Liquid effluents from various dyeing industries often have a high concentration of dyes that diffuse into river systems and can be toxic and non-degradable in the environment. In this study, the potential of the use of timbaúva seed husks in the preparation of four adsorbents tested in the removal of methylene blue was analyzed: in natura, chemically activated material (qₘₐₓ = 1.24 ± 0.04 mg g⁻¹), carbonized (qₘₐₓ = 1.96 ± 0.03 mg g⁻¹), and activated carbon (qₘₐₓ = 1.983 ± 0.04 mg g⁻¹). The adsorbents were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and CHN elemental analysis to assist in the proposed dye adsorption mechanism in the adsorbents tested. In the adjustment of the kinetic parameters, the pseudo-second order model was predominant by the statistical analysis of the ARE and R². The carbonized samples were better adjusted to Langmuir isotherms. The removal efficiency of the methylene blue dye in aqueous solutions at the concentrations and conditions studied was 86.78%. The coal from the seed husks of timbaúva has shown excellent performance in adsorption of the methylene blue dye and, therefore, can have technological application.

To solve the issues of serious wear, blockage, and poisoning of the catalyst in the denitration process of industrial furnaces such as glass furnaces and cement kiln, it was proposed to integrate the high-temperature dual-layer granular bed filter and the selective catalytic reduction (SCR) reactor into a device to realize the denitration of the SCR catalyst in a dust-free state. In the device, the upper part was a dual-layer granular bed filter and the lower part was a V₂O₅-WO₃/TiO₂ honeycomb ceramic catalyst. In the self-built dust removal and denitration integrated test equipment with an inner diameter of 100 mm, the effects of flue gas temperature, flue gas flow rate, nitric oxide (NO) concentration, and catalyst height on the denitration efficiency of the catalyst were investigated by orthogonal testing under dust-free conditions. The results show that the flue gas flow rate had the greatest influence on the denitration efficiency of the catalyst. With an increase in flue gas flow rate, the denitration efficiency first increased and then decreased. When the flue gas flow rate was 0.3 m/s, the denitration efficiency reached a maximum. The denitration test was carried out using flue gas with a dust concentration of 15 g/m³. The results show that the denitration efficiency continued to decrease with the deposition of dust on the catalyst surface (from an initial value of 96.51 to 80.59% at the 140th min), and the pressure drop correspondingly increased from 100 to 630 Pa. Additional integration testing of dust removal and denitration showed that the average dust removal efficiency of the integrated device for dust removal and denitration using a dual-layer granular bed filter could reach 99.84%, and the average denitration efficiency could reach 95.07%.

Development of an efficient bioremediation strategy for the mitigation of low pH (3.21), high dissolved SO₄²⁻ (6285 mg/L), and Fe (7292 mg/kg)-rich acid mine drainage–impacted soil (AIS) was investigated through amendment of readily available organic carbon substrates (rice husk, compost, leaf litter, and grass clippings). An organic carbon mixture (OCM) formulated by mixing the test substrates was used to biostimulate microbial processes (SO₄²⁻/Fe³⁺reduction) necessary for efficient attenuation of the hazards imposed by AIS. OCM amendment in calcium carbonate–treated AIS enhanced reductive processes and removed dissolved SO₄²⁻ and Fe³⁺ considerably raising the pH close to neutrality. 16S rRNA gene amplicon sequencing performed with total DNA and RNA elucidated the microbial population dynamics of treated AIS. Metabolically active populations comprised of fermentative (Clostridium sensu stricto 1 and Fonticella), iron-reducing (Acidocella, Anaeromyxobacter, and Clostridium sensu stricto 1), and sulfate-reducing (Desulfovibrio, Desulfotomaculum, Desulfosporosinus, and Desulfobacteraceae) bacteria. Microbial guilds obtained highlighted the synergistic role of cellulolytic, fermentative, and SO₄²⁻/Fe³⁺-reducing bacteria in attenuation of hazardous contaminants. Quantitative PCR analysis well supported the role of OCM in stimulating the indigenous bacterial populations, including those harboring the dissimilatory sulfite reductase (dsrB) gene and involved actively in SO₄²⁻ reduction. The study demonstrated the suitability of locally available organic substrates as a low-cost and efficient biostimulation agent for in situ bioremediation of acid mine drainage (AMD)–impacted soil system.

The present study has been designed to optimise certain important process parameters for Scenedesmus vacuolatus to achieve efficient carbon dioxide extenuation as well as suitable fatty acid profile in context to improve biodiesel properties. The effect of varying sodium bicarbonate concentration was evaluated in single and multicomponent system such as nitrate, phosphate, inoculum size to observe interactive effects on algae biomass production, carbon dioxide (CO₂) removal efficiency and fatty acid methyl ester (FAME) profile. Maximum biomass productivity of 117.0 ± 7.7 mg/L/day with 3 g/L of sodium bicarbonate was obtained i.e. approximately 2 folds higher than the control. Under multicomponent exposure, maximum biomass of 1701.5 ± 88.8 mg/L and maximum chlorophyll concentration of 15.3 ± 6.4 mg/L were achieved on 14th day at 3 g/L sodium nitrate, 0.1 g/L dipotassium hydrogen phosphate, 2 g/L of sodium bicarbonate and initial cell density of 0.3 (N₃P₀.₁B₂OD₀.₃). FAME content of 46.1 mg/g of biomass was obtained at this combination which is approximately 3 folds higher than the FAME content obtained under nitrogen and phosphate deprivation (16.6 mg/g at N₀P₀B₂OD₀.₃). Confocal microscopy images confirmed the results with enhanced lipid droplet accumulation at high bicarbonate concentration as compared with the control. This interactive study concluded the variability in FAME profile along with the exposure to varying nutrient concentrations.

This study aimed to define the optimum weight ratio between Berea Red sand (BRS)/zero-valent iron (ZVI) combinations to be used in the treatment of nitrate contaminated water. The effect of competing ions (phosphate and sulfate) on the nitrate removal efficiency of the best performing BRS-ZVI w/w ratio was also assessed. To achieve this objective, batch tests were performed under anoxic and acidic conditions (pHi = 4.5), using two combinations: 50%BRS-50%ZVI (w/w) and 25%BRS-75%ZVI (w/w), as well as 100%ZVI as a control. BRS and ZVI had 1 to 2-mm grain size. pH and nitrogen species were tested during these batch tests. Kinetic analysis was also carried out. While the removal efficiencies of 100%ZVI and 25%BRS-75%ZVI (w/w) were 70.2% and 83.1%, respectively, the experimental results showed that the combination of 50%BRS-50%ZVI (w/w) had the highest nitrate removal efficiency (99.5%), implying a synergistic effect between BRS and ZVI. Likewise, the kinetic analysis showed that the nitrate removal rate (k) increased as the BRS mass in the BRS-ZVI combination increased. Furthermore, the presence of phosphate and sulfate negatively affected the nitrate removal performance of the 50%BRS-50%ZVI combination, which was the best performing weight ratio. However, this weight ratio still showed high nitrate removal capacities in the presence of phosphate and sulfate, respectively. The 50%BRS-50%ZVI combination demonstrated to be the optimum among the used ones. However, further investigation in a large-scale reactor on this combination is recommended for further optimization of its performance.

We investigated the removal of metals from a circum-neutral mine discharge over a 0.5-km distance in a series of sequentially interconnected ponds from the exit of an 8-km tunnel that drains a gold mine. The geochemical and mineralogical processes controlling the evolution of metals in the drainage ponds were the focus of this research. We measured the pH and concentrations of dissolved inorganic carbon (DIC) and alkalinity in the aqueous phase and the concentrations of Ca, Mg, Na, Fe, K, Mn, Sr, and Zn in the aqueous phase and in sediments on the beds of the ponds. We calculated the saturated indices of metal oxides, metal carbonates, and the partition coefficients (D) for Mg, Sr, Mn, and Zn. The pH of the mine discharge increased while the concentrations of DIC and alkalinity decreased over the 0.5-km distance. The concentrations of Ca, Mg, Na, Fe, K, Mn, Sr, and Zn generally decreased while their concentrations in the sediment phase increased. Mineralogical and acid-base accounting and modeling results showed that all the metals in equilibrium with the aqueous phase were oversaturated, and the dominant mineral in the precipitated sediments was calcite. Forward geochemical modeling in combination with the Dₘg, DSᵣ, DMₙ, and DZₙ showed a low ionic strength solution indicating that these metals were removed from the mine discharge by adsorption and coprecipitation of calcites. Forward geochemical modeling results indicated that the groundwater exiting the tunnel had reached equilibrium with respect to ferrihydrite and goethite, suggesting that the precipitation of Fe-oxides were responsible for removing these metals from solution. Calcite precipitation removed about 16% of Ca²⁺, while 15% of Sr and 5% of Mg were scavenged from the mine water by coprecipitation with calcite and/or adsorption into calcite lattices. About 52% of total Fe from the mine water was scavenged through amorphous Fe(OH)₃ and goethite precipitation. About 23% of the Zn in the mine water was removed by sorption on Fe-oxides surfaces or coprecipitation with calcite, and 30% of the Mn in the mine water was removed by rhodochrosite precipitation and/or coprecipitation with calcite. Settling ponds, therefore, provide a framework where minerals precipitate, are adsorbed, or coprecipitated, such that mine water at acceptable contaminant level is released into the natural environment.

Graphene oxide–supported β-cyclodextrin was prepared with graphene oxide and β-cyclodextrin as raw materials and epichlorohydrin as crosslinking agent, respectively. It was characterized by the methods of Raman spectroscopy, FT-IR, and SEM. The graphene oxide–supported β-cyclodextrin showed excellent adsorption performance for p-nitrophenol, and the absorption equilibrium can be achieved within 2 h. The adsorptive capacity is 117.28 mg/g at adsorption temperature of 313 K and pH at 8.0. Adsorption isotherms showed that the adsorption capacity increases with the increases of temperature and adsorption process could be better fitted by Langmuir isotherm (R² > 0.995). Thermodynamic functions (ΔG, ΔH, and ΔS) investigation showed that the adsorption is spontaneous, endothermic, and random. The adsorption kinetics of p-nitrophenol over graphene oxide–supported β-cyclodextrin is conformed to a pseudo-second-order process. This study has suggested that the graphene oxide–supported β-cyclodextrin could play an efficient and beneficial source of the adsorbent for the purpose of eliminating p-nitrophenol from aqueous solution.

Zeolitic imidazolate framework-8 (ZIF-8) has a sodalite topology. ZIF-8 is composed of zinc ion coordinated by four imidazolate rings. The pore aperture of ZIF-8 is 3.4 Å, which readily retains large gas molecules like N₂. In this work, mixed-matrix membranes (MMMs) have been fabricated by utilizing ZIF-8 and pristine cellulose acetate (CA) for O₂/N₂ separation. Membranes of pristine CA and MMMs of ZIF-8/CA at various ZIF-8 concentrations were prepared in tetrahydrofuran (THF). Permeation results of the fabricated membranes revealed increasing selectivity for O₂/N₂ with increasing pressure as well as ZIF-8/CA concentration up to 5% (w/w). The selectivity of O₂/N₂ increased 4 times for MMMs containing 5% (w/w) of ZIF-8/CA as compared with the pristine CA membrane. A thermodynamic model has also been developed to predict the permeability of gases through polymeric membranes. The results were compared with literature data as well as the pristine CA membrane produced in this work for model validation.

The concentrations of phosphorus (P) and nitrogen (N) in runoff from cropland areas may be influenced by accumulation and release of P and N by stalk residues. A laboratory study was conducted to measure the effects of time since harvest and immersion period on accumulation and release of P and N by corn, soybean, and wheat stalks. Experimental variables included type of stalk material (corn, soybean, and wheat), time since harvest (six residue collection dates over an approximate 1-year period), and stalk immersion period (25 s (0.42 min), 250 s (4.2 min), 2500 s (42 min), 25,000 s (6.9 h), and 86,400 s (24 h)). The initial concentration of each of the P and N constituents in a test solution was 6 μg mL⁻¹. The soybean, wheat, and corn residue released PO₄-P at mean rates of 40, 69, and 141 μg g⁻¹ residue, respectively. The amount of PO₄-P that was released consistently increased as immersion period became greater. Corn and wheat residue either accumulated or released NO₃-N depending on residue collection date. Soybean residue accumulated an average of 20 μg NO₃-N g⁻¹ residue. Wheat residue obtained on five of the collection dates accumulated an average of 13 μg NO₃-N g⁻¹ residue. Residue collection date also influenced accumulation of NH₄-N by soybean and wheat residue. Corn residue released an average of 77 μg NH₄-N g⁻¹ residue. The type of crop residue material, the amount of time the residue has remained in the field following harvest, and residue immersion period were found to influence nutrient concentrations of solution.

Groundwater contamination risk assessment is a useful tool for groundwater pollution prevention and control. Previous study has evaluated groundwater contamination risk at Yinchuan Plain, China, according to aquifer vulnerability. The present study enriches the assessment of contamination risk by adding pollution loading, which represents the hazard from human activities, and groundwater value, which represents the economic loss as a result of groundwater pollution. An approach that combines toxicity, release possibility, and the potential release quantity of pollutants on the ground surface was used to estimate the pollution loading. An integrated approach that considered both the in situ and extractive values was used to estimate groundwater value. In addition, a basic risk map was constructed by overlying the vulnerability and pollution loading maps showing the potential probability of pollution, while a value-weighted risk map was produced by overlying the basic risk and value map indicating the urgency of protection. The validation by specific contaminants shows the reliability of the basic risk assessment. Both the basic and value-weighted risk maps indicate a very high groundwater contamination risk in Yinchuan City, and the southern part of Yinchuan Plain exhibited a relatively high contamination risk. As a result of not only high vulnerability but also very high pollution loading and groundwater value, Yinchuan City is the most urgent area requiring groundwater protection. The produced maps provide effective information for decision-making regarding the optimization of monitoring network, preferential treatment, and allocating future potentially hazardous.