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The lack of carbon sources severely inhibits denitrification in wastewater with a low C/N ratio. Corncob and rice straw were chosen as supplementary carbon sources to bring into the wetland system to supplement the carbon sources needed for denitrification, and the enhancing effects of the two carbon sources on nitrogen removal from the wetland were studied. The cumulative release of carbon was in the order of rice straw[(145.17±9.44) mg·g -1 ]>corncob[(57.41±5.04) mg·g -1 ] based on the 11-day pure water extraction and release experiment, whereas the cumulative release of nitrogen was in the order of rice straw[(2.31±0.09) mg·g -1 ]>corncob[(0.66±0.08) mg·g -1 ]. The average carbon/nitrogen ratios released and accumulated by corncob and rice straw during the observation period were 94.78 and 63.64, respectively. Corncob was more suited as an additional carbon source than rice straw. COD concentrations in the effluent from the corncob and straw constructed wetlands were found to be below 50 mg·L -1 for the 58-day pilot test of subsurface flow constructed wetlands, except on days 8 to 12. The NO 3 - -N removal rates of the corncob-added built wetlands were 93%-99% over the observation period, with good denitrification performance. In comparison, the lowest NO 3 - -N removal rate of the constructed wetland with the addition of rice straw was only 76.8% at the late stage of operation, and the denitrification rate dropped dramatically. The control group removal rates of NO 3 - -N were only 76.2%-77.7%, indicating a clear lack of carbon sources. The accumulation of NO 2 - -N was also induced by a lack of carbon supply. NO 2 - -N effluent concentrations were 2.5-6 times and 6-26 times higher in the constructed wetlands with rice straw and the control groups, respectively, than those in the wetlands constructed with corncob. The addition of corncob resulted in a more substantial reduction in NO 2 - -N content in the constructed wetland than the addition of rice straw ( P <0.05). The TN removal rates of wetlands constructed with corncob and rice straw and the control group were 83.75%-93.49%, 76.59%-78.85%, and 67.85%-72.56%, respectively, with significant differences among the three ( P <0.01). Finally, pretreatment with dilute alkali heating raised the cumulative carbon release of corncob to (93.73±17.49) mg·g -1 and the carbon/nitrogen ratio to 175.8, significantly improving the carbon release performance of corncob and demonstrating that it is a suitable source of extra carbon.

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 CH 4 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 CH 4 emissions in both the aeration and non-aeration sections. The ferric-carbon micro-electrolysis substantially reduced N 2 O emissions. In comparison with CW-Ⅳ, CW-, and CW-Ⅱ achieved N 2 O 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 CH 4 and N 2 O 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.

Investigate the effects of plastic film mulching on CH 4 and N 2 O 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 CH 4 and N 2 O 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 CH 4 emissions in the field ridges ( P <0.05); the average CH 4 flux from ridges during the pepper-growing season was 0.110 mg·(m 2 ·h) -1 and 0.028 mg·(m 2 ·h) -1 , and 0.011 mg·(m 2 ·h) -1 and -0.019 mg·(m 2 ·h) -1 during the radish-growing season, under the conventional and film mulching treatments, respectively. However, across the entire experiment, CH 4 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·(m 2 ·h) -1 and 0.057 mg·(m 2 ·h) -1 , and 0.083 mg·(m 2 ·h) -1 and 0.092 mg·(m 2 ·h) -1 during the radish-growing season, for conventional and plastic film mulching, respectively. Except for the conventional treatment during the pepper-growing season, CH 4 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 CH 4 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 N 2 O emission flux from the ridges during the pepper-growing season was 65.41 μg·(m 2 ·h) -1 and 68.39 μg·(m 2 ·h) -1 under the conventional and film mulching treatments, respectively, and the N 2 O emission flux during the radish-growing season was 78.43 μg·(m 2 ·h) -1 and 66.19 μg·(m 2 ·h) -1 , respectively. The N 2 O flux between conventional treatment and film mulching treatment in ridges or furrows were not significantly different ( P >0.05), while the N 2 O emissions from the ridges were significantly higher than that from the furrows. CH 4 emission flux was significantly positively correlated with surface and subsurface temperature, while N 2 O emission flux was only significantly positively correlated with alkaline nitrogen and ammonium nitrogen content.