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

Synergistic reduction of pollution and carbon mitigation in constructed wetlands-microbial fuel cell using sludge-derived biochar

Integrating microbial fuel cells (MFC) into constructed wetland systems (CW) has been an efficient wastewater treatment to improve the pollutants removal and regenerate power energy. This study fabricated a sludge biochar material (SBM) to sequestrate the carbon of residual sludge. Thereafter used SBM and modified SBM as the substrate materials to construct three groups of CW-MFC for decreasing the greenhouse gas (GHG) emission. The water quality improvement in removal efficiency achieved (2.59 %, 3.10 %, 5.21 % for COD; 3.31 %, 3.60 %, 6.71 % for TN; 1.80 %, 7.38 %, 4.93 % for TP) by the application of MFC, SBM, and modified SBM in wastewater treatment, respectively. Additionally, the reduction in global warming potential (GWP) realized 17.2 %, 42.2 %, and 64.4 % resulting from these applications. The carbon flow and fate diagrams showed MFC shifted the gas phase‑carbon flow from CH4 to CO2, and SBM promoted this shift trends. Microbial diversity indicated enrichment of electrochemically active bacteria (EAB), denitrifying bacteria, and phosphate accumulating organisms (PAOs) by SBM. Metabolic pathways analysis showed that introduction of MFC and SBM exhibited significant increases of key functional genes in metabolic pathway of anaerobic oxidation of methane (AOM). This study highlights the benefit of CW-MFC in and provides a new strategy for removing pollutants and abating GHG emissions in wastewater treatment.

Carbon-negative and high-rate nutrient recovery from municipal wastewater using mixotrophic Scenedesmus acuminatus

The efficiency of mixotrophic microalgae in enhancing the recovery of waste nutrients has been well established; however, the recovery rate is crucial in meeting the needs of field applications. This study evaluated the impact of media characteristics on nutrient recovery under mixotrophic conditions. The mixotrophic N recovery rate with S. acuminatus in modified BG-11 reached 2.59 mg L-1h-1. A mixotrophic growth optimization strategy was applied to achieve a high-rate nutrient recovery from municipal wastewater treatment plant effluents. The contribution of waste chemical oxygen demand (COD) to nutrient recovery was assessed using secondary effluent (SE) under heterotrophy. The results highlighted a significant increase in total nitrogen (TN) and total phosphorus (TP) recovery rates when glucose was supplied, indicating the additional carbon requirements for efficient nutrient recovery. The TN and TP recovery rates under mixotrophic conditions with the addition of trace metals and high cell density were enhanced by 91.94% and 92.53%, respectively, resulting in recovery rates of 3.43 mg L-1h-1 and 0.30 mg L-1h-1. The same conditions were used for nutrient recovery from primary effluent (PE), and the results were more satisfactory as the TN and TP recovery rates reached 4.79 and 0.55 mg L-1h-1, respectively. Additionally, the study estimated the carbon footprints (C-footprints) and areal footprints of mixotrophy-based nitrogen recovery. The findings revealed carbon footprints and areal footprints of -15.93 ± 4.57 tCO2e t-1 N recovery and 0.53 ± 0.19 m3 m-2d-1 wastewater, respectively. This high-rate nutrient recovery, achieved under a carbon-negative (C-negative) budget through mixotrophy, presents a novel strategy for efficiently recovering resources from municipal wastewater, thus facilitating resource recycling and ensuring environmental sustainability.

Reassessing the greenhouse effect of biogenic carbon emissions in constructed wetlands

Biogenic carbon emissions, including carbon dioxide (CO2) and methane (CH4), have emerged as a major concern during organic pollutant degradation within constructed wetlands (CWs). Since these organic compounds primarily originate from the photosynthetic fixation of atmospheric CO2, it potentially introduces uncertainty when assessing the greenhouse effect of biogenic carbon emissions in CWs based on direct field observations. To objectively assessing this effect, this study proposed a new strategy by quantifying CO2-equivalent (CO2-eq) changes as carbon passes through CWs and tested it in various types of CWs based on 64 literature records. The findings reveal that CWs can contribute to CO2-eq additions, yet are only responsible for 15.6% derived from direct field observations. The type of CWs plays a crucial role in these CO2-eq additions, with vertical flow CWs causing the lowest levels (6.8%), followed by surface flow CWs (14.2%). In contrast, horizontal flow CWs are associated with the strongest CO2-eq addition (25.7%). The findings provide new insights for the objective assessment of the greenhouse effect of biogenic carbon emissions in CWs, which will be beneficial for future life cycle assessment.

Utilization of polyphenylene sulfide as an organic additive to enhance gas separation performance in polysulfone membranes

Many studies have shown that sulfur-containing compounds significantly affect the solubility of carbon dioxide (CO2) in adsorption processes. However, limited attention has been devoted to incorporating organic fillers containing sulfur atoms into gas separation membrane matrices. This study addressed the gap by developing a new membrane using a polysulfone (PSf) polymer matrix and polyphenylene sulfide (PPs) filler material. This membrane could be used to separate mixtures of H2/CH4 and CO2/CH4 gases. Our study investigated the impact of various PPs loadings (1%, 5%, and 10% w/w) relative to PSf on membrane properties and gas separation efficiency. Comprehensive characterization techniques, including Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM), were employed to understand how adding PPs and coating with polydimethylsiloxane (PDMS) changed the structure of our membranes. XRD and FTIR analysis revealed distinct morphological disparities and functional groups between pure PSf and PSf/PPs composite membranes. SEM results show an even distribution of PPs on the membrane surface. The impact of adding PPs on gas separation was significant. CO2 permeability increased by 376.19%, and H2 permeability improved by 191.25%. The membrane's gas selection ability significantly improved after coating the surface with PDMS. CO2/CH4 separation increased by 255.06% and H2/CH4 separation by 179.44%. We also considered the Findex to assess the overall performance of the membrane. The 5% and 10% PPs membranes were exceptional. Adding PPs to membrane technology may greatly enhance gas separation processes.