Cleaner red mud residue production at an alumina plant by applying experimental design techniques in the filtration stage

Red mud is a residue obtained by the Bayer process during alumina production, and its disposal is an environmental problem due to its caustic nature, metal and radionuclide content and alkalinity. The present study analyzed five different filtration factors with two levels each in order to improve filtration and, thus, reduce the caustic content of this residue. This study was conducted at the Alumina do Norte do Brasil S.A (ALUNORTE) alumina plant, located in Pará, Brazil, in one of the six filters at the plant. Results show that the condensate is the primary factor in caustic red mud concentrations, followed by dilution, rotation and level of the basin filter. The interactions between dilution and the level of the basin filter were considered significant, as was the interaction amongst the three effects: dilution, level of the basin filter and vacuum. The model adjustment regarding the filtration process allows for the production of a final red mud product with lower caustic concentrations, resulting in economic advantages due to higher caustic recovery in filtration and lower caustic concentration in the red mud residue, which leads to an environmentally safer residue.     

Toxicological responses in Laeonereis acuta (annelida, polychaeta) after arsenic exposure

Several environmental pollutants, including metals, can induce oxidative stress. So, the objective of this study was to evaluate the effects of arsenic (As(III), as As(2)O(3)) on the antioxidant responses in the polychaete Laeonereis acuta. Worms were exposed to two environmentally relevant concentrations of As, including the highest previously allowed by Brazilian legislation (50 microg As/l). A control group was kept in saline water (10 per thousand) without added metal. It was observed that: (1) a peak concentration of lipid peroxide was registered after 2 days of exposure to 50 microg As/l (61+/-3.2 nmol CHP/g wet weight) compared to the control group (43+/-4.5 nmol CHP/g wet weight), together with a lowering of the activity of the antioxidant enzyme catalase (-47 and -48%, at 50 or 500 microg As/l respectively) and a higher superoxide dismutase activity (+305% at 50 microg As/l with respect to the control group); (2) a lower conjugation capacity through glutathione-S-transferase activity was observed after 7 days of exposure to 50 microg As/l (-48% compared to the control group); (3) a significant increase in As concentration was verified after 1 week of exposure to both As concentrations (50 and 500 microg/l); (4) worms exposed to As showed a limited accumulation of related methylated As species and the levels of non-toxic As species like arsenobetaine (AsB) and arsenocholine (AsC) remained unchanged during the exposure period when compared with the controls. Overall, it can be concluded that As interfered in the antioxidant defense system of L. acuta, even at low concentrations (50 microg/l) that Brazilian legislation previously considered safe. The fact that worms exposed to As showed high levels of methylated As species indicates the methylation capability of L. acuta, although the high levels of inorganic As suggest that not all the administered As(III) (as As(2)O(3)) is completely removed or biotransformed after 7 days of exposure.     

How does the brown mussel Perna perna respond to environmental pollution? A review on pollution biomarkers

The brown mussel Perna perna (Linnaeus, 1758) is a valuable resource for aquaculture in tropical and subtropical coastal regions. It presents desirable characteristics for biomonitoring, including being sessile, widely distributed and abundant, and is a filter-feeder able to accumulate several classes of pollutants (e.g., metals, hydrocarbons, among others). Mussels’ biological responses to pollution exposure can be measured as biomarkers, which include alterations ranging from molecular to physiological levels, to estimate the degree of environmental contamination and its effects on biota. This full review compiles two decades (2000–2020) of literature concerning biological effects on P. perna mussel caused by environmental pollutants (i.e., metals, hydrocarbons, and emerging pollutants), considering environmental and farm-based biomonitoring. Biochemical markers related to mussels’ oxidative status were efficient for the biomonitoring of metals (i.e., antioxidant enzymes associated with oxidative damage in biomolecules). Genotoxicity and cytotoxicity indicators (i.e., comet, micronucleus, and neutral red assays) provided a depiction of hydrocarbon contamination. The neutral red assay gave a time-concentration cytotoxic response to a wide range of pollutants, including emerging pollutants (e.g., pharmaceuticals and biocides) and hydrocarbons. Perna perna hemocyte parameters provided a useful approach for biocide biomonitoring. This paper summarizes useful biomarkers from molecular to physiological levels in this mussel species used to identify and quantify the degree of coastal pollution. An integrated biomarker analysis may provide a way to overcome possible biomarker variations and assess multi-polluted sites. Nevertheless, it is necessary to investigate biomarker variations according to natural factors (e.g., season and gonad maturation stage) to standardize them for trustworthy biomonitoring.     

Statistical analysis in estimating probable concentrations of representative chemical species in leachate: a solution for the source term of new or unmonitored landfills

Journal of Material Cycles and Waste Management - Leakage modeling can be crucial for environmental management and control of waste landfills. However, defining boundary conditions for these models...     

Solanum nigrum L. weed plants as a remediation tool for metalaxyl-polluted effluents and soils

In this work, the phytoremediation potential of metalaxyl, a commonly used persistent, mobile and leachy fungicide, by Solanum nigrum L. plants was studied. The study revealed that this plant species can be used as an excellent metalaxyl phytoremediation tool, thus providing a cost effective and environmentally friendly clean technology for the decontamination of sites and effluents. As it can be sowed directly in the remediation site, is able to complete its life cycle without suffering major stress. Because it accumulates high amounts of the fungicide in the aboveground tissues, enables its concentration and proper disposal by cutting off the corresponding plant part. The study also suggests that the tolerance to metalaxyl is due to a suitable antioxidant response comprising proline accumulation and guaiacol peroxidase and glutathione-S-transferase enhanced activities, that reduce oxidative damage to the plant organs.     

Antioxidant responses and reactive oxygen species generation in different body regions of the estuarine polychaeta Laeonereis acuta (Nereididae)

The aim of this study was to analyze the total antioxidant capacity (TOSC), generation of reactive oxygen species (ROS) and lipid peroxidation (LPO) in the different body regions of the estuarine polychaeta Laeonereis acuta (Nereididae) sampled at non-polluted (NOPOL) and polluted (POL) sites from Lagoa dos Patos (Southern Brazil). Organisms collected at POL during summer showed similar (p>0.05) TOSC values along the body, but worms collected at NOPOL presented higher (p<0.05) TOSC values in the posterior (P) region in respect of anterior (A) region and middle (M) region. TOSC in the P region at NOPOL was higher (p<0.05) compared with the same body region of worms at POL. In summer, ROS concentration was higher in A and M regions of worms at POL in respect of the organisms at NOPOL. During winter all the regions showed higher ROS in worms sampled at POL. It was registered absence of season influence on LPO content, but in the P region at NOPOL in summer there were lower LPO levels compared with the others regions (p<0.05). In vitro assays showed that P region, despite a higher basal ROS, presented a higher competence to cope with pro-oxidants compared with A and M regions (p<0.05), corroborating the field results. A lower proteic sulfhydril content was observed in P in respect of the other regions (p<0.05) supporting the idea of a highest oxidant condition in this region. The results indicate that worms collected at the POL site are confronted to higher ROS concentrations, affecting its antioxidant capacity, a result that depends of body regions.     

Physical and chemical characteristics of water from the hydrographic basin of the Poxim River, Sergipe State, Brazil

The Poxim River is one of Sergipe State’s major waterways. It supplies water to the State capital, Aracaju, but is threatened by urban and agricultural developments that compromise both the quantity and the quality of the water. This has direct impacts on the daily lives of the region’s population. In this work, a multivariate analytical approach was used to investigate the physical and chemical characteristics of the water in the river basin. Four sampling campaigns were undertaken, in November 2005, and in February, May, and September 2006, at 15 sites distributed along the Poxim. The parameters analyzed were conductivity, turbidity, color, total dissolved solids, dissolved oxygen, alkalinity, hardness, chlorophyll-a, and nutrients (total phosphorus, dissolved orthophosphate, nitrite, nitrate, ammoniacal nitrogen, and total nitrogen). Dissolved oxygen contents were very low in the Poxim-Açu River (1.0–2.8), the Poxim River (1.6–4.6), and the estuarine region (1.7–5.1), due to the dumping of wastes and discharges of domestic and industrial effluents containing organic matter into fluvial and estuarine regions of the Poxim. Factor analysis identified five components that were indicative of the quality of the water, and that explained 81.73 % of the total variance.     

Quantification of reef benthos communities and variability inherent to the monitoring using video transect method

Long-term monitoring program of organisms is the most recommended for understanding changing processes on reefs. The video transect method presents advantages for that. Specialists state that it is important to make sure that the recorded coverage is always the same between campaigns, so that differences in results may be entirely attributed to environmental changes. This study aimed to test the capability of implementing this requirement through tracking simulation and its validity for monitoring the benthic communities of reefs using the video transect method. Ten transects 20 m long were established in Todos os Santos Bay coral reefs. Subsequent to the first transect capture, a second diver repeated the same track, simulating two different monitoring campaigns. Data were transformed and a matrix of similarity was generated using Bray–Curtis’ Index. ANOSIM analysis was performed to test the similarity of the ten transects and its repetitions. The result, R = 0.08 (P = 0.928), shows that reef monitoring using video transect, the way it is described in the literature, is appropriate, but it is important to consider some premises discussed in this work.     

Assessment of solar driven TiO2-assisted photocatalysis efficiency on amoxicillin degradation

The objective of this work was to evaluate the efficiency of a solar TiO₂-assisted photocatalytic process on amoxicillin (AMX) degradation, an antibiotic widely used in human and veterinary medicine. Firstly, solar photolysis of AMX was compared with solar photocatalysis in a compound parabolic collectors pilot scale photoreactor to assess the amount of accumulated UV energy in the system (Q _UV) necessary to remove 20 mg L^?1 AMX from aqueous solution and mineralize the intermediary by-products. Another experiment was also carried out to accurately follow the antibacterial activity against Escherichia coli DSM 1103 and Staphylococcus aureus DSM 1104 and mineralization of AMX by tracing the contents of dissolved organic carbon (DOC), low molecular weight carboxylate anions, and inorganic anions. Finally, the influence of individual inorganic ions on AMX photocatalytic degradation efficiency and the involvement of some reactive oxygen species were also assessed. Photolysis was shown to be completely ineffective, while only 3.1 kJ_UV?L^?1 was sufficient to fully degrade 20 mg L^?1 AMX and remove 61 % of initial DOC content in the presence of the photocatalyst and sunlight. In the experiment with an initial AMX concentration of 40 mg L^?1, antibacterial activity of the solution was considerably reduced after elimination of AMX to levels below the respective detection limit. After 11.7 kJ_UV?L^?1, DOC decreased by 71 %; 30 % of the AMX nitrogen was converted into ammonium and all sulfur compounds were converted into sulfate. A large percentage of the remaining DOC was in the form of low molecular weight carboxylic acids. Presence of phosphate ions promoted the removal of AMX from solution, while no sizeable effects on the kinetics were found for other inorganic ions. Although the AMX degradation was mainly attributed to hydroxyl radicals, singlet oxygen also plays an important role in AMX self-photosensitization under UV/visible solar light.     

Sugarcane straw management and soil attributes on alachlor and diuron sorption in highly weathered tropical soils

This research evaluated the effects of the new sugarcane harvesting system (without straw burning) and soil attributes on the organic carbon (OC) accumulation and sorption of alachlor (2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide) and diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) in highly weathered Brazilian soils. Alachlor was more likely to leach (K _d,app = 1.0–7.0 L kg^?1 and mean K _oc,app = 174 L kg^?1) than diuron (K _d,app = 6.2–116.3 L kg^?1 and mean K _oc,app = 1789 L kg^?1). The sorption coefficient (K _d,app) values correlated better with soil OC contents, but the Fe-oxides also played an important role in these highly weathered soils. Sorption was enhanced in the areas without straw burning mostly due to OC accumulation that was higher in the clayey soils, but it was not enough to change their mobility classification.