The aboveground tissue of plants is important for providing roots with constant photosynthetic resources. However, the aboveground biomass is usually harvested before winter to maintain the permanent removal of nutrients. In this work, the effects of harvest on plants’ involvement in oxygen input as well as in microbial abundance and activity were investigated in detail. Three series of constructed wetlands with integrated plants (“unharvested”), harvested plants (“harvested”), and fully cleared plants (“cleared”) were set up. Better performance was found in the unharvested units, with the radial oxygen loss (ROL) rates ranging from 0.05 to 0.59 μmol O₂/h/plant, followed by the harvested units that had relatively lower ROL rates (0.01 to 0.52 μmol O₂/h/plant). The cleared units had the lowest removal efficiency, which had no rhizome resources from the plants. The microbial population and activity were highest in the unharvested units, followed by the harvested and cleared units. Results showed that bacterial abundances and enhanced microbial activity were ten times higher on root surfaces compared with sands. These results indicate that late autumn harvesting of the aboveground biomass exhibited negative effects on plant ROL as well as on the microbial population and activity during the following winter.

The aim of this study was to compare the pollution levels of risk elements in flooded and non-flooded alluvial soils as a function of inundation frequency and river distance, depth of soil horizon, and pollution origin. Totally, 43 soil profiles of flooded and non-flooded soils were sampled in two layers (topsoil and subsoil). The total contents of As, Cd, Co, Cr, Cu, Mo, Ni, Pb, V, and Zn were measured and grouped according to the assumed geogenic or anthropogenic origin. Flooded soils were classified according to inundation stage/river distance. Concerning the depth gradient, it can be concluded that the content of anthropogenic risk elements decreased with the depth, while geogenic risk elements revealed no trend. The distance from the river had no influence on the distribution of anthropogenic risk elements in soil. On the contrary, geogenic risk elements showed increasing concentrations with increasing distance. These results indicate that frequency of floods has no influence on the risk elements distribution in soil. The process of sedimentation seems to be the main factor influencing the level of pollution, it differs between groups of anthropogenic and geogenic risk elements. The result of this countrywide study shows higher levels of soil contamination in flooded areas even without significant point sources of pollution, than in non-flooded areas in standard agricultural conditions.

Eutrophication is a main cause for impairment of freshwater ecosystems, and diffuse phosphorus (P) loss from agricultural land is usually the main cause for freshwater eutrophication. The P index is a simple and practical tool for estimating the potential P loss risk. In a preceding study, a refined P index scheme was developed and validated. In the current study, the relative importance of the 14 input variables used is assessed in order to determine their relative significance to the final P index value. The backpropagation network with Garson’s algorithm was employed in order to capture the significance of interactions among the input variables. The study clearly shows the source factors, especially the degree of P saturation (DPS), along with management practices regarding application of inorganic P fertilizer and livestock manure, are the most important factors governing the P loss in the very high and high risk areas. Conversely, the transportation factors governed P loss risk in the low and very low risk areas. Recommended management strategies for mitigation of P loss from the different risk zones are proposed based on the relative importance analysis and practical constraints. A scenario analysis, based on a gradient reduction of DPS, through decreased application of both inorganic P fertilizer and P emissions factors from livestock manure, gave a reduction of average P index from 7.3 to 57 %. Moreover, the proportion of high- and very-high-risk area may be reduced from 38 to 23 % and 24 to 13 %, respectively.

In many parts of the world, fluoride in drinking water is responsible for notable public health issues. The present study is aimed to prepare a new adsorbent magnesia-hydroxyapatite (Mg-HAP) that can serve as a valuable defluoridating agent. Characterization of the synthesized adsorbent was done by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Transmission electron microscope (TEM), and Scanning electron microscope (SEM)/Energy-dispersive X-ray spectroscopy (EDX) analysis to reveal the bonding patterns, phase characteristics, and microstructural and morphological details. The influences of pH, adsorbent dose, contact time, and initial fluoride concentration and the effect of interfering anions were studied. The defluoridation capacity was evaluated to be 1.4 mg/g, and the adsorbent showed very good capability to remove fluoride from contaminated water over a wide range of pH. Equilibrium modeling was done, and the experimental data was fitted into Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherms. Study of the kinetic data for the adsorption process revealed that it follows pseudo-second-order reaction. It also indicated that the intraparticle diffusion contributes to the rate-determining step in the process. The quality of treated water was analyzed for total dissolved solids (TDS), turbidity, residual calcium, residual phosphorus content, electrical conductivity, hardness, and total alkalinity. The results obtained were very promising and confirmed the prospects of usage of Mg-HAP in defluoridation of drinking water.

To obtain a good catalytic effect of removing refractory organics from water by Fenton process, granular activated carbon (GAC) supported nano-zero valent iron (nZVI) composite (nZVI/GAC) was prepared by adsorption–reduction method, and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDS). The catalytic degradation activity of the composite was evaluated to remove nitrobenzene (NB) pollutant via a heterogeneous Fenton-like system, and the initial pH value, nZVI/GAC dosage, and H₂O₂concentration influencing on NB removal were also investigated at room temperature. Experimental results showed that nZVI particle was uniformly dispersed over GAC matrix, and average particle size was 40–100 nm without agglomeration. The nZVI/GAC composite was very efficient in removing NB with average percentage of more than 85 %. However, the removal rate of Fenton-like reaction was highly affected by pH value, H₂O₂concentration, and nZVI/GAC dosage. The optimal reaction conditions were pH 4.0, 40 mg/L NB, 5.0 mmol/L H₂O₂, and 0.4 g/L nZVI/GAC in this study. Stability and repeatability tests as well as mechanism analysis illustrated that GAC improved catalytic action via enhancing nZVI dispersion and accelerating Fe(III)/Fe(II) cycle attributing to internal iron–carbon microelectrolysis in nZVI/GAC composite. Iron utilization efficiency, which played an important role in NB degradation by Fenton-like greatly increased resulting in dissolved iron <0.6 mg/L. This phenomenon strongly implied that the nZVI/GAC Fenton-like process was not only a practical combination of adsorption and Fenton oxidation but also some synergetic effects existing in such an nZVI/GAC composite.

The feasibility of batch and continuous (60, 80, and 100 mL/min) mode photocatalysis systems in real-time livestock wastewater treatment was investigated. The photocatalytic experiments were conducted with two types of photocatalysts namely slurry titanium-dioxide (UV-TiO₂) and granular activated carbon supported TiO₂(GAC-TiO₂). The performance of the systems was compared using economic analysis based on cost and time required to attain maximum efficiency. The photocatalytic reactors operated with GAC-TiO₂was highly effective under both batch (total volatile solids (TVS) removal of 100 % within 6 min and a total operational cost of 0.68 USD per kg of TVS removal) and continuous (at 60 mL/min) (TVS removal of 63 % at a hydraulic retention time (HRT) of 240 min and a total operational cost of 62.16 USD per kg of TVS removal) mode experiments. The economic analyses indicated that cost reduction was a function of optimum time taken for maximum removal efficiency. Subsequently, the experiments were repeated with ultraviolet light (UV) alone, UV-GAC, and GAC alone to quantify effects of adsorption and photolysis. The results confirmed that the effect of GAC in the treatment/degradation of livestock wastewater by adsorption was negligible. However, the presence of GAC in UV systems propelled the rate of biochemical oxygen demand (BOD) and TVS removals. The entire observations reveal that the degradation was mainly by two reaction mechanisms: firstly, adsorption on the GAC surface and secondly by photocatalytic degradation on the GAC-TiO₂surface. Therefore, GAC-TiO₂photocatalysis could be cost-effectively applied for high-rate treatment of industrial wastewaters.

Arbuscular mycorrhizal fungi (AMF) can alter the dynamics of soluble nitrogen in paddy field soils by promoting nitrogen assimilation by rice. However, it is unknown whether this affects N₂O emissions from rice paddies. This study was designed to assess the effects of AMF on N₂O emissions by analyzing the relationships between AMF and the parameters affecting N₂O emissions. Path analysis was used to quantitatively partition the direct and indirect effects of different parameters on N₂O emissions. Results showed that N₂O emissions were controlled by environmental pathways (transpiration, evaporation, and precipitation affecting soil water content) and biotic pathways (soluble nitrogen assimilation by the rice, which varies according to rice biomass). Under different water conditions, the contributions of the two pathways to N₂O emissions varied strongly. During the flooding stage, the environmental pathways were dominant, but inoculation with AMF promoted the contribution of the biotic pathway to the reduction of N₂O emissions. During the draining stage, the environmental pathways were dominant in the non-inoculated treatment, but inoculation made the biotic pathways dominant by increasing the biomass of rice. During the growing stage, N₂O emissions from inoculated soil (17.9–492.9 μg N₂O-N m⁻² h⁻¹) were significantly lower than those in non-inoculated soil (22.1–553.1 μg N₂O-N m⁻² h⁻¹; p < 0.05). Consequently, inoculating with AMF has the potential for mitigating N₂O emissions from rice paddies.

2,3-Dihydroxybenzaldehyde modified silica gel (SGDHB) was prepared and then used for the removal of boron. Adsorption of boron on the SGDHB was examined with respect to the equilibrium adsorption, kinetics and as a function of pH. Boron is strongly retained on the SGDHB between pH 7 and pH 9. The results indicated that the adsorption equilibrium was well described by the Langmuir equation. The SGDHB exhibited an excellent sorption capacity with 3.812 mmol B/g SGDHB under experimental conditions. The material shows reasonably rapid sorption ability, with boron in 25 mL of 0.01 M H₃BO₃ solution being removed almost completely within 30 min of contact time with 0.12 g of the modified silica gel. The SGDHB was demonstrated to be an efficient sorbent for the removal of boron.

The selected strains of microscopic fungi, Haematonectria haematococca (BwIII43, K37) and Trichoderma harzianum (BsIII33), decolorized the following monoathraquinone dyes with different efficiency: 0.03 % Alizarin Blue Black B, 0.01 % Carminic Acid, 0.01 % Poly R-478, and 0.2 % post-industrial lignin. The most effective was the removal of 0.03 % Alizarin Blue Black B (50–60 %) and 0.01 % Carminic Acid (55–85 %). The principal component analysis (PCA) method was applied to determine the main enzyme responsible for the biodecolorization process of the dye substrates and indicated that horseradish-type (HRP-like), lignin (LiP), and manganese-dependent (MnP) peroxidases were responsible for the decolorization of anthraquinone dyes by the strains tested. The participation of particular enzymes in the decolorization of monoanthraquinone dyes ranged from 44.48 to 51.70 % for 0.01 % Carminic Acid and from 38.46 to 61.12 % for Poly R-478. The highest precipitation in decolorization of these dyes showed HRP-like peroxidase, respectively, 54–74 and 70–95 %. The degree of decolorization of 0.2 % post-industrial lignin by the selected strains of H. haematococca and T. harzianum amounted to 58.20, 61.38, and 65.13 %, respectively. The rate of 0.2 % post-industrial lignin decolorization was conditioned by the activity of HRP-like (71–90 %) and LiP (87–94 %) peroxidases.

The dust removal performance of two types of modified electrode electrostatic precipitator systems was evaluated and compared with that of a conventional aluminum plate electrode using laboratory-scale experiments. In the novel electrode systems, the electrode surface was coated with activated carbon using a mixed slurry containing carbon black, polyvinyl acetate, and methanol. The modification of the electrode surface improved dust precipitation by increasing the specific capacitance of the electrode. The modification also lowered the electrode’s resistance and increased its specific surface area. The optimum electrode spacing and electric voltage supply were determined using batch-type tests. In addition, dielectric insulators were applied as a partition between the oppositely charged electrodes equipped with the modified electrode plates. Multi-layered office paper cut to the same size as the electrodes was used as an insulating material. The addition of the insulator resulted in excellent improvement in the dust removal performance by minimizing the back-corona discharge phenomenon as well as doubling the dust collecting surface. Continuous dust removal tests with the three electrode systems revealed that whereas the conventional aluminum electrode exhibited 54 % dust removal, the activated carbon (AC)-coated system showed 85 % and AC-coated + insulator system showed 90 % and higher dust removal efficiency.