Previous research has demonstrated that post-anoxic denitrification and biological nutrient removal could be achieved in the oxic/anoxic/extended-idle wastewater treatment regime. This study further investigated the effect of different carbon sources on post-anoxic denitrification and biological nutrient removal. Acetate, propionate (volatile fatty acids (VFAs)), glucose (carbohydrate), methanol, and ethanol (alcohol) were used as the sole carbon source, respectively. The experimental results showed that VFA substrates led to an improvement in nitrogen and phosphorus removal. The total nitrogen and phosphorus removal efficiency values driven by acetate achieved 93 and 99 %, respectively. In contrast, glucose present in mixed liquor deteriorated total nitrogen and phosphorus removal efficiency values to 72 and 54 %. In the reactors cultured with methanol and ethanol, 66 and 63 % of the total nitrogen were removed, and phosphorus removal efficiency values were 78 and 71 %, respectively. The mechanism studies revealed that different carbon sources affected the transformations of intracellular polyhydroxyalkanoates (PHAs) and glycogen. PHAs are the dominant storages for microorganisms cultured with VFA substrates. Though glycogen is not the favorable energy and carbon source for polyphosphate-accumulating organisms, it can be consumed by microorganisms related to biological nitrogen removal and is able to serve as the electron donor for post-anoxic denitrification.

Exposure to environmental chemicals and oxidative stress particularly at low dose levels may produce additive or synergistic interactions not seen in single component exposure. Exposure to cadmium, lead, and ultraviolet rays occurs in many occupational settings, such as pigment and battery production, galvanization, and recycling of electric tools. However, little is known about interactions between heavy metals and ultraviolet rays. This study aimed to evaluate the interactions of ultraviolet rays of 254 nm (UV-B) with cadmium or lead on Bacillus cereus. B. cereus was treated with different concentrations of cadmium or lead followed by exposure to UV-B radiation as combined effect. Photoirradiation of B. cereus with UV-B with exposure to cadmium or lead results in DNA damage, cytotoxicity, depletion of glutathione, and formation of lipid peroxidation. UV-B rays alone enhanced glutathione production which was depleted with lead and high doses of cadmium. Lead alone does not increase DNA breaking. The mechanism behind these interactions might be repair inhibition of oxidative DNA damage, since a decrease in repair capacity will increase susceptibility to reactive oxygen species generated by cadmium or lead. Lipid peroxidation was increased with exposure to UV-B and cadmium or lead. DNA, glutathione, and lipid peroxidation can be used as biomarkers to identify possible environmental contamination in bacteria. One conclusion from this model is the existence of more than multiplicative effects for co-exposures of cadmium or lead and UV rays.

A combined system employing photochemical oxidation (UV/H₂O₂) and adsorption for arsenic removal from water was designed and evaluated. In this work, a bench-scale photochemical annular reactor was developed being connected alternately to a pair of adsorption columns filled with titanium dioxide (TiO₂) and granular ferric hydroxide (GFH). The experiences were performed by varying the relation of As concentration (As (III)/As (V) weight ratio) at constant hydrogen peroxide concentration and incident radiation. Experimental oxidation results were compared with theoretical predictions using an intrinsic kinetic model previously obtained. In addition, the effectiveness of the process was evaluated using a groundwater sample. The mathematical model of the entire system was developed. It could be used as an effective tool for the design and prediction of the behaviour of these types of systems. The combined technology is efficient and promising for arsenic removal to small and medium scale.

The expansion in knowledge of the microbial community structure can play a vital role in the electrochemical features and operation of microbial fuel cells (MFCs). In this study, bacterial community composition in a dual chamber MFC fed with brewery waste was investigated for simultaneous electricity generation and azo dye degradation. A stable voltage was generated with a maximum power density of 305 and 269 mW m⁻² for brewery waste alone (2000 mg L⁻¹) and after the azo dye (200 mg L⁻¹) addition, respectively. Azo dye degradation was confirmed by Fourier transform infrared spectroscopy (FT-IR) as peak corresponding to –N=N– (azo) bond disappeared in the dye metabolites. Microbial communities attached to the anode were analyzed by high-throughput 454 pyrosequencing of the 16S rRNA gene. Microbial community composition analysis revealed that Proteobacteria (67.3 %), Betaproteobacteria (30.8 %), and Desulfovibrio (18.3 %) were the most dominant communities at phylum, class, and genus level, respectively. Among the classified genera, Desulfovibrio most likely plays a major role in electron transfer to the anode since its outer membrane contains c-type cytochromes. At the genus level, 62.3 % of all sequences belonged to the unclassified category indicating a high level of diversity of microbial groups in MFCs fed with brewery waste and azo dye. HIGHLIGHTS: • Azo dye degradation and stable bioelectricity generation was achieved in the MFC. • Anodic biofilm was analyzed by high-throughput pyrosequencing of the 16S rRNA gene. • Desulfovibrio (18.3 %) was the dominant genus in the classified genera. • Of the genus, 62.3 % were unclassified, thereby indicating highly diverse microbes. Graphical Abstract A schematic diagram of a dual chamber microbial fuel cell for azo dye degradation and current generation (with microbial communities at anode electrode)

Soils located adjacent to the Jiaojia gold mine were sampled and analyzed to determine the degree of which they were contaminated by trace elements (Hg, As, Cd, Pb, Cu, and Zn) in Shandong Province, China. All 18 samples exhibited mean Hg, As, Cd, and Pb concentrations in excess of local background values, while the mean concentrations of Cu and Zn were below the background values. In addition, the concentrations of trace elements in gold smelter (GS) soils were higher than in the gold mine (GM) soils. The result from a modified Tessier sequential extraction procedure was that with the exception of Cu in soils near the smelter, the trace elements were predominantly associated with the residual fraction. After residual fraction, most Hg was mainly humic acid and strong organic fraction, while most As was the humic acid. Cd was associated with the water soluble, ion exchange, and carbonate fractions compared with the other trace elements. Furthermore, Cu, Pb, and Zn were more concentrated in the humic acid and Fe/Mn oxide fraction. The fractions of trace elements were affected by soil pH and Ec (Electrical conductivity). The humic acid fraction of Hg as well as the ion exchange fraction of Cd and Zn displayed negative correlations with soil pH. The strong organic fraction of Hg, the Fe/Mn oxide fraction of Cd, and the carbonate fraction of Zn were positively related to the soil Ec. The strong organic fraction and ion exchange fraction of Zn were negatively related to soil Ec. However, the ion exchange and carbonate fractions of As showed significant positive correlations with soil pH. A calculated individual availability factor (A f ⁱ) is used; the values of each trace element in the soils are in the following order: Cu > Cd > Pb > Zn > As > Hg. When combined with a risk assessment code, data suggest that Hg, As, Pb, and Zn levels showed low risk for the environment, whereas Cd levels in soils adjacent to the GM and Cu levels in soils adjacent to the GS showed medium risk to the environment, and Cd levels in soils adjacent to the GS exhibited higher environment risk.

Various nitric oxide (NO) regulators [including the NO donor sodium nitroprusside (SNP), the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), the NO-synthase inhibitor N ᴳ-nitro-L-Arg-methyl ester (L-NAME), and the SNP analogues sodium nitrite/nitrate and sodium ferrocyanide] were investigated to elucidate the role of NO in white clover (Trifolium repens L.) plants after long-term (5 days) exposure to cadmium (Cd). A dose of 100 μM Cd stress significantly restrained plant growth and decreased the concentrations of chlorophyll and NO in vivo, whereas it disrupted the balance of stress-related hormones and enhanced the accumulation of Cd, thereby inducing reactive oxygen species (ROS) burst. However, the inhibition of plant growth was relieved by 50 μM SNP through its stimulation of ROS-scavenging compounds (ascorbic acid, ascorbate peroxidase, catalase, glutathione reductase, non-protein thiol, superoxide dismutase, and total glutathione), regulation of H⁺-ATPase activity of proton pumps, and increasing jasmonic acid and proline but decreasing ethylene in plant tissues. Even so, the alleviating effect of SNP on plant growth was counteracted by cPTIO and L-NAME and was not observed with SNP analogues, suggesting that the protective roles of SNP are related to the induction of NO. These results suggest that NO may improve the Cd tolerance of white clover plants by eliminating oxidative damage, re-establishing ATPase activity, and maintaining hormone equilibrium. Improving our understanding of the role of NO in white clover plants is key to expanding the plantations to various regions and the recovery of pasture species in the future.

Blue-green algae bloom is of great concern globally since they adversely affect the water ecosystem and also drinking water treatment processes. This work investigated the removal of Microcystis aeruginosa (M. aeruginosa) by combining the conventional coagulant polyaluminum chloride (PACl) with nano-Fe₃O₄ particles as a coagulant aid. The results showed that the addition of nano-Fe₃O₄ significantly improved the removal efficiency of M. aeruginosa by reducing the amount of PACl dosage and simultaneously hastening the sedimentation. At the M. aeruginosa density of an order of magnitude of 10⁷, 10⁶, and 10⁵ pcs/mL, respectively, the corresponding PACl dose of 200, 20, and 2 mg/L and the mass ratio of PACl to nano-Fe₃O₄ of 4:1, the removal efficiency of M. aeruginosa could be increased by 33.0, 44.7, and 173.1 %, respectively. Compared to PACl, PACl combined with the nano-Fe₃O₄ as a coagulant aid had higher removal efficiency at a wider pH range. SEM images showed that nano-Fe₃O₄ first combined with PACl to form clusters and further generated the flocs with algae. Results from the laser particle analyzer further suggested that the floc size increased with the addition of nano-Fe₃O₄. It was noted that the addition of nano-Fe₃O₄ led to aluminum species change after PACl hydrolyzed in the algae solution, from Alₐ to Alb and Alc subsequently. As a coagulant aid, the nano-Fe₃O₄, in conjunction with PACl, apparently provided nucleation sites for larger flocs to integrate with M. aeruginosa. In addition, increased floc density improved the removal of M. aeruginosa.

This study was conducted to determine whether phytoscreening techniques could be used to characterize the distribution of Hg in soil at the South River, VA. An estimated 500 to 1000 kg of Hg was released to the South River in the 1930s and 1940s from a synthetic fiber manufacturing plant located in Waynesboro, contaminating the floodplain downstream. Under background conditions (soil Hg <0.03 μg/g), phytoscreening sample Hg concentrations ranged from 1.9 to 3.9 ng/g. With soil Hg concentrations ranging from 0.1 to 94 μg/g in the top 30.5 cm of nearby soil, phytoscreening sample Hg concentrations ranged from 5.0 to 145 ng/g. The variability of Hg concentrations in soil solution over the scale of the entire rhizosphere of the large trees sampled was likely high. Furthermore, the mean depth of water uptake and the exact proximity of the soil profile samples for each tree could not be determined. Nevertheless, the phytoscreening results of this study could be used to reliably provide a qualitative delineation of Hg-contaminated soil.

Soil pollution with heavy metals is an increasingly serious threat to the environment, food security, and human health. Therefore, it is urgent to develop economic and highly efficient soil restoration technology for environmental improvement; phytoremediation is an option that is safe, has low cost, and is environmentally friendly. However, in selecting hyperaccumulators or tolerant plants, theories and operation technologies for optimal restoration should be satisfied. In this study, the switchgrass growth response and performance of phytoextraction under the coupling effect of Cd and pH were investigated by evaluating seed germination, seedling growth, and the Cd content in the plant to evaluate the potential use of switchgrass as a phytoremediation plant in cadmium contaminated soil. This study conducted three sets of independent experiments with five levels of Cd concentrations, including two orthogonal matrix designs of combining Cd with pH values. The results showed that switchgrass was germinated well under all treatments (Cd concentration of 0–500 μM), but the seedling growth was significantly affected by Cd and pH, as shown by multivariate regression analyses. Hormesis was found during the growth of switchgrass plants exposed to low Cd concentrations under hydroponic conditions, and switchgrass plants were capable of developing with a Cd concentration of 100–175 μM and pH of 4.1–5.9. Mild acidic conditions can enhance the ability of Cd to accumulate in switchgrass. Switchgrass was moderately tolerant to Cd and may be used as a phytoremediation plant for Cd-contaminated soils in the future. Our results also suggest that hormetic effects should be taken into consideration in the phytoremediation of Cd-contaminated soils. We discuss the physiological and biochemical mechanisms contributing to the effective application of the plant for the phytoremediation of Cd-contaminated soils.

Several studies have pointed to the potential benefits of riparian vegetation as buffer zones for agricultural and industrial pollutants harmful to aquatic ecosystems. However, other studies have called into question its use as an ecological filter, questioning the widths and conditions for which they are effective as a filter. In this work, we have investigated the buffering capacity of the riparian one to retain pesticides in the water-saturated zone, on 27 sites composed by riparian buffer zones with different vegetation structure (woody, shrubs, or grass vegetation) and width (12, 36, and 60 m). Five pesticides were analyzed. The effectiveness of the filtering was largely influenced by the width and vegetation type of the buffer zone. In general, decreasing pesticide removal followed in this order wood > shrubs > grass. The 60 m woody buffer zone was the most effective in the removal of all the pesticides. Only atrazine was detected in this case (0.3 μg L⁻¹). Furthermore, a linear correlation (R ² > 0.97) was observed in their removal for all compounds and buffer zones studied. Thus, preserving the woody vegetation in the riparian zone is important for watershed management and groundwater quality in the no-tillage system in temperate climate.