the Promotion of Science (JSPS), Tokyo.
References (41)
- et al.
Anaerobic biological treatment of phenolic wastewater at 15-18 degrees
C. Water. Res.
(2005) - et al.
Monitoring the stability of an Anammox reactor under high salinity conditions
Biochem. Eng. J.
(2010) - et al.
Short- and long-term effects of temperature on the Anammox process
J. Hazard Mater.
(2008) - et al.
Biofilm and granular systems to improve Anammox biomass retention
Biochem. Eng. J.
(2008) - et al.
Kinetic study on nitrogen removal performance in marine anammox bacterial culture
J. Biosci. Biotechnol.
(2014) - et al.
Evaluating the recovery performance of the ANAMMOX process following inhibition by phenol and sulfide
Bioresour. Technol.
(2013) - et al.
Adaptation of a freshwater anammox population to high salinity wastewater
J. Biotechnol.
(2006) - et al.
Enrichment culture of marine anaerobic ammonium oxidation (anammox) bacteria from sediment of sea-based waste disposal site
J. Biosci. Bioeng.
(2009) - et al.
Temperature effect on nitrogen removal performance and bacterial community in culture of marine anammox bacteria derived from sea-based waste disposal site
J. Biosci. Bioeng.
(2012) - et al.
Effect of inoculum conditioning on hydrogen fermentation and pH effect on bacterial community relevant to hydrogen production
J. Biosci. Bioeng.
(2005)