Intermittent micro-aeration control of methane emissions from an integrated vertical-flow constructed wetland during agricultural domestic wastewater treatment

Reduction of methane and nitrous oxide emissions from stormwater bioretention cells through microbial electrolytic cells

This study investigated the reduction of methane (CH4) and nitrous oxide (N2O) emissions from stormwater bioretention cells through microbial electrolytic cell (MEC), showing the largest reduction of 32.21 % (CH4) at 9.2 μA/m2 of current density and 56.16 % (N2O) at 3.5 μA/m2 of current density, compared with the corresponding in the control (0 μA/m2 of current density). Kinetic of CH4 and N2O emissions could be well fitted by Logistic model with high correlation coefficient (R2 > 0.9500) and model efficiency (ME > 0.95) but low relative root mean square error (RRMSE < 7.88). The increase of pmoA and polysaccharide (PS) were responsible for CH4 reduction, while N2O reduction was attributed to the decrease of nirS and the increase for nosZ and protein (PN), which could explain the lowest GWPd (10.67 mgCO2-eq/m2/h) at 3.5 μA/m2 of current density, suggesting that MEC could be promising for the reduction of CH4 and N2O emissions from bioretention cells.

Metagenomics insights into the performance and mechanism of soil infiltration systems on removing antibiotic resistance genes in rural sewage

The removal of antibiotic resistance genes (ARGs) in sewage is of great concern, but advanced sewage treatment technologies are not suitable for rural areas, so the multi-layer soil infiltration system (MSL) has been developed for rural sewage treatment. However, little is known about the performance and function of MSL in the treatment of ARGs in rural sewage. Here, we optimized the matrix composition and structure of MSL and explored the efficacy and mechanism of MSL systems for ARG removal under different hydraulic conditions. The ARGs removal rate of MSL ranged from 41.51% to 99.67%, in which MSL with the middle hydraulic load, high pollution load, and continuous inflowing conditions showed the best removal performance. In addition, this system can operate stably and resist the temperature fluctuation, which showed an equivalent removal rate of ARGs in warm and cold seasons, amounting to 69.0%. The structural equation model revealed that microorganisms in sewage could significantly affect ARG removal (path coefficient = 0.91), probably owing to their interspecies competition. As for the internal system, the reduction of ARGs was mainly driven by microorganisms in the system matrix (path coefficient = 0.685), especially soil-mixture-block (SMB) microorganisms. The physicochemical factors of the matrix indirectly reduce ARGs by affecting the microorganisms that adhere to the matrices. Note that the pairwise alignment of nucleotide analysis demonstrated that the system matrix, especially biochar in the SMB, adsorbed ARGs and their hosts from the sewage, and in turn eliminated them by inhibiting the spread and colonization of hosts, thereby reducing the abundance of ARGs. Collectively, this study provides a deeper insight into the removal of ARGs from rural sewage by MSL, which can help improve sewage treatment technologies.

Recent advances in constructed wetlands methane reduction: Mechanisms and methods

Constructed wetlands (CWs) are artificial systems that use natural processes to treat wastewater containing organic pollutants. This approach has been widely applied in both developing and developed countries worldwide, providing a cost-effective method for industrial wastewater treatment and the improvement of environmental water quality. However, due to the large organic carbon inputs, CWs is produced in varying amounts of CH4 and have the potential to become an important contributor to global climate change. Subsequently, research on the mitigation of CH4 emissions by CWs is key to achieving sustainable, low-carbon dependency wastewater treatment systems. This review evaluates the current research on CH4 emissions from CWs through bibliometric analysis, summarizing the reported mechanisms of CH4 generation, transfer and oxidation in CWs. Furthermore, the important environmental factors driving CH4 generation in CW systems are summarized, including: temperature, water table position, oxidation reduction potential, and the effects of CW characteristics such as wetland type, plant species composition, substrate type, CW-coupled microbial fuel cell, oxygen supply, available carbon source, and salinity. This review provides guidance and novel perspectives for sustainable and effective CW management, as well as for future studies on CH4 reduction in CWs.

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 (y_Eh = -0.44X_PMS + 6.82X_DO + 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.

Efficiency and kinetics of conventional pollutants and tetracyclines removal in integrated vertical-flow constructed wetlands enhanced by aeration

The integrated vertical-flow constructed wetland (IVCW) is considered as a potential alternative for domestic wastewater treatment of towns and small cities. Oxygen supply is the main limitation of pollutants removal in IVCWs. In the present study, a field experiment was conducted to evaluate the capacity and kinetics of pollutants removal in IVCWs with/without artificial aeration. Two IVCWs constructed with Canna indica and Phragmites australis were running in continuous flow to remove high concentrations of conventional pollutants and low concentrations of tetracyclines (TETs), which are at similar levels of domestic wastewater. The results showed that IVCWs had a good performance on COD, phosphorus, and TETs with removal efficiencies over 80%, 64%, and 75%, respectively, with a hydraulic retention time (HRT) of 3.0 d. However, the removal of nitrogen was limited, showing as TN removal efficiency of about 30%. The IVCW with Phragmites australis had a higher removal efficiency and rate. A kinetics based on Monod Equation and solved with Matlab 2018a could describe the degradation of conventional pollutants. Artificial aeration improved the oxygen supply and remarkably raised the removal capacity for COD, N, and P in IVCWs. The q_1/2 values, which was defined as the average removal loading before half of the pollutants was removed and represented the removal capacity without limitation of pollutants concentration, were increased by 5-30 times after aeration. In conclusion, IVCWs could remove conventional pollutants and TETs simultaneously showing a great potential in domestic wastewater treatment. Artificial aeration enhanced removal capacity of IVCWs on conventional pollutants while showed little influence on TETs.