Search

The present study explored treatment performance and nitrogen removal mechanisms of a novel tidal flow constructed wetland (TF CW) under C/N ratios ranging from two to 12. High and stable COD (83–95%), NH 4 + − N (63–80%), and TN (50–82%) removal efficiency were simultaneously achieved in our single-stage TF CW without costly aeration. Results showed that a C/N ratio exceeding six was required to achieve complete denitrification without NO 2 − − N and NO 3 − − N accumulation in the system. Molecular biological analyses revealed aerobic ammonia oxidation was the dominant NH 4 + − N removal pathway when the C/N ratio was less than or equal to six. However, when the C/N ratio was greater than six, anammox was notably enhanced, resulting in another primary NH 4 + − N removal pathway, in addition to the aerobic ammonia oxidation. Quantitative response relationships between nitrogen transformation rates and nitrogen functional genes were established, and these relationships confirmed that different nitrogen transformation processes were coupled at the molecular level (functional genes), and collaboratively contributed to nitrogen removal in the TF CW. Specifically, NH 4 + − N transformation rates were collectively determined by amoA , nxrA , anammox, narG , nirS , nirK , and nosZ ; and TN removal was influenced primarily by amoA and anammox. [ABSTRACT FROM AUTHOR]

Abstract: This study explores a bibliometric approach to quantitatively evaluate global scientific constructed wetlands research, and statistically assess current trends, and future directions using the Science Citation Index Expanded (SCI-EXPANDED) database from 1991 to 2011. Articles referencing constructed wetlands were analyzed by accessing the following: publication language, output characteristics, publication performance by country and institution, author keywords, title words, and KeyWords Plus. Synthetically analyzing three keyword types, we concluded that the dominant constructed wetlands research hotspots from 1991 to 2011 included water, nutrients, plants, and flow. These four hotspots remained the most dominant research areas throughout our study period, and are predicted to remain the top research emphases in the near future. “Soil” also exhibited a notable increase since 2005, and is likely to become another notable area of research interest in the future. “Phytoremediation” and “horizontal” were not identified in 1991–1995, but exhibited marked increases from 136th (0.5%) and 169th (0.7%) in 1996–2000, to 9th (3.8%) and 11th (4.3%) in 2006–2011, respectively. Therefore, given the heightened attention during the last 15years, these topics are likely to become a primary research focus in upcoming years. [Copyright &y& Elsevier]

Abstract: The present study, a quantitative investigation of distribution patterns of functional gene communities, including Anammox bacteria 16S rRNA, amoA, nxrA, narG, napA, nirK, qnorB, nosZ, nas, and nifH in two multimedia constructed wetland systems (CWs) was conducted. DGGE results showed similar distribution patterns in two constructed wetland groups. Lactococcus sp. and Moraxella sp. were the dominant organic nitrogen and denitrification flora; Acinetobacter sp. were the dominant NO3 − to NH4 + transformation flora; and Bacillus sp. and β-Proteobacteria sp. were the dominant NH4 + removal flora in the two constructed wetland groups. Quantitative real-time PCR results showed the qnorB and nas functional genes were predominantly enriched in the 15cm and 60cm layers of the CW, which was prepared by multi-media packing of 1% zero-valent iron. The nirK was predominantly enriched in the 60cm layer of the CW, which was prepared by multi-media packing of 2% zero-valent iron. Other functional nitrogen transformation genes were predominantly enriched in the 15cm layer of CWs. [Copyright &y& Elsevier]

A pilot subsurface flow constructed wetland (CW) has been constructed in the Liaohe Delta, China to treat heavy oil-produced water with large amounts of dissolved recalcitrant organic compounds. Pollutant concentrations and change of wetland plants were periodically monitored. Treatment effectiveness was evaluated and indicated high mean removal efficiencies, 81% for chemical oxygen demand (COD), 89% for biochemical oxygen demand (BOD5), 89% for mineral oil, and 81% for total Kjeldahl nitrogen (TKN) achieved in reed bed#2, to produce wetland effluent average concentrations with COD 77 mg l−1, BOD5 3.5 mg l−1, TKN 2.2 mg l−1, and mineral oil 2.9 mg l−1. We observed that during the vegetation growth period there was no influence of heavy oil-produced water on the numbers of leaves of reeds in CW, whereas, the biomasses and heights of reeds showed significant loss with increasing hydraulic loading. The heavy oil-produced water had no obvious effect on the reed indices of cellulous, lignin, pentose and the length/width ratio of cellulose. [Copyright &y& Elsevier]

The present study explored treatment performance and nitrogen removal mechanisms of a single-stage tidal flow constructed wetland (TFCW) under flooded time ranging from 12 to 48 h. The TFCW achieved high and stable COD (77–94%), NH 4 + –N (55–82%), and TN (60–84%) removal efficiencies simultaneously, without costly aeration. Quantitative response relationships between nitrogen transformation rates and nitrogen functional genes were established, and these relationships confirmed that, under the FT constraints, the anammox 16S rRNA was the key factor of the NH 4 + –N transformation rates, whereas, ( napA + narG ) was the key factor regulating the NO 3 − –N transformation rate. The analysis also revealed that the simultaneous nitrification, anammox, and denitrification (SNAD) process was the dominant nitrogen removal pathway in the TFCW. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Adding an external source under low C/N can significantly improve nitrogen removal efficiency. • N transformation processes were coupled at the functional genes level. • The vertical distribution of the microbial community in CWs was a remarkable discrepancy. • Adding rice husk as a carbon source could be conducive to the complete nitrification process. Abstract The effect of adding rice husk as an electron donor on the genetic and metabolic diversity of denitrifying communities in a long-term flooded constructed wetland (D1) was compared with the control group without external carbon source addition (D2). The underlying molecular mechanisms responsible for nitrate removal were quantified under different nitrate loading rates. The results showed that D1 achieved higher and more stable removal efficiencies for NO 3 −-N (90–97%) and total nitrogen (73–87%) under different nitrate loading rates, which were approximately 10 times higher than those of D2. This corresponded with much higher absolute abundances of bacterial and nitrogen functional genes in D1 than D2. Additionally, the vertical distribution of microbial communities in D1 and D2 showed significant differences. This pattern suggested that adding rice husk in flooded CWs had beneficial effects on the denitrifying community. Quantitative response relationships and network analysis indicated that denitrification was the dominant nitrogen removal pathway. Moreover, the present study indicated that using rice husk as an external carbon source could be conducive to completing the nitrification process, which was first confirmed at the molecular level. The present study indicated that using rice husk as an external carbon source can significantly enhance denitrification rates and thus improve nitrogen removal in CWs for wastewater treatment process. [ABSTRACT FROM AUTHOR]

Constructed wetlands (CWs) have been widely used for ecological remediation of micro-polluted source water. Nitrous oxide (N 2 O) from CWs has caused great concern as a greenhouse gas. However, the contribution of ammonia oxidation driven by ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) to N 2 O emission, especially at low temperature, was unknown. This study aimed to quantify the contributions of AOA and AOB to N 2 O through lab-scale subsurface CWs. The N 2 O emission flux of CW at 8 °C was 1.23 mg m−2·h−1, significantly lower than that at 25 °C (1.92 mg m−2·h−1). The contribution of ammonia oxidation to N 2 O at 8 °C (33.04%) was significantly higher than that at 25 °C (24.17%). The N 2 O production from AOA increased from 1.91 ng N·g−1 at 25 °C to 4.11 ng N·g−1 soil at 8 °C and its contribution increased from 23.38% to 30.18% (P < 0.05). Low temperature impaired functional gene groups and inhibited the activity of AOB, resulting in its declined contribution. Based on the transcriptional analysis, AOA was less affected by low temperature, thus stably contributing to N 2 O. Moreover, community diversity and relationships of AOA were enhanced at 8 °C, while AOB declined. The results confirmed the significant contribution of AOA and demonstrated molecular mechanisms (higher activity and community stability) of the increased contribution of AOA to N 2 O at low temperature. [Display omitted] • N 2 O emission from ammonia oxidation in constructed wetlands was first quantified. • AOA produced 90.2% more N 2 O at low temperature than at room temperature. • The relative contribution of AOA to N 2 O at 8 °C was 121.61% of that at 25 °C. • Low temperature impaired functional gene groups and decreased the activity of AOB. • Contributions of AOA and AOB to N 2 O could not be ignored especially at low temperature. [ABSTRACT FROM AUTHOR]

• Nitrogen removal in constructed wetlands is achieved mainly through microorganisms. • Coupling of nitrogen transformation functional microorganisms in nitrogen removal conserves oxygen and energy. • The activity and diversity of nitrifiers and denitrifiers are significantly affected by plant species. • Coupling mechanisms for which substrates play the role of electron donor enhancing microbial denitrification are emphasized. • Microbial autotrophic denitrification induced by Fe, S, H and other inorganic elements can improve nitrogen removal rates. Nitrogen removal through microorganisms is the most important pathway in constructed wetlands (CWs). In this review, we summarize the microbial coupling mechanisms of nitrogen removal, which are the common methods of nitrogen transformation. The electron pathways are shortened and consumption of oxygen and energy is reduced during the coupling of nitrogen transformation functional microorganisms. The highly efficient nitrogen removal mechanisms are cultivated from the design conditions in CWs, such as intermittent aeration and tidal flow. The coupling of microorganisms and substrates enhances nitrogen removal mainly by supplying electrons, and plants affect nitrogen transformation functional microorganisms by the release of oxygen and exudates from root systems as well as providing carriers for microbial attachment. In addition, inorganic elements such as Fe, S and H act as electron donors to drive the autotrophic denitrification process in CWs. [ABSTRACT FROM AUTHOR]