Variations of methane fluxes and methane microbial community composition with soil depth in the riparian buffer zone of a sponge city park.

Riparian buffers benefit both natural and man-made ecosystems by preventing soil erosion, retaining soil nutrients, and filtering pollutants. Nevertheless, the relationship between vertical methane fluxes, soil carbon, and methane microbial communities in riparian buffers remains unclear. This study examined vertical methane fluxes, soil carbon, and methane microbial communities in three different soil depths (0-5 cm, 5-10 cm, and 10-15 cm) within a riparian buffer of a Sponge City Park for one year. Structural equation model (SEM) results demonstrated that vertical methane fluxes varied with soil depths (λ = -0.37) and were primarily regulated by methanogenic community structure (λ = 0.78). Notably, mathematical regression results proposed that mcrA/pmoA ratio (R2 = 0.8) and methanogenic alpha diversity/methanotrophic alpha diversity ratio (R2 = 0.8) could serve as valid predictors of vertical variation in methane fluxes in the riparian buffer of urban river. These findings suggest that vertical variation of methane fluxes in riparian buffer soils is mainly influenced by carbon inputs and methane microbial abundance and community diversity. The study's results quantitatively the relationship between methane fluxes in riparian buffer soils and abiotic and biotic factors in the vertical direction, therefore contributing to the further development of mathematical models of soil methane emissions.

Controlling methane emissions from Integrated Vertical-Flow Constructed Wetlands by using potassium peroxymonosulfate as oxidant.

It is very important to control methane emissions to reduce global warming. In this study, a new attempt of one oxidant (potassium peroxymonosulfate (PMS)) was made to adjust the oxidation-reduction potential (Eh) by adding different mass of (0 g, 31.25 g, 62.5 g, 125 g, 250 g and 500 g) for the reduction of methane emissions from integrated vertical-flow constructed wetland (IVCW), where the IVCW system has been divided into the root-water system and the stem-leaf system of methane emissions. Results show that the reduced CH4 emission from IVCW was the highest with decreased by 43.5% compared to blank group (PMS = 0), when adding 125 g PMS. Importantly, the reduced CH4 from the root-water system of IVCW was higher than that of the stem-leaf system of IVCW, when adding PMS. It's found that Eh not only has a significant correlation with CH4 flux, but also has a significant relationship between PMS quality, DO, water temperature and sampling time (yEh = -0.44XPMS + 6.82XDO + 0.38t - 264.1, R2 = 0.99). It concludes that PMS, as an oxidant, is a very feasible method for controlling methane emissions from IVCW. It's concluded from this study that it is a feasible engineering method by using PMS as an oxidant for reducing methane emissions from IVCWs when treating artificial domestic sewage. Further research may combine other methods together such as microbiology, physical control and hydrology control for mitigating the CH4 emissions from constructed wetlands for more types of wastewater.

Carbon dioxide and methane emission of denitrification bioreactor filling waste sawdust and industrial sludge for treatment of simulated agricultural surface runoff.

Carbon dioxide (CO2) and methane (CH4) produced by denitrification bioreactors in processing agricultural surface runoff have contributed to increasing proportion of greenhouse gases (GHG) emissions. It is the first time to monitor and quantify the emission flux of CO2 and CH4 produced by laboratory-scale denitrification bioreactors which recycled waste Cunninghamia lanceolata sawdust (CLS) and industrial sludge (IS) as fillers to process simulated agricultural surface runoff. Sludge-water ratio, inflow rate and water flow direction are used as experimental factors to study the effect on the emission flux of CO2 and CH4. Results show that emission flux of CO2 from denitrification bioreactors with different sludge-water ratio approached 20 mg m-2h-1, simultaneously the average emission flux of CH4 produced by all bioreactors was 1.785 mg m-2h-1. The addition of sludge increased the emission flux of CH4 and had no significant effect on the emission flux of CO2. Increasing the inflow rate reduced the CO2 emission flux from 21.57 to 1.27 mg m-2h-1, and at the same time increased the CH4 emission flux from 0.007 to 9.54 mg m-2h-1. The gravity flow of wastewater reduced the emission flux of CO2 and CH4. The emissions of CO2 and CH4 from folded plate denitrification bioreactor with CLS and industrial sludge with a volume ratio of 1:2 can be reduced by 24.67% and 73.3%, respectively. There was no need to add special gas collection and treatment devices because CO2 and CH4 emission fluxes produced by the folded plate denitrification bioreactor and gravity denitrification bioreactor are not enough to increase the greenhouse effect. This study quantified the CO2 and CH4 produced by denitrification bioreactors filling CLS and IS, and provided a reference for future research on the gases produced by the denitrification process.