Denghua Yan

Nitrate removal and bioenergy production in constructed wetland coupled with microbial fuel cell: Establishment of electrochemically active bacteria community on anode.

The constructed wetland coupled with microbial fuel cell (CW-MFC) systems operated at different substrate concentration and pH influents were evaluated for bioelectricity generation, contaminant removal and microbial community structure. Performance of CW-MFC was evaluated at organic loading rate of 75.3gCODm-3d-1 and pH gradients of (5.18±0.14, 7.31±0.13, and 8.75±0.12) using carbon fiber felt as electrodes. Peak power density was observed at slightly neutral influent condition. Compared with the open circuit CW-MFC, average COD and NO3-N removal efficiency in CW-MFC increased by 8.3% and 40.2% respectively under slightly neutral pH of influents. However, the removal efficiency and bioenergy production have been inhibited with acidic influents. The relative abundance of beta-Proteobacteria, nitrobacteria and denitrifying bacteria was significantly promoted in closed-circuit CW-MFC. Using of CW-MFC as a biochemical method for nitrate removal and bioelectricity generation under slightly neutral and alkaline influent conditions was a promising technology.

Microbial community structure of different electrode materials in constructed wetland incorporating microbial fuel cell

The microbial fuel cell coupled with constructed wetland (CW-MFC) microcosms were operated under fed-batch mode for evaluating the effect of electrode materials on bioelectricity generation and microbial community composition. Experimental results indicated that the bioenergy output in CW-MFC increased with the substrate concentration; maximum average voltage (177mV) was observed in CW-MFC with carbon fiber felt (CFF). In addition, the four different materials resulted in the formation of significantly different microbial community distribution around the anode electrode. The relative abundance of Proteobacteria in CFF and foamed nickel (FN) was significantly higher than that in stainless steel mesh (SSM) and graphite rod (GR) samples. Notably, the findings indicate that CW-MFC utilizing FN anode electrode could apparently improve relative abundance of Dechloromonas, which has been regarded as a denitrifying and phosphate accumulating microorganism.

High efficiency of inorganic nitrogen removal by integrating biofilm-electrode with constructed wetland: Autotrophic denitrifying bacteria analysis

The constructed wetland coupled with biofilm-electrode reactor (CW-BER) is a novel technology to treat wastewater with a relatively high level of total inorganic nitrogen (TIN) concentration. The main objective of this study is to investigate the effects of C/Ns, TIN concentrations, current intensities, and pH on the removal of nitrogen in CW-BER; a control system (CW) was also constructed and operated with similar influent conditions. Results indicated that the current, inorganic carbon source and hydrogen generated by the micro-electric field could significantly improve the inorganic nitrogen removal with in CW-BER, and the enhancement of average removal rate on NH3-N, NO3-N, and TIN was approximately maintained at 5-28%, 5-26%, and 3-24%, respectively. The appropriate operation conditions were I=10mA and pH=7.5 in CW-BER. In addition, high-throughput sequencing analysis implied that the CW-BER reactor has been improved with the relative abundance of autotrophic denitrifying bacteria (Thiobacillus sp.).

Effect of supplying a carbon extracting solution on denitrification in horizontal subsurface flow constructed wetlands

Denitrification strongly depends on the availability of carbon source in constructed wetlands (CWs). In this study, several relevant carbon source extracting solutions made from hydrolyzate of selected wetland litters were added to CWs for nitrogen removal enhancement. The feasibility of supplying a carbon extracting solution to improve potential denitrification rate in horizontal subsurface flow constructed wetland was deeply investigated. Combinations of different hydraulic retention time (HRT, especially for 2-day and 4-day) with different influent COD/N ratios were designed to prove the enhancement on denitrification by carbon source supplement. In addition, specific denitrification rate (SDNR) was calculated for the comparison of the nitrogen removal at different COD/N ratios. The sequential operation results on total nitrogen (TN) and nitrate (NO3−-N) removal efficiencies were obtained in CW system with an influent COD/N ratio of 4.0. The accumulation of nitrite (NO2−-N) was found to be closely related to the removal of NO3−-N. Meanwhile, no obvious accumulation of NO2−-N was found when the removal of NO3−-N was relatively high.

Bioenergy generation and rhizodegradation as affected by microbial community distribution in a coupled constructed wetland-microbial fuel cell system associated with three macrophytes

Rhizodeposits excreted by various macrophytes might lead to the potential discrepancy of microbial community distribution in constructed wetland coupled with microbial fuel cell (CW-MFC), which has been considered as main factors for the variations of bioelectricity generation during wastewater treatment. In this study, CW-MFC has been associated with three macrophytes (J. effuses, T. orientalis and S. validus) for domestic sewage treatment, also unplanted CW-MFC was performed as a control system. Macrophyte T. orientalis and S. validus can significantly strengthen the bioenergy output in CW-MFC. Highest current (94.27mAm-2) and power densities (21.53mWm-2) were obtained in CW-MFC planted with T. orientalis. Removal efficiencies of COD, NO3-N and NH3-N in CW-MFC planted with S. validus was respectively 5.8%, 7.2%, and 23.9% higher than that of unplanted system. Notably, the oxygen depletion in S. validus CW-MFC reactor during the dark cycle was higher that of other reactors. Results of high-throughput sequencing analysis showed that higher biodiversity was observed in rhizosphere than that of anode material, and the relative abundance of Desulfobulbus sp. and Geobacter sp. has been apparently promoted in the samples of rhizosphere. However, a higher relative abundance of electrochemically active bacteria (Proteobacteria) was observed on the surface of anode electrode material. In addition, microbes (Cytophagales, Clostridium sp., and Dechloromonas sp., and so forth) found in rhizosphere show a capability to decompose refractory contaminants. These contaminants and death roots in the upper part of wetland could be oxidized to fat acids, which may be used as the electrons acceptors for promoting the bioelectricity generation during wastewater treatment.

Effects of Elevated CO2 and Drought on Plant Physiology, Soil Carbon and Soil Enzyme Activities

Abstract Global climate models have indicated high probability of drought occurrences in the coming future decades due to the impacts of climate change caused by a mass release of CO 2 . Thus, climate change regarding elevated ambient CO 2 and drought may consequently affect the growth of crops. In this study, plant physiology, soil carbon, and soil enzyme activities were measured to investigate the impacts of elevated CO 2 and drought stress on a Stagnic Anthrosol planted with soybean (Glycine max). Treatments of two CO 2 levels, three soil moisture levels, and two soil cover types were established. The results indicated that elevated CO 2 and drought stress significantly affected plant physiology. The inhibition of plant physiology by drought stress was mediated via prompted photosynthesis and water use efficiency under elevated CO 2 conditions. Elevated CO 2 resulted in a longer retention time of dissolved organic carbon (DOC) in soil, probably by improving the soil water effectiveness for organic decomposition and mineralization. Drought stress significantly decreased C:N ratio and microbial biomass carbon (MBC), but the interactive effects of drought stress and CO 2 on them were not significant. Elevated CO 2 induced an increase in invertase and catalase activities through stimulated plant root exudation. These results suggested that drought stress had significant negative impacts on plant physiology, soil carbon, and soil enzyme activities, whereas elevated CO 2 and plant physiological feedbacks indirectly ameliorated these impacts.

Wastewater treatment potential of Moringa stenopetala over Moringa olifera as a natural coagulant, antimicrobial agent and heavy metal removals

Abstract Moringa is a multipurpose tree with considerable economic and social potential and its cultivation is currently being actively promoted in many developing countries. Seeds of this tropical tree contain water-soluble, positively charged proteins that act as an effective coagulant for water and wastewater treatment. This study evaluated the effectiveness of Moringa oleifera and Moringa stenopetala seed powder in water purification as a replacement coagulant. Water treatment with M. stenopetala was found to be more effective for water purification than treatment with M. oleifera seed. Indeed, it has been given little research and development attention. Unlike M. oleifera, little scientific research has been conducted on the properties and potential uses of M. stenopetala in general and its seeds in particular. However, the method should be encouraged in communities without safe water supply.