This research was conducted to determine the connections between dissolved oxygen (DO), chemical oxygen demand (COD), permanganate index (CODMn), five-day biochemical oxygen demand (BOD₅), and ammonia nitrogen (NH₃-H) across five reservoirs of Yunmeng County, China, from January to November 2022. Each month, water samples were collected and subjected to analysis using standard methods. The samples were collected and analyzed using standard methods: dissolved oxygen was determined using the electrochemical probe method, COD was measured via the rapid digestion spectrophotometric method, CODMn was detected using the potassium permanganate oxidation method, BOD₅ was determined using the dilution and inoculation method, and NH₃-N was measured by using the Nessler reagent spectrophotometry method. The results confirmed strong positive correlations between COD and CODMn, with different intensities from reservoir to reservoir. More specific and demanding COD parameters were used to estimate the level of oxygen consumption; hence, a more variable correlation strength was observed between BOD₅ and the other two parameters. Thus, BOD₅ was found to be the main indicator of biodegradable organic matter and bacterial oxygen consumption. However, the results were negative, showing a decreasing trend. This means that the oxygen content was lower in the majority of reservoirs, which is attributed to the decomposition of ammonia nitrogen and the presence of organic matter. These findings significantly contribute to the development of appropriate programs for efficient water quality monitoring and the development of reservoir-specific management strategies. This study suggests that there is a need for continuous monitoring of these parameters, together with the extension of the program to additional reservoirs and water quality indicators, along with the use of advanced modeling techniques to clarify the underlying factors that connect water quality parameters in these complex reservoir ecosystems.

The objectives of this study were to evaluate the cadmium adsorption capacity of iron–organic associations (Fe-OM) formed by laccase-mediated modification and assess the effect of Fe-OM on the immobilization of cadmium in paddy soil. Leaf organic matter (OM) was extracted from Changshan grapefruit leaves, and then dissolved organic matter (Lac-OM) and precipitated organic matter (Lac-P) were obtained by laccase catalytic modification. Different Fe-OM associations were obtained by co-precipitation of Fe with OM, Lac-OM, and Lac-P, respectively, and the adsorption kinetics, adsorption edge, and isothermal adsorption experiments of Cd on Fe-OM were carried out. Based on the in situ generation of Fe-OM, passivation experiments on Cd-contaminated soils with a high geological background were carried out. All types of Fe-OM have a better Cd adsorption capacity than ferrihydrite (FH). The theoretical maximum adsorption capacity of the OM-FH, Lac-OM-FH, and Lac-P-FH were 2.2, 2.53, and 2.98 times higher than that of FH, respectively. The adsorption of Cd on Fe-OM is mainly chemisorption, and the -OH moieties on the Fe-OM surface form an inner-sphere complex with the Cd ions. Lac-OM-FH showed a higher Cd adsorption capacity than OM-FH, which is related to the formation of more oxygen-containing groups in the organic matter modified by laccase. The immobilization effect of Lac-OM-FH on active Cd in soil was also higher than that of OM-FH. The Lac-OM-FH formed by laccase-mediated modification has better Cd adsorption performance, which can effectively inactivate the activity of Cd in paddy soil.

Despite the consensus that keeping global temperature rise within 1.5 °C above pre-industrial level by 2100 reduces the chance for climate change to reach the point of no return, the newest Intergovernmental Panel on Climate Change (IPCC) report warns that the existing commitment of greenhouse gas emission reduction is only enough to contain the warming to 3–4 °C by 2100. The harsh reality not only calls for speedier deployment of existing CO₂ reduction technologies but demands development of more cost-efficient carbon removal strategies. Here we report an ocean alkalinity-based CO₂ sequestration scheme, taking advantage of proton consumption during nitrate assimilation by marine photosynthetic microbes, and the ensuing enhancement of seawater CO₂ absorption. Benchtop experiments using a native marine phytoplankton community confirmed pH elevation from ~8.2 to ~10.2 in seawater, within 3–5 days of microbial culture in nitrate-containing media. The alkaline condition was able to sustain at continued nutrient supply but reverted to normalcy (pH ~8.2–8.4) once the biomass was removed. Measurements of δ¹³C in the dissolved inorganic carbon revealed a significant atmospheric CO₂ contribution to the carbonate alkalinity in the experimental seawater, confirming the occurrence of direct carbon dioxide capture from the air. Thermodynamic calculation shows a theoretical carbon removal rate of ~0.13 mol CO₂/L seawater, if the seawater pH is allowed to decrease from 10.2 to 8.2. A cost analysis (using a standard bioreactor wastewater treatment plant as a template for CO₂ trapping, and a modified moving-bed biofilm reactor for nitrate recycling) indicated that a 1 Mt CO₂/year operation is able to perform at a cost of ~$40/tCO₂, 2.5–5.5 times cheaper than that offered by any of the currently available direct air capture technologies, and more in line with the price of $25–30/tCO₂ suggested for rapid deployment of large-scale CCS systems.

Groundwater pollution in landfill-adjacent regions presents a critical environmental and public health issue. This study evaluates groundwater quality in Xiangyang City, focusing on drinking water sources and key pollution points near landfill sites. The investigation involved a comprehensive field survey, systematic sampling, and laboratory analysis to determine pollutant types, sources, and concentrations. A total of 13 landfill sites were examined, with 178 groundwater samples analyzed for physical, chemical, and biological indicators during both wet and dry seasons. The findings reveal that 27.0% of groundwater samples meet Class I standards, while 46.1% and 27.0% fall into Class IV and V categories, respectively, indicating a significant prevalence of poor-quality groundwater. Seasonal variations were observed, with both wet and dry seasons showing consistent distributions of Class I, IV, and V samples. Heavy metals such as lead and arsenic, along with organic pollutants like polychlorinated biphenyls and pesticides (e.g., hexachlorobenzene), were significant contaminants in several sites. Key indicators such as nitrate, ammonia nitrogen, manganese, and total hardness consistently exceeded standard limits, with the most affected sites including L4 and L5 in Xiangyang. This study identifies leachate infiltration as the primary cause of pollution, exacerbated by geological and agricultural non-point sources. Based on these findings, a robust framework for monitoring and controlling groundwater pollution is proposed, emphasizing stricter regulations, advanced monitoring systems, and cross-regional coordination. The results underscore the urgency of immediate intervention to safeguard groundwater quality in landfill-adjacent regions.

Crystal twinning, a common growth phenomenon, can substantially affect material performance in fields such as semiconductors, nonlinear optics, and drug development, yet its elimination during crystallization is challenging. This study presents a method for the controlled synthesis of ZSM-5 zeolite as either single crystals or twinned crystals using kaolin as the primary raw material. The method leverages the etching effect of ammonium fluoride (NH${⁠}_4$F) on the aluminosilicate structure derived from pre-treated kaolin. By adjusting the concentrations of NH${⁠}_4$F and the structure-directing agent tetrapropylammonium bromide (TPABr), pure ZSM-5 single crystals and twinned crystals were selectively synthesized. Conventionally, NH${⁠}_4$F is employed to introduce defects into zeolite structures. In contrast, this work demonstrates its utility in controlling crystal habit. The synthesis utilizes kaolin, an abundant and low-cost aluminosilicate mineral, to provide the entire aluminum source and a portion of the silicon source, offering an economical alternative to expensive precursors like aluminum isopropoxide. The resulting single and twinned crystals exhibited high crystallinity, demonstrating the viability of using natural minerals to produce high-quality zeolites. The physical and chemical properties of the kaolin-derived ZSM-5 were characterized and compared to those of ZSM-5 synthesized from conventional chemical reagents. A growth mechanism for the formation of single and twinned crystals is also proposed.