How does microorganism in different zones cooperatively promote N2O emissions from SWIS during freeze-thaw?

Subsurface wastewater infiltration systems (SWIS) are environmentally-friendly technologies for domestic wastewater treatment, where pollutants are removed by physical, chemical and biological reactions. However, SWIS also produce nitrous oxide (N2O), a potent greenhouse gas. Distribution of dissolved oxygen and nitrogen in SWIS determines denitrification process, which affects microbial activity and N2O release degree in different layers of system. Top layer of SWIS substrate is exposed to environmental factors such as freeze-thaw (FT), which changes microbial community structure in different substrates. Exact mechanisms of microbial-mediated N2O emissions in SWIS are still unclear despite extensive research. Therefore, this study simulated FT process using in-situ SWIS, to investigate how FT disturbance affects microbial community structure and N2O release in SWIS profiles. Results showed that after the ninth freeze-thaw cycle, FT stimulated anaerobic bacteria activities such as Euryarchaeota, accounting for 78.4 % of total Euryarchaeota population in middle (60 cm) and 33.97 % in the lower layer. Under low oxygen conditions, NO2--N accumulation in middle and lower layers provided a sufficient nitrogen source for Euryarchaeota. Canonical correlation analysis (CCA) showed Euryarchaeota was significantly correlated with N2O emissions in middle and lower layers during FT, contributing 31.68 %-32.01 % and 61.78 %-65.15 %, respectively. These results suggested that FT disturbance enhanced denitrification by anaerobic bacteria in middle and lower layers of SWIS, significantly increasing N2O emissions. However, specific pathways and mechanisms of N2O production by Euryarchaeota remain to be elucidated in future studies.

Adsorption behaviour of microplastics on the heavy metal Cr(VI) before and after ageing.

As the important carriers of environmental pollutants, microplastics have a significant impact on the migration, transformation and toxicology of heavy metals. In this paper, the adsorption behavior of Cr(VI) on PE/PS/PA microplastics under UV irradiation was studied. The research results show that the adsorption capacity of original PA is the strongest, followed by PS and PE. The specific surface area of the aged microplastics increased and new functional groups were formed, so the adsorption of three microplastics for Cr(VI) was stronger than that before aging. The average saturation adsorption of Cr(VI) by PA/PS/PE increased respectively from 730.69 µg/g, 146.11 µg/g and 75.61 µg/g to 736.31 µg/g, 318.75 µg/g and 136.78 µg/g. The Langmuir and Freundlich models showed that the adsorption is more consistent with the Freundlich model, indicating that adsorption is mainly based on multi-molecular layer adsorption on non-homogeneous surfaces. In the Cu-Cr polluted water, Cu has different effects on the adsorption behavior. Cu can promote the adsorption of Cr(VI) by PE and PS, while inhibited the adsorption by PA. In addition, environmental conditions such as temperature, pH and dissolved organic matter also have significant effects on adsorption behavior. Mechanistic analysis confirmed that electrostatic interaction plays an important role. Secondly, based on the surface physicochemical properties of the microplastics, surface complexation and van der Waals forces also significantly enhance the adsorption of Cr(VI) on the aged microplastics.

The life cycle of micro-nano plastics in domestic sewage.

As a kind of novel pollutant, microplastics and nanoplastics have been commonly found in all regions of the world and have attracted widespread attention in recent years. Wastewater treatment plants are considered an important "source" and "sink" of micro-nano plastics pollution, so it is significant to study its transportation and fate in wastewater plants. This review summarizes the types and sources of micro-nano plastics in domestic wastewater and compares their removal efficiency and migration in different treatment processes in wastewater plants. The interlinkages and ecological risks among surface water, soil and atmospheric environments are also analyzed, providing a reference for future research on the impact of wastewater treatment plants on micro-nano plastics pollution.

Clogging in subsurface wastewater infiltration beds: genesis, influencing factors, identification methods and remediation strategies.

Subsurface wastewater infiltration (SWI) is an environmentally friendly technology for the advanced treatment of domestic sewage. Clogging (including physical, chemical and biological clogging) of the porous medium not only directly reduces the hydraulic load (treatment efficiency), but also reduces the service life. Although clogging has become one of the key issues discussed in several reports, there are still several gaps in understanding, especially in its occurrence process and identification. SWI clogging causes, development process and solutions are different from those of constructed wetlands. This article quotes some reports on constructed wetlands to provide technical ideas and reference for revealing SWI clogging problems. Based on the analysis of the clogging genesis, this review gathers the main factors that affect the degree of clogging, and new methods for the identification of clogging conditions. Some preventive and unclogging measures/strategies are presented. Finally, it is suggested that to effectively alleviate the clogging phenomenon and extend the service life, priority should be given to the comprehensive analysis of wastewater quality and solid constituents accumulated in the pores. Then, the effectiveness of in-situ strategies, such as alternating operation will be the main focuses of future research.

Early oxidation of the martian crust triggered by impacts.

Despite the abundant geomorphological evidence for surface liquid water on Mars during the Noachian epoch (>3.7 billion years ago), attaining a warm climate to sustain liquid water on Mars at the period of the faint young Sun is a long-standing question. Here, we show that melts of ancient mafic clasts from a martian regolith meteorite, NWA 7533, experienced substantial Fe-Ti oxide fractionation. This implies early, impact-induced, oxidation events that increased by five to six orders of magnitude the oxygen fugacity of impact melts from remelting of the crust. Oxygen isotopic compositions of sequentially crystallized phases from the clasts show that progressive oxidation was due to interaction with an 17O-rich water reservoir. Such an early oxidation of the crust by impacts in the presence of water may have supplied greenhouse gas H2 that caused an increase in surface temperature in a CO2-thick atmosphere.