Due to the unique characteristics of subcritical water, the use of a subcritical water extraction (SCWE) process for the remediation of contaminated soil has become more attractive. Although this process has proved to be effective in lab-scale studies, the knowledge of its capability to treat distinct types of contaminants in a larger scale is still scarce. In this work, a semi-pilot scale SCWE system was used to remove petroleum hydrocarbon (diesel fuel and lubricating oil) and polycyclic aromatic hydrocarbons (PAHs) from contaminated soils. Experiments were carried out at an extraction time ranging from 1 to 3 h and a temperature ranging from 200 to 275 °C, maintaining the minimum pressure where water remains in a liquid state (e.g., 4 MPa at 250 °C). Experimental results showed that the higher removal efficiency was obtained in static-dynamic mode than that for dynamic mode operation. With 2 h (4 cycles of static-dynamic step) of SCWE, 99 % of the diesel fuel was removed from the sand at 250 °C. At the same operating conditions, the silty loam soil showed a removal of 77 % of the diesel, and that was 92 % when the treatment time increased to 2.5 h. At 275 °C, the removal efficiency of PAHs was 91–99 % after 1 h, and that of lubricant oil was 76 % after 3 h. Although the extraction run time increased from 1 to 3 h, it seems to marginally affect the removal efficiency of lubricating oil; rather, it was observed that the effect of temperature is more pronounced.

Optimization of sludge conditioning and dewatering is a continuing challenge for wastewater treatment plants. This study investigated the use of an in-line UV–vis spectrophotometer to optimize the polymer dose during sludge dewatering. The study established a relationship between the optimum polymer dose and residual polymer concentration in filtrate using UV–vis absorbance measurements at 191.5 nm. Experiments were carried out with four different polymers (FloPolymer CA 475, CAB 4500, FloPolymer CB 4350, and FloPolymer CA 4600), and similar results were obtained from all polymers. Detection limits of the polymers ranged from 0.35 to 0.95 mg/L in centrate. The optimum polymer dose was determined based on capillary suction time (CST) and filtration tests, and a relationship between the filtrate absorbance at 191.5 nm and optimum polymer dose was established. In the under-dose range, increasing the polymer dose resulted in a decrease in filtrate absorbance due to improvement in filtrate quality. The optimum polymer dose corresponded to the minimum filtrate absorbance at 191.5 nm. When the optimum dose was exceeded, absorbance values started to increase corresponding to the increase in the residual polymer concentration in filtrate in the over-dose range. These results indicate that real-time optimization of polymer dose can potentially be achieved at wastewater treatment plants using an in-line UV–vis spectrophotometer based on the absorbance of centrate or filtrate samples at 191.5 nm.

Ciprofloxacin, griseofulvin, and rifampicin are three human antibiotics that are also widely used in the shrimp culture of Cangio coastal wetland (Vietnam, 10° 24’ 38” N, 106° 57’ 17” E). They have been detected in shrimp larvae pond and receiving water bodies. However, the environmental fate of these antibiotics in coastal wetland milieu is currently unknown. The aim of this study was to determine the degradation potential of these antibiotics in water and sediments from Cangio coastal wetlands. The effects of light, microbial activities, and presence of sediments on the degradation of all three antibiotics were investigated in “water-only” and “water–sediment” experiments. Results indicate that the environmental fate of those antibiotics was quite complex. Photodegradation seemed to play a major role in “water-only” system, since shorter t ₁/₂ was observed for ciprofloxacin, griseofulvin, and rifampicin, with light than in the dark, for both sterile and non-sterile conditions. Biodegradation played a minor role in the disappearance of the antibiotics and was overlaid by photodegradation. In addition, sorption to sediment was of major importance for antibiotics, especially for ciprofloxacin and rifampicin. The t ₁/₂ of these antibiotics in aqueous phase of “water–sediment” system was higher than for “water-only” experiments, indicating that a part of antibiotics were adsorbed by sediment. The biodegradation did not play a major role on sediment sorption of CIP and RIF, since no statistically significant differences between non-sterile and sterile conditions were observed. Only for GRI, the impact of the biodegradation to the sediment sorption could be found and led to the weak affinity to sediment sorption of this antibiotic. All three antibiotics were more sensitive to photodegradation than to biodegradation; however, the degradation rate was low. In addition, the sorption by sediment occurred also with a slow rate, so these antibiotics could recalcitrant persist in the coastal wetland environment.

Development and utilization of low-cost and effective adsorbents for the adsorption processes is a research focus in recent years. In this work, the porous and flexible film was prepared without any pretreatment from the feather keratin deposits produced during the extraction of soluble keratin from chicken feathers. Characteristics of the prepared biosorbent were investigated using thermogravimetric apparatus, X-ray diffraction, Fourier transform infrared, and scanning electron microscopy. Batch adsorption assays were carried out to remove methylene blue (MB) from aqueous solution. The results showed that the extent of MB adsorption on the biosorbent increased with an increase in initial dye concentration, contact time, solution pH, and biosorbent dosage. The equilibrium data were best described by Langmuir isotherm than other isotherm models. The maximum monolayer adsorption uptake was 156.5 mg/g at pH 7 for an initial dye concentration of 200 mg/l. Kinetic studies indicated that the adsorption process of MB followed pseudo-second-order kinetics. Nevertheless, the intra-particle diffusion model confirmed that the adsorption of MB was a two-step process: a rapid surface adsorption followed by intra-particle diffusion. Thermodynamic parameters such as ΔG°, ΔH°, and ΔS° were calculated, indicating that the adsorption process was spontaneous and endothermic.

The objective of this study was to compare the relative impact of humic and non-humic natural organic matter (NOM) on the aggregation behaviors of engineered TiO₂nanoparticles (nano-TiO₂). After exposure of nano-TiO₂to varying concentrations of Suwannee River fulvic acid (SRFA) and Bacillus subtilis exudate in high and low ionic strength (IS) solutions at pH 3 to pH 7.5, aggregation behaviors were evaluated via dynamic light scattering (DLS) measurements and sedimentation studies. Although pH, IS, and NOM concentration exerted strong controls on nano-TiO₂aggregation behaviors, suspensions exposed to either SRFA or bacterial exudate at normalized dissolved organic carbon (DOC) concentrations exhibited remarkably similar behaviors. In high IS systems, nano-TiO₂exposed to either SRFA or bacterial exudate sedimented rapidly, except in the presence of high NOM concentrations at pH 6 and 7.5. Low IS treatments exhibited a larger range of effects. In fact, relative to NOM-free controls, nano-TiO₂aggregates in SRFA and bacterial exudate exposures sedimented up to 14 times faster at pH 3 and up to 13 times slower at pH 7.5. Adsorption of organic molecules onto nano-TiO₂can enhance aggregation via colloidal bridging and/or charge neutralization, or with more complete surface coverage, can diminish aggregation via electrostatic repulsion and/or steric hindrance. Collectively, these data suggest that solution pH, IS, and NOM concentration, and to a lesser extent NOM origin, can control the fate and mobility of nano-TiO₂in geologic systems.

We analyzed, for the first time, the different fractions of metals present in the spent catalyst and changes they undergone during bioleaching and chemical leaching. Before bioleaching, Al (83.9 %) was found mainly in the residual fraction of the pretreated spent catalyst. Ni (61.3 %) was mainly present in the exchangeable fraction exhibiting its high environmental mobility. V (58.5) and Mo (49.3 %) mainly existed in the oxidizable fraction suggesting that highly oxidizing conditions would liberate these metals from the spent catalyst. During bioleaching with Acidithiobacillus thiooxidans, almost complete solubilization of the exchangeable as well as of reducible fraction was observed. Due to strong acidic conditions, part of oxidizable fraction of these metals was also solubilized. Bioleaching also affected the fractionation of metals remaining in the treated spent catalyst. At the end of the process, most of the metals remaining in the spent catalyst were found in the more stable fractions ensuring the safe disposal of spent catalyst. The leaching yields and fractionation behavior of metals during chemical leaching was found to be identical. The results of the present study strongly suggest that bioleaching is an effective method for removing metals from the spent catalyst.

A laboratory-scale study was conducted to test whether biochar from cow dung as a soil amendment can reduce nutrient leaching from soil irrigated with biogas slurry. Polyvinyl chloride (PVC) columns were packed with soils containing 0, 20, and 40 g kg⁻¹of biochar. The biogas slurry was applied at 0, 200, and 400 ml per column, equivalent to 0, 130, and 260 kg N ha⁻¹. The biogas slurry was diluted to 1,500 ml with water and then applied five times every 6 days at 300 ml each time. All leached solutions were collected separately. Results showed that soil available phosphorus (P) and potassium (K) increased significantly with increased biogas slurry rates and biochar rates. The concentrations of total N, P, and K in leached solutions increased significantly as biogas slurry rates increased. Biochar significantly increased the concentrations of total and available P, total K, and electric conductance in leached solution. Contributions of biochar and biogas slurry treatments to the net amount of N, P, and K in leached solution increased with increased biochar and biogas slurry rates except at 4 % biochar rate where total N was decreased. Nutrient removal rate of biochar was over 10.6 % for total N and negative for total K at 2 % biochar rate. Nutrient removal rate of biochar was over 7.19 % for total P and negative for total N and total K at 4 % biochar rate. It is suggested that both biogas slurry and biochar have the potential to pollute water when leaching happens although biochar has the ability to adsorb N and P from biogas slurry.

We determined basal levels of cholinesterase (ChE) and carboxylesterase (CbEs; two substrates: α-naphthyl acetate and 4-nitrophenylvalerate) in different tissues of tadpoles and adults of the frog Pseudis paradoxa and evaluated their use as complementary biomarkers of anti-cholinesterase pesticide exposure. ChE and CbEs sensitivity to malaoxon was also evaluated. Adults and tadpoles were collected with sweep net from temporary ponds located in natural riparian forests along the Paraná River (Garay Department, Santa Fe province, Argentina). We found significant differences in B-esterase activities between adults and tadpoles and among different tissues. The in vitro inhibition tests indicated that ChE is more sensitive to inhibition than CbEs. Our results suggest that basal ChE and CbE (α-NA and 4-NPV) activities in different tissues of adult and tadpoles P. paradoxa would be suitable biomarkers of pesticide exposure, and this amphibian species could be used as sentinel in field monitoring.

This study was undertaken to synthesise a novel biomass-based chemically activated carbon from Australian pine cone and to investigate its effectiveness in the removal of anionic dye Congo red from aqueous solution. The effect of activation parameters such as the concentration of phosphoric acid and temperature were identified as the most efficient parameters for activation in the Congo red removal. The synthesised activated carbon was characterised by Fourier transform infrared and different physical properties, such as bulk density, CHNS analysis, carbon yield, particle size, zeta potential and Brunauer–Emmett–Teller surface area were also determined. Batch adsorption study showed that the amount of adsorption depends on various physico-chemical process parameters, such as solution pH, dye concentration, temperature and adsorbent dose. It was observed that Langmuir maximum adsorption capacity was 500 mg/g at a pH of 3.5. Furthermore, pseudo-first-order, pseudo-second-order, Elovich and intra-particle diffusion models were fitted to examine the adsorption kinetic and mechanism of adsorption. Equilibrium data were fitted with Langmuir, Freundlich and Tempkin adsorption isotherm models. Thermodynamic parameters such as ΔG⁰, ΔH⁰, and ΔS⁰were also calculated. Finally, a single-stage batch adsorber design for the Congo red adsorption onto activated carbon particles was presented based on the Freundlich isotherm model equation. These results indicated pine cone biomass is a good and cheap precursor for the production of an effective activated carbon adsorbent and alternative to commercial-activated carbon.