The present study deals with the synthesis and subsequent application of Fe₃O₄@n-SiO₂nanoparticles for the removal of Cr(VI) from aqueous solutions. Rice husk, an agrowaste material, was used as a precursor for the synthesis of nanoparticles of silica. Synthesized nanoparticles were characterized by XRD and SEM to investigate their specific characteristics. Fe₃O₄@n-SiO₂nanoparticles were used as adsorbent for the removal of Cr(VI) from their aqueous solutions. The effects of various important parameters, such as initial Cr(VI) concentration, adsorbent dose, temperature, and pH, on the removal of Cr(VI) were analyzed and studied. A pH of 2.0 was found to be optimum for the higher removal of Cr(VI) ions. It was observed that removal (%) decreased by increasing initial Cr(VI) concentration from 1.36 × 10⁻²to 2.4 × 10⁻² M. The process of removal was found to be endothermic, and the removal increased with the rise in temperature from 25 to 45 °C. The kinetic data was better fitted in pseudo-second-order model in comparison to pseudo-first-order model. Langmuir and Freundlich adsorption capacities were determined and found to be 3.78 and 1.89 mg/g, respectively, at optimum conditions. The values of ΔG⁰were found to be negative at all temperatures, which confirm the feasibility of the process, while a positive value of ΔH⁰indicates the endothermic nature of the adsorption process. The present study revealed that Fe₃O₄@n-SiO₂nanoparticles can be used as an alternate for the costly adsorbents, and the outcome of this study may be helpful in designing treatment plants for treatment of Cr(VI)-rich effluents.

The Tubarão River rises in Santa Catarina, Brazil, and has been historically affected by coal mining activities around its springhead. To evaluate its water conditions, an investigation regarding a possible decontamination gradient associated with the increased river flow toward the estuary, as well as the influence of seasonality over this gradient was performed through a series of biomarkers (vitellogenin, comet assay, lipid peroxidation, protein carbonylation, gluthatione, gluthatione S-transferase, acetylcholinesterase, light microscopy in liver, and scanning electron microscopy in gills) and chemical analysis (polycyclic aromatic hydrocarbons (PAHs) in bile and metal analysis in sediment) in the cichlid Geophagus brasiliensis. Two collections (summer and winter) were made in four distinct sites along the river, while sediments were sampled between those seasons. As expected, the contamination linked exclusively to mining activities was not observed, possibly due to punctual inputs of contaminants. The decontamination gradient was not observed, although seasonality seemed to have a critical role in the responses of biomarkers and availability of contaminants. In the summer, the fish presented higher histopathological damages and lower concentrations of PAHs, while in the winter they showed both higher genetic damage and accumulation of PAHs. The Tubarão suffers impacts from diverse activities, representing health risks for wild and human populations.

The accumulation of metals and nutrients in biosolid-amended soils and the risk of their excess uptake by plants is a topic of great concern. This study examines the elemental uptake and accumulation in five vegetable plants grown on biosolid-applied soils and the use of spectral reflectance to monitor the resulting plant stress. Soil, shoot, root, and fruit samples were collected and analyzed for several elemental concentrations. The chemical concentrations in soils and all the plant parts increased with increase in applied biosolid concentrations. The Cu and Zn concentrations in the plant shoots increased in the order of collard < radish < lettuce < tomato < pepper. The Cu and Zn concentrations accumulated significantly in the fruits of the tomato plants compared to other plants. Among all the plants, the shoot concentration factor (SCF) of Zn was significantly higher for pepper plants, indicating increase in uptake of Zn. The shoot relative uptake index (SRUI) of Cu and Zn increased in the order of collard < radish < lettuce < tomato < pepper. The shoot dry weight and spectral reflectance of the radish plants in the near-infrared (NIR) region (800–1,300 nm) decreased significantly with increase in biosolid concentration compared to other plants. Increase in plant stress with increase in biosolid dose was evident in radish plants through significant reduction in Normalized Difference Vegetative Index (NDVI). This study indicates the potential use of spectral reflectance as a tool for the screening and monitoring of stress-sensitive plant species and their physiology and as a result, indirectly assesses the chemical concentrations in soils and plants.

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.

The effects of radiation pollution on the population diversities and metabolic characteristics in soil microorganisms from radiation pollution areas were investigated. Microbial diversities were determined by using methods of cultured isolates and carbon source utilization on Biolog EcoPlate™. The results showed that radiation changed soil microbial community structure and function. With the increasing of radiation pollution, the number of bacteria and actinomycetes declined gradually. Carbon utilizations of microbial community were significant ly different from each other (ρ < 0.05). Microbial activity decreased gradually; Simpson index and McIntosh index increased, but Shannon-Wiener index was not significant different; the major utilized substrates indicated that microbes more tend to use carboxylic acids and polymers as carbon sources, instead of carbohydrates. In conclusion, the community composition of microorganisms as well as population diversity in soils was impacted obviously by radiation pollution.

A comparative study of indicator bacteria concentrations obtained by laboratory analysis of grab samples of storm water, which were collected manually or by automatic samplers, was carried out in two urban catchments. Samples were analyzed for four types of indicator bacteria, total coliforms, Escherichia coli (E. coli), enterococci, and Clostridium perfringens and further documented by measurements of total suspended solids (TSS) and turbidity. Analysis of complete data sets (N = 198) indicated no statistically significant differences in the geometric means of all the constituent samples collected automatically or manually, but there were some small differences between the results produced by the two sampling methods applied. Total coliform concentrations were positively biased in samples collected by automatic samplers, but for the three remaining indicator bacteria (E. coli, enterococci, and C. perfringens), the opposite was true. Risk of sample cross-contamination in automatic samplers was assessed in the laboratory by sampling consecutively synthetic storm water with high and low concentrations of E. coli and enterococci. The first low-concentration samples preceded by high-concentration samples were cross-contaminated and the measured concentrations were positively biased. This cross-contamination was explained by storm-water residue in the sampling line. Such a residue remained in place even after line purging by compressed air, and its mass depended on the sampling line length (tested up to 5 m), as verified by measurements in the laboratory. The study findings should be helpful for improving field protocols for indicator bacteria sampling.

In this work, a mesoporous carbon material was modified by nitrogen atom by two different ways. The X-ray photoelectron spectroscopy (XPS) results show that the N atoms at the surface mainly exist in pyridine- and pyridone-like forms (around 80 % in atom ratio). The adsorption capacity of phenol and nicotine on mesoporous carbon and two N-containing mesoporous carbons was studied through adsorption isotherms. The adsorption isotherms were interpreted by three models (Freundlich, Langmuir, and Sips equations). Heat-flow microcalorimetry in liquid phase was used to determine the bonding strength between the organic pollutants and the surface of the adsorbents. In addition, the possibility of regeneration of adsorbents was investigated by temperature-programmed desorption (TPD) technique. The obtained values of differential heats and isotherms showed the heterogeneous properties of the mesoporous carbon materials. Comparing the different results obtained from the experiments, the surface area is a key factor for the adsorption of phenol and nicotine in water. The introduction of N improved the adsorption of phenol but did not affect the adsorption of nicotine.

In order to assess and accurately predict the self-purification capabilities of rivers with respect to enteric pollution, a thorough understanding of mechanisms such as dispersion, particle association, and inactivation in the water column is crucial. In this study, we firstly performed particle size distribution analyses of wastewater and investigated the Escherichia coli and enterococci loadings of each size fraction. It was seen that 91 % of E. coli and 83 % of enterococci were associated with particle sizes less than or equal to 12 μm. Particles larger than 63 μm contributed less than 1 % to overall E. coli and enterococci loadings. Based on these results, batch experiments were performed to investigate the effect of particle size and total suspended solids (TSS) concentration on UV inactivation of the two fecal indicator bacteria (FIB). A direct relationship between the particle size to which FIB were associated and their UV inactivation rate was noted. E. coli and enterococci associated with particles smaller than or equal to 12 μm were inactivated on average 2 × and 1.7 × faster than those associated with the larger particle fraction of 12 to 63 μm. It was additionally seen that as the TSS concentrations increased, the UV inactivation rates decreased. A tailing effect of UV inactivation was however noted at TSS concentrations above approximately 100 mg L⁻¹.

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.

Continual discharge of textile wastewaters loaded with a variety of synthetic dyes and metals is considered as a huge threat to surrounding ecosystems. In order to treat these undesirable pollutants, microbial bioremediation is considered as an efficient and economical technique. This study was conducted to evaluate the use of bacterial strains for simultaneous removal of azo dyes and hexavalent chromium [Cr(VI)]. Fifty-eight bacterial strains were isolated from Paharang drain wastewater and tested for their potential to decolorize reactive red-120 (RR-120) in the presence of 25 mg L⁻¹of Cr(VI). Among the tested isolates, FA10 decolorized the RR-120 most efficiently and was identified as Acinetobacter junii strain FA10. Based on quadratic polynomial equation and response surfaces given by the response surface methodology (RSM), Cr concentration and pH were found to be the main factors governing the RR-120 decolorization by FA10. The strain FA10 also exhibited a substantial salt resistance since it showed a considerable decolorization of RR-120 even in the presence of 150 g L⁻¹of NaCl. Moreover, the strain FA10 also showed the potential to simultaneously remove the Cr(VI) and the selected azo dyes in the same medium. More than 80 % of the initially added Cr(VI) was removed over 72 h of incubation along with the appreciable decolorization efficiency. The strain FA10 also exhibited good tolerance to considerable levels of different heavy metals. The findings of this study suggest that the strain FA10 might serve as an efficient bioresource to develop the biotechnological approaches for simultaneous removal of different azo dyes and heavy metals including Cr(VI).