This paper aims to demonstrate the benefits of using a natural coagulant to enhance gravitational sedimentation of pig slurry. The separation process would lead to a liquid fraction, more biodegradable and with lower nutrient content, and a solid fraction highly concentrated in organic matter. Experimental trials were conducted in order to achieve the following objectives: (i) compare the effect of gravitational sedimentation with coagulation–flocculation process, (ii) compare the efficiency of conventional coagulants (such as aluminium sulphate or ferric chloride) with chitosan biopolymer and (iii) test the optimum coagulation–flocculation operational conditions to slurry sample. Assessment criteria included removal efficiencies but also took into consideration the advantages/disadvantages regarding sludge management. Results showed that gravitational sedimentation process can be improved by addition of coagulants; turbidity and COD removal increased around 2 and 3 times, respectively.

The performance of a laboratory-scale biofilter packed with a mixture of compost and woodchip on formaldehyde removal from polluted air streams was investigated. The reactor was inoculated with aerobic sludge as a source of bacteria, obtained from a municipal wastewater treatment plant. A nutrient solution was daily added to the reactor media. An airflow containing different concentrations of formaldehyde (from 20 ± 2 to 276 ± 5 mg m⁻³) was introduced into the reactor. In inlet formaldehyde concentration, an average removal efficiency and elimination capacity of 91 % and 0.36 g m⁻³ h⁻¹were attained, respectively, at180 s empty bed residence time (EBRT). After acclimatization of the system for increased formaldehyde concentrations of up to 276 ± 5 mg m⁻³and for EBRT of 180 s, those values were stabilized at around 72 % and 3.98g⁻³ h⁻¹, respectively. The experimental results showed that the system was effective for a high loading rate of formaldehyde with an acceptable EBRT. Compared to the application of compost alone as a media, a mixture of compost and woodchip (50/50 v/v%) enhanced the performance of the biofilter. The most predominant microorganism involved in the biodegradation of formaldehyde was a species of citrobacter called Citrobacter freundii, an aerobic gram-negative bacillus. Pressure drop of the reactor over the entire operations was about 1 mmH₂O m⁻¹.

Mercury (Hg) in aquatic ecosystems is of great concern due to its toxicity, bioaccumulation, and magnification in the food web. The Tibetan Plateau (TP) is endowed with the highest and largest lakes on earth, whereas Hg distribution and behavior in lake waters are least known. In this study, surface water samples from 38 lakes over the TP were collected and determined for the total Hg (THg) concentrations. Results revealed a wide range of THg concentrations from <1 ng to 40.3 ng L⁻¹. THg in lake waters exhibited an increasing trend along the southeast to northwest transect over the TP. Strong positive correlations were observed between THg concentrations and salinity and salinity-related environmental variables, especially for total dissolved solids (TDS) and some of the major ions such as Na⁺, K⁺, and Cl⁻, suggesting the enrichment of Hg in saline lakes. The large-scale geographical pattern of climatic and environmental factors shows a decreasing precipitation and an increasing evaporation northwards and westwards and thereby induces gradient-enhanced enrichment of soluble substances in lake waters, which are likely to complex more Hg in northwestern TP. Our study provides the first comprehensive baseline data set of Hg in Tibetan lake waters and highlights the concurrent high Hg and salinity, representing valuable references and fundamental rules in further understanding the behavior and fate of Hg in lakes over the TP and perhaps high-altitude regions beyond.

Effects of pH, As species, and Fe/Mn minerals on the fractions of adsorbed As in aquifer sediments were evaluated. Kinetic data showed that As adsorption was controlled by diffusion through the external film. Isothermal data of both As(III) and As(V) fitted the Langmuir isotherm well, revealing a monolayer adsorption process. Sequential extraction demonstrated that water-soluble As and non-specifically sorbed As were the major fractions of adsorbed As. Assessing the relationship between the Freundlich K F and the increases in the amounts of As fractions showed that the pH played a key role in weakly adsorbed As, especially water-soluble As. Although inorganic As species converted each other during the adsorption processes, more non-specifically sorbed As was adsorbed in As(V)-treated sediment than in As(III)-treated sediment, showing that the electrostatic selectivity controlled the non-specific adsorption. Additionally, specifically sorbed As and As associated with the amorphous phases were predominated by Fe/Mn minerals, especially Fe(III) (hydr)oxides. These results suggested that pH, As species, and Fe/Mn minerals would regulate the As fractions in aquifer sediments, and therefore control As cycling in aquifer systems.

The impact of Fe₂O₃and TiO₂nanoparticles (NPs) on the removal of trichloroethylene (TCE) in a granular activated carbon (GAC)-fixed bed adsorber was investigated in the presence of humic acid (HA). The surface charges of GAC and NPs were obtained in the presence and absence of HA with the NPs behaving similarly. Isotherm and column studies were conducted in the presence and absence of the NPs and HA. NPs had no effect on TCE adsorption during isotherm studies. However, in the column studies conducted with organic-free water, the presence of NPs resulted in a reduction in TCE capacity most likely due to pore blockage by aggregating NPs. This effect was completely mitigated in the presence of HAs that prevented an association between the GAC and the NPs, and between NPs. The presence of HA provided a high negative charge on the GAC and on the nanoparticles resulting in repulsive forces between the GAC and the NPs, and between NPs, thereby preventing pore blockage. Both Fe₂O₃and TiO₂NPs demonstrated that charge characteristics are more important than chemical characteristics. Pore-size distribution of the fresh and the spent GAC confirmed the adsorption data but points to some HA and NP interaction with the carbon.

This study examined a single underground coal mine and investigated two aspects of its operation: the disposal of the mine waste through a discharge to a nearby river and the impact of subsidence from an underground longwall to a small waterway above. Water quality of the two waterways was monitored over a 2-year period with a monthly investigation over a 6-month period, which included collection of stream macroinvertebrates. Both mine activities modified surface water geochemistry and macroinvertebrate communities. Mean electrical conductivity (EC) increased in surface waters below the mine discharge, rising 4.8 times from (186 μS/cm) upstream to 1078 μS/cm below the waste inflow. Mean EC increased in a small stream that was disturbed by subsidence from longwall mining, rising 3.8 times from (247 μS/cm) upstream to 1195 μS/cm below. The mineral constituents of the increased salinities were different. The coal mine wastewater discharge was enriched with sodium and bicarbonate ions compared to sodium and chloride ions in the subsidence affected creek. Both the waste discharge and the subsidence caused increases in the concentrations of zinc by about four times and nickel by 20 to 30 times the background levels. The subsidence reduced dissolved oxygen to ecologically stressful levels and increased iron and manganese concentrations by about 20 times the background levels. Two of the key changes in stream ecosystems were a reduction in the proportion of mayfly larvae downstream of the mine waste discharge and mosquito larvae dominating (60–70 % of total abundance) the invertebrate community in the subsidence affected creek.

Featured with biodegradability and biocompatibility properties, gelatin (GE) was selected as the backbone to graft poly(acrylic acid) (PAA) to fabricate a granular hydrogel at room temperature in air. Using attapulgite (APT) as an inorganic component, the resulting GE-g-PAA/APT hydrogel was characterized by means of Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and zeta potential analysis and then used as the adsorbent to be applied in a mixed dye solution containing malachite green and orange G. The addition of APT can significantly reduce the swelling degree during the adsorption process, though its influences on the adsorption capacity are not so expectable. The as-prepared hydrogel shows a wide pH-independent adsorption from 3.0 to 10.0, with the maximum adsorption capacity of 1370 mg/g for GE-g-PAA and 1190 mg/g for GE-g-PAA/APT (5 wt%). More importantly, the as-prepared hydrogel shows high adsorption selectivity for cationic dyes and the dye-loaded hydrogel can be easily regenerated and recovered for successive adsorption cycles. Graphical Abstract Gelatin-based granular hydrogel for selective removal of MG in a mixed dyes containing MG and OG-G.

To facilitate the mapping of pollution fluxes under different flow conditions when a limited number of gauging stations are available, a method relying on geographic data was developed to estimate the mean daily stream discharge at each sampling station. It has been tested on a rural river watershed that is located in northeast France (Madon River). The stretch of 100 km is equipped with three gauging stations. Surface water samples were collected at 30 stations under different flow conditions. In a participatory research project, samples were also collected by school children at one of the stations (once a week during the school year over a 2-year period). Dissolved organic carbon and nitrogen species were measured for all samples. These data illustrate the variation in the pollution in the river that is associated with agricultural activities and discharges of untreated wastewater. This method was used to obtain localized points of nutrient discharge, to identify the zones that favor nutrient removal, and to propose remediation work.

Multifunctional sorbents, activated carbons (AC), were prepared by one-step microwave activation utilizing peanut shells and sunflower seed husks. The influence of the original particle size of raw materials on the yield and specific surface area of AC was studied, which reached 33.5 % and 1133.27 m²/g, respectively. The repetitive and competitive uptakes of perfluorooctane sulfonate (PFOS) and chromium were applied to investigate the sorption properties of AC. The sorption mechanisms were demonstrated using sulfur K-edge X-ray absorption near edge structure analysis (XANES). In the repetitive experiment, AC made from peanut shells (ACP₀₅) still retained 70 % removal efficiency of PFOS after the fourth sorption because sorbed PFOS might form a new organic phase that supplied effective sites for the hydrophobic partition of PFOS. However, the removal efficiency of Cr(VI) decreased dramatically from 60 to 11 % after the fourth uptake because electrostatic attraction was its only removal pathway. In the binary solutes system, ACP₀₅ possessed perfect sorption performance for both PFOS and Cr(VI), which were 885 and 192 mg/g, respectively. In the multivariate solutes system, the XANES spectra indicated that the thiol functional group existed in the resulting AC and a metal chelate was formed between thiol and Zn²⁺/Cu²⁺. Hence, the presence of Zn²⁺/Cu²⁺ further promoted the removal of PFOS and Cr(VI) through the electrostatic attraction between the anions and positive metal chelate.