Phosphogypsum (PG), the waste byproduct resulting from wet process phosphoric acid production, is employed as a selective and effective adsorbent for total rare earth elements (REEs) from aqueous solution and leach liquor. The elaboration of PG adsorbent complemented after some physical treatments. Adsorption and elution studies carried out in experimental batches, including the effect of pH, adsorbent dose, initial REE concentration, and equilibrium time. Adsorption of REEs onto PG fitted well with Langmuir isotherm with a theoretical capacity surpassed 357 mg/g. REEs were effectively eluted from loaded PG with 2 mol L⁻¹ HCl acid with an efficiency of 94%. PG showed an outstanding selectivity towards REEs in the presence of many cations and anions, for instance (Fe³⁺, UO₂²⁺, Ca²⁺, SO₄²⁻, NO₃⁻). Different qualitative techniques such as EDS, SEM, and FTIR used to emphasize the adsorption of REEs onto PG. The film diffusion model was the preponderant adsorption mechanism for REEs; also, the adsorption process has a good accordance with pseudo-second-order kinetic model.

Over the last few decades, many classes of micropollutants have been detected in aquatic environments worldwide and paracetamol is one of the micropollutant agents detected in the aquatic environment. New treatment methods based on biologically produced metal and metal oxides have been developed for micropollutant removal. Biogenic manganese oxides are also one of the most important biogenic metal oxide species. In this study, biogenic manganese oxides produced by manganese-adapted Pseudomonas putida NRRL B-14878 were used for removing paracetamol. A complete removal of paracetamol could be achieved within 216 h at pH 7, biogenic manganese oxide amount of 5 g/L, and paracetamol concentration of 2 mg/L. Response surface methodology (RSM) was applied to determine interaction between solution pH, paracetamol concentration, and biogenic manganese oxide amount being individual variables and to optimize operating conditions. According to results of variance analysis (ANOVA), the second-order polynomial model was statistically significant and coefficient of determination value was high. The optimal conditions were obtained as the solution pH of 6.81, the paracetamol concentration of 9.82 mg/L, and the biogenic manganese oxide amount of 6.36 g/L. Transformation products including the dimers, higher-degree oligomers, 3-hydroxyacetaminophen, 4-aminophenol, 4-methoxyphenol, 1,4-dimethoxybenzene, and butenedioic acid were identified by LC-MS/MS. The results of this work indicate that biogenic manganese oxide is an effective material for removing micropollutants.

The use of engineered nanomaterials (ENMs) increases concerns relating to their fate, behavior, and toxicity due to their increased exposure to the environment. These ENMs end up in wastewater treatment plants (WWTPs), and the bacteria in these systems are sensitive to compounds such as heavy metals, which reduces the functionality of the WWTP. In this work, the fate and behavior of Bi₂O₃-BiVO₄ in a WWTP using the OECD 303A guideline was studied. The Bi₂O₃-BiVO₄ NPs were synthesized through a hydrothermal and impregnation method. X-ray diffraction showed monoclinic phases of both Bi₂O₃ and BiVO₄ NPs. The effect of Bi₂O₃-BiVO₄ NPs was monitored using chemical oxygen demand (COD) and 5-day biological oxygen demand (BOD₅). The COD and BOD₅ for the sludge retention time where the NPs were added was > 70%. This showed that the NPs had no effect on the functionality of the treatment processes as it was further affirmed by the TPC measurements. Inductively coupled plasma–optical emission spectroscopy (ICP-OES) showed that the fate of the NPs was through the activated sludge than the effluent, whereby 90% of Bi and V were absorbed in the activated sludge and 10% in the effluent. The results indicate that the NPs have the potential to permeate through the environment segments through the wastewater sludge compared to the effluent. XRD analysis of the test sludge showed that the crystal phases of the heterojunction remained unchanged, and this could ascertain that the treatment conditions did not transform the NPs into toxic forms.

A comparative experiment was conducted based on a non-road diesel engine to investigate the effects of two after-treatment devices on the engine’s emission characteristics as well as their power and fuel consumption performances. The first after-treatment device is a combination of a diesel oxidation catalyst (DOC) and a catalytic diesel particulate filter (CDPF). The second device is a single CDPF-coated improved noble metal catalyst. Results showed that the two after-treatment devices had almost no effect on the power and fuel consumption performance. The gaseous and particulate emissions of the engine depended on the operation conditions including the speed and load. However, the dual DOC+CDPF system and the single CDPF reduced more than 81% of the carbon monoxide (CO) and 73% of the hydrocarbon (HC) emissions. Notably, the reduction efficiency by the single CDPF was higher than that of the DOC+CDPF system. In terms of the particulate emissions, both after-treatment devices achieved more than 96% reduction of the particle number (PN) and up to 88% reduction of the particulate mass (PM). Similarly, the single CDPF outperformed the dual DOC+CDPF system in reducing particle emissions. Although no changes occurred in the bimodal particle size distribution of the engine after the installation of the two after-treatment devices, they performed differently in reducing particles with different sizes. The particles reduction efficiency of the DOC+CDPF system was higher than that of the single CDPF for the particles smaller than 14.3 nm, and this trend converted for particles larger than 14.3 nm. Improving the noble metal catalyst load in the CDPF ensured a performance that rivaled the DOC+CDPF system. Apart from the NOx emissions, the installation of a single CDPF with an improved noble metal catalyst load can make the non-road diesel engine meet the limits of the China IV emission regulations.

One of the most common anthropogenic impacts on river ecosystems is the effluent discharge from wastewater treatment plants. The effects of this contamination on stream biota may be intensified in Mediterranean climate regions, which comprise a drought period that leads to flow reduction, and ultimately to stagnant pools. To assess individual and combined effects of flow stagnation and sewage contamination, biofilm and gastropod grazers were used in a 5-week experiment with artificial channels to test two flow velocity treatments (stagnant flow/basal flow) and two levels of organic contamination using artificial sewage (no sewage input/sewage input). Stressors’ effects were determined on biofilm total biomass and chlorophyll (Chl) content, on oxygen consumption and growth rate of the grazers (Theodoxus fluviatilis), and on the interaction grazer-biofilm given by grazer’s feeding activity (i.e., biofilm consumption rate). The single effect of sewage induced an increase in biofilm biomass and Chl-a content, simultaneously increasing both grazers’ oxygen consumption and their feeding activity. Diatoms showed a higher sensitivity to flow stagnation, resulting in a lower content of Chl-c. Combined stressors interacted antagonistically for biofilm total biomass, Chl-b contents, and grazers’s feeding rate. The effect of sewage increasing biofilm biomass and grazing activity was reduced by the presence of flow stagnation (antagonist factor). Our findings suggest that sewage contamination has a direct effect on the functional response of primary producers and an indirect effect on primary consumers, and this effect is influenced by water flow stagnation.

San Juan de los Planes agricultural valley (SJPV) was studied to determine the pollution of the soils and the source of the pollutants, and revise possible ecological risks and health risks for the inhabitants due to the presence of these elements. On average, the total concentration order was As > Zn > Cu > Co > Cd. A multivariate analysis was made to identify the source of the elements and a correlation analysis to relate the concentrations and soil properties. Seven geochemical indices, two ecotoxicological, and two health risk indices were estimated. The enrichment factor (EF) showed minor or no enrichment, and the geoaccumulation index (Igeo) defined the valley as uncontaminated to moderately contaminated. The contamination factor (Cf), contamination degree (CD), and modified contamination degree (mCD) showed low or moderate contamination. The pollution load index (PLI) and comprehensive pollution index (Pn) indicated that four sites are moderately to seriously polluted with As and Cd. The potential ecological risk factor (Er) classified the area with a low potential, and the potential ecological risk index (RIEc) resulted as low ecological risk for 87% of the sites. The hazard index (HI) revealed that the contents of As and Cd can cause non-carcinogenic health problems and the carcinogenic risk index (RI) showed that As is a potential threat to the inhabitants. Given that the pollution with As and Cd is occurring in only four of the sites and that they were correlated with silt fraction, it can be said that this is related to the agrochemicals and not from the mining activities uphill.

The integrated algal pond system (IAPS) is a passive wastewater treatment technology that can be used to remediate liquid waste from domestic, industrial and agricultural sources. The system exploits the mutualistic interaction between microalgae and bacteria to generate water of a quality suitable for discharge and/or reuse. During the treatment process, biomass in the form of microalgal–bacterial flocs (MaB-flocs) is generated, and this can be harvested and beneficiated in downstream processing. Here, we review literature on MaB-floc and extracellular polymeric substance (EPS) formation and discuss how essential microalgal–bacterial mutualism is at effecting IAPS-based wastewater treatment. Aggregation of microalgae and bacteria into MaB-flocs is clearly an outcome of EPS production by these microorganisms and arises for purposes of chemical and developmental interaction, protection, communication, aggregation and adhesion. The polymeric compounds which form the scaffold of this extracellular matrix comprise polysaccharides, proteins, uronic acid and nucleic acid. Natural EPS can be used as bioflocculant in water purification and in the dewatering and settling of sludge and is therefore an ideal natural replacement for commercially available synthetic polymers. Additionally, EPS are considered high value and can be used in many commercial applications. Thus, and to ensure sustained MaB-floc production in IAPS-based wastewater treatment plants, it is important that correct levels of EPS are maintained to facilitate settling and biomass recovery. Furthermore, it is the associated environmental and operational conditions that most impact EPS production and in turn, MaB-floc formation, and quality of the final IAPS-treated water.

Epoxiconazole is a broad-spectrum fungicide described as highly persistent in soil and as such can be considered as an abiotic agent like other problematic agrochemicals. Furthermore, the plant phenotyping tool involving non-invasive monitoring of plant-emitted volatile organic compounds (VOCs) may be useful in the identification of metabolic markers for abiotic stress. We therefore decided to profile the VOCs from secondary metabolism of oilseed rape through a dose-response experiment under several epoxiconazole concentrations (0, 0.01, 0.1 and 1 mg L⁻¹). VOC collections of 35-day-old whole plantlets were performed through a dynamic headspace sampling technique under defined and controlled conditions. The plantlets grew freely within a home-made, laboratory and high-throughput glass chamber without any disturbance. Putative metabolic markers were analysed using a targeted metabolomic approach based on TD-GC-MS method coupled with data acquisition in SIM mode in order to focus on terpenes and sulphur-containing volatiles. Chromatograms of emitted terpenes were achieved accurately for the 35-day-old oilseed rape plantlets. We also analysed the presence of sulphur-containing volatiles in samples of shoot and root tissues using an innovative DHS-TD-GC-MS method, but no difference was found between qualitative profiles. Nevertheless, we demonstrated through this experiment that sesquiterpenes such as β-elemene and (E,E)-α-farnesene are involved in epoxiconazole dose-response. In particular, (E,E)-α-farnesene could serve as a metabolic marker of fungicide exposure for oilseed rape plantlets.

The aim of this work is to evaluate the application of a steel waste, basic oxygen furnace sludge (BOFS), rich in iron, to treat water contaminated with elevated arsenic and sulfate concentrations. In the first step, three doses (10, 60, and 80 g L⁻¹) of BOFS were tested to investigate the removal of As(III) and As(V) (67 mg L⁻¹) and sulfate (3700 mg L⁻¹) separately from an aqueous solution. In the second step, the efficacies of BOFS (10 g L⁻¹) and commercial ZVI (5 g L⁻¹) were compared to simultaneously remove arsenic and sulfate. The pH of the feed solution was adjusted to 2.5 and monitored during the experiment. The use of BOFS achieved arsenic removal up to 92% and sulfate removal of nearly 40% after 72 h of contact time. Use of BOFS also increased the solution pH to 12. Similar removal levels were achieved with both BOFS and ZVI. These results confirm the potential application of BOFS to remove high arsenic and sulfate concentrations from acidic solutions. The data obtained here should be used as a basis for further studies on the remediation of acid mine drainage with high concentrations of arsenic and sulfate using an abundant and low-cost steel waste.

The use of ultraviolet light in photoreactors for wastewater treatment has become popular as an alternative of known chemical oxidative substances. UV LED light represents cheaper, robust, and versatile alternative to traditional UV lamps. In this study, it was designed and evaluated a photoreactor with an approach of chemical fluid dynamics (CFD) and experimental validation. The evaluation consisted of (1) CFD velocity profile analysis, (2) characterization of the average light distribution with potassium ferrioxalate actinometry, (3) degradation of a typical recalcitrant metallic cyanocomplex Fe(CN)₆³⁻, and (4) scavenger effect analysis in the photodegradation using potassium persulfate. Actinometrical essay concluded that the system was able to receive 1.93 μE/s. The reactor operated under turbulent regime and best result for Fe(CN)₆³⁻ degradation was obtained at 4 h of operation, using 5-W UV-A LEDs, with pH ~ 7 and 10 mM de S₂O₈²⁻. Baffled photoreactor demonstrated to be useful for this type of illumination and wastewater treatment.