When manure is applied to crops on a nitrogen basis, it often creates a buildup of phosphorus (P) in the soil. Phosphorus recovery as struvite is one strategy to capture excess P prior to land application. To form struvite from dairy cow manure, an acid pH is required to break the calcium phosphate bonds present in the manure. Oxalic acid is desirable because, in addition to breaking bonds, its anion binds calcium. An experiment was designed to measure struvite precipitation from dairy manure after addition of commercial grade oxalic acid to result in varying pH points for maximum struvite production. Initially decreasing the pH of the dairy manure to 6.0 and later increasing the pH to 8.7 removed the most P (90%); however, this high pH can lead to magnesium phosphate precipitation and a pH of 6.0 was not low enough to completely disassociate the calcium from phosphate. Therefore, we recommend initially decreasing the pH to 5.5 and later increasing it to pH 8.2 which achieved 80%P removal.

The phytoremediation of copper (Cu)-contaminated sandy soils can be influenced by the addition of vermicompost to the soil and the mycorrhization of plants. The objective of this study was to evaluate the effects of inoculation with the mycorrhizal fungus Rhizophagus clarus and the addition of different doses of bovine manure vermicompost on the phytoremediation of a sandy soil with a high Cu content using Canavalia ensiformis. Soil contaminated with 100 mg kg⁻¹ Cu received five doses of vermicompost and was cultivated with C. ensiformis, with and without inoculation with mycorrhizal fungus, and the Cu and nutrients in the soil and soil solution were evaluated. The concentrations of Cu and other nutrients and the biomass and Cu phytotoxicity in the plants were quantified by gauging the photochemical efficiency, concentration of photosynthetic pigments and activity of oxidative stress enzymes. The vermicompost increased the soil pH and nutrient concentrations and reduced the Cu content of the solution. When the vermicompost was applied at a dose equivalent to 80 mg phosphorus (P) kg⁻¹, the phytoextraction efficiency was higher, but the phytostabilization efficiency was higher for vermicompost doses of 10 and 20 mg P kg⁻¹. The presence of mycorrhizal fungi increased Cu phytostabilization, especially at vermicompost doses of 10 and 20 mg P kg⁻¹. The use of vermicompost at low doses and inoculation with mycorrhizal fungi increase the phytostabilization potential of C. ensiformis in sandy soil contaminated by Cu.

Removal of arsenic from water reservoirs is the issue of great concern in many places around the globe. As adsorption is one of the most efficient techniques for treatment of As-containing media, thus the present study concerns application of iron oxides-hydroxides (akaganeite) as adsorbents for removal of this harmful metal from aqueous solution. Two types of akaganeite were tested: synthetic one (A) and the same modified using hexadecyltrimethylammonium bromide (AM). Removal of As was tested in batch studies in function of pH, adsorbent dosage, contact time, and initial arsenic concentration. The adsorption isotherms obey Langmuir mathematical model. Adsorption kinetics complies with pseudo-second-order kinetic model, and the constant rates were defined as 2.07 × 10⁻³and 0.92 × 10⁻³ g mg⁻¹ min⁻¹ for the samples (A) and (AM), respectively. The difference was caused by significant decrease in adsorption rate in initial state of the process carried out for the sample AM. The maximum adsorption capacity achieved for (A) and (AM) akaganeite taken from Langmuir isotherm was 148.7 and 170.9 mg g⁻¹, respectively. The results suggest that iron oxides-hydroxides can be used for As removal from aqueous solutions.

Artificial sweeteners are food additives widely used, mainly in reduced sugar or sugar-free foods and beverages. Acesulfame potassium (ACE-K) and sodium saccharin (SAC) are among the most widely consumed sweeteners worldwide. These compounds when ingested are not metabolized by the body, being excreted unchanged. They arrive at treatment plants, where they are partially degraded and consequently released directly into water bodies. For this reason, artificial sweeteners have been detected in the most diverse aquatic environments, being recognized as emerging contaminants. In this work, aqueous solutions of ACE-K and SAC, submitted to heterogeneous photocatalysis (TiO₂/UV-A) for 60 min, showed degradations of more than 99% and maximum mineralization of 57% for ACE-K and 49% for SAC. The effects of certain variables were evaluated, with pH having a greater influence on the degradation of acesulfame and the mass of semiconductor on that of saccharin. The degradation of ACE-K and SAC followed a pseudo-first-order kinetic model according to the Langmuir–Hinshelwood model. Assays using Artemia salina as the test organism demonstrated the low toxicity of the photocatalyzed solutions of ACE-K and SAC. The contribution of different reactive species to the photocatalysis was investigated using specific radical inhibitors; the results indicate that singlet oxygen (¹O₂) has a fundamental role in the photocatalytic degradation of ACE-K and SAC. Graphical Abstract ᅟ

In the present work, we have applied a green method for the synthesis of silver nanoparticles (AgNPs) onto amino-functionalized silica using Nigella sativa (black seed) aqueous extract as an eco-friendly and efficient reducing agent. The factors influencing the functionalization of silica and AgNPs loading have been considered. The samples were characterized by elemental analysis, FTIR, XRD, TGA, SEM, and EDX and used for the removal of indigo carmine (IC) dye from aqueous solution. The mean particle size of immobilized AgNPs was calculated from the XRD pattern using the Scherrer equation and is equal to about 26 nm. Adsorption experiments were carried out as batch studies at different contact times, temperature, adsorbent dosage, and initial dye concentrations. The IC adsorption equilibrium was attained after about 20 min of contact time. The equilibrium data shows that the Langmuir model was more reasonable to depict the IC adsorption, and the maximum adsorption capacity of IC is 73.05 mg/g. Based on the kinetic analysis, the adsorption process follows a pseudo-second-order equation. The estimation of the thermodynamic parameters such as the Gibbs free energy, entropy, and enthalpy changes of the adsorption process indicated the feasibility and endothermic nature of IC adsorption. The modified surface was found to be extremely stable in the aqueous medium, and no significant leaching of AgNPs was observed. Thus, immobilization of AgNPs may advance reuse, reduce environmental risks associated with leaching of AgNPs, and enhance cost-effectiveness.

Rivers may receive pharmaceuticals, personal care products, and environment estrogens, which are emerging concerns, from various sources. Understanding the fate of these emerging contaminants (ECs) from the sources to their receiving river is important for assessing their ecosystem risk. Here, the occurrence, seasonal variation, spatial distribution, and ecological risk of 22 ECs in water and sediments from the Jilin Songhua River, as well as in the effluents from the riverside Jilin wastewater treatment plant (WWTP) were investigated. Results indicated that estriol with the highest median concentration of 21.5 ng L⁻¹ in the river water and with the highest median concentration of 481.5 ng g⁻¹ in the sediments, and methylparaben with the highest concentration of 29.6 ± 2.9 ng L⁻¹ in the WWTP effluents were the predominant contaminants. The total concentration of ECs in the river water in the dry season was about 1.5 times higher than that in the wet season. The concentrations of these ECs close to the contaminated tributary and the WWTP were relatively high. Risk assessment showed that the maximum risk quotient value of estrone was 1.07 in the river water and estriol was 2.10 in the effluents. In addition, erythromycin posed generally medium risk in the river water and WWTP effluents. It should be paid attention to the prior control of the three contaminants in the river region.

Chemical phosphorus removal with hydrated lime was evaluated on effluents from different biological treatment processes applied to swine manure. The objective of this study was to establish the most suitable process for this kind of wastewater treatment. Effluents a UASB reactor, a nitrification reactor (NR), a modified Lutzak–Ettinger (MLE) reactor and a deammonification (DMX) reactor were evaluated. A comprehensive study was developed at laboratory scale to evaluate the effect of possible interferences, including alkalinity, total organic carbon, and ammonia, on phosphorus precipitation. The highest soluble phosphorus (Pₛₒₗ) removal efficiency and the lowest Ca:P molar ratio were obtained for the NR effluent (92% and 2.0, respectively). The good performance of the NR effluent could be attributed to the low level of ammoniacal nitrogen and alkalinity and to the presence of a relatively high concentration of calcium. Highly promising results were also obtained in field experiments, where a phosphorus removal unit was installed as the last step in a swine manure treatment system, and precipitation was applied to effluent from the NR. In this case, efficiencies of Pₛₒₗ removal higher than 90% were obtained. The produced sludge was rich in phosphorus and could be used as, for example, fertilizer. The results obtained in this work showed the importance of applying an efficient treatment system to swine manure for reduction of ammoniacal nitrogen, alkalinity, and carbon before chemical removal of phosphorus by precipitation with hydrated lime.

Freshwater resources in semi-arid countries are under constant threat from pollution. One of the major pollutants is acid mine drainage (AMD), which not only lowers the pH of the water, but contains high sulphuric acid and high metal concentrations. Bacteria and algae are the first organisms to respond to stressors such as reduced pH and high metal concentrations. The bacterial community in a natural freshwater wetland impacted by AMD and steel plant effluent was identified, with the objective to include bacterial indicator communities in an ecotoxicological screening tool for wetland ecosystem health estimation. Five study sites at the Grootspruit canal valley bottom wetland in Mpumalanga, South Africa, were identified as case study areas which include a reference site and four AMD-impacted sites displaying various degrees of degradation. Physical, chemical and microbiological parameters were measured at each site. The bacterial community was sampled from both the water column and bottom sediment and subjected to next-generation sequencing for identification. The bacterial diversity was high, even at the most impacted sites. The phyla that were predominant in all the samples were the alpha-, beta- and gamma-Proteobacteria and Bacteriodetes. The bacterial based bio-assessment tool scored the reference site as mostly unaffected by anthropogenic impacts, while the AMD and steel plant effluent-impacted sites were classified as modified to severely modify. The outcome of the study showed that the proposed bacterial bioindicators can potentially be employed as part of the ecotoxicological screening tool to determine wetland ecosystem health.

An evaluation of the concentration of metals in terrestrial and aquatic environments near Artigas Antarctic Scientific Base was assessed. Granulometric characteristics, total organic matter content, concentration of metals (Cd, Cr, Cu, Mn, Ni, Pb and Zn) and metalloid (As) in soil, marine and freshwater sediments were determined. The geoaccumulation index (Igeo) was used in order to analyse the contamination magnitude. Samples were collected in summer 2015–2016 covering 31 sampling stations; 15 terrestrial/soil stations (T0–T14) were placed considering the distribution of Artigas Base buildings and the septic tanks’ location. Eleven freshwater stations were placed along the three meltwater streams near Artigas Base (S0–S10), and two in Uruguay Lake (L1 and L2). Finally, three marine stations in Maxwell Bay were placed one near the Artigas Base (AB) and two far from it in North Cove (NC1, NC2). Some of the terrestrial stations (T2, T10, T11 and T13) presented the highest concentration of metals and Igeo values, which was associated to anthropic activities. Highest metal levels were related to fuel storage and handling, but also, with sewage release and the presence of old leaded paint residues. These polluted sites were limited to a restricted area of Artigas Base, not affecting surrounding environments. Concentrations of the analysed metals in unpolluted sites had the same order of magnitude recorded in other unpolluted areas of the Fildes Peninsula and other Antarctic regions.