[Effect of Ferric-carbon Micro-electrolysis on Greenhouse Gas Emissions from Constructed Wetlands].

As the problem of global warming becomes increasingly serious, the greenhouse gas (GHG) emission reduction measures of constructed wetlands (CWs) have drawn significant attention. Ferric-carbon micro-electrolysis exhibits an excellent effect on wastewater purification as well as the potential to reduce GHG emissions. Therefore, to explore the impact of ferric-carbon micro-electrolysis on GHG emissions from intermittent aeration constructed wetlands, four kinds of different wetlands with different fillers were constructed. The four fillers were ferric-carbon micro-electrolysis filler+gravel (CW-Ⅰ), ferric-carbon micro-electrolysis filler+zeolite (CW-Ⅱ), zeolite (CW-Ⅲ), and gravel (CW-Ⅳ). Intermittent aeration technology was used to aerate the wetland systems. The results show that ferric-carbon micro-electrolysis significantly improved the nitrogen removal efficiency of the intermittent aeration constructed wetlands and reduced GHG emissions. Compared with CW-Ⅳ, the CH4 fluxes of CW-Ⅰ, CW-Ⅱ, and CW-Ⅲ decreased by 32.81% (P<0.05), 52.66% (P<0.05), and 54.50% (P<0.05), respectively. Among them, zeolite exhibited a stronger reduction effect on CH4 emissions in both the aeration and non-aeration sections. The ferric-carbon micro-electrolysis substantially reduced N2O emissions. In comparison with CW-Ⅳ, CW-, and CW-Ⅱ achieved N2O emission reduction by 30.29%-60.63% (P<0.05) and 43.10%-73.87% (P<0.05), respectively. During a typical hydraulic retention period, the comprehensive GWP caused by CH4 and N2O emitted by each group of wetland system are (85.21±6.48), (49.24±3.52), (127.97±11.44), and (137.13±11.45) g·m-2, respectively. The combined use of ferric-carbon micro-electrolysis and zeolite effectively reduces GHG emissions in constructed wetlands. Overall, ferric-carbon micro-electrolysis combined with zeolite (CW-Ⅱ) can be regarded as one of the valuable filler combination methods for constructed wetlands, which can ensure high removal efficiency of pollutants and effective GHG emission reduction in constructed wetlands.

[Wastewater Treatment Effects of Ferric-carbon Micro-electrolysis and Zeolite in Constructed Wetlands].

Ferric-carbon micro-electrolysis fillers and zeolite have been increasingly used as substrates in constructed wetlands due to their good wastewater pollution-removal efficiencies. To explore the effects of different fillers on wastewater treatment in constructed wetlands, four constructed wetlands were examined with vertical subsurface flow areas filled with ferric-carbon micro-electrolysis filler+gravel (CW-A), ferric-carbon micro-electrolysis filler+zeolite (CW-B), zeolite (CW-C), and gravel (CW-D). In addition, intermittent aeration was used to improve the dissolved oxygen (DO) environment. The results showed that, compared with CW-D, the ferric-carbon micro-electrolysis filler significantly increased the dissolved oxygen (DO, P<0.05) and pH (P<0.05) of the effluent from the wetlands. The mean removal efficiency of chemical oxygen demand (COD) in the four constructed wetlands were more than 95% (P>0.05). For TN, the mean removal efficiency of CW-A,-B, and-C was 7.94% (P<0.05), 9.29% (P<0.05), and 3.63% (P<0.05) higher than that of CW-D, respectively. The contribution of ferric-carbon micro-electrolysis filler and zeolite to improving the TN removal efficiency of the constructed wetlands was 73.55% and 26.45%, respectively. The mean removal efficiency of NH4+ in the four wetlands ranged from 67.93% to 76.90%, and compared with CW-D, the other treatments significantly improved the removal efficiency of NH4+ (P<0.05). The ferric-carbon micro-electrolysis filler had an excellent removal effect on NO3-, with a removal efficiency of more than 99%, which was significantly higher than the constructed wetlands without ferric-carbon micro-electrolysis (P<0.05). Considering the treatment effect of the organic pollutants and the nitrogen-containing pollutants, CW-B achieved the best removal efficiency in constructed wetlands with intermittent aeration.

[Effect of Plastic Film Mulching on Methane and Nitrous Oxide Emissions from the Ridges and Furrows of a Vegetable Field].

Investigate the effects of plastic film mulching on CH4 and N2O emissions from a vegetable field, a one-year in situ field observation was conducted using a static opaque chamber in a pepper-radish cropping system at the Key Field Station for Monitoring of Eco-Environment of Purple Soil of the Ministry of Agriculture of China at Southwest University, Chongqing. Two treatments (conventional and film mulching) were used to study the influence of film mulching on CH4 and N2O emissions. The results showed that mulching significantly increased the annual average soil pH (P<0.01), annual surface and subsurface (5 cm) temperature (P<0.05), and soil moisture content during the radish-growing season (P<0.05). The mulching also significantly reduced CH4 emissions in the field ridges (P<0.05); the average CH4 flux from ridges during the pepper-growing season was 0.110 mg·(m2·h)-1 and 0.028 mg·(m2·h)-1, and 0.011 mg·(m2·h)-1 and -0.019 mg·(m2·h)-1 during the radish-growing season, under the conventional and film mulching treatments, respectively. However, across the entire experiment, CH4 flux from field furrows was not significantly different between the two mulching treatments (P>0.05), with mean flux values during the pepper-growing season of 0.058 mg·(m2·h)-1 and 0.057 mg·(m2·h)-1, and 0.083 mg·(m2·h)-1 and 0.092 mg·(m2·h)-1 during the radish-growing season, for conventional and plastic film mulching, respectively. Except for the conventional treatment during the pepper-growing season, CH4 emissions from ridges were significantly higher than from furrows, but for other treatments, including conventional and film mulching treatments during radish-growing season and film mulching treatment during the pepper-growing season, the CH4 emissions from furrows were all significantly higher than those from ridges. This was related to the stable anoxic environment created in furrows under high rainfall conditions in Southwest China. The N2O emission flux from the ridges during the pepper-growing season was 65.41 µg·(m2·h)-1 and 68.39 µg·(m2·h)-1 under the conventional and film mulching treatments, respectively, and the N2O emission flux during the radish-growing season was 78.43 µg·(m2·h)-1 and 66.19 µg·(m2·h)-1, respectively. The N2O flux between conventional treatment and film mulching treatment in ridges or furrows were not significantly different (P>0.05), while the N2O emissions from the ridges were significantly higher than that from the furrows. CH4 emission flux was significantly positively correlated with surface and subsurface temperature, while N2O emission flux was only significantly positively correlated with alkaline nitrogen and ammonium nitrogen content.

[Characteristics of Aerosol Optical Depth in the Urban Area of Beibei and Its Correlation with Particle Concentration].

To understand the atmospheric quality of the Beibei District of Chongqing, using the simultaneous observation data of aerosol optical depth and particulate matter concentration in 2014, we analyzed the characteristics of aerosol optical depth (AOD) in the urban area of Beibei and its correlation with particle concentration. The results showed that the annual average of AOD500nm in Beibei District is 1.46±0.69, which varies significantly by month. The highest value in November was 2.90±1.85, and the lowest in September was 0.54±0.05. There is particulate matter pollution in Beibei District. The annual average values of PM2.5 and PM10 are (62±40)µg·m-3 and (94±51)µg·m-3, respectively, which exceed the secondary standard of GB 3095-2012 Ambient Air Quality Standard. The limit values, the daily average over-standard rates of PM2.5 and PM10, are 26% and 15%, respectively. There was significant correlation between fine particle PM2.5 and PM10 concentration of respirable particulate matter. The annual coefficient of determination R2 could reach 0.95 (P<0.01). The correlation between AOD and PM2.5 and PM10 was positive throughout the year. The coefficient of determination R2 was 0.48 and 0.46, respectively, and the coefficient of determination and correlation function were different in different seasons, among which the correlation in winter was the best and the correlation in summer was the worst. AOD and air quality index showed positive correlation characteristics throughout the year, and the coefficient of determination R2 was 0.15 (P<0.05). The AOD value was affected by the comprehensive effects of weather elements. The temperature, humidity, water vapor, and other factor data should also be collected synchronously during the observation period.