The medium most directly affected by anthropic contamination is soil and, hence, groundwater (saturated and unsaturated zones). In the phytoremediation process, the direct absorption of soil contaminants through the roots is a surprising pollutant removal mechanism. Plants can act as a natural filter of shallow groundwater contamination, controlling and reducing the vertical percolation of contaminants into the soil, and after reaching the level of the water table, the roots can absorb contaminants dissolved in the water, thus reducing the size of the plume and protecting receptor sites (water supply wells, rivers, lakes) from possible contamination. In the first phase of the research, assays were performed to evaluate the tolerance of plant species to the direct injection of a benzene solution into the roots. Subsequent experiments involved direct absorption and spraying. The aim of this study was to evaluate the potential for tolerance and reaction to high levels of benzene. Three plant species were used, an herbaceous ornamental plant (Impatiens walleriana), a fern (Pteris vittata), and forage grass (Brachiaria brizantha). At the end of the study, the surface changes caused by VOCs (aerial structures) of benzene were evaluated, using an environmental scanning electron microscope (ESEM) to identify possible mechanisms of resistance of the plant to air pollution, i.e., hydrocarbon pollution. The plant material used here was young plant species selected for study. For the analysis by gas chromatography (GC), the plant material was separated into aerial (stem, leaves, and flowers) and underground parts (roots). A comparison of the benzene content in different parts of the plant indicated a higher concentration in the stem + leaves, followed by the roots, which is justified by its translocation inside the plant. P. vittata showed low uptake (5.88 %) mainly in the root and (<2 %) in the leaves, which was also observed in the tolerance experiment, in which visual symptoms of toxicity were not observed. I. walleriana showed benzene removal rates of approximately 18.7 % (injection into the soil) as a result of direct absorption through the roots. After the treatment was suspended, I. walleriana gradually reacted to the detoxification process by recovering its stem stiffness and normal color. B. brizantha showed intermediate behavior and did not react to the detoxification process.

This work presents an evaluation of the remediation efficiency and of the environmental impact of a zero-valent iron commercial substrate used for the removal of heavy metals from groundwater in different conditions. A specific feature of the substrate is the presence of zero-valent iron (ZVI), organic carbon, and sulfate. The authors analyzed its composition and performances by means of batch tests in different boundary conditions. In detail, the efficacy was evaluated for metals (Cu, Cr, Pb, and Zn) and for nitrates and sulfates. Neutral and acidic pH values, imputable to dangerous waste landfill leachate or to acid mine drainage, were considered. The environmental impact of the substrate was also assessed for the investigated pHs. The product showed a high efficiency in the removal of metals (mainly described by a pseudo-second-order kinetic model), with a noticeable variability according to the pH of the polluted phase. Nitrate ion removal was inhibited by sulfates at all the considered pH values. Characterization and batch studies revealed that the substrate was a source of Mn, Cr, Pb, Cu, and sulfate ions, besides Fe. This study shows that the employment of an optimized amount of reagent, while achieving good performances, is essential to contain the leaching of undesirable substances into aqueous environment.

Ombrotrophic peatlands are highly sensitive to atmospheric heavy metal deposition. Previous attempts to quantify peatland lead pollution have been undertaken using the inventory approach. However, there can be significant within-site spatial heterogeneity in lead concentrations, highlighting the need for multiple samples to properly quantify lead storage. Field portable x-ray fluorescence (FPXRF) continues to gain acceptance in the study of contaminated soil, but has not thus far been used to assess peatland lead contamination. This study compares lead concentrations in surface peat samples from the South Pennines (UK) derived using (a) FPXRF in the field, (b) FPXRF in the lab on dried samples and (c) ICP-OES analysis. FPXRF field and lab data are directly comparable when field measurements are corrected for water content, both can be easily used to estimate acid extractable lead using regression equations. This study is a successful demonstration of FPXRF as a tool for a time- and cost-effective means of determining the lead content of contaminated peatlands, which will allow rapid landscape scale reconnaissance, core logging, surface surveys and sediment tracing.

Adsorptive water purification methods were studied for the removal of phenol-type compounds (such as phenol/thymol) and humic acid applying sodium bentonite modified by cationic surfactant hexadecyltrimethylammonium bromide (HTAB). The effect of humic acid on adsorption of phenols was examined in pure and model thermal water. It was found that the efficiency of the removal of individual pollutants can be highly influenced if another pollutant is present. The main reason for the increased efficiency was identified by the means of infrared spectroscopy which proved that each pollutant modifies decisively the organophilicity of the clay surface. Furthermore, the studies performed in model thermal waters revealed that the presence of specific cations could further increase the removability of these pollutants.

The purpose of this research was to thoroughly analyze the influences of environmental factors on denitrification processes in urban riparian soils. Besides, the study was also carried out to identify whether the denitrification processes in urban riparian soils could control nonpoint source nitrogen pollution in urban areas. The denitrification rates (DR) over 1 year were measured using an acetylene inhibition technique during the incubation of intact soil cores from six urban riparian sites, which could be divided into three types according to their vegetation. The soil samples were analyzed to determine the soil organic carbon (SOC), soil total nitrogen (STN), C/N ratio, extractable NO₃⁻-N and NH₄⁺-N, pH value, soil water content (SWC), and the soil nitrification potential to evaluate which of these factors determined the final outcome of denitrification. A nitrate amendment experiment further indicated that the riparian DR was responsive to added nitrate. Although the DRs were very low (0.099 ~ 33.23 ng N₂O-N g⁻¹ h⁻¹) due to the small amount of nitrogen moving into the urban riparian zone, the spatial and temporal patterns of denitrification differed significantly. The extractable NO₃⁻-N proved to be the dominant factor influencing the spatial distribution of denitrification, whereas the soil temperature was a determinant of the seasonal DR variation. The six riparian sites could also be divided into two types (a nitrate-abundant and a nitrate-stressed riparian system) according to the soil NO₃⁻-N concentration. The DR in nitrate-abundant riparian systems was significantly higher than that in the nitrate-stressed riparian systems. The DR in riparian zones that were covered with bushes and had adjacent cropland was higher than in grass-covered riparian sites. Furthermore, the riparian DR decreased with soil depth, which was mainly attributed to the concentrated nitrate in surface soils. The DR was not associated with the SOC, STN, C/N ratio, and pH. Nitrate supply and temperature finally decided the spatiotemporal distribution patterns of urban riparian denitrification. Considering both the low DR of existing riparian soils and the significance of nonpoint source nitrogen pollution, the substantial denitrification potential of urban riparian soils should be utilized to reduce nitrogen pollution using proper engineering measures that would collect the polluted urban rainfall runoff and make it flow through the riparian zones.

Cadmium (Cd) is a toxic and nonessential element. Because of its toxicity, Cd soil contamination is a major environmental risk to living organisms. Several studies have reported on the successful use of biochar to immobilize Cd in soil as it reduces Cd accumulation in plant parts. This research reports on the contrasting effect of biochar on enhancing Cd uptake by plants. A cassava stem biochar produced through low-temperature pyrolysis was applied to natural Cd-contaminated soil that also had a high zinc (Zn) concentration. Vigna radiata L. (a green bean) was grown in treatments receiving three biochar rates, i.e., 5, 10, and 15 %, respectively. The results showed that the 10 % biochar-amended soil had a positive effect on promoting plant growth and seed yield. Unfortunately, 15 % biochar-amended soil caused an adverse effect to plant growth. Cadmium uptake by plants increased with increasing biochar application rate. Zinc uptake by plants tended to decrease with biochar application. Cadmium and Zn bioavailability in soil was significantly reduced with an increasing biochar application rate. The results also showed that the biochar-amended soil could be an alternative and cost-effective method to promote plant growth and decrease Cd mobility in soil. The ratio of Cd concentration in plant root to soil was higher than 1, while the translocation factor from root to shoot was less than 1. These results indicate that the cultivation of V. radiata L. coupled with biochar application is an appropriate method to enhance Cd phytostabilization efficiency of V. radiata L. in Cd-polluted sites.

Chemically prepared activated carbon derived from durian seed (DSAC) was used as adsorbent to adsorb Malachite green (MG) dye. The prepared DSAC was characterized using Brunauer–Emmet–Teller (BET), Fourier transform infrared (FTIR), scanning electron microscope (SEM), and proximate analysis, respectively. Batch adsorption studies were carried out for the removal of MG dye from aqueous solutions by varying operational parameters like contact time, initial MG dye concentration, solution temperature, and initial solution pH. Maximum dye removal of 97 % was obtained at pH 8. Experimental data were analyzed by eight model equations—Langmuir, Freundlich, Temkin, Dubinin–Radushkevich, Radke–Prausnitz, Sips, Vieth–Sladek, and Brouers–Sotolongo isotherms—and it was found that the Freundlich isotherm model fitted the adsorption data the most. Adsorption rate constants were determined using pseudo-first-order and pseudo-second-order rate equations, Elovich, intraparticle diffusion, and Avrami kinetic model. The results clearly showed that the adsorption of MG dye onto DSAC followed the pseudo-second-order model, and the mechanism of adsorption was controlled both by film diffusion and intraparticle diffusion. Thermodynamic parameters such as ∆G, ∆H, and ∆S were also calculated for the adsorption process. The process was found to be spontaneous and endothermic in nature. This work provided an attractive adsorbent for the removal of MG dye from wastewaters.

Sugarcane is a major crop in Brazil that generates huge amounts of organic residues that are usually left deposited in, or applied to the soil, and thereby affect the behavior of herbicides. This study assessed the effects of sugarcane residues (straw, ash, and compost) and residence time (“aging”) on the sorption of alachlor and diuron in two contrasting soils (LVd and LVAd), as well as the effects of these residues on the leaching of alachlor. Adding straw and compost had no effect, whereas adding ash significantly increased sorption of both herbicides. Aging (28 days) increased apparent sorption distribution coefficients (Kd,ₐₚₚvalues) by 1.2 to 2.3 times. Straw and ash amendments resulted in less leaching of alachlor (<1.0 % of the applied amount) than compost or control soil (~6 % of the applied amount). The straw retained ~80 % of the applied alachlor during leaching. Although this may be overrated due to an artifact of the methodology adopted, alachlor retention in the straw could not be predicted by the use of Kd,ₐₚₚ. The transport potential of alachlor may be overestimated if aging and sugarcane straw management are not factored into the models.

Adsorption onto powdered activated carbon (PAC) is a promising option to remove organic micro-pollutants (OMP) from drinking water sources or wastewater. Since this treatment option requires continuous PAC dosing, sufficient contact time and subsequent separation of the PAC, the integration into existing process chains is challenging. In the present investigation, the pre-loading of a deep bed filter with PAC used as fixed bed adsorber was investigated. The retention and distribution of an exemplary PAC in a pumice rapid filter were determined. Gravimetry combined with combustion of the PAC at 550 °C was applied to differentiate between PAC and filter material residues and revealed comparably high PAC immobilization in the upper third of the pumice filter. Comparative adsorption experiments in batch with suspended PAC and continuous filtration tests with immobilized PAC showed advantageous results for immobilized PAC with regard to the removal of OMP and the sum parameters dissolved organic carbon and UV light absorption at 254 nm wavelength. The results indicate that a conventional rapid filter together with PAC can be effectively utilized as fixed bed adsorption filter.

Performance of a laboratory-scale integrated baffled reactor for the treatment of raw palm oil mill effluent (POME) was investigated. Initially, the reactor was fed with diluted POME (COD = 1,830 mg/L and OLR = 0.46 g COD/L day) which was then increased gradually to actual concentration (COD = 45,500 mg/L and OLR = 11.38 g COD/L day). Reactor operation was studied in two different hydraulic retention times (HRTs) (4 and 6 days) using POME with no effluent-recycled feed and after alkalinity supplementation. Chemical oxygen demand (COD) removal of 79 and 83 % at an HRT of 4 and 6 days were attained at the highest organic loading rate (OLR = 11.38 g COD/L day). The presence of Arcella-like and Metopus-like species and pH profile in the bioreactor’s compartments imply that anaerobic system is active in the reactor throughout the study. Use of methanogen-enriched inocula, smooth OLR augmentation, and appropriate separation of acidogens and methanogens in the reactor were the reasons for satisfactory performances of the system.