In this study, the optimum conditions for the ammonia removal from aqueous solution by microwave-assisted air stripping have been investigated at pH 11. Ammonia solution with five different initial ammonia concentrations was prepared synthetically. The Taguchi method was applied to optimize the ammonia removal conditions. Initial ammonia concentration, air flow rate, temperature, stirring speed, microwave radiation power, and radiation time were defined as the optimization parameters. Experiments were carried out at five different levels for each operational parameter. The results of the experiments revealed that 1800 ppm of initial ammonia concentration, 7.5 L min⁻¹ of air flow rate, 60 °C of temperature, 500 rpm of stirring speed, and 500 W of microwave radiation power for 180 min. of microwave radiation time are optimum conditions for complete ammonia removal. In addition to present experimental data, the optimum operational conditions predicted by the balanced characteristics of orthogonal array were confirmed experimentally. Finally, the effect of optimization parameters was discussed in detail. Graphical Abstract ᅟ

Increasing soil contamination by heavy metals is a major threat to environmental safety and global food security. The present study examined the influence of Cd and As stresses on morpho-physiological growth and yield of two contrasting maize cultivars (Run Nong 35 and Dong Dan 80). The Cd (100 μM) and As (200 μM) were applied individually as well as in combination (Cd + As) at 30 DAS. A control without Cd or As stress was also maintained for comparison. Application of Cd and As alone or in combination substantially reduced the growth (plant height, number of leaves per plant, leaf area, stem diameter, and shoot fresh and dry weight) and yield (number of ears per plant, number of kernels per ear, and 100-kernel weight) contributing traits in both maize cultivars particularly in Run Nong 35. Furthermore, pronounced reductions in gas exchange attributes (photosynthesis, stomatal conductance, transpiration rate, and intercellular CO₂) and chlorophyll contents were observed in metal-stressed plants. The combined application of Cd and As was more detrimental for maize, and this treatment recorded the maximum reductions in morpho-physiological growth and yield of both cultivars. Cultivar variations were also apparent, and Dong Dan 80 performed better than Run Nong 35 for all the studied attributes. The higher tolerance of Dong Dan 80 was associated with better leaf gas exchange and maintenance of chlorophyll contents in this cultivar under Cd and As stress.

Activated carbon-coated electrode was developed and applied in electrostatic precipitator to remove volatile organic compound gases simultaneously with dust particles from a contaminated air. The activated carbon coating mixture was made up of powdered activated carbon (AC), carbon black (CB), and polyvinyl acetate (PVA), and methanol was added as a solvent to control the thickness of the mixture for best coating performance. During the coating process, the Brunauer-Emmett-Teller (BET) surface decreased to 86% of the original AC while pore volume percentages of macro pore increased, compared to micro- and meso-sized pores. The adsorption isotherm of benzene, toluene, ethyl benzene, and xylene (BTEX) gases onto the original AC and AC coating mixture (AC thoroughly mixed with PVA and methanol for coating and powdered again after dry) were tested and compared to each other, and it was found that both isotherm were best fitted to Freundlich and Langmuir isotherm with the order of adsorption capacities; ethyl benzene > m-xylene > toluene > benzene. The difference between adsorption capacities was clearer with the absorbent AC but became little with the AC coating mixture. In removing BTEX at increasing linear velocities up to 6.7 cm/s, it appeared that the surface area of AC electrode was directly proportional to its removal rate of BTEX. The thermal desorption was applied to regenerate the AC electrode, and 200 °C was found to be most efficient for benzene desorption, but higher temperature would be required for entire BTEX gases desorption.

The discharge of effluents containing organic dyes extensively used in the industry is a matter of concern because these pollutants can cause harmful effects in the environment and human health. In this work, magnetic iron oxide nanoparticles coated with κ-carrageenan/silica organic/inorganic hybrid shells were synthesized and used as novel adsorbents for the magnetically assisted removal of methylene blue (MB) from water. The kinetics of adsorption was well predicted using the pseudo-second-order equation. These hybrid materials exhibited high adsorption capacity (530 mg/g maximum) that could be ascribed to surfaces enriched with ester sulfate groups due to extensive grafting of κ-carrageenan over the siliceous domains by using a new surface modification method. The sorbents were long-term colloidal stable and could be easily regenerated after rinsing with KCl aqueous solution. The MB removal efficiency over six consecutive adsorption/desorption cycles was above 97%, which demonstrates the reusability potential and robustness of these hybrid sorbents. This is a new type of adsorbent that promises extensive application in the removal of organic dyes from wastewaters using magnetic separation technologies.

Zinc oxide nanoparticles were evaluated for the removal of hydrogen sulfide from low-temperature gases, as well as swine manure gas using laboratory and semi-pilot scale systems. Effects of gas flow rate (200 and 450 mL min⁻¹), H₂S concentration (90–1500 ppmv), temperature (1–41 °C), and particle size (18, 80–200 nm) were investigated in the laboratory scale system using premixed gases (H₂S-balanced N₂). The breakthrough and equilibrium adsorption capacities increased with an increase of H₂S concentration. Application of high gas flow rates saturated the adsorbent faster and decreased the adsorption capacities. Adsorption capacities of 18 nm particles were higher than those of 80–200 nm. Regardless of H₂S concentration, the equilibrium adsorption capacity was not affected by temperature in the range 1 to 22 °C but increased when a higher temperature of 41 °C was applied. Among the evaluated isotherms, Langmuir-Freundlich described the equilibrium data obtained with 18 and 80–200 nm particles with a higher level of accuracy. Experiments in a semi-pilot scale adsorption system with 18 nm ZnO and gases emitted from the stored swine manure demonstrated the effectiveness of ZnO nanoparticles in removal of H₂S from these representative gases. Specifically, treatment of manure gas in the semi-pilot scale adsorption system decreased the level of H₂S from an average inlet value of 235.7 ± 85.2 ppmv to a negligible level.

With an annual production of about 10 Gt concrete is by far the most used solid man-made material. In order to adjust the workability of fresh concrete most often so-called superplasticisers, essentially water-soluble organic polymers, are utilised. As concrete is commonly in direct contact with soil or water, the leaching of organic and inorganic compounds and their environmental impact need to be assessed. The present study contributes to this purpose by investigating leachates from hardened cement pastes gained using the horizontal dynamic surface leaching test. Pastes were prepared with and without superplasticiser. The root growths as well as the germination behaviour of cress (Lepidium sativum) and white mustard (Sinapis alba) were examined with respect to phytotoxicity. Different proportions (100, 50, 25 and 12.5%) of the leachates were considered in the test scheme. The results indicate a positive effect of most of the leachates on seed germination and root growth, although statistical significance was only found in some cases. Both test species showed no or only slight harmful effects as relative root growth exceeded always 66% for S. alba and 74% for L. sativum. Seed germination was not negatively influenced by the leachates. Slight beneficial effects on both test species could be observed for leachates containing superplasticiser compared to samples in absence of superplasticiser.

Although differential sensitivity of lichens to calcium excess has been documented previously at the community level, ecophysiological studies, which would shed light on the calcifuge or calcicole nature of lichens, are virtually absent. In the present study, we compared physiological responses of two morphologically similar foliose lichens, Dermatocarpon miniatum (calcicole lichen) and Umbilicaria hirsuta (calcifuge lichen) to Ca excess (up to 100 mM). The degree of total Ca uptake by the lichens after 24-h prolonged exposure was compared with selected physiological markers including levels of assimilation pigments, chlorophyll a fluorescence, soluble proteins, ergosterol, TBARS, and hydrogen peroxide. Both tested lichens accumulated Ca from the applied solutes of CaCl₂ by a dose-dependent manner, although excess of Ca did not change content of assimilation pigments in both tested lichens, as well as integrity of lichen symbiont membranes (tested as TBARS, K content, and ergosterol content) when compared to respective controls. However, we observed significant, concentration-dependent decrease of chlorophyll a fluorescence, content of soluble proteins, and hydrogen peroxide production in U. hirsuta, while in D. miniatum were all these parameters stable through all tested Ca concentrations.

Greenhouse gas emissions from paddy soils respond differently to different combinations of crop root residues and N forms. An incubation experiment was carried out to explore the effect of four crop residues (milk vetch, ryegrass, winter wheat, and rape) and four nitrogen treatments (without fertilizer, urea, (NH₄)₂SO₄, and KNO₃) on CH₄, CO₂, and N₂O emissions in a paddy soil. Except in KNO₃ application treatments, CH₄ emissions of milk vetch residue treatments were significantly higher than those of the rest residue treatments. In the presence of milk vetch and ryegrass residues, urea application significantly increased CH₄ emissions in comparison to treatments without fertilizer. Urea significantly promoted CO₂ emissions, whereas (NH₄)₂SO₄ and KNO₃ significantly inhibited CO₂ emissions at all root residue treatments. Urea did not increase N₂O emissions, but (NH₄)₂SO₄ and KNO₃ promoted N₂O emissions at all residue treatments. In addition, KNO₃ had more effects on the increase of N₂O emissions than (NH₄)₂SO₄ in milk vetch-amended soils. Urea addition had no effect on global warming potentials, and (NH₄)₂SO₄ and KNO₃ addition significantly increased global warming potentials at all residue treatments except KNO₃ + winter wheat residue combination. Our results indicated that urea application had no additive effect on global warming when root residues were left in paddy soils, whereas (NH₄)₂SO₄ and KNO₃ application could increase the risk of global warming.

Organic matter and nutrient in pig manure were treated using an integrated filter system. The influent flowed into an anaerobic filter (AF), and the AF effluent was polished in a biological aerated filter (BAF). The filter system was operated with recirculation ratios of 1–3. The filter system was operated with two recirculation methods. When a filter system was operated under bottom recirculation conditions, the nitrated effluent from the BAF was mingled with the influent in the AF. For upper recirculation conditions, the nitrated effluent from the BAF was injected into a height of 36% from the bottom in the AF. Removal of organic matter and nitrogen under upper recirculation conditions was greater than those under bottom recirculation conditions. The average chemical oxygen demand and solids removals were over 99 and over 97% under upper recirculation conditions. Total nitrogen and total phosphorus removals were over 77 and over 69% at recirculation 3 under upper recirculation conditions.

The selection of emergent plants is of primary importance during the construction of floating treatment wetlands (FTWs). Focusing on the comparison of the nitrogen removal, pot-culture experiments were carried out in floating treatment wetlands constructed with Phragmites australis and Acorus calamus in northeast China, a cold temperate zone. Nitrogen removal and transformation processes were investigated to explore the pathways and factors that influence the nitrogen removal. FTWs showed a high capacity for nitrogen removal. In water with TN concentrations of 9.63 and 4.58 mg L⁻¹, the average TN removal efficiencies of the FTWs constructed with P. australis were 91.5 and 84.2%, respectively, and those of FTWs constructed with A. calamus were 84.2 and 82.8%, respectively. Plant uptake accounted for 36.4 to 77.1% of total N removal. The average TN removal rates of P. australis systems in the first 2 days were 4.20 and 1.77 mg L⁻¹ day⁻¹ for treatments with TN concentrations of 9.36 and 4.58 mg L⁻¹, respectively, significantly higher than those of the A. calamus system, which were 1.75 and 1.04 mg L⁻¹ day⁻¹, respectively. Our results suggested that plant uptake was the main pathway for nitrogen removal in FTWs, and P. australis was a suitable emergent plant species for use in FTW construction in a cold temperate zone.