Overlooked in-situ sulfur disproportionation fuels dissimilatory nitrate reduction to ammonium in sulfur-based system: Novel insight of nitrogen recovery

Sulfur-based denitrification is a promising technology in treatments of nitrate-contaminated wastewaters. However, due to weak bioavailability and electron-donating capability of elemental sulfur, its sulfur-to-nitrate ratio has long been low, limiting the support for dissimilatory nitrate reduction to ammonium (DNRA) process. Using a long-term sulfur-packed reactor, we demonstrate here for the first time that DNRA in sulfur-based system is not negligible, but rather contributes a remarkable 40.5 %-61.1 % of the total nitrate biotransformation for ammonium production. Through combination of kinetic experiments, electron flow analysis, 16S rRNA amplicon, and microbial network succession, we unveil a cryptic in-situ sulfur disproportionation (SDP) process which significantly facilitates DNRA via enhancing mass transfer and multiplying 86.7-210.9 % of bioavailable electrons. Metagenome assembly and single-copy gene phylogenetic analysis elucidate the abundant genomes, including uc_VadinHA17, PHOS-HE36, JALNZU01, Thiobacillus, and Rubrivivax, harboring complete genes for ammonification. Notably, a unique group of self-SDP-coupled DNRA microorganism was identified. This study unravels a previously concealed fate of DNRA, which highlights the tremendous potential for ammonium recovery and greenhouse gas mitigation. Discovery of a new coupling between nitrogen and sulfur cycles underscores great revision needs of sulfur-driven denitrification technology.

Enhanced adaptability of pyrite-based constructed wetlands for low carbon to nitrogen ratio wastewater treatments: Modulation of nitrogen removal mechanisms and reduction of carbon emissions

Pyrite-based constructed wetlands (CWs) stimulated nitrate removal performance at low carbon to nitrogen (C/N) ratio has been gaining widely attention. However, the combined effects of pyrite and C/N on the nitrate removal mechanisms and greenhouse gases (GHGs) reduction were ignored. This study found that pyrite-based CWs significantly enhanced nitrate removal in C/N of 0, 1.5 and 3 by effectively driving autotrophic denitrification with high abundance of autotrophs denitrifiers (Rhodanobacter) and nitrate reductase (EC 1.7.7.2), while the enhancement was weakened in C/N of 6 by combined effect of mixotrophic denitrification and dissimilatory nitrate reduction to ammonium (DNRA) with high abundance of organic carbon-degrading bacteria (Stenotrophobacter) and DNRA-related nitrite reductase genes (nrf). Moreover, pyrite addition significantly reduced GHGs emissions from CWs in all stages with the occurrence of iron-coupled autotrophic denitrification. The study shed light on the potential mechanism for pyrite-based CWs for treating low C/N ratio wastewater.

Efficient rural sewage treatment with manganese sand-pyrite soil infiltration systems: Performance, mechanisms, and emissions reduction

The application of soil infiltration systems (SISs) in rural domestic sewage (RDS) is limited due to suboptimal denitrification resulting from factors such as low C/N (<5). This study introduced filler-enhanced SISs and investigated parameter impacts on pollutant removal efficiency and greenhouse gas (GHG) emission reduction. The results showed that Mn sand-pyrite SISs, with hydraulic load ratios of 0.003 m3/m2·h and dry-wet ratios of 3:1, achieved excellent removal efficiency of COD (92.7 %), NH4+-N (95.8 %), and TN (76.4 %). Moreover, N2O and CH4 emission flux were 0.046 and 0.019 mg/m2·d, respectively. X-ray photoelectron spectroscopy showed that the relative concentrations of Mn(Ⅱ) in Mn sand and Fe(Ⅲ) and SO42- in pyrite increased after the experiment. High-throughput sequencing indicated that denitrification was mainly performed by Thiobacillus. This study demonstrated that RDS treatment using the enhanced SIS resulted in efficient denitrification and GHG reduction.

[Motives, goals and anticipated barriers as experienced by employees engaged in an initiative promoting sustainability at a general hospital - A qualitative analysis]

BACKGROUND

As a consequence of the climate crisis, a drastic reduction of greenhouse gas emissions and a transformation towards a sustainable economy are indispensable for the health care sector.

METHODS

For the present study, barriers and facilitators in implementing a transformation towards more sustainability were evaluated in qualitative interviews with members of an initiative attempting to establish more sustainability at a general hospital.

RESULTS

In 12 interviews, the interviewees were asked about the necessary personal characteristics for their commitment, short- and long-term ideas about how to reduce green house gas emissions, as well as barriers and facilitators of the organization's structure and of the societal context.

CONCLUSION

The methods for implementing more sustainability at a general hospital are mostly known. However, more knowledge is needed about the capacity to withstand both organizational barriers and feelings of hopelessness and impotence in order to preserve one's ability to act.

Application of calcium oxide/ferric oxide composite oxygen carrier for corn straw chemical looping gasification

Biomass chemical looping gasification (CLG) technology is an important utilization form of renewable energy. In order to obtain high-quality syngas, CaO/Fe₂O₃ was used as a composite oxygen carrier for biomass CLG in this study. The CLG experiment of corn straw and the study of oxygen carrier recycling were carried out, simultaneously, the reaction mechanism was further discussed. Results shown adding CaO to oxygen carrier could significantly improve the quality of syngas through increasing the H₂ and reduce Greenhouse gas (CO₂ and CH₄, about 14% reduction). Besides, the ratio of Fe₂O₃ to CaO, steam to biomass, and oxygen carrier to biomass all affected the syngas composition (the H₂/CO variation from 1.82 to 2.19), while the temperature had obvious influence on the gas yield of CLG. The most possible reaction mechanism shown that the variation of Ca might be the main factor of gas composition fluctuation.

Comparison of the energetic, environmental, and economic performances of three household-based modern bioenergy utilization systems in China

The methods of life cycle assessment and cost-effectiveness analysis were employed to compare the energetic, environmental, and economic performances of three household-based modern bioenergy (MBE) utilization systems: biogas utilization (BGs), biomass briquette utilization for energy only (BBs), and biomass briquette utilization for energy and biochar (BCs). The results showed that all the three MBEs performed positive results in net energy output, which ranged from 0.86 to 3.75 MJ (kg crop residues)^-1. The positive greenhouse gas reductions also can be acquired when using these three MBEs to substitute for traditional energy, respectively. The cost-effectiveness values of three MBE systems ranged from 343 RMB (tCO_2e)^-1 for BGs to 598 RMB (tCO_2e)^-1 for BCs (the CO_2e indicates the CO₂ equivalent). Considering the supply index analysis results furtherly, the BGs is regarded as the best strategy for the development of MBE in rural households. However, BG leakage during BG digester operations should be received much greater attention to avoid adverse impacts on GHG mitigation.

Field assessment of semi-aerobic condition and the methane correction factor for the semi-aerobic landfills provided by IPCC guidelines

According to IPCC guidelines, a semi-aerobic landfill site produces one-half of the amount of CH4 produced by an equally-sized anaerobic landfill site. Therefore categorizing the landfill type is important on greenhouse gas inventories. In order to assess semi-aerobic condition in the sites and the MCF value for semi-aerobic landfill, landfill gas has been measured from vent pipes in five semi-aerobically designed landfills in South Korea. All of the five sites satisfied requirements of semi-aerobic landfills in 2006 IPCC guidelines. However, the ends of leachate collection pipes which are main entrance of air in the semi-aerobic landfill were closed in all five sites. The CH4/CO2 ratio in landfill gas, indicator of aerobic and anaerobic decomposition, ranged from 1.08 to 1.46 which is higher than the values (0.3-1.0) reported for semi-aerobic landfill sites and is rather close to those (1.0-2.0) for anaerobic landfill sites. The low CH4+CO2% in landfill gas implied air intrusion into the landfill. However, there was no evidence that air intrusion has caused by semi-aerobic design and operation. Therefore, the landfills investigated in this study are difficult to be classified as semi-aerobic landfills. Also MCF of 0.5 may significantly underestimate methane emissions compared to other researches. According to the carbon mass balance analyses, the higher MCF needs to be proposed for semi-aerobic landfills. Consequently, methane emission estimate should be based on field evaluation for the semi-aerobically designed landfills.