Advanced oxygenation efficiency and purification of wastewater using a constant partially unsaturated scheme in column experiments simulating vertical subsurface flow constructed wetlands.

The presence of sufficient dissolved oxygen (DO) in a constructed wetland (CW) is vital to the process of removing ammonia nitrogen and organics from wastewater. To achieve total nitrogen removal, which is characterised by enhanced ammonia nitrogen removal, this study offers an efficient strategy to increase the oxygen supply by establishing constant unsaturated zones and baffles in simulating constructed wetlands (SCWs). Henceforth, this strategy is addressed as a partially unsaturated SCW. A centrally located high tube was set up inside the wetland to create an unsaturated zone at a higher level. The effectiveness of the unsaturated zone to supplement the oxygen content was evaluated by comparing with controls (an unaerated SCW and an aerated SCW). The results show the chemical oxygen demand removal rate (85 ±â€¯6%) in the partially unsaturated SCW was equivalent to that in the aerated SCW (83 ±â€¯6%), while the ammonia nitrogen removal rate was 11 times higher compared to that of the unaerated SCW. The removal potential of the partially unsaturated SCW under different HRT (hydraulic retention time)s (12, 24, and 36 h) was examined, and the 36 h-SCW performed the best in the removal of organics and nitrogen. The mechanisms behind the unsaturated zone strategy were studied by analysing water and microbe samples along the pathway. The results from the water quality indicators and the quantitative polymerase chain reactions along the pathway showed the unsaturated zone contributed to the removal of primary organics and ammonia nitrogen. The superior performance of unsaturated zone strategy was discussed further using the enrichment of ammonia-oxidising bacteria, mass of oxygen uptake, and baffle design. The results indicate that the amoA gene/16s rRNA gene abundance ratio and the oxygen uptake (336 ±â€¯44 g m-3 d-1) in the partially unsaturated SCW was higher than that observed in the two controls.

The configuration, purification effect and mechanism of intensified constructed wetland for wastewater treatment from the aspect of nitrogen removal: A review.

Constructed wetland (CW) for wastewater treatment has attracted increasing attention. In this review, the system configuration optimization, purification effect and general mechanisms of nitrogen removal in CW are systematically summarized and discussed. Ammonia oxidation is a crucial and primary process for total nitrogen (TN) removal in domestic or livestock wastewater treatment. Aeration, waterdrop influent and tidal operation are three main methods to strengthen the oxygen supplement and nitrification process in CW. Aeration significantly increases the ammonia removal rate (almost 100%), followed by the removal of chemical oxygen demand (COD) and TN. Solid carbon source, iron and anode material can be filled as electron donor for the denitrification process. The co-adjustment of oxygen and carbon/electron donor can form different conditions for different nitrogen removal pathways (e.g. the simultaneous nitrification-denitrification, the partial nitrification-denitrification and the anammox process), and achieve the optimal removal of nitrogen.

Carbon dioxide emissions from the electricity sector in major countries: a decomposition analysis.

The electric power sector is one of the primary sources of CO2 emissions. Analyzing the influential factors that result in CO2 emissions from the power sector would provide valuable information to reduce the world's CO2 emissions. Herein, we applied the Divisia decomposition method to analyze the influential factors for CO2 emissions from the power sector from 11 countries, which account for 67% of the world's emissions from 1990 to 2013. We decompose the influential factors for CO2 emissions into seven areas: the emission coefficient, energy intensity, the share of electricity generation, the share of thermal power generation, electricity intensity, economic activity, and population. The decomposition analysis results show that economic activity, population, and the emission coefficient have positive roles in increasing CO2 emissions, and their contribution rates are 119, 23.9, and 0.5%, respectively. Energy intensity, electricity intensity, the share of electricity generation, and the share of thermal power generation curb CO2 emissions and their contribution rates are 17.2, 15.7, 7.7, and 2.8%, respectively. Through decomposition analysis for each country, economic activity and population are the major factors responsible for increasing CO2 emissions from the power sector. However, the other factors from developed countries can offset the growth in CO2 emissions due to economic activities.

[Research on a special model of nerve impulse propagation].

Hodgkin-Huxley (HH) nerve model is a famous model which is used to describe nerve impulse propagation in nerve fibre. FitzHugh-Nagumo (FHN) model is a simplification of HH model, and Huxley equation is a special case of FHN equation. It has been shown that Huxley equation possesses the basic characteristics of nerve model. Researching on these models was often carried out in virtue of numerical techniques in the past. And, in so for as is known, an efficient and simple method which can be used to obtain analytic solutions is lacking. Yet, a qualitative analysis on Huxley equation's traveling system has been carried through in this paper. There is a bounded heteroclinic orbit having its one end in connection with a saddle point for the traveling wave system. Then a linear plane autonomous system whose singular point is a saddle point is chosen. By means of the system orbit vector's slope, and according to homogeneous balance principle, the traveling wave solutions of Huxley equation's traveling system are constructed. The method used here is called LS method.