To develop an efficient adsorbent for humic acid, the present study represents the first attempt to investigate the capability of zeolitic imidazole frameworks to remove humic acid from water. Zeolitic imidazole framework-8 (ZIF-8) is particularly selected as a prototype ZIF to adsorb humic acid owing to its high stability in aqueous solutions. ZIF-8 was synthesized and characterized using scanning electronic microscopy (SEM), powder X-ray diffraction pattern (PXRD), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analyzer (TGA) and then used to adsorb humic acid under various conditions. The structure of ZIF-8 was found to remain intact after the exposure to humic acid in water. Factors affecting the adsorption were examined, including solid-to-liquid ratio, mixing time, temperature, pH, presence of salt, and surfactants. The adsorption capacity of ZIF-8 was found to be much higher than that of activated carbon, fly ash, zeolites, graphite, etc., showing its promising potential for removal of humic acid. The adsorption mechanism could be attributed to the electrostatic interaction between the positive surface of ZIF-8 and the acidic sites of humic acid, as well as the π–π stacking interaction between imidazole of ZIF-8 and benzene rings of humic acid. The humic acid adsorption to ZIF-8 could be enhanced in the acidic conditions, and the adsorption process remained highly stable in the solutions of a wide range of NaCl concentrations. ZIF-8 can be also regenerated by simple ethanol-washing process and reused for humic acid adsorption. These features enable ZIF-8 to be an efficient and stable adsorbent to remove humic acid from water.

The novel titanium oxide/active carbon fiber (TiO₂/ACF) electrode was prepared, and electrosorptive properties for As(V) in aqueous solution were investigated. The structure of TiO₂/ACF was characterized with transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Furthermore, the As(V) electrosorptive properties of TiO₂/ACF electrodes with calcination temperature, ionic species, and loaded amount of TiO₂ were measured, and the electrosorption isotherm and kinetics were investigated at the applied voltage of 1.5 V. The optimal load quality of TiO₂ was 0.80 g per ACF electrode (length × width × height = 2 cm × 1 cm × 0.4 cm, 0.30 g), and optimum calcination temperature was 450 °C. The maximum electrosorption capacity of TiO₂/ACF was 8.09 mg/g, about 200 % higher than that of ACF. Moreover, the electrode performance was stable than other materials such as pure ACF, manganese oxide/ACF, and iron oxides/ACF. It can process 100 ppb As(V) of water to 6 ppb (reach the drinking water standards of WHO), demonstrating that our novel electrode is with potential practical application.

This paper presents the results of a study on mercury distribution in urban wells from the town of Almadén (central Spain), a site that not only hosted the world’s largest mercury mine but also a large roasting plant for cinnabar (HgS). The study includes data on Hg contents in the underground waters and also quality and physical-chemical parameters such as pH, conductivity, oxidation-reduction potential (ORP), dissolved oxygen, and water temperature from 27 wells and 2 monitoring drill holes. An important proportion of the wells (16 %) display Hg concentrations above the European Union Commission (EUC) and Spanish threshold (at 1 μg L⁻¹) and only 10 % exceeded the US EPA recommendation (at 2 μg L⁻¹). As expected, the highest concentrations of dissolved and total Hg are found in wells near to the mine. Hydrochemical water types depend on geogenic and anthropogenic factors, for example, higher mercury concentrations are linked to water-rock interactions (e.g., oxidation, leaching) in sectors where soluble mercury compounds have formed. Hg concentrations show a decrease from 2013 to 2015, a fact that may be due to the encapsulation of the main calcines waste dump or to dilution effects related to strong rainfall events previous to the sampling survey.

The aim of this study is to develop a process that combines electrocoagulation and electroperoxidation (EC-EP) and to evaluate its performance in treating domestic wastewaters (DWW). Electrolysis was performed using a parallelepipedic electrolytic cell (0.5 L) containing one sacrificial anode (mild steel or aluminum) and one cathode (vitreous carbon). The effects of the treatment time, current density, and type of anode electrode on the process performance were examined. The experimental results revealed that a current density of 4.0 mA cm⁻² was beneficial for DWW treatment. There was a decrease in the chemical oxygen demand (COD), suspended solid (SS), turbidity, color, and total phosphorus (Pₜₒₜ) by 67 ± 9, 98 ± 2, 55 ± 10, 61 ± 9, and 97 ± 0 %, respectively, for a treatment time of 60 min in the electrolysis cell in the presence of mild steel (anode) and vitreous carbon (cathode) electrodes. The process was also determined to be effective for removing pathogens (99 ± 1 % removal), such as fecal coliform (the log-inactivation was higher than 2 units).

The feasibility of using cell-free extracts of nitrifying sludge to treat synthetic wastewater containing 4-methylphenol and ammonium was examined. Nitrifying cells were broken by sonication and encapsulated into calcium alginate. Cell-free extracts (CFE) of nitrifying sludge oxidized 4-methylphenol threefold faster than whole-cells, but CFE were not able to oxidize ammonium. The CFE encapsulated into calcium alginate (CFEA) displayed partial nitrification and 4-methylphenol oxidation. Five hours was enough to oxidize 100 % of ammonium and 4-methylphenol, at volumetric rates of 20.80 mg N/L h and 42.86 mg C/L h, respectively. It is inferred that an interaction between the CFE and calcium alginate resulted in the protection of the enzymes.

Bacterial antibiotic resistance has long been a public health concern worldwide. Although antibiotic abuse highly correlates with occurrence of resistant pathogens in hot spots like animal feedlots, it remains obscure how frequently these resistance genotypes would emerge and/or retain in natural circumstances. In this study, we monitored seven antibiotic resistance genes in various surface waters. All seven resistance genes were detectable in Puzih River samples, including strA (40.6 %), cmlA (29.7 %), blaTEM (9.1 %), tet(B) (8.5 %), sul1 (7.9 %), mecA (3.6 %), and tet(A) (2.4 %). Among these genes, strA was observed in four out of five sampling occasions during the 1.5-year monitoring period and most of the genes were detected at least two times over five samplings. These results imply that surface waters in Taiwan act as potential reservoirs for several resistance genotypes. Moreover, high prevalence of tet(A) (92.0 %) and sul1 (96.0 %) in swine farm wastewater samples suggests routine antibiotic usage and particularly, the fodder supplements could indeed be a risk factor to antibiotic resistance in environments. sul1, tet(A), blaTEM, and strA were detectable in domestic water treatment plants and reservoirs, suggesting that several resistance genotypes against antibiotics as streptomycin, ampicillin, tetracycline, and sulfonamides are likely to persist in natural circumstance and may consequently contaminate the drinking water systems.

In the present work, goethite (α-FeO(OH)) impregnated calcium alginate (Cal-Alg-Goe) beads were used to sorb the arsenic from groundwater without disturbing its physicochemical characteristics. Beads were formed by dropwise addition of homogenized mixer of goethite and 4 % sodium alginate solution in 0.2 M CaCl₂solution. Charge, size, and morphology of sorbents were characterized by using various techniques. The results of batch sorption experiments suggest that Cal-Alg-Goe beads are very effective for removal of arsenic in the pH range 3.0 to 7.5, and sorption was more than 95 % in the concentration range of 10–10,000 ng mL⁻¹. Beads were successfully tested for groundwater samples collected from areas having elevated levels of arsenic. Equilibrium sorption follows Langmuir isotherm model, and the maximum arsenic uptake calculated was 30.44 mg g⁻¹. The sorption kinetics could be explained by pseudo-first-order model, and the time needed for equilibrium was 24 h.

Flatford Swamp, a 2800-acre forested wetland in east Manatee County, Florida, serves as the headwaters of the Myakka River. Over the last two decades, Flatford swamp has experienced significant tree mortality. The cause of this mortality, as well as dramatic encroachment of several invasive herbaceous and shrub species, is thought to be linked to hydrologic alterations that resulted in increased inundation during the wet and dry seasons. A biogeochemical characterization of wetland soils was conducted to (1) establish a baseline spatial distribution of soil P and N in Flatford Swamp, (2) determine if soil biogeochemistry could be related to tree mortality, and (3) determine if soil biogeochemical conditions may affect future restoration efforts. Mean total nitrogen and total carbon in sampled soils ranged from 13.8 to 24.9 mg kg⁻¹ and 211 to 468 mg kg⁻¹, respectively, indicating that soils are predominantly organic. Environmental conditions suggest that the nitrate-reduction process occurs readily in Flatford Swamp, and thus N abatement will continue naturally during restoration. Soil total phosphorus content is significantly higher than expected and is likely one of several contributing factors that led to observed changes in vegetation community structure. Levels of total sulfur, total calcium, and conductivity, indicative of agricultural use of groundwater for irrigation, suggest sulfide toxicity as a plausible contributing mechanism in the observed dieback of Nyssa sylvatica var. biflora.

The removal of fluoride from water by an aluminum-modified hematite and a zeolitic tuff using column adsorption techniques, as well as the effects of temperature, were investigated. Column experiments were carried out using aqueous solutions and drinking water with different bed depths. The dynamics of the adsorption process were fitted to Adams–Bohart, Thomas and bed depth service time (BDST) models. The Thomas model was found suitable for the description of breakthrough curve at all experimental conditions, while Adams–Bohart model was only useful for an initial part of dynamic behavior of the removal of fluoride from water by aluminum-modified hematite and zeolitic tuff columns. The highest uptake capacities (3.24 and 2.37 mg/g for the modified zeolitic tuff and hematite respectively) were obtained with a 4-cm bed depth column, an inlet 10 mg/L fluoride solution, and a flow rate of 1 mL/min, but the adsorption capacities decreased when drinking water were used. Experimental data were good fitted to both models, and the parameters of the processes calculated indicated that these materials are suitable for removal of fluoride from water in column systems. Thermodynamic parameters (ΔS, ΔG, and ΔH) were calculated for the aluminum-modified hematite and zeolitic tuff from the sorption data at temperatures between 287 and 333 K, indicating spontaneous and thermodynamically favorable adsorption and suggest that the sorption of fluoride ions by both adsorbents is an endothermic process and the mechanism is physical sorption.

In this study, two carbon materials [chicken manure biochar (CMB) and black carbon (BC)] were investigated for their effects on the reduction of hexavalent chromium [Cr(VI)] in two spiked [600 mg Cr(VI) kg⁻¹] and one tannery waste contaminated [454 mg Cr(VI) kg⁻¹] soils. In spiked soils, both the rate and the maximum extent of reduction of Cr(VI) to trivalent Cr [Cr(III)] were higher in the sandy loam than clay soil, which is attributed to the difference in the extent of Cr(VI) adsorption between the soils. The highest rate of Cr(VI) reduction was observed in BC-amended sandy loam soil, where it reduced 452 mg kg⁻¹ of Cr(VI), followed by clay soil (427 mg kg⁻¹) and tannery soil (345 mg kg⁻¹). X-ray photoelectron microscopy confirmed the presence of both Cr(VI) and Cr(III) species in BC within 24 h of addition of Cr(VI), which proved its high reduction capacity. The resultant Cr(III) species either adsorbs or precipitates in BC and CMB. The addition of carbon materials to the tannery soil was also effective in decreasing the phytotoxicity of Cr(VI) in mustard (Brassica juncea L.) plants. Therefore, it is concluded that the addition of carbon materials enhanced the reduction of Cr(VI) and the subsequent immobilization of Cr(III) in soils.