Synthesis and characterisation of acid/basic modified adsorbents. Application for chlorophenols removal.

A commercial activated carbon was modified with acid and basic reagents -an acidic one via treatment with sulphuric acid and a basic via treatment with pentaethylenehexamine- to yield adsorbents with different surface acid/base character. These modified adsorbents were characterised by elemental and immediate analysis, N2 adsorption, XPS and point zero charge measurements. The new adsorbents were tested for chlorophenols removal in water (4-chlorophenol, 3,5-dichlorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol and pentachlorophenol) at different temperatures. Although the calculated process enthalpy was positive for all cases, indicating an endothermic process, the entropy was positive, resulting in a negative Gibbs free energy and spontaneous process. The adsorption capacity increases with temperature and decreases when the phenols' number of substituents increases. The modified acid-activated carbon demonstrated an exciting higher adsorbing capacity from 426.9 to 742.3 mg g-1 for 2,4,6-trichlorophenol, whereas the adsorption capacity for the basic ranged between 142.9 and 238.0 mg g-1. The Langmuir model satisfactorily fitted the adsorption equilibrium data for all chlorophenol contaminants.

New trends on green energy and environmental technologies, with special focus on biomass valorization, water and waste recycling: editorial of the special issue.

In this editorial piece, the Editors of the Virtual Special Issue (VSI) "New Trends on Green Energy and Environmental Technologies, with Special Focus on Biomass Valorization, Water and Waste Recycling", present summarized data corresponding to the accepted submissions, as well as additional comments regarding the thematic of the VSI. Overall, 83 manuscripts were received, with final publication of those having the highest quality, accepted after peer-reviewing. The Editors think that the result is a set of very interesting papers that increase the knowledge on the matter, and which would be useful for researchers and the whole society.

Sonochemical degradation of neonicotinoid pesticides in natural surface waters. Influence of operational and environmental conditions.

Neonicotinoids sonochemical oxidation at high-frequency ultrasound (MHz range) has been carried out in ultrapure and natural surface-water matrices (river, reservoir and wastewater treatment plant effluent). To evaluate the influence of the operating variables, that is initial pollutant concentration, ultrasound frequency, ultrasound power, and pulse-stop time a Box-Behnken experimental design was planned. Optimal results were obtained using a frequency of 578 kHz, a power of 40 W L-1, with a pollutant concentration of 1 µM (for each pesticide), and using a pulse-stop time of 100 ms. The experimental data adjustment using the Langmuir-Hinshelwood heterogeneous kinetic model showed that neonicotinoids oxidation was carried out in the bubble-liquid interface by the attack of hydroxyl radicals. Experiments performed in the presence of radical scavengers, that is, methanol, ethanol and tert-butyl alcohol corroborated this reaction mechanism. The influence of some environmental conditions such as pH, presence of soluble inorganic species (Cl-, SO42-, NO3-, HPO42-, HCO3-) and soluble organic species (humic acids content) were established. Finally, the aqueous matrix's influence was investigated for three natural surface water cases, and the results were rationalized according to the main water physicochemical characteristics.

New research on water, waste and energy management, with special focus on antibiotics and priority pollutants.

The Editors of the Virtual Special Issue (VSI) "New Research on Water, Waste and Energy Management, with Special Focus on Antibiotics and Priority Pollutants" (VSI WWEM-20) here present details corresponding to papers that have been accepted, as well as further comments on the matter. It should be noted that the VSI should be associated to a Conference that had been initially programmed to be held in Rome during the summer of 2020, Unfortunately, it was postponed due to the COVID-19 pandemic. That conference was one of those within the series called "International Congress on Water, Waste and Energy Management". Although the Conference was postponed, the Call for Papers for the VSI was maintained by this journal. As a result, a set of very interesting papers were accepted after a careful peer-review process. We hope that it will be complemented with additional VSIs associated to future conferences corresponding to the series, increasing the knowledge on the topic.

New research on reduction and/or elimination of hazardous substances in the design, manufacture and application of chemical products.

The Virtual Special Issue (VSI) "New research on reduction and/or elimination of hazardous substances in the design, manufacture and application of chemical products" was initially associated to the "International Conference on Green Chemistry and Sustainable Engineering, GreenChem-20" that was postponed due to the COVID-19 pandemic. Anyway, the international conference will take place in the near future. However, the VSI was maintained in this journal, received a high number of submissions, and selected manuscripts have been accepted after peer-reviewing. The published papers constitute a set of high-quality contributions, which, in the future, could be complemented with others related to additional conferences about similar topics. In this editorial piece, the Editors include brief comments on papers accepted for publication in the Special Issue, as well as additional aspects of interest related to the subject.

Electrochemical and sonochemical advanced oxidation processes applied to tartrazine removal. Influence of operational conditions and aqueous matrix.

Tartrazine degradation was investigated by electrochemical and sonochemical oxidation processes. Anodic oxidation was carried out using boron-doped diamond (BDD) electrodes. The influence of current density and dye initial concentration on the removal of tartrazine from water was analyzed. The experimental results indicate that total removal of tartrazine was obtained, and Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) removals of up to 94.4% and 72.8% were achieved, respectively. To optimize the process, the pollutant removal percentage, the kinetic rate constant, and the TOC removal efficiency were chosen as target variables. Moreover, sonochemical oxidation experiments at a high-frequency range of cavitation (up to 1 MHz) were performed to establish the influence of three different operating variables, namely ultrasound frequency (0.5-1.1 MHz), ultrasound power (2.0-26.6 W ⋅L-1), and pulse-stop ratio (5:1-1:1). The process was also analyzed in terms of kinetics and energy costs. The kinetics resulted to be three times faster for the electrochemical process. However, the calculated energy costs were very similar, at least at long treatment times. Finally, the influence of three aqueous matrices was investigated. According to the experimental results, the natural occurrence of chloride and/or nitrate ions in water strongly conditions the rate of the process, although at least 90% of tartrazine removal was achieved within the first 50 min of treatment.

BDD electrochemical oxidation of neonicotinoid pesticides in natural surface waters. Operational, kinetic and energetic aspects.

Neonicotinoids pesticides were introduced to the market in the 1990s to control various pests. Its accumulation in the environment supposes a severe problem that can affect human health. This study investigates the electrochemical degradation of four common neonicotinoid pesticides; thiamethoxam (TMX), imidacloprid (ICP), acetamiprid (ACP) and thiacloprid (TCP), in different natural surface waters by a boron-doped diamond anode (BDD). The most influencing variable was the current density (j), and to a lesser extent, the supporting electrolyte concentration (Ce). In optimal conditions (j = 34.14 mA cm-2 and Ce = 10.00 mM, using Na2SO4 as electrolyte) pesticide removals for TMX, ICP, ACP and TCP were 97.2, 96.9, 87.8 and 98.2 %, respectively. The obtained results with different support electrolytes (Na2SO4, NaCl, NaNO3 and HK2PO4) suggest that sulphate electrolyte was the optimum for TMX, ICP and ACP. However, for TCP, a total removal was achieved in less than 10 min using NaCl. It was also verified that the initial pH of the solution did not significantly influence the process in the range 3-9. All these results were rationalized in this paper. Finally, to evaluate the matrix influence, some experiments were carried out in different natural surface water matrices (river, reservoir and two different WWTP effluents). The factors influencing the process were the conductivity of the solution and the organic matter content. It was noticeable that the specific energy consumption (SEC) reduced by approximately 15 % for river water and WWTP effluent. High mineralization rates were obtained for all water matrices, with TOC removals ranging between 60 and 80 %.

Neonicotinoids removal by associated binary, tertiary and quaternary advanced oxidation processes: Synergistic effects, kinetics and mineralization.

The degradation of four representative neonicotinoids, namely Thiamethoxam, Imidacloprid, Acetamiprid and Thiacloprid, was carried out by the sequential association of different advanced oxidation processes, including Ozonation, Electro-chemical Oxidation, Ultrasound, Ultraviolet radiation, and their different possible associations. There are no published papers in the literature on the removal of this type of insecticides through these associated oxidation processes. Single oxidation processes did not achieve total pollutants removal in less than 3 h (only UV radiation treatment obtain a total removal of Thiamethoxan in 150 min, but with mineralization below 15% TOC). For double sequential processes, Electro-oxidation-Ozone treatment obtains a total removal of Imidacloprid in 120 min and an increase of mineralization to 50% TOC. Three or four sequential processes are recommended to improve degradation and mineralization rates in a significant way, Electro-oxidation-Ozone-UV treatment obtains a total removal of Thiamethoxan in 80 min with mineralization over 75% TOC. These results confirm important synergistic effects which were quantified. The global trend indicates that Thiamethoxam is the most oxidizable neonicotinoid, whereas Acetamiprid is the most recalcitrant compound. The degradation rate of each neonicotinoid followed pseudo-first-order kinetics and the different oxidation pathways were also quantified from a kinetic point of view.

Combined treatment of olive mill wastewater by Fenton's reagent and anaerobic biological process.

This work presents the application of Fenton's reagent process combined with anaerobic digestion to treat an olive mill wastewater (OMW). Firstly, OMW was pre-treated by chemical oxidation in a batch reactor with Fenton's reagent, using a fixed H2O2/COD ratio of 0.20, pH = 3.5 and a H2O2/Fe(2+) molar ratio of 15:1. This advanced oxidation treatment allowed reaching reductions of 17.6 and 82.5% of chemical oxygen demand (COD) and total polyphenols (TP), respectively. Secondly, OMW treatment by anaerobic digestion was performed using previously adapted microorganisms immobilized in Sepiolite. These biological tests were carried out varying the substrate concentration supplied to the reactor and COD conversions from 52 to 74% were obtained. Afterwards, Fenton's reagent followed by anaerobic digestion was applied to OMW treatment. This combined process presented a significant improvement on organic load removal, reaching COD degradations from 64 to 88%. Beyond the pollutant load removal, it was also monitored the yield of methane generated throughout anaerobic experiments. The methane produced ranged from 281 cm(3) to 322 cm(3) of CH4/g COD removed. Additionally, a methane generation kinetic study was performed using the Monod Model. The application of this model allowed observing a kinetic constant increase of the combined process (kFN = 0.036 h(-1)) when compared to the single anaerobic process (kF = 0.017 h(-1)).