Short CommunicationNitrogen removal through “Candidatus Brocadia sinica” treating high-salinity and low-temperature wastewater with glycine addition: Enhanced performance and kinetics
Graphical abstract
Introduction
Anaerobic ammonia oxidation (anammox) is widely applied in biological nitrogen removal from wastewater due to its unique characteristics such as negligible sludge production, low energy consumption and no requirement for additional external carbon (Xing et al., 2015). Anammox bacteria form a distinct phylogenetic group belonging to the phylum Planctomycetes, and six candidatus genera including 21 species have been tentatively proposed for anammox taxonomic group (Mao et al., 2017). “Candidatus Brocadia sinica” affiliated with freshwater-derived genera “Candidatus Brocadia”, which was first identified from laboratory wastewater treatment in 2010 (Hu et al., 2010). The metabolic pathway of “Candidatus Brocadia sinica” is hydroxylamine-dependent and different from other anammox bacteria (Oshiki et al., 2016). Moreover, Oshiki et al. (2011) reported that “Candidatus Brocadia sinica” was sensitive to high-salinity and low temperature conditions.
High-salinity wastewater originated from many industries can induce cell plasmolysis due to rapid increase in osmotic pressure (Liu et al., 2014). Li et al. (2018) reported that marine anammox bacteria (MAB) had good tolerance to salinity and good nitrogen removal performance at 3.5% salinity. However, MAB accounts for a relatively small proportion in nature and is not easily to enrich (Jin et al., 2011). The physiology of “Candidatus Brocadia sinica” indicated that their activity decreased by 70% in the presence of 3% salinity (Oshiki et al., 2011). Low temperature inhibited the activity of anammox bacteria and resulted in ammonium and nitrite accumulations (Jin et al., 2013a). Oshiki et al. (2011) reported that 25–45 °C was the optimum temperature for “Candidatus Brocadia sinica” and the activity of “Candidatus Brocadia sinica” at 15 °C decreased by 25% compared to the activity at 40 °C. However, the temperature of collected wastewater is usually below 25 °C, which limits the nitrogen removal through “Candidatus Brocadia sinica” (Xing et al., 2015). Therefore, it is necessary to take some measures to enhance nitrogen removal performance of “Candidatus Brocadia sinica” treating high-salinity and low-temperature wastewater.
Compatible solutes (CSs) are organic compounds with low molecular weight, functioning inside the cell with no need for special adaptation of intracellular enzymes (Vyrides and Stuckey, 2017). The CS can not only reconcile high osmotic pressure but also alleviate other environmental stresses such as low temperature and freezing (Boetius et al., 2015). Vyrides and Stuckey (2017) reported that methane production during batch anaerobic digestion under high-salinity and low-temperature condition was four times higher when CS was added. Glycine, one of the CSs, widely exists in pharmaceutical and chemical wastewater. Ai et al. (2009) reported that glycine could improve growth of “Streptomyces albidoflavus DUT_AHX” in the presence of 10% salinity. Cao et al. (2017) found that the tolerance of glycine-treated rice to cold stress strengthened. Although the enhancement of glycine on organism activity under low temperature or high salinity stress has been reported, no literature is available that glycine can increase the activity of anammox bacteria under the combined stresses of low temperature and high salinity.
According to the facts presented above, in this work, nitrogen removal performance of “Candidatus Brocadia sinica” treating high-salinity and low-temperature wastewater with glycine addition was investigated. Besides, metabolic enzyme activity of “Candidatus Brocadia sinica” throughout the process was evaluated. Still, three kinetic models were performed to analyze nitrogen removal in an operating cycle with glycine addition.
Section snippets
Reactor configuration and operating conditions
Double-jacketed sequencing batch reactor (SBR) was fabricated with polymethyl methacrylate with an effective volume of 7.0 L (presented in Fig. 1a). The reactor was covered with aluminum caps to prevent growth of phototrophic micro-organisms. Stirring speed was set at 100 rpm and operational temperature was controlled at 15 ± 0.5 °C. Operating mode of the reactor consisted of 0.5 h influent feeding, 5 h anoxic stirring reaction, 0.5 h sludge settling and 0.5 h effluent discharging. In addition,
Nitrogen removal performance of “Candidatus Brocadia sinica” with glycine addition
Nitrogen removal performance of “Candidatus Brocadia sinica” treating high-salinity and low-temperature wastewater with glycine addition was presented in Fig. 2. As shown in Fig. 2a, when glycine was no more than 0.8 mM, effluent NH4+-N and NO2−-N decreased with increasing glycine. At 0.6 mM glycine, effluent NO3−-N was achieved the maximum (13 mg/L). Qi et al. (2018) reported that NO3−-N production was an indicator of the growth of anammox bacteria. It suggested that appropriate glycine could
Conclusions
With glycine addition, SBR was used to explore nitrogen removal performance of “Candidatus Brocadia sinica” treating high-salinity and low-temperature wastewater. Optimum nitrogen removal was obtained at 0.8 mM glycine. ARR and NRR increased by 45.4% and 95.7%, respectively. Nitrite reductase and hydrazine synthase activities were increased at low glycine content, which brought about enhancement in nitrogen removal performance. Nitrogen removal of “Candidatus Brocadia sinica” in an operating
Acknowledgements
The work was financially supported by National Natural Science Foundation of China (51878362) and China Postdoctoral Science Foundation (2017M610410 and 2018T110665).
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