Microalgae-based bioremediation processes pose dual abilities of simultaneous CO₂ fixation through photosynthesis and degradative effect on environmental pollutants. This study intends to investigate the tolerance and biodegradation capability of Spirulina maxima for removal of phenol. An assimilation study of the phenol-carbon was also conducted to elucidate if the phenol removal was dominated by physical adsorption on cell walls or through metabolic activities. S. maxima cells were found to be capable of growing on phenol up to a concentration of 400 mg l⁻¹, and they had a highest specific growth rate at a phenol concentration of 50 mg l⁻¹. The results suggested that the removal of phenol (as high as 97.5 %) was mainly due to biodegradation processes rather than a bioadsorption process. Moreover, it was evident that nearly 30 % of the ¹³C-labeled phenol content was discovered in the cellular fraction, indicating that the ¹³C-phenol-carbon was indeed assimilated to biomass followed by mineralize the carbon to CO₂.

Many products contain dyes, such as fabrics. However, most of the industry-generated waste is improperly handled, which causes serious environmental problems for the bodies of water that receive textile effluents. This study aimed to analyze the effect of biosorbents and biosorption techniques on decolorizing the textile azo dye Acid Blue 29 in an aqueous solution employing pine sawdust. Pine sawdust is low-cost substrate with minor environmental impact. A toxicity test was performed with Lactuca sativa seeds to determine the LC₅₀ of the dye. Subsequently, a biosorption test was performed to determine the toxicity of the resulting solutions. We observed that biosorption is a very feasible technique for the discoloration of the solutions and promotes reduction in their toxicity.

The purpose of this review is to describe how plants take up lead and its distribution to plant parts, morphological, physiological, and biological effects of lead on plants, sequestration strategies, and tolerance mechanisms including detoxification. How lead despite its lack of essential function in plants, causes phytotoxicity by changing cell membrane permeability, by reacting with active groups of different enzymes involved in plant metabolism by reacting with the phosphate groups of adenosine diphosphate (ADP) or adenosine-5′-triphosphate (ATP). Moreover, we also address role of hyperaccumulating plants in lead absorption. How synthetic chelators such as ethylenediaminetetraacetic acid (EDTA) enhances the availability of heavy metal lead in soils and increase phytoextraction efficiency in aboveground harvestable plant parts through enhancing the metal solubility and translocation from roots to shoots, metal tolerance, and future prospectives to decrease lead pollution.

Several laccases from different sources have been used in dye decolourization processes. However, only in a reduced number of studies have efforts been done to identify the metabolites produced by the enzymatic treatment as well as to evaluate the toxicity of degradation products. Taking these gaps into account, the objective of this work was to use a laccase from Ganoderma lucidum in the decolourization of the synthetic dye Congo red (C.I. No. 22120, Direct Red 28), largely used in the textile industry. After 6 h of treatment at pH 4.0 and 40 °C, the enzyme was able to decolourize 80 % of Congo red. Fourier transform infrared spectroscopy (FTIR), photoacoustic spectroscopy (PAS) and mass spectrometry allow concluding that laccase effectively changed the structure of Congo red, reducing the colour by modifying the chromophore groups and other parts of the molecule. Several degradation products with m/z ⁺ ranging from 298 to 745 were identified. It is proposed that the first degradation step could be an asymmetric cleavage of the azo bond present in the Congo red structure forming the intermediate with m/z ⁺ 298. The results also suggest a reduction in the toxicity of Congo red after laccase treatment, as indicated by the lettuce seed germination model. In conclusion, G. lucidum laccase could be used in a novel azo dye bioremediation strategy.

A high concentration of dissolved gaseous mercury (DGM) was detected in post-desulfurized waste seawater, which was discharged from a coal-fired power plant equipped with a seawater desulfurization system and which was located in a coastal area. A large amount of DGM was converted from other forms of mercury during transformation processes, such as photo-reduction. The present study targeted the photo-reduction of mercury and the effects of various environmental parameters on DGM production in the post-desulfurized seawater discharged. The results suggested that the photo-reduction of mercury was significantly induced under UV radiation, especially with UVB. The particulate mercury on suspended solids was easily photo-reduced and considered as an important source of DGM. It was confirmed that the suspended solids in post-desulfurized seawater could enhance the reduction process of mercury under UV radiation. The pseudo-first-order rate constants of DGM production, which were determined through the concentration gradient and trial methods, were 1.39 × 10⁻³ min⁻¹and 1.45 × 10⁻³ min⁻¹, respectively. The values showed no significant difference and were both much higher than the reported results, indicating that the photo-reduction of mercury in post-desulfurized seawater deserved more attention. In addition, the initial mercury level was observed when mixing the post-desulfurized seawater with fresh seawater, and this suggested that a significant amount of initial mercury would be produced when the post-desulfurized seawater was discharged into the adjacent sea area and thus becomes another considerable source of DGM.

Microbial Cr(VI) reduction is a significant process in detoxification of Cr(VI) pollution. In this study, a new Cr(VI)-reducing bacterial strain, Cr-4, was isolated from soil around the chromium-containing slag. The analysis of the 16S ribosomal RNA (rRNA) gene sequence revealed that the newly isolated strain was closely related to Bacillus anthracis. The response to Cr(VI) stress and reduction capacity of the isolate were investigated. Cell growth decreased with the increase of Cr(VI) concentration. Cell morphology varied and cell growth was inhibited remarkably in the presence of 125 mg/L Cr(VI). The strain grew well and removed Cr(VI) effectively at a Cr(VI) concentration lower than 50 mg/L. Cr(VI)-reducing activity was inhibited by Zn²⁺, while significantly stimulated by Cu²⁺. The activity of Cr(VI) reduction by cell-free extract was demonstrated. Total chromium analysis and the energy-dispersive X-ray analysis (EDAX) spectrum revealed that Cr(VI) removal was caused mainly by microbial reduction rather than by biosorption and the main part of the reduced Cr(III) existed as soluble form in solutions.

The degradation of hexachlorobenzene (HCB) is of great concern and attracts considerable scientific and regulatory interests, due to the high toxicity, great bioaccumulation, and persistence of HCB in the environment. However, in the real HCB-contaminated soil, the effect of coexisting chlorobenzene congeners on the degradation capacity of HCB is poorly known. In this work, the anaerobic degradation behaviors of three coexisting chlorobenzene congeners pentachlorobenzene (PeCB), 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB), and 1,2,4-trichlorobenzene (1,2,4-TCB) and the influence of initial pH and reaction temperature on the dechlorination of HCB in HCB-contaminated soil from the dye plant were studied. The amount and extent of accumulated coexisting chlorobenzenes was analyzed under different environmental conditions. The results indicate that the concentrations of three coexisting chlorobenzene congeners change in the form of wave. The anaerobic degradation activity of HCB is reduced due to the feedback inhibition caused by accumulation of coexisting chlorobenzene congeners, and the feedback inhibition varies from environmental conditions.

The capability of W⁶⁺-impregnated ZnO photocatalysts for sunlight mineralization of a variety of structurally different dyes has been investigated. Compared to bare ZnO, the W⁶⁺-loaded photocatalysts showed significantly higher activity for the decolorization as well as mineralization of dyes, and complete mineralization was noticed in a short span of 150 min. The results obtained by various analytical tools were correlated to estimate the mechanistic aspects of the decolorization/mineralization process and to identify the nature of the oxidizing species involved in the process. A strong dependence of the decolorization/mineralization process was observed on the nature and number of auxochromes attached to color-generating conjugated system. The rapid decolorization/mineralization of the dyes and release of corresponding anions with the decolorization of dyes suggested the involvement of charged rather than radical reactive oxygen species (ROS) in the oxidation process. Langmuir-Hinshelwood kinetic model was found to be best suited for evaluating the kinetics of mineralization process. The effectiveness of the catalysts for the decolorization/mineralization of a mixture of dyes was also examined. The suitability of the catalysts for successive use in sunlight exposure was also evaluated.

Sugarcane molasses, which is a kind of microbial carbon source, is a viscous by-product of the refining of sugarcane into sugar. However, experiments were designed to ascertain the mechanism and kinetics of Cr(VI) reduction with sugarcane molasses without adding microbes in aqueous solution. Results indicated that sugarcane molasses can reduce Cr(VI) to Cr(III) at pH values that range from 2.0 to 6.1 when no bioreduction occurs in the reaction. Furthermore, the reaction mechanism was proven to be that Cr(VI) acts as an electrophile that readily accepts electrons from the phenolic hydroxyl group of plant polyphenol, and it is then reduced to Cr(III) and in the process oxidizes the phenolic hydroxyl group to a quinone. Meanwhile, the reaction could be described by the pseudo-first-order kinetic model with respect to Cr(VI) concentration. The reaction rate constants were 324.2, 65.9, 21.9, and 14.4 h⁻¹ when pH values were 2.0, 3.5, 5.0, and 6.1, respectively, at 20 °C. The k ₒbₛ increased 3.36, 7.02, and 13.48 times with the temperature adjusted from 5 to 10, 20, and 30 °C.

River plumes are the major source of nutrients, sediments, and other pollutant into the coastal waters. The predictive capability of a 3D hydrodynamic model (POMGL), a version of the common Princeton Ocean Model (POM), adapted for the Great Lakes, is assessed versus field measurements. The model was applied to simulate the nearshore hydrodynamics as the Grand River plume entering Lake Michigan. A nesting technique was adapted to represent the circulation and thermal structure of the surface river plume with a higher resolution. The model was compared with extensive field studies in the vicinity of Grand Haven. The current predictions showed fairly good agreement with observations, although the thermal structure of the flow especially near the river mouth was not very well represented. The model showed a weak stratification and a mild temperature transition from the plume to the lake water and therefore more diffusion. Application of hydrostatic models in exchange flows (e.g., buoyant river plumes) is recommended with reservations and coupling of these models with near field entrainment or empirical models to consider the nonhydrostatic nature of lake-river interface currents.