Environmental Technology最新文献

Polyurethane grouting is a type of chemical grouting with the potential to immobilize contaminants in the deep vadose zone (DVZ), which lies above the groundwater table and typically below the depth at which open excavation is practical or cost-effective. One concern with grouting is the risk of mobilizing contaminants and dispersing them over a wider area, potentially worsening the situation. This study presents laboratory grouting tests to investigate the contaminant displacement during polyurethane grouting in the DVZ at the Hanford Site. Additionally, the study evaluates the effectiveness of soil desiccation and soil freezing in reducing contaminant displacement by reducing the amount of movable containing contaminant water. The test results indicate that polyurethane grouting immobilizes 9.1 ± 3.5% of contaminants. Soil desiccation effectively reduces contaminant displacement to 2.3%. In contrast, soil freezing does not significantly reduce contaminant displacement, primarily due to two factors: polyurethane flushing and gas production during curing. Gas generated during polyurethane curing can mobilize soil water, leading to contaminant displacement. Test results with different rates of gas production also indicate higher rates of gas production lead to a larger iodide displacement ratios. The resin with the highest measured gas production rate of 1.56 × 10^-4 mol/(mL·h) resulted in a displacement ratio of 0.351, whereas the resin with the lowest measured gas production rate 7.00 × 10^-5 mol/(mL·h) resulted in a much lower displacement ratio of 0.101 when both tests used soil water content of 5%. These findings offer valuable insights for using polyurethane grouting to immobilize contaminants in DVZs.

Electrochemical reduction is an efficient method for treating high-concentration nitrate wastewater, providing benefits such as enhanced controllability and the elimination of secondary pollution. In this study, the CuNi/NF electrode was fabricated by direct current electrodeposition of copper and nickel onto nickel foam, which served as the cathode for the electrochemical reduction of nitrate. The electrode demonstrated superior nitrate removal performance, achieving an NO₃^--N removal rate of 83% after 5 h of reaction at an initial concentration of 500 mg/L, significantly outperforming the Cu/NF electrode (76%) and Ni/NF electrode (57%). The influence of key operating parameters on nitrate reduction was systematically investigated. The results indicated that the electrode prepared with a deposition time of 20 min exhibited the highest removal efficiency. Under optimal conditions (current density of 25 mA/cm², Cl^- concentration of 2 g/L, and initial pH of 7), the NO₃^--N removal rate reached 85%, with N₂ selectivity as high as 93.7%. The CuNi/NF electrode also exhibited good stability over five consecutive cycles. Finally, a plausible mechanism for nitrate reduction was proposed. This study provides fundamental data and theoretical support for the practical application of electrochemical methods in treating high-concentration nitrate wastewater.

The following study uses Life Cycle Assessment as a tool to determine the impacts generated by the treatment of sludge from municipal wastewater treatment plants (EWC 190805). In this paper, four scenarios of technologies used for sludge disposal are presented: scenario A considers dewatered and undigested sludge sent to landfill; in scenario B the sludge undergoes a stabilization process for use on land; scenario C considers incineration of the dried sludge; and in scenario D the sludge undergoes the same treatment as in scenario B but for final use as compost. The system boundaries include transport to the various disposal centers, using functional units equal to one ton of dried sludge. House made software was used to calculate the impacts, using input data from an existing plant located in central Italy. The environmental categories analyzed were global warming potential, acidification potential and eutrophication potential. The results per functional unit indicate that land application has the lowest GWP impact, while incineration without recovery produces the highest. The analysis was then extended to the national level with data from the ISPRA database. Research using LCA can be useful for decision-makers and stakeholders on strategies to improve environmental performance on the topic.

The present study attempted to investigate the impact of the micro-aerobic condition in a conventional Up-Flow Anaerobic Sludge Blanket Reactor (UASB) using different media for the treatment of municipal wastewater. The Hydraulic Retention Time (HRT), Dissolved Oxygen (DO), intermittent and continuous aeration were the important operating conditions of this study carried out for more than 1015 days. Fourier transform infra red (FTIR) spectra and SEM analysis indicate the significant growth of the microbiota responsible for the removal of nutrients. Significant increase in the removal of the chemical oxygen demand (COD)∼ 91%, biochemical oxygen demand (BOD)∼ 90%, suspended solids (SS)∼ 92%, and ammonical nitrogen (NH₄⁺-N)∼ 90%, were observed at lower DO levels. Sulphate was dominant due to sulphide oxidation during micro-aerobic conditions in almost all study phases, which resulted in an increase of up to 90% of the influent sulphates. The micro-aerobic UASB process could be a feasible option for achieving the latest treated effluent disposal norms and significantly reducing the energy demand for wastewater treatment.

Polyhydroxyalkanoates (PHAs) are eco-friendly, biodegradable thermoplastics that have the potential to replace conventional plastics with sustainable biopolymers for several applications. This study aimed to isolate and identify halotolerant strains and to optimise the parameters influencing PHA production using response surface methodology. Furthermore, enhancing PHA production and evaluating the effects of low-dose gamma irradiation on Halomonas mongoliensis AL-ARS. Fifteen bacterial isolates were screened using Sudan Black B for PHA production. The most efficient isolate was Halomonas mongoliensis AL-ARS, identified through morphological, biochemical, and molecular techniques. Response surface methodology using Plackett-Burman and central composite design models is used to optimise factors influencing PHA synthesising. Additionally, the effect of low-dose gamma irradiation was examined. The purified PHA polymer was structurally characterised using FTIR, XRD, and ¹H-NMR. Glucose was the optimal carbon source, while minimal salt media was the most suitable media for PHA production. The best production conditions (10 g/L glucose, 40.5°C, 6.5 days, 2.5% inoculum) yielded 0.0960 g/L of PHA. Remarkably, gamma irradiation at 0.5 kGy significantly increased PHA production by 76%, confirming its role as a stress-inducing factor and highlighting irradiation's potential to overcome production bottlenecks. Structural analyses confirmed the purified polymer as a standard PHA. This work is the first study highlighting the integration of gamma irradiation with a statistical optimisation to boost PHA biosynthesis using Halomonas mongoliensis AL-ARS, a halophilic strain with no previous study on PHA improvement, presenting a scalable strategy for sustainable, eco-friendly, cost-effective bioplastic production, and bridging the gap between lab-scale and industrial application.

This study addressed the issue of elevated ammonia nitrogen pollution in wastewater from ionic rare earth mining operations. Given the high costs and limited efficiency of conventional biological denitrification methods, the sulphur-based autotrophic denitrification (SAD) process was explored as a cost-effective alternative to improve nitrogen removal performance. A sequencing batch reactor was operated over 70 days to cultivate and maintain granular sludge, successfully enriching sulphur-oxidising bacteria (SOB). During this cultivation phase, the average sludge particle size increased from 228.69 μm to 709.95 μm, the granulation rate reached 84.56%, and the relative abundance of the SOB genus Thiobacillus rose to 13.57%. An orthogonal experimental design was employed to optimise the operational parameters of the SAD granular sludge. Single-factor experiments were first conducted to assess the effects of sodium bicarbonate concentration (0-2000 mg/L), sludge concentration (3500-6000 mg/L), reaction duration (2-12 h), and sodium sulfide concentration (0-300 mg/L) on the removal efficiencies of total inorganic nitrogen (TIN). The results indicated that sodium bicarbonate concentration was the most influential factor. Subsequently, an L₉(3⁴) orthogonal experiment was designed to determine the optimal operational conditions: 1600 mg/L sodium bicarbonate, 5000 mg/L sludge concentration, 8 h of reaction time, and 37.5 mg/L sodium sulphide. Under these optimised conditions, the TIN removal efficiency reached 67.64%. Economic analysis demonstrated that the unit denitrification cost of the SAD process was 31.83% lower than that of the heterotrophic denitrification process, highlighting its potential as a low-carbon and efficient solution for treating rare earth mining wastewater.

The biomass in agricultural and forestry waste has a high value for resource utilization. In this study, biochar materials were prepared for treating wastewater containing polycyclic aromatic hydrocarbons (PAHs). To eliminate pyrene rather than transfer it onto the adsorbent, this study employed a chemical oxidation method to degrade pyrene using persulfate as the oxidant and biochar as the activator. When the pH of the solution was 3 and the dosage of biochar was 0.9 g/L, the biochar (BC₁, BC₂ and BC₃) prepared from sawdust, coconut shells and agricultural straw reduced the C/C₀ value to 0.12, 0.09 and 0.05 respectively, indicating that the biochar had a good adsorption effect on pyrene. BC₃ was chosen to activate persulfate to degrade pyrene, and under the conditions of solution pH of 3, persulfate concentration of 10 mM, and BC₃ dosage of 1.5 g/L, the C/C₀ value decreased to 0.04 and the removal efficiency of pyrene was 96%. In the BC₃/persulfate oxidation system, oxidative degradation played a dominant role in the removal of pyrene. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FITR) analyses demonstrated that the catalysis of persistent free radicals (PFRs) on the biochar surface was the main mechanism for the activation of persulfate to produce SO₄^•- for the degradation of pyrene.

Volatile organic compounds (VOCs) endanger the environment and human health. Among various control methods, activated carbon (AC) adsorption has become an industrial mainstream due to its high removal efficiency. The traditional iodine value (IV) assessment method is time-consuming and difficult to apply in real time. It is important to note that AC, after adsorbing VOCs, is classified as hazardous waste. This study explores indirectly characterizing the adsorption performance of AC through electrical resistance (ER) measurements. Experiments conducted at 26°C and 50% RH using an optimized device (with dimensions of 78 × 157 × 72 mm, equipped with graphite electrodes and applying a pressure of 750 Pa) revealed a significant negative correlation between ER and IV: ER increases monotonically as IV decreases, and both stabilize when the adsorption reaches saturation. The ER of the initial AC is significantly affected by the environment: for every 15% increase in relative humidity, ER decreases by 27.2%; for every 10°C increase in temperature, ER increases by 1.5 Ω. Based on this, a temperature-humidity compensation model was established to correct environmental interferences, with an IV prediction coefficient of determination (R²) of 0.85. This ER-IV correlation, combined with the compensation model, provides a new method for the rapid assessment of the adsorption performance of AC; further optimization is required to improve its universality and accuracy under different conditions.

Municipal solid waste incineration (MSWI) fly ash is a hazardous waste, and traditional landfill disposal lacks sustainability. Resource utilization offers a viable pathway for its future management. Heavy metals are key hazardous components in fly ash, and their stabilization is essential for resource utilization. However, traditional high-temperature treatments are energy-intensive and costly, limiting large-scale application. This study proposed an energy-efficient, medium-temperature treatment method for fly ash and evaluated its environmental risks. Molecular dynamics simulations were conducted to elucidate the underlying mechanisms of heavy metal stabilization. The study revealed that co-sintering fly ash with clay at 750°C and 950°C led to a significant reduction in heavy metal leachability, with Pb and Zn concentrations decreasing by 97.4% and 61.7%, respectively. The sintered products developed new fibrous mineral phases, predominantly wollastonite and rankinite, within which heavy metal ions were incorporated through isomorphic substitution for Ca²⁺ in the crystal lattice, leading to stable immobilization. Sequential extraction analysis showed that the chemical forms of heavy metals shifted from acid-soluble to more stable reducible and oxidizable fractions after treatment. Consequently, the environmental risk levels of Zn and Pb decreased from moderate to negligible, while that of Cd was reduced from high to negligible. Long-term leaching tests under simulated acid rain conditions confirmed that the sintered products maintain high stability during prolonged environmental exposure.