Simultaneous heterotrophic nitrification and aerobic denitrification by bacterium Rhodococcus sp. CPZ24
Highlights
► Rhodococcus sp. CPZ24 was isolated from swine wastewater and identified. ► Rhodococcus sp. CPZ24 generates primarily inert N2 rather than N2O. ► Rhodococcus sp. CPZ24 performs simultaneous heterotrophic nitrification and aerobic denitrification.
Introduction
Nitrogen (N) is a key nutrient for plants. The N cycle is a critical biogeochemical cycle in aquatic and terrestrial ecosystems. However, a series of environmental consequences has been resulted from the massive increases in fixed N within the aquatic environment (Conley et al., 2009), e.g., eutrophication problems in waterbodies and high nitrate concentrations in drinking water. Those problems are largely caused by livestock and poultry industries (Zhang, 2009). In China, the livestock and poultry industries produce approximately 173 billion tons of manure per year and an estimated 1.6 billion tons of nitrogen per year (Zhou, 2005). Furthermore, most of livestock manure runs out directly into fresh water from livestock houses and so has seriously degraded local water quality. Controlling and reducing nitrogen content in wastewater from livestock farming prior to discharge and developing appropriate nitrogen management technologies are critical for the quality of water systems. Biotreatment is an effective and low-cost technology for reducing the nitrogen content in the wastewater. Biological nitrification–denitrification is one of the most economical processes for nitrogen removal from wastewaters (Gupta and Gupta, 2001).
Inorganic nitrogen can be removed traditionally by both autotrophic nitrifying and heterotrophic denitrifying microorganisms (Fu et al., 2009). Such strategies require separate treatment processes and strict treatment condition control, making these technologies prohibitively expensive (Khardenavis et al., 2007, Kim et al., 2005). Simultaneous nitrification and denitrification (SND) is an attractive method to treat wastewater. It implies that nitrification and denitrification occur concurrently in the same reaction vessel under identical overall operating conditions (Schmidt et al., 2003). Recent studies showed that most heterotrophic-nitrifying bacteria are capable of aerobic denitrification, including Alcaligenes faecalis (Joo et al., 2007), Pseudomonas stutzeri (Su et al., 2001), Microvirgula aerodenitrificans (Patureau et al., 2001), Alcaligenes faecalis (Joo et al., 2007), P. putida (Kim et al., 2008), and Acinetobacter calcoaceticus (Zhao et al., 2010a, Zhao et al., 2010b).
Rhodococcus species being capable of heterotrophic nitrification have been studied (Zhang et al., 2003). However, little has been examined about the removal of ammonium from wastewater through SND by Rhodococcus bacteria. In this study, Rhodococcus sp. CPZ24 was isolated from swine wastewater and shown the ability of heterotrophic nitrification and aerobic denitrification not only in batch flasks, but also in bioreactor settings. Moreover, nitrogen gas from the bioreactor was detected to confirm SND by Rhodococcus sp. CPZ24.
Section snippets
Sampling and culture medium preparation
Six wastewater samples were collected from swine wastewater ponds in Xiaoshan County, Zhejiang Province, China in April 2008 and used to isolate heterotrophic nitrification and aerobic denitrification bacteria.
The enrichment medium (EM) consisted of 0.5 g L−1 ammonium sulphate, 2.17 g L−1 sodium succinate dibasic hexahydrate (C4H4Na2O4·6H2O) at pH 7.2. 50 mL of a trace element solution were added to 950 mL EM medium. The trace element solution contained 6.5 g L−1 dipotassium hydrogen phosphate
Isolation and characterization strain CPZ24
A heterotrophic nitrification-aerobic denitrification bacterium, strain CPZ-24 was isolated from swine wastewater pond. The CPZ24 cells were Gram-positive and non-motile. The cells were rod-shaped and demonstrate branched filaments during the early growth phase; cells then fragmented into short rods or cocci. The partial 16S rDNA sequence (1437 bp) of strain CPZ24 was determined and deposited in the GenBank database (GenBank ID: HQ123621). A phylogenetic tree was constructed based on 16S rDNA
Conclusions
Rhodococcus sp. CPZ24 was a newly isolated bacterium from swine wastewater. It can remove nitrate and ammonium at a rate of 3.1 mg L−1 h−1 and 0.93 mg L−1 h−1, respectively, in batch flasks. These values are higher than most bacterial species with similar functions such as Bacillus sp. LY and P. alcaligenes AS-1 (Su et al., 2006, Zhao et al., 2010a, Zhao et al., 2010b). Rhodococcus sp. CPZ24 is capable of heterotrophic nitrification and aerobic denitrification as demonstrated in 50-L steel sealed
Acknowledgements
This work was funded by the National Science and Technology Support Plan (No. 2009BADC2B04, 2006BAD17B09 and 2006BAD10B09) and National “973” Plan (No. 2012CB417100) from MOST, China.
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