Amphibians are the most threatened vertebrate group with a third of currently known species endangered with extinction, as a result of climate change, habitat loss, disease-introduced exotic species, and pollution. Because of their vulnerability, they have often been used as environmental quality indicators, as well as laboratory models for toxicological research. Given the sensitivity of amphibians to changes in their surrounding environment, including pollution, it was deemed important to define a non-lethal technique based on the evaluation of a set of biomarkers in different tissues of neotenic individuals of Ambystoma velasci. The levels of acetylcholinesterase (AChE), butyrylcholinesterase (BChE), carboxylesterase (CaE), alkaline and acid phosphatases (ALP, ACP), glutathione s-transferase (GST), 7-ethoxyresorufin-O-deethylase (EROD), and superoxide dismutase (SOD) activities, as well as the oxygen radical absorption capacity (ORAC) were measured in tail, gills, liver, plasma, and brain samples. Significant tissue-specific differences were observed for all biomarkers with the exception of ACP. The highest values of specific activity for most biomarkers were detected in the liver. However, the levels measured in gills were very close to those observed in the liver and showed fewer variations than other tissues. These findings suggest that the sampling of gills could be used to evaluate pollution biomarkers in salamanders without apparent harm, as this tissue quickly regenerates.

In tropical countries like Colombia, a large variety of available aquatic plants have yet to be investigated for phytodepuration processes. The aim of this study was to assess the effect of Cyper-us ligularis and Echinocloa colona¸ two local plants of Colombian Caribbean region, on removal of dissolved organic matter (COD) and nutrients (N-NH₄⁺, N-NO₃⁻ and P-PO₄⁻³) from domestic wastewater. Experiments were conducted in replicate pilot-scale Horizontal Subsurface Flow Constructed Wetlands (HSSF CWs) (0.66 m²). Four wetland treatment units were installed in parallel. Two were planted with C. ligularis and the other two remained with E. colona. The experimental system was connected to a 0.76-m³ primary sedimentation tank that fed experimental wetland treatment units. Wetlands were filled with granite gravel (~8 mm and 0.4 of porosity). During a period of 4 months, each treatment unit received a continuous loading at the rate of 42 L day⁻¹ and a hydraulic retention time of 2.3 days approximately. Wastewater samples from influent and effluents were collected three times each week in order to monitor temporal/spatial changes in removals efficiencies of COD, N-NH₄⁺, N-NO₃⁻, and P-PO₄⁻³. Results showed that removals of COD, N-NH₄⁺, and N-NO₃⁻ were not significantly different between treatments (p > 0.05). Nevertheless, P-PO₄⁻³ removal for E. colona was significantly higher than C. ligularis (p < 0.05), showing that this plant can assimilate important amounts of P. Further investigations must be conducted to evaluate the potential of native aquatic macrophytes for phytodepuration.

The use of treated grey water (GW) for home gardens, peri-urban agriculture and landscaping is becoming popular in many water stressed countries such as Oman. This study aims to investigate the treatment efficacy, health and chemical concerns, cost-benefits and maintenance protocol of a GW treatment system as well as the effect of irrigation with GW on crop yield. Therefore, a decentralized homemade GW treatment system was installed in a newly constructed house in Muscat, Oman and studied over a 2-year period. The treated GW was found to be suitable for irrigation as per Omani standards. GW when mixed with kitchen effluent substituted the use of nutrient supplements for plants and did not show any harmful chemical or biological contamination. The capital cost of the system was around US $980, and the annual operating cost was US $78 with annual income and savings from the system being around US $572 indicating a payback period of nearly 2 years. It was found that the system required simple but regular maintenance particularly cleaning of the top layer of the filter. It can be concluded from this study that such a GW system should be technically, economically and environmentally feasible in Oman. Also, wider acceptance by the general public to the idea of GW reuse will help in mitigating the water shortage problem of the country to some extent.

Batch experiment at COD/NO₃ ⁻-N ratio of 8.0 was conducted to investigate the initial performance of the simultaneous denitrification and methanogenesis (SDM) process and corresponding granular sludge (SDMGS). The results showed a high level of inhibition of methanogenesis activity with nitrate addition, and the particle size, settling performance, and morphologies of the SDMGS were also different from conventional methanogenesis granular sludge. The structure and succession of bacterial communities of the granular sludge during the initial stage of the SDM process were determined using the high-throughput sequencing method. Sequence analysis indicated that diversity of bacterial communities was significantly decreased due to nitrate addition. Proteobacteria, Bacteroidetes, Firmicutes, and Spirochaetes were identified to be the dominant bacterial communities (96.06%) of the SDMGS samples, and microbes associated with anaerobic fermentation were reorganized. Alpha-, Beta- and Gamma-proteobacteria, and Bacteroides might be the sources of denitrificans. Lastly, species associated with animal and human infections, such as Enterobacteriaceae, Bacteroides, and other common human enteric pathogens, were found to be recovered during the initial stage. Short-term assessment of bacterial communities of the SDMGS would strengthen understandings of the effects of nitrate contamination in water bodies and provide vital guidance for operation of nitrate-containing wastewater treatment.

The aim of this study was to evaluate the redox mediating capacity of anthraquinone-2,6-disulfonate (AQDS) immobilized on granular activated carbon (GAC) during the reductive decolorization of direct blue 71 (DB71) under microbial and chemical conditions. The immobilization of AQDS on GAC was conducted by adsorption, and it has obtained an uptake capacity of 0.227 mmol g⁻¹. The anchorage of AQDS on GAC improved its electron transfer capacity (ETC) up to 2.05 times higher than the raw material. Similarly, the addition of GAC-AQDS increased up to 1.75- and 1.16-fold the rate of decolorization (k d) of DB71 under microbial and chemical conditions, respectively, in comparison to the unmodified GAC. Surprisingly, a higher k d value was achieved in incubations without either GAC or GAC-AQDS because of the generation of aromatic amines, from the reduction DB71, taking into account that these species may act as a catalyst in the DB71 reduction process. In contrast, adsorption of aromatic amines on either GAC or GAC-AQDS decreased its redox mediating capacity as evidenced by spectrophotometric screenings of the decolorized solution and the supporting material. The development of materials with enhanced both redox and adsorption properties, as the GAC used in this study, offers a promising way to increase the redox conversion of recalcitrant pollutants commonly found in industrial wastewaters.

In the present paper, α-FeOOH and α-Fe(Al)OOH were prepared, and the adsorption of Cr(VI) on the two samples was investigated. The influence of pH, initial concentration, and some anions such as SO₄ ²⁻, H₂PO₄ ⁻, C₂O₄ ²⁻, CO₃ ²⁻, and SiO₃ ²⁻ on the adsorption of Cr(VI) on α-FeOOH and α-Fe(Al)OOH was studied by batch techniques. The results show that the adsorption capacity of Cr(VI) on α-Fe(Al)OOH increases with the introduction of aluminum, but decreases with the increase of pH. The adsorption irreversibility of Cr(VI) on α-Fe(Al)OOH is much higher than that on pure α-FeOOH. The adsorbed Cr(VI) species mainly exists in the form of *Fe(wk)-OHCrO₄ ²⁻ on the surface of the samples. With the presence of SiO₃ ²⁻, CO₃ ²⁻, C₂O₄ ²⁻, SO₄ ²⁻, and H₂PO₄ ⁻, the binding of Cr(VI) is inhibited by different degree. The inhibition of those anions is larger in the pure goethite than that in the Al-substituted goethite system. After Al was introduced into α-FeOOH, Cr(VI) ions are preferentially adsorbed on Al sites rather than Fe sites on α-Fe(Al)OOH.

A novel adsorbent was prepared by introducing xanthate group onto pristine multi-walled carbon nanotubes (MWCNTs) for removing Pb (II) from aqueous solution. The structure and property of xanthate-modified MWCNT (MWCNT-X) were detected by the technologies of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET). The investigation of various parameters, such as initial metal concentration, pH, contact time, and temperature, was taken to illustrate the adsorption behaviors of Pb (II) on MWCNT-X. Based on experimental data, Langmuir isotherm and pseudo-second-order kinetic provided a better correspondence to the adsorption process. The negative values of ΔG ᶿ and ΔH ᶿ indicated that the adsorption process is exothermic and spontaneous. Besides, the maximum uptake of MWCNT-X reached to 83.01 mg/g, which was much higher than that of pristine MWCNT and hydroxylated MWCNT (MWCNT-OH). Thus, the MWCNT-X can be potentially applied in heavy metal treatment.

Effect of harvesting and hydraulic retention time (HRT) on the performance of a sequencing batch reactor (SBR), growing a green alga Botoryococcus braunii, was investigated. In this continuous tertiary treatment, relieving limitations of light, inorganic carbon, nitrogen, and phosphorous can make photoautotrophy active through the rapid fixation of the building blocks into microalgal biomass together with heterotrophy promoted by organics and self-shading effect. Analysis of the results reveals that the control over CO₂ supply and the extension of solid retention time (SRT) are the keys to maintaining higher biomass productivity and better treatability in the mixotrophic SBR. Among HRTs tested, the shortest HRT of 2 days could demonstrate the best removal efficiencies of ammonia (98.8%) and total phosphorus (96.2%) while keeping the highest specific growth rate of 0.23 day⁻¹. Those results provide understanding on the impact of settling sequence, which extends SRT to 5~7 days and prevents significant limitations of light and essential building blocks. With the interplay between photoautotrophic and heterotrophic metabolisms of microalgae, this study identifies how the mixotrophic SBR perform resource recovery during tertiary treatment of livestock wastewater, and how limitation is associated with the effluent quality in the SBR.

Imazethapyr and imazapic are widely used in South Brazil to control weeds in rice fields, mainly through agricultural aviation. The environmental legislation requires that agricultural aviation companies have environmental licensing, which implies that the effluent treatment system must be compliant with the regulations of the Brazilian Ministry of Agriculture, which advises the use of an ozone-based system. An evaluation of the efficiency of this system through the analysis of the content of imazethapyr and imazapic (from the herbicide Only®) in the treatment of effluent with two distinct rates of ozone (1.0 and 2.0 g O₃/h) was performed. It was found that for each tank wash is generated an average volume of 132 L of effluent (112 L of water plus 20 L of surplus diluted spray solution). After the treatment with 1.0 and 2.0 g O₃/h, imazethapyr concentration decreased − 92.4 and − 95.2%, respectively. For imazapic, the concentration in the washing effluent decreased − 69.1 and − 80.1%, respectively. The results indicate that the system was effective in the treatment of the effluent containing residues of the herbicide Only®.

Imazalil (IMZ) is a widely used fungicide for the post-harvest treatment of citrus, classified as “likely to be carcinogenic in humans” for EPA, that can be only partially removed by conventional biological treatment. Consequently, specific or combined processes should be applied to prevent its release to the environment. Biological treatment with adapted microorganism consortium, photo-Fenton, and coupled biological photo-Fenton processes were tested as alternatives for the purification of water containing high concentration of the fungicide and the coadjutants present in the commercial formulation. IMZ-resistant consortium with the capacity to degrade IMZ in the presence of a C-rich co-substrate was isolated from sludge coming from a fruit packaging company wastewater treatment plant. This consortium was adapted to resist and degrade the organics present in photo-Fenton-oxidized IMZ water solution. Bacteria colonies from the consortia were isolated and identified. The effect of H₂O₂ initial concentration and dosage on IMZ degradation rate, average oxidation state (AOS), organic acid concentration, oxidation, and mineralization percentage after photo-Fenton process was determined. The application of biological treatment to the oxidized solutions notably decreased the total organic carbon (TOC) in solution. The effect of the oxidation degree, limited by H₂O₂ concentration and dosage, on the percentage of mineralization obtained after the biological treatment was determined and explained in terms of changes in AOS. The concentration of H₂O₂ necessary to eliminate IMZ by photo-Fenton and to reduce TOC and chemical oxygen demand (COD) by biological treatment, in order to allow the release of the effluents to rivers with different flows, was estimated.