Application potential of a newly isolated indigenous aerobic denitrifier for nitrate and ammonium removal of eutrophic lake water
Introduction
Over the last few years, tremendously amount of artificial nitrogen fertilizer has been used for high crop yields to meet the rapidly growing human population (Galloway et al., 2008, Lunau et al., 2012, Tilman et al., 2002). Accordingly, substantial amount of nitrate and ammonium entered into water bodies such as lakes, reservoirs and seas (Zhou et al., 2007) via tributary rivers, and hence, an increasing number of aquatic ecosystems in China occurred hyper eutrophication and serious algal blooms in recent years. A large (area 2338 km2) shallow (mean depth 1.9 m) freshwater lake, Lake Taihu, which is the third largest one in China, has suffered greatly from anthropogenic eutrophication since 1980s (Qin et al., 2007), especially in the northern areas. The proliferation of toxic algae in summer is seriously impacting the public health, local economy and ecosystem in Lake Taihu regions. Moreover, the increased presence of aqueous nitrate and ammonium is a serious environmental problem because ammonium is toxic to fish and other aquatic life (Siljeg et al., 2010) and nitrate damages their immune system (Grguric et al., 2000). Thus nitrogen removal efficiently in eutrophic water bodies is a stringent research.
Conventional nitrogen removal means from wastewater and natural lakes include physical, chemical and biological approaches. Biological aerobic nitrification and anaerobic denitrification have been found to be reliable and should be encouraged due to their easy implementation and efficiency (Borges et al., 2003). Nevertheless, in order to remove ammonium and nitrate in the natural environment, a creation of aerobic and anoxic conditions alternately is needed but technological and economical constrained (van Rijn et al., 2006). The finding of organism Thiosphaera pantotropha in 1988 (Robertson et al.) realized the simultaneous nitrification and denitrification and could tolerate oxygen. Nitrogen removal becomes easy in open water body because this process can happen in aerobic environment instead of anoxic environment. Furthermore, alkalinity generated during denitrification can partly compensate for the acidification caused by nitrification. Therefore, it is procedural simplicity and can reduce the cost.
In recent decades, more and more heterotrophic nitrification–aerobic denitrification microorganisms were screened and characterized, such as Alcaligenes faecalis (Anderson et al., 1993), Microvirgula aerodenitrificans (Patureau et al., 1998), Pseudomonas sp. (Zhang et al., 2011), Rhodococcus sp. (Chen et al., 2012a), Bacillus methylotrophicus (Zhang et al., 2012), Agrobacterium sp. (Chen and Ni, 2011) and so on. These microorganisms were mostly isolated from activated sludge or wastewater treatment plants. However, these strains may meet acclimation problems in eutrophic freshwater lakes because of the low carbon source level which could limit the denitrification process (Obaja et al., 2005) and the relatively low nitrate and ammonium concentrations. To overcome this problem, an autochthonous strain which can perform heterotrophic nitrification–aerobic denitrification in eutrophic aquatic niche might be helpful.
The aim of this research was to isolate a novel autochthonous heterotrophic nitrification–aerobic denitrification strain from the eutrophic Lake Taihu in order to overcome the acclimation problems in utilization, and evaluate its application potential in both nitrate and ammonium removal from aquatic eutrophication.
Section snippets
Media
The media used in aerobic denitrifiers isolation were screening medium (SM), solid and semisolid bromothymol blue medium (BTB). The SM (pH 7.2) included the following reagents per liter: sodium succinate, 2.84 g; NaNO3, 10 mM; KH2PO4, 1.36 g; (NH4)2SO4, 0.27 g; yeast extract, 1 g; MgSO4·7H2O, 0.19 g; TE (trace element) solution, 1 ml. The ingredients of solid BTB (pH 7.0–7.3) were as follows per liter: agar, 20 g; KNO3, 1 g; KH2PO4, 1 g; FeCl2·6H2O, 0.5 g; CaCl2·7H2O, 0.2 g; MgSO4·7H2O, 1 g; sodium
Characterization of the isolated strain
In a typical experiment 48 strains which could denitrify in semisolid BTB tube medium were obtained. According to previous studies, nitrate consumption, pH increasing and bubble formation indicated a denitrification process (Bonin et al., 2002). pH increasing and bubble formation were observed for three strains in less than 1 day during incubation at the same conditions, and the most promising one (named strain T1) was characterized and identified.
The 16S rRNA sequence of strain T1 was 99%
Conclusions
In this study, a newly isolated indigenous aerobic denitrifier, which was identified as P. stutzeri strain T1, was evaluated the potential for removing nitrate and ammonium in the eutrophic Lake Taihu of China. The isolated strain exhibited heterotrophic nitrification–aerobic denitrification characteristics and showed the strong growth and nitrogen removal capabilities. The optimum conditions for nitrate and ammonium removal were C/N ratio of 8, citrate as the carbon source in natural lake
Acknowledgement
This work is supported by grants from National Special Program of Water Environment (2012ZX07101006).
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