A mathematical model to simulate the release of Fe and Mn from sediments in a drinking water reservoir.

Fe and Mn release from sediments promotes the release of other chemicals and jointly affects downstream water safety, especially in drinking water reservoirs. Quantitative research on release processes and flux estimation methods for endogenous Fe and Mn in reservoirs is still limited. Static incubation experiments were designed to systematically explore the effects of water temperature (WT), dissolved oxygen (DO), pH, carbon sources, and microbial activity on Fe and Mn release. The results showed that increased WT and carbon source addition promoted the release of acid-extractable Fe and Mn from the sediments; hypoxia and acidification promoted the dissolution of reducible sediment Fe and Mn; and microorganisms participated in the cycling of Fe and Mn. Based on the experimental results, first-order kinetic equations for sediment Fe and Mn release to overlying water were proposed, and the relationships between release rate and environmental factors were mathematically represented by a surface equation (R2 = 0.88 and 0.86, respectively). A diffusion gradients in thin films (DGT) device based on the diffusion model was used in situ to obtain the diffusion fluxes of Fe (JFe = 13.93 mg m-2 d-1) and Mn (JMn = 3.48 mg m-2 d-1). When environmental factors obtained in the field were introduced into the established mathematical model, the modeled release fluxes of Fe and Mn were RFe = 20.92 mg m-2 d-1 and RMn = 13.12 mg m-2 d-1, respectively. The established model filled gaps in the diffusion model, which does not account for differences in release fluxes under changing physicochemical water conditions. This work serves as a reference for studying the release fluxes of endogenous chemicals in sediments.

Enhanced adsorption of tetracycline by the modified tea-based biochar with the developed mesoporous and surface alkalinity.

A tea residue-based biochar, Fe-BCK0.5-VB6, was obtained by pyrolysis with KOH activation and alkalization with vitamin B6, to develop the mesopore structure and functionalized surface to improve the adsorption performance on tetracycline (TC). An increased specific surface area of 455 m2·g-1 and expanded mesopore volume of 0.138 cm3·g-1 for Fe-BCK0.5-VB6, were observed. The Avrami-fractional order kinetics and Langmuir isotherm models best fitted the experimental data, indicating the characteristics of multiple kinetic stages and monolayer of TC adsorption process. Several possible interactions, including acid-base reaction, pore filling, electrostatic interactions, π-π interactions, and hydrogen bonding forces, were participated in the attachment of TC. This novel mesoporous biochar with enhanced surface alkalinity is expected with a viable future role as an efficient adsorbent in the remedies of acidic antibiotics wastewater pollution.

Transfer characteristic of fluorine from atmospheric dry deposition, fertilizers, pesticides, and phosphogypsum into soil.

Fluorine (F) is widely dispersed in the environment and frequently used in industry and agriculture with a high migration ability. Thus, it is essential to understand the leaching characteristic of F in soil from industry and agriculture sources. Several sources of F pollutants in soil, including fertilizers, pesticides, phosphogypsum, and atmospheric deposition, were selected to investigate leaching characteristics of F in soil by leaching experiments. The addition of phosphate fertilizer and compound fertilizer (N:P:K = 20:10:15) enhanced the leachability of F in soil and the proportion of F leached out from soil treated by these fertilizers were 0.25% and 0.24%, respectively. However, unanticipated lower leachability of F appeared in compound fertilizer (N:P:K = 17:17:17), nitrogen fertilizer, dipterex, fluoroglycofen, fluopimomide, simulative dry deposition (YF3), and phosphogypsum loaded soils compared with additive-absent treatment. Although phosphogysum had a high F concentration, minimum proportion of F released (0.18%) was observed in phosphogypsum-coverd soil. The amounts of F leaching-out from surface soils (0-25 cm) treated with nitrogen fertilizer decreased 1.03 kg ha-1 comparing with blank control. Soil with phosphate fertilizer leached 5.47 kg F ha-1 a year, having the highest environment risk to deeper soil and groundwater. However, phosphogypsum and dry deposition of airbone F chemical had few effects on F leaching in soil. F-containing materials from agricultural process may leach more F from surface soils than industrial sources.

Innovative technology of municipal wastewater treatment for rapid sludge sedimentation and enhancing pollutants removal with nano-material.

This study aims to develop a novel technology for actual municipal wastewater treatment to achieve rapid sludge sedimentation and high pollutants removal efficiency. The SBRs were modified and operated with periodic addition of 20 µL·L-1 nanofloc®. Results revealed that NH4+-N and chemical oxygen demand (COD) was efficiently removed in both laboratory- and pilot-scale SBRs, and the average removal efficiency of total nitrogen (TN) and total phosphorus (TP) was as high as 72.43 ± 2.66% and 98.63 ± 0.74%, respectively, with hydraulic retention time (HRT) of 8 h. Besides, the sludge volume index at 30 min (SVI30) was only 40.06 ± 1.99 mL·g-1, comparable with aerobic granular sludge (AGS). This novel technology could be proposed as a competitive method to upgrade, reconstruct and delay the expansion of municipal wastewater treatment plants (WWTPs) due to its rapid sludge sedimentation and efficient pollutants removal with low HRT.

Distribution, health risk assessment, and anthropogenic sources of fluoride in farmland soils in phosphate industrial area, southwest China.

The high concentration of fluoride (F) in soils has become a rising concern for its toxicity to microbes, plants, animals and human health. In the present study, the spatial and vertical distribution, health risk assessment and anthropogenic sources of F in farmland soils in an industrial area dominated by phosphate chemical plants were studied. Concentrations of total fluoride (TF) and water soluble fluoride (WSF) in the surface soils decreased with distance within the range of 2500 m at the prevailing downwind of the industrial area. The soil TF and WSF concentrations in 0-40 cm profiles were higher than those in 40-100 cm layers in the industrial area. At the prevailing downwind of the industrial area within 700 m, the hazard quotient values of human exposure to surface soils were higher than 1, indicating that a potential risk may exist for human health in this area. The main exposure pathway for children and adults was oral ingestion and particulate inhalation, respectively. The source apportionment model of soil F was modified based on years' historical data and experimental data. The results showed that the proportion of anthropogenic sources of soil F was dustfalls (69%) > irrigation water (23%) > air (5%) > chemical fertilizers (3%) in the industrial area. The high F concentration of dustfalls was mainly due to the phosphate rock, phosphogypsum, and surface soils with high F contents from the factories. In order to safeguard human health and alleviate hazards of F to surroundings, the control of pollutants emission from factories was a basic and vital step to reduce F in the soils in industrial areas.

Vertical distribution of fluorine in farmland soil profiles around phosphorous chemical industry factories.

High concentration of fluorine (F) in agricultural soils has got significant attention considering its impacts on human health, but little information was available about F distribution in farmland soil profiles around phosphorous chemical industry factories. In present study, farmland soil profiles and relevant medium samples were collected from farmlands around a main phosphorous chemical base in southwest China. At 0-100-cm profiles, concentrations of soil total F (Ft, 400.9-1612.0 mg kg-1) and water soluble F (Fw, 3.4-26.0 mg kg-1) decreased with profile depth in industrial areas. Industrial activities enhanced F concentration in soil mainly at 0-40-cm profiles. No disparity for both Ft and Fw distributions in paddy-dry land rotation field and dry land indicates short-term land utilization could not affect the F distribution in soil profiles. Correlation analysis showed soil organic matter and wind direction were important factors influencing the distribution of F in soil profiles. The shutdown of factory and government control of industrial emissions effectively decreased the ambient air F (Fa) concentrations in industrial areas. In where Fa and dustfall F concentrations were high, high soil Ft, Fw, and crop edible part F concentrations were found.

Effect of lead on plant availability of phosphorus and potassium in a vegetable-soil system.

Two typical red soils were sequentially cultivated with celery (Apium graveolens L.) and Chinese cabbage (Brassica chinensis L.) in a greenhouse to determine the effect of lead (Pb) on plant availability of phosphorus (P) and potassium (K) in the soils. The concentrations of available P as estimated by the 0.05 mol L-1 HCl-0.025 mol L-1 (1/2 H2SO4) extraction and available K estimated by the NH4OAc extraction method in the crop-free soils were not affected by Pb treatment. Plant P concentrations in the above-ground part of celery and Chinese cabbage exposed to Pb were either lower or showed no significant difference to the control.