Biochar is frequently applied for the reduction of mercury (Hg) migration in soil; however, most of the studies only focused on the adsorption capacity evaluation of fresh biochar. We investigated the Hg adsorption capacities of biochar prepared from wheat straw, corn straw, and sunflower seed shells. Biochar aging was simulated via natural aging, high-temperature aging, and freeze-thaw aging. The adsorption capacities of all the aged biochar were increased, and wheat straw biochar and seed shells biochar treated with high-temperature aging (wBC-Ha500 and sBC-Ha600) and corn straw biochar treated with freeze-thaw aging (cBC-Fta500) showed an observable improvement on the equilibrium adsorption amounts. The kinetics of the fresh biochar samples fitted the pseudo-first-order kinetic model and the pseudo-second-order kinetic model, while the kinetics of the aged biochar samples fitted the pseudo-second-order kinetic model. Biochar adsorption capacity increased with higher initial concentrations and increasing temperatures. Elemental analysis, Fourier-transform infrared spectroscopy (FT-IR) spectra, cation-exchange capacity (CEC), surface area (SA), zeta potential, and X-ray photoelectron spectroscopy (XPS) showed that the aging mechanism consisted of hydroxylation and carboxylation caused by the functional groups on the biochar surface. According to the different climatic zones in China, wheat straw biochar and seed shell biochar are suitable for the tropical zone and the subtropical zone, while corn straw biochar is more suitable for the cold and the mid-temperate zones.

Raw coal fly ash (RCFA) was recycled as three kinds of adsorbents by hydroxyl anion (OH⁻), hydrogen ion (H⁺), and thermal activation, respectively, for the adsorption of Cr(VI) from water. The H⁺ activation can explore the adsorptive potential of RCFA more effectively than the other two methods. The specific surface areas of the adsorbents are 12.33, 16.32, and 13.89 m² g⁻¹ for OH⁻, H⁺, and thermal activation, respectively. The adsorption process follows the pseudo-second-order kinetic model and the Langmuir model better and exhibits exothermic property. The activation energy (20.65–31.88 kJ mol⁻¹) and the negative Gibbs free energy reveal that the adsorption is a physical and spontaneous process. The adsorbents derived from OH⁻, H⁺, and thermal activation can be used at least 5, 7, and 4 times, respectively, while the one from H⁺ activation has the best adsorption capacity (6.41 μg g⁻¹ for the first run). The adsorption process can introduce other metallic/toxic elements, but within the Chinese standard. The preparation cost of the H⁺ activation is $1103 ton⁻¹ adsorbent, while the treatment cost is $1.6 ton⁻¹ water. The more accurate parameters in the pseudo-second-order kinetic model and Langmuir model can be calculated by nonlinear method and provided by the error function of the sum of the squares of the errors.

Commercial activated carbon fiber (ACF) has been employed as particle electrodes to degrade aqueous m-cresol in 3-D electrode systems. To enhance the electrooxidation performance, three types of new ACF modification modes (anodic oxidation, cathodic reduction, and aqueous oxidation with concentrated HNO₃) were introduced in this paper. These pretreated samples were characterized by N₂ adsorption, scanning electron microscopy (SEM), cyclic voltammetry (CV), temperature-programmed desorption mass (TPD-MS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR). It was revealed that the two new modification methods could efficiently modify the surface morphology as well as the chemical property. Eight types of surface oxygen groups (SOGs) were identified on the surface of ACF, and the types and amount of SOGs might be related to the oxidation effect of ACF on the 3-D electrodes. The effect and mechanism of these SOGs on electrooxidation performance were discussed with the aid of the frontier molecular orbital theory. It was demonstrated that the H₂O₂–·OH reaction mechanism was improved in the 3-D electrode system and the mechanism was elucidated.

To deliver accurate particulate matter information to citizens, a detailed particulate matter dispersion model including factors such as land use and meteorological information was developed and used to create particulate matter concentration distribution maps for Daejeon Metropolitan City (South Korea). The results showed differences from existing particulate matter concentration distribution maps created using established methods. For PM2.5, approximately 3600 concentration maps were constructed. Taking a map as an example, according to existing methods, the PM2.5 concentration was “good” in 56% and “moderate” in 44% of areas. However, according to our modeling, the PM2.5 concentration was good in 31%, moderate in 26%, “unhealthy” in 28%, and “very unhealthy” in 15% of areas. Furthermore, the existing methods indicated that no portion of the population was exposed to poor particulate matter concentrations, while the proposed model found that over 170,000 people were exposed to such concentrations. These results will contribute to sustainable urban and environmental planning.

Multi-level ditch area is a major component of the hydrographic net of plain area, China. Given the high concentration of nitrogen (N) in the surface water and vigorous biogeochemical interactions, ditch is likely to be the hot spots of N₂O emission. However, N₂O emission flux and emission factor (EF₅ᵣ) of multi-level ditches have not been determined. To address this knowledge gap, a 1-year field work in three ditches with different levels in Chengdu Plain was conducted. It is found that the annual flux of N₂O emission and EF₅ᵣ was higher in the lateral (0.0020 and 83.94 μg m⁻² h⁻¹) and field ditches (0.0019 and 110.75 μg m⁻² h⁻¹) than in the branch ditch (0.0016 and 46.38 μg m⁻² h⁻¹, P < 0.05). It is found that parameters of groundwater level, discharge, precipitation, and NH₄⁺ were the primary factors, and these parameters can model the N₂O flux well. Furthermore, the content of NH₄⁺ in the surface water of ditches presented better correlation with the emission of N₂O than the content of NO₃⁻. Therefore, controlling NH₄⁺ emission and lessening fertilizer usage in summer may be key solutions for indirect reduction of N₂O in Chengdu Plain.

The adverse effects of air emissions from animal feeding operations (AFOs) on public health, environment, and quality-of-life have been well-documented. Regulations or lawsuits may force AFOs to reduce their air emissions. Since livestock barn particulate matter (PM) has relatively high particle density and diameter and many gasses adsorb onto PM, its filtration might reduce air emissions. A porous windbreak wall that imposes acceptable backpressure (< 12.5 Pa) and covers the fan could be a promising option. Seventy-two different porous windbreak wall scenarios were modeled to compare their backpressure on the fan as well as average airspeed over the ground. These scenarios were combinations of shape (box, chamfered, curved), size (lengths of 2, 2.5, and 3 fan diameters), presence or absence of an opening (opened and closed), screen porosity (mosquito screen or clean screen, SunBlocker 70% or clogged screen), and fan angle and height. Backpressure and airspeed decreased with increasing windbreak wall length. Generally, the box-shaped windbreak wall had lower backpressure and airspeeds than the other shapes. The increased backpressure with clogged screen even at two fan diameters (2d) was acceptable. The tilted fan commonly used in poultry houses had higher backpressure and airspeed over the ground than the non-tilted fan used in swine houses due to the former’s lower surface area and tilt towards the ground. Overall, taking into account cost considerations and footprint size (for retrofittability), despite its higher airspeed over the ground (vs. larger footprints) and modest reduction in airflow rate, the 2d, open box model seems the most promising option.

Triclosan (TCS) is a potential endocrine-disrupting compound (EDC), which produces an adverse impact on aquatic life and human beings. Wastewater discharge is considered as the primary source of triclosan in water bodies. The study is aimed to investigate the occurrence and environmental risk of triclosan released by municipal wastewater treatment plants (WWTP). An analytical protocol was developed and validated to determine the presence of TCS in the samples through offline solid-phase extraction (SPE) and liquid chromatography - electron spray ionization (ESI)—quadrupole mass spectrum (LC/ESI/MS). The limit of detection and quantification of protocol was estimated as 2.8 ng/L and 6.25 ng/L, respectively. The season-wise influent and effluent samples from two WWTP in Chennai, India, were monitored. The TCS concentrations in samples were found in the range of 443 to 1757 ng/L. The Risk Quotient (RQ) method was performed to evaluate the environmental (ecotoxicological and human health) risk associated with the exposure of TCS-containing wastewater. The results of the study revealed that primary producer (algae) was highly vulnerable to exposure of TCS in the aquatic environment. The estimated daily intake of TCS was much lower than the reference dosage, and this indicates that TCS did not produce any considerable risk to human health. Also, it suggested that additional treatment was required for complete removal of triclosan residues.

Residues from mining, as metabasalt powder from amethyst exploration, can be used to improve soil properties. Although there is a high-load content of clay minerals in metabasalt, the effects of this residue on cooper (Cu²⁺) and zinc (Zn²⁺) sorption and desorption have not been studied. The aim of this work was to evaluate Cu²⁺ and Zn²⁺ sorption capacity of metabasalt powder and to discuss the mineralogical behavior facing this phenomenon. This residue sorption capacity was compared to reference clay minerals under two Cu²⁺ and Zn²⁺ concentrations (8 and 16 cmolc/kg) in a competitive system (Cu²⁺ + Zn²⁺). The sorption capacity was estimated by sequential desorption using cation exchange resin. A survey of mineralogical and Cu²⁺ and Zn²⁺ concentrations was performed on metabasalt before and after sorption, and after desorption tests. All materials sorbed higher amounts of Cu²⁺ than Zn²⁺. The sorption magnitude decreased in the following order: metabasalt > montmorillonite > illite > kaolinite. Cu²⁺ and Zn²⁺ desorption from metabasalt is lower than the standard clay minerals, since the metabasalt sorption sites are expandable interlayers of clay minerals. The relevance and application of our findings are critical in providing information for the management of metabasalt residue, suggesting potential use as a remediation agent in contaminated water, especially those with high Cu²⁺ and Zn²⁺ loading. It also suggests that the Cu²⁺ and Zn²⁺ enrichment of this residue could potentially be used for converting the metabasalt into a useful source of slow nutrient supply for agricultural soils.

Low-quality water such as sodic alkaline industrial wastewater is often used to irrigate crops of intensively managed urban gardening systems in the semi-arid tropics to help meet the fresh food demands of a rapidly increasing city population. An on-farm experiment was established to examine the effects of sodium (Na) and bicarbonate (HCO₃₋)-loaded industrial wastewater on soil and crops on the one hand, and to determine melioration effects on soil condition and plant development on the other hand. To ameliorate the sodified soil, fine-powdered gypsum (CaSO₄) was applied as soil amendment onto the upper soil (0–20 cm) before sowing of crops. Depending on soil pH and exchangeable sodium percentage (ESP), which reflected the level of soil degradation (SDL), two different amounts of gypsum were applied: 6.8 t ha⁻¹ in moderate and 10 t ha⁻¹ in high SDL plots. Subsequently rainfed maize (Zea mays L.) and irrigated spinach (Spinacia oleracea L.) under two irrigation water qualities (clean and wastewater) were cultivated. Chemical and physical soil parameters, as well as plant root density (RLD), crop yield and concentrations of major plant nutrients and Na were determined. The results showed that gypsum application reduced soil pH on average below 8 and reduced ESP below 18%. Furthermore, gypsum-treated soils showed a significant reduction of sodium absorption rate (SAR) from 14.0 to 7.9 and aggregate stability was increased from 44.2 to 51.2%. This in return diminished Na concentration in plant tissues up to 80% and significantly increased RLD of maize. Overall, calcium (Ca) addition through the gypsum amendment changed the soil cation balance by increasing the Ca:Mg ratio from 3.5 to 7.8, which likely influenced the complex interactions between competing cations at the exchange surfaces of the soil and cation uptake by plant roots.

This paper presents an experimental study of suspended particle transport through sand layer using a new self-developed sand layer transportation-deposition testing system, and the study aims to identify the effects of temperature on the transport of suspended particles through porous medium. Four typical temperatures (5 °C, 15 °C, 25 °C, and 35 °C) were considered in our study, and the experiments were conducted under four size compositions and three flow velocities (1.5 cm/s, 0.2 cm/s, and 0.04 cm/s). The tests were conducted using quartz sand as the porous medium and quartz powder as particles to monitor the change in turbidity under the different conditions. The breakthrough curves were analyzed, and the results demonstrated that changes in temperature can affect the breakthrough curves, especially at the peak. The influence is particularly significant under lower flow velocities and for smaller particles. In regard to the influence factors on the transport process, water viscosity and adsorption effect can be regarded as promoting factors, while kinetic energy of particles can be classified as constraining factors.