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CO2 is a promising renewable, cheap, and abundant C1 feedstock for producing valuable chemicals, such as CO and methanol. In conventional reactors, because of thermodynamic constraints, converting CO2 to methanol requires high temperature and pressure, typically 250 °C and 20 bar. Nonthermal plasma is a better option, as it can convert CO2 at near-ambient temperature and pressure. Adding a catalyst to such plasma setups can enhance conversion and selectivity. However, we know little about the effects of catalysts in such systems. Here, we study CO2 hydrogenation in a dielectric barrier discharge plasma-catalysis setup under ambient conditions using MgO, γ-Al2O3, and a series of CoxOy/MgO catalysts. While all three catalyst types enhanced CO2 conversion, CoxOy/MgO gave the best results, converting up to 35% of CO2 and reaching the highest methanol yield (10%). Control experiments showed that the basic MgO support is more active than the acidic γ-Al2O3, and that MgO-supported cobalt oxide catalysts improve the selectivity toward methanol. The methanol yield can be tuned by changing the metal loading. Overall, our study shows the utility of plasma catalysis for CO2 conversion under mild conditions, with the potential to reduce the energy footprint of CO2-recycling processes., CO2 hydrogenation to CO and methanol was achieved near room temperature and atmospheric pressure using plasma-enhanced catalysis. The catalyst metal loading and cobalt oxide dispersion influence the product distribution.

The current study is focused on the simple synthesis of two novel biosorbent beads: BASB/STMP and CNFB/STMP, derived respectively from bleached almond shell (BAS) and cellulose nanofiber from almond shell (CNF) by means of chemical crosslinking with sodium trimetaphosphate (STMP). These biosorbents were thoroughly characterized in terms of structure (FTIR), texture (N2 adsorption-desorption), thermal behavior (TGA/DTG), morphology (SEM), and surface properties (XPS). The adsorption kinetics of Cu(II) ions onto BASB/STMP and CNFB/STMP materials proved the chemisorption interaction between Cu(II) ions and the STMP functionalized beads. The BASB/STMP equilibrium data were successfully described by the Redlich-Peterson model and the CNFB/STMP data by the Sips model which disclosed maximum adsorption capacities of 141.44 mg g−1 and 147.90 mg g−1, respectively. Furthermore, the BASB/STMP bioadsorbent offers easy regeneration and better reusability with high efficiency (> 83%). This study sheds light on the preparation of low-cost adsorbents for wastewater treatment in order to improve the competitiveness and eco-friendliness of agrowaste-based processes.

As the wide variety of compounds that are solubilised and generated during hydrothermal treatments of sewage sludge cannot be defined individually, this study proposes a classification based on chemical characteristics and biodegradability. Moreover, it has deepened understanding of the role of oxygen in the reaction mechanisms and the evolution of chemical oxygen demand (COD) fractions and their components during hydrothermal treatments (180 °C, 80 bar). This information is necessary before separating specific compounds or using the hydrolysates directly as fertiliser or fermentation media. Results revealed the existence of an initial stage of sludge solubilisation (30 – 60 min), mainly produced by hydrolysis reactions and without mineralisation, followed by a second stage where oxygen promoted the conversion of solubilised compounds, mineralisation and the minimisation of the solid fraction. Total COD and total suspended solids (TSS) were reduced by 48% and 75% after 210 min of wet oxidation, compared to 28% and 50% after thermal hydrolysis. Oxygen led to a final liquid hydrolysate with fewer easily assimilable compounds (38% of the initial total COD converted into readily biodegradable), inorganic elements (17 g/kg TSSo) and refractory, inhibitory and less assimilable compounds (1.1 g O2/L of slowly and non-biodegradable COD) compared to that obtained in its absence (61%, 24 g/kg TSSo and 2.3 g O2/L, respectively). Oxidation mechanisms favoured the conversion of non-volatile hydroxy acids (NVHA) and intermediate compounds to volatile fatty acids (VFA), with VFA concentration being almost 3 times higher under an oxidising atmosphere, but with NHVFA 57% lower.

Science, Innovation and University Office of the Principality of Asturias (Spain) through the Severo Ochoa pre-doctoral aid programme [BP19-041] & project GRUPIN AYUD/2021/51041

Spanish Ministry of Science, Innovation and Universities (MCIU) [RTI2018-094218-B-I00]; FEDER funds from European Union; FEDER funds from Employment, Industry and Tourism Office of the Principality of Asturias (Spain) [AYUD/2021/51041]; Principality of Asturias, Spain [BP19-093]

Two-dimensional (2D) transition metal nanosheets are promising catalysts because of the enhanced exposure of the active species compared to their 3D counterparts. Here, we report a simple, scalable, and reproducible strategy to prepare 2D phosphate nanosheets by forming a layered structure in situ from phytic acid (PTA) and transition metal precursors. Controlled combustion of the organic groups of PTA results in interlayer carbon, which keeps the layers apart during the formation of phosphate, and the removal of this carbon results in ultrathin nanosheets with controllable layers. Applying this concept to vanadyl phosphate synthesis, we show that the method yields 2D ultrathin nanosheets of the orthorhombic β-form, exposing abundant V4+/V5+ redox sites and oxygen vacancies. We demonstrate the high catalytic activity of this material in the vapor-phase aerobic oxidation of ethyl lactate to ethyl pyruvate. Importantly, these β-VOPO4 compounds do not get hydrated, thereby reducing the competing hydrolysis reaction by water byproducts. The result has superior selectivity to ethyl pyruvate compared to analogous vanadyl phosphates. The catalysts are highly stable, maintaining a steady-state conversion of ∼90% (with >80% selectivity) for at least 80 h on stream. This “self-exfoliated” synthesis protocol opens opportunities for preparing structurally diverse metal phosphates for catalysis and other applications.

The catalytic oxidative dehydrogenation of lactates with molecular oxygen is a promising yet challenging route for producing high‐value pyruvates from biomass. Here we report a simple synthetic strategy for preparing nitrogen‐doped carbon nanosheets (NCNs) starting from two abundant precursors, cheap melamine and glucose, and using a simple thermal‐annealing process. The resulting NCNs feature numerous edges and holes for anchoring vanadium oxides (V‐NCNs). This creates cooperative catalytic sites that boost the catalytic oxidation of ethyl lactate to ethyl pyruvate. Additionally, we systematically studied the surface nitrogen species of NCNs by varying the pyrolysis temperature, and found that the active pyridinic N‐oxide species formed in a high thermal‐annealing treatment, acting synergistically with vanadium active sites in converting ethyl lactate with oxygen into ethyl pyruvate under mild conditions.

A new mesoporous Ag/ZnO@NiFe

As a mandatory first step to assess the implementation of wet oxidation in the current approach of paper mills as biorefineries, this paper discusses for the first time ever the effect of this treatment on the chemical composition of intermediates and final products, as well as the evolution of sulphur, nitrogen, ions, Gross Calorific Value and the properties related to the subsequent handling and downstream processing of Kraft black liquor. It was found that around 50% of the initial carbon was transformed into carboxylic acids, mainly acetic and lactic; thus showing the high potential of black liquor as a renewable resource for the production of these compounds. The oxidation of organic sulphur into sulphates and the no formation of SOx involve odourless and low-polluting emissions during the wet oxidation. The wet oxidised black liquor is also less viscous (30% lower pumping costs) and easier to purify than the raw material. The treatment did not have a significant effect on evaporation rates, but decreased the Gross Calorific Value, although the heat generated per unit of total organic carbon remained constant.

Hydrolysis and the solubilization of sewage sludge processes are important tools to obtain small and medium molecules with different application perspectives. Although the production of biomethane and other products such as biohydrogen from sludge as biofuel alternatives has been profusely studied, the current perspectives are mainly focused on the use of the sludge hydrolysate to produce non-energy bioproducts and biomaterials. In this review, the most recent bibliography dealing with the use of sludge hydrolysates as fermentation media for the bioproduction of new non-energetic products with industrial interest is here revised and discussed. In this regard, the main research effort has been focused on the bioproduction of short-chain fatty acids due to their direct use in industrial applications or as a carbon source for polyhydroxyalkanoates-producing microorganisms. The use of sludge hydrolysates as fermentation media using pure cultures to produce more complex biomolecules, such as enzymes or lipids, is gaining interest, but it remains an undervalued topic. The literature has been divided into processes where hydrolysis and fermentation stages took place simultaneously or separately, centering them on the effect of the main operational conditions on the yields and properties of the corresponding metabolites produced. In general, the main limiting step of these kinds of processes is the proper solubilization and hydrolysis of the sludge, which can improve the bioassimilation of nutrients and, subsequently, the productivities and compositions of the metabolites obtained. Biological and/or thermal pretreaments are the options more profusely employed, which are frequently assisted by different promoters such as oxidants, surfactants, or cation exchange resins.

The present study is focused on the removal of copper(II) ions on date palm “Bouhattam” seeds (DS), bleached date seed (BDS) and cellulose nanofibers from date seed (CNFs) biosorbents. The synthesized materials were characterized by several techniques, including FT-IR, SEM, TEM, N2 adsorption-desorption, and TGA/DTG. The effects of solution pH, temperature, heavy metal concentration, and contact time on adsorption capacities were presented. Thus, at 30 °C and pH 5, the adsorption capacity of DS, BDS, and CNFs was 22, 23, and 34 mg g−1, respectively. This study has proved the interesting properties of CNFs to be used as an effective adsorbent in the wastewater treatment. The adsorption isotherms were better fitted to the Freundlich model, whereas the kinetic data were successfully correlated to the pseudo-second order model, which suggested that chemisorption is involved in the adsorption process. The adsorption of copper(II) was a spontaneous, entropy-increasing, and endothermic process. In addition, the adsorbed copper was effectively desorbed by 0.1 mol L−1 HCl solution. These adsorbents have important potential for the removal of Cu(II) from aqueous solution.

In this work, six different types of protic ionic liquids (PILs) have been studied. For all these PILs, the bacteria toxicity and environmental biodegradability have been investigated, as well as their corrosive behavior and miscibility in different types of lubricating base oils. The PILs studied showed poor to moderate biodegradability (BOD5/COD from 0.072 ± 0.002 to 0.18 ± 0.01) and slight toxicity (TU values between from 1.18 ± 0.04 and 2.7 ± 0.1). However, these environmental properties are much better than those obtained for the reference lubricant additive used in industry (ZDDP). In addition, five of the PILs did not show corrosive activity on steel. Only one of the PILs showed some miscibility in an ester as a base oil and the rest of the mixtures were highly unstable.

The aim of the present study is to prepare the eco-friendly and effective adsorbents for the removal of Cu(II) ions in wastewaters through the trisodium trimetaphosphate (STMP) functionalization of cellulose (CBBAS) and cellulose nanofibers (CBCNFs) beads obtained from the almond shell. The structure and properties of the STMP-functionalized cellulose beads were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermal gravimetric (TGA/DTG), and N2 adsorption–desorption. Cu(II) ions were adsorbed at a great extent within the first 2 h, at 30 °C, and pH 6. The experimental isotherms were successfully fitted to the Redlich–Peterson model for the CBBAS/STMP adsorbent and Sips model for the CBCNFs/STMP one, yielding adsorption capacities of 141 mg g−1 and 147 mg g−1, respectively. The adsorption process onto both biosorbents followed a pseudo-second-order kinetic model, suggesting that chemisorption is the dominant mechanism of the metal ions onto the modified beads. CBBAS/STMP and CBCNFs/STMP biosorbents are easily regenerated using HCl (0.1 M) solution.

Different iron-containing materials (named as S1–S5) obtained through an oxidative digestion in acid media of basic oxygen furnace (BOF) slag were studied for the activation of sodium persulfate (SPS) to generate active radicals for the oxidation of propylparaben (PP), a model endocrine disruptor, in water. It was found that the materials with magnetite in its composition (S1, S2 and S3) effectively catalyze SPS for the removal of PP, and the reaction followed a pseudo-first-order kinetic pattern (r2 > 0.96). Within 90 min, a removal of approximately 90% of 0.4 mg/L of PP was accomplished by 1 g/L of SPS in presence of 50 mg/L of S1 catalyst with negligible iron leaching. Besides, the oxidation of PP was favored by higher dosages of S1 catalyst and SPS oxidant, lower initial PP concentration and neutral or alkaline pH. The generation of sulfate and hydroxyl radical was indirectly validated from the scavenging tests, using tert-butanol and methanol as scavenging agents. Based on the XPS analysis, it can be pointed out that the radical generation was due to the presence of Fe2+–Fe3+ on the surface of the catalysts. A degradation pathway based on the transformation products (TPs) resulting from PP degradation was also proposed.

The present study analyses the combined effects of temperature (from 160 to 200 °C), and, for the first time ever, type of atmosphere (oxidising or inert) and pressure (from 60 to 100 bar) on the solubilisation of heavy metals during the hydrothermal treatment of wet no-diluted sewage sludge. Results revealed that Cd, Pb, Al and Fe were hardly affected by neither the atmosphere nor temperature, remained almost completely in the solid phase during all the hydrothermal treatments tested; while Cr, Ni, Cu and Zn were partially solubilised, being this solubilisation favoured by the presence of an oxidising atmosphere. In contrast, initial dissolved Hg was partially precipitated under both types of atmosphere, although it was re-dissolved after 30 min under an inert atmosphere. Regarding the working conditions, the highest temperature (200 °C) caused the greatest metal immobilisation, whereas the range of pressures tested barely had any effect on it. Concerning the reaction time, the lowest concentration of metals in the liquid fraction of the hydrolysed sludge was obtained during the initial 30 min of treatment.

Dust emission is one of the main environmental pollution impacts associated with steelmaking. In this sense, electrostatic precipitators (ESP) are regarded as the best available technique for treating this type of emission, thus generating two differentiated fractions: coarse and fine. Thorough chemical and structural characterization of both materials was carried out to recycle these byproducts in either the sintering process or other steps of pig iron production. Both types of dusts are crystalline heterogeneous materials mainly composed of sepiolite (Mg8Si12(OH)2·12H2O), hematite (Fe2O3) and calcite (CaCO3), the coarse fraction containing low amounts of Na (0.38 ± 0.04%) and K (0.17 ± 0.02%), which adversely affect blast furnace operation. Hence, the coarse fraction is suitable for recycling, whereas the fine one presents higher concentrations of these alkali elements. Besides, textural characterization revealed that dust particulates are essentially macroporous materials, with specific surface area values of 21.6 m2/g for the coarse fraction and 33.7 m2/g for dust fines. In order to ensure inoffensive dumpsites, the environmental behavior associated with dust particles accumulated in disposal areas was also evaluated by performing leaching studies simulating different rainfall scenarios. It was found that the specific leaching rates of Ca, Mg, K and S varied between 0.072 ± 0.001 and 0.75 ± 0.01 µgelement/(gdust·d), whereas slower leaching rates were obtained for heavy metals (Fe, Mn and Cu), the values ranging from (1.20 ± 0.1) × 10−4 to (1.8 ± 0.1) × 10−3 µgelement/(gdust·d). These low rates indicate that the leaching of sinter dusts compounds has minimal environmental impact.

Hormuz Red Soil (HRS), as a naturally hematite-containing mineral was used to enhance the catalytic ozonation process (COP) of Acetaminophen (ACT) elimination. The surface properties and particle size of HRS mainly composed of ɑ-Fe2O3 were modified via calcination (C-HRS) demonstrating notable catalytic activity. The catalytic activity of C-HRS was evaluated for the ozonation of ACT under various conditions. Complete degradation of 50 mg L−1 ACT was obtained within 10 min at natural conditions with 1.0 g L−1 of C-HRS which was > 10 times faster than single ozonation process (SOP). The C-HRS accelerated the decomposition of ozone to hydroxyl radical on the catalyst’s surface. Moreover, the C-HRS efficiently catalyzed the peroxone reaction for the degradation and mineralization of ACT. The C-HRS exhibited high stability and reusability in consecutive catalytic cycles. This work offers a new, effective, and low-cost catalyst for accelerating of ozone decomposition that can be used in oxidation of pollutants.

Spent brewer’s yeast is an underused by-product, whose current management offers low returns. This article studies, for the first time ever, the hydrothermal treatment of spent brewer’s yeast, paying special attention to the effect of the presence of oxygen on the physical properties, composition and potential recovery of valuable products from the hydrolysed yeast, as previous step towards the employment of these recovered proteins as renewable chemical feedstock for green industrial uses. Results showed a higher VSS disintegration employing an oxidising atmosphere, as well as a better solubilisation in terms of solid COD reduction, although it also lowered soluble COD but without significantly reducing soluble TOC. Both treatments led to an almost complete solubilisation of protein and carbohydrates from yeast, which were subsequently degraded in presence of oxygen if reaction times were lengthened. Looking at biopolymer recovery, protein precipitation by pH adjustment worked better in hydrolysates obtained in presence of oxygen, with almost 90% of protein precipitation and good selectivities at pH 2.5 and 3. Salting out was more effective, in terms of selectivity, for samples obtained in absence of oxygen and low concentrations of ammonium sulphate. The application of IMAC showed better results on yeast hydrolysates obtained under an inert atmosphere, reaching maximum sorption capacities of almost 100 mg protein/g dry resin, three times higher than those observed using the hydrolysate produced in presence of oxygen. A new perspective in yeast management during beer production is open as renewable chemical feedstock for protein, although further studies are required to optimise protein recovery and purification with respect to its applications.

A first step in assessing the potential of the hydrothermally treated sludge as a fermentation medium or as fertiliser, among other more innovative uses, is to study in depth the compositional changes that take place during the hydrothermal treatment of secondary sewage sludge. Thus, the present study analyses, for the first time, the effects of the reaction time, temperature, pressure and atmosphere on the properties of the hydrolysates obtained and, in particular, on the fate of the four main macronutrients (C, N, P and K). Under the most aggressive operational conditions tested (200 °C, 50 bar, 210 min and oxidising atmosphere), 76% of total suspended solids were disintegrated and 94%, 96%, 12% and 41% of C, N, P, and K were solubilised, with the majority of these changes occurring during the first 60 min of treatment. Nevertheless, these conditions also resulted in significant mineralisation of the organic carbon (77% total Chemical Oxygen Demand reduction) and the formation of notable concentrations of ammonium (around 64 g/kg dry matter) and small amounts of nitrates and nitrites (0.14 g/kg dry matter). After long reaction times, the re-alkalinisation of the reaction medium favoured the binding of soluble P to dissolved metal ions and its subsequent precipitation. Temperature and type of atmosphere did not significantly influence the soluble K concentration, suggesting that this element mainly interacts with tightly bound extracellular polymeric substances in the raw sludge. Finally, pressure did not have significant effects on the final macronutrient composition of the treated sludge.

In this study, the effect of wet oxidation on the main properties of the structural components of the sludge were analysed for the first time ever. For this purpose, an activated sludge was separated into its structural fractions: soluble microbial products (SMP), loosely bound extracellular polymeric substances (LB-EPS), tightly bound extracellular polymeric substances (TB-EPS) and naked cells, and these were treated, either individually or simultaneously (raw sludge), by wet oxidation at 190 °C and 65 bar. Findings revealed that naked cells were the fraction oxidised to a greatest extent followed by TB-EPS, LB-EPS and, finally, SMP, thus concluding that the more internal the biopolymer is located in the cell, the more effectively it is attacked by free radicals. LB-EPS fraction, whose initial biodegradability (10%) was the lowest one of all the fractions, also showed the most intense colour per unit of total organic carbon. Nevertheless, once the EPS fractions were subjected to the wet oxidation separately, the increase in the proportion of readily biodegradable material was particularly remarkable for this fraction (65%), observing higher biodegradabilities after the treatment for those components which are closer to the cell centre. A similar behaviour was observed for decolourisation capacity of wet oxidation. Finally, for the raw sludge and the naked cells, wet oxidation caused a fast initial worsening of settleability and dewaterability in both samples, although this effect was more marked when EPS were previously extracted. However, such properties were improved once a high degree of solubilisation and oxidation was reached. In addition, synergetic effects between the structural fractions during the wet oxidation of raw sludge were discarded.

Isothermal and dynamic methodologies were used to study the thermal degradation of three [NTf 2 ] anion-based ionic liquids (ILs): [C12MIM][NTf 2 ], [N 4441 ][NTf 2 ] and [N 8881 ][NTf 2 ]. Although it is well known that thermal stability is clearly dominated by the coordination ability of the anion, results showed that the cation exerted a significant effect, this being greater in pyrolytic conditions than in oxidising ones. The selected atmosphere also affected the thermal degradation even though the stability trend remained practically constant. In addition, the imidazolium-based IL was the one with the greatest thermal stability, with the chain length of alkyl ammonium cations also affecting their thermal stability. Longer alkyl chains reduce the intermolecular electrostatic interaction and consequently the thermal stability. As the dynamic methodology usually overestimates the long-term thermal stability, an isoconversional methodology is an excellent way for predicting the stability of these ILs in order to be used as base oil or additive in lubricants formulation. Finally, the effectiveness of the model-free methodology can be determined by comparing the results with those obtained in isothermal conditions, with both techniques in good agreement, especially for [N 8881 ][NTf 2 ].

New alternatives for sludge management have been developed in recent years, with hydrothermal treatments being one of the most attractive ones. Even though many studies have been made on the application of hydrothermal treatments as pre-treatment or end-line technologies for sludge stabilisation and/or minimization, there is a lack of knowledge about the products generated during the process and its characteristics. This information is a crucial step for the assessment of the recovery of valuable products of the sludge, mainly proteins, humic acids and carbohydrates, which can considerably improve the economic balance of the hydrothermal treatment. This work assesses, for the first time, the potential of hydrothermally hydrolysed sludge as renewable source for proteins recovery. For this purpose, firstly, the concentrations and properties of the main soluble biopolymers generated during the hydrothermal treatment, either in presence (wet oxidation, WO) or absence (thermal hydrolysis, TH) of oxygen, were measured, determining the reaction time necessary for a maximum solubilisation. Peak concentrations of 7.7g/l (0.291g/gVSSo) of proteins for WO and 7.2g/l (0.272g/gVSSo) for TH, were achieved at 87min of experiment. Afterwards, different separation methods, usually applied at industrial scale, were assessed for the separation of protein from the hydrolysed sludge, in terms of protein recovery and selectivity. Ammonium sulphate addition was found to be the best separation method, achieving 87% and 86% of protein recovery for TH and WO samples respectively, and the highest selectivity. Although further studies are required in order to achieve complete protein purification, a new perspective in sludge management is now open, by recovering valuable compounds.

New edible films were developed using egg yolk, yolk fractions (granules and plasma) and their purified protein fractions as a raw material. All films were characterized by means of texturometry, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetry (TGA). Regarding texture analysis, protein content was the key parameter in case of films prepared with non-purified yolk and yolk fractions, whereas the conformation of the proteins was the significant factor when purified yolk and yolk fractions were employed. FTIR measurements proved that heating steps during the film preparation had a determinant effect on the secondary structure of plasma and its protein fraction. In all films, micrographs were similar showing heterogeneous surfaces with round-shaped particles, excepting purified granule film, which exhibited rough surface organized by layers. TGA indicated a decrease in the thermal stability of non-purified yolk and fractions in comparison to the purified ones.

This study is focused on the adsorption of Cu(II) ions on chemically modified almond shell-based adsorbents, namely bleached almond shell (BAS), lyophilized-bleached almond shell (L-BAS), and TEMPO ((2,2,6,6-Tetramethyl-piperidin-1-yl)oxyl) oxidized cellulose nanofibers (TOCN1 and TOCN2). Such materials were characterized by FTIR-ATR, N 2 adsorption-desorption, SEM, TEM, and TGA/DTG. The adsorption isotherms and kinetics of Cu(II) onto the prepared biosorbents and the effect of temperature and pH on the removal efficiency were thoroughly analyzed. The maximum adsorption capacity of BAS, L-BAS, TOCN1 and TOCN2 at 30 °C and pH 6 was found to be 18.71, 28.27, 23.80, and 21.57 mg g −1 , respectively. Therefore, these materials can be used as effective adsorbents for Cu(II)-containing wastewaters. The results of all the biosorbents, except for the BAS one, were fitted to the pseudo-first-order model with a good degree of concordance. It was also proved that the adsorption process onto L-BAS, TOCN1, and TOCN2 was exothermic and spontaneous.

This study investigates, for the first time ever, the performance of iron(II) as homogeneous catalyst during the catalytic wet oxidation of thiocyanate. The results revealed the suitability of iron salts as cheap, non-toxic catalysts for the homogeneous wet oxidation of thiocyanate in acidic medium, greatly enhancing the oxidation rate and achieving efficiencies above 95% (75 min, 3.58 mM of catalyst). Ammonium, sulphate and bicarbonate were identified as the main reaction products. Other toxic intermediates such as cyanide, cyanate, nitrates or nitrites were not detected at any reaction time. According to the results obtained, a complete reaction pathway, based on the formation of two iron (III)-thiocyanate complexes, was proposed for the degradation of thiocyanate. Finally, a kinetic model, including the effect of the main operating conditions (temperature, pressure and initial concentrations of iron and thiocyanate), was successfully fitted to the experimental data.

Sewage sludge is considered a costly waste, whose benefit has received a lot of attention for decades. In this sense, a variety of promising technologies, such as thermal hydrolysis and wet oxidation, are currently employed. Thermal hydrolysis is used as a pretreatment step ahead of anaerobic digestion processes and wet oxidation is intended for the solubilization and partial oxidation of the sludge. Such processes could be utilized for solubilizing polysaccharides, lipids, fragments of them and phosphorus (thermal hydrolysis) or for generating carboxylic acids (wet oxidation). This article compiles the available information on the production of valuable chemicals by these techniques and comments on their main features. Temperature, reaction duration times and sludge characteristics influence the experimental results significantly, but only the first two variables have been thoroughly studied. For thermal hydrolysis, a rise of temperature led to an increase in the solubilized biomolecules, but also to a greater decomposition of proteins and undesirable reactions of carbohydrates with themselves or with proteins. At constant temperature, the amounts of substances that can be recovered tend to become time independent after several minutes. Diluted and activated sludges seem to be more readily hydrolyzable than the thickened and primary ones. For wet oxidation, the dependence of the production of carboxylic acids with temperature and time is not simple: their concentration can increase, decrease or go through a maximum. At high temperatures, acetic acid is the main carboxylic acid obtained. Concentrated, fermented and secondary sludge seem to be more suitable for yielding higher amounts of acid than diluted, undigested and primary ones.

The release of graphene and its derivatives in soil, air and water seems an inevitable consequence of the massive future use of these carbonaceous allotropes. From an environmental engineering point of view, it should be noted that part of the aqueous streams containing these nanomaterials will end up in wastewater treatment plants, and there will be interactions between the nanomaterials, the other pollutants in the sewage and the microorganisms of the secondary treatment, which could affect the effectiveness of the depuration process. The present work reviews the available literature on the behaviour of these nanoallotropes in wastewater treatment plants (a literature which is almost exclusively focused on graphene oxide and reduced graphene oxide), and also includes research dealing with simpler systems: i) graphene in purified water, ii) graphene in purified water with salt, and iii) graphene in purified water with organic matter and salt. It is probable that the fate of most of the graphene-family nanomaterials will be the primary/secondary sludge, and that a small portion (mainly in the form of graphene oxide) will pass to the tertiary treatment. Besides, graphene oxide has a negative effect on the biological treatment.

Centrifugation of anaerobically digested sewage sludge gives rise to a solid phase, which could be employed as a fertilizer, and a liquid fraction (ADL), which should be treated before being spilled out. This is not an easy task because this liquor is characterized for presenting high COD (~16000 mg O2/L), high ammonium content (~4000 mg/L) and low biodegradability (BOD5/COD ~0.2). With the objective to pre-treat this aqueous waste before its treatment by means of more traditional aerobic processes, different physico-chemical methods (ultrasound, ozonation, hydrolysis and wet air oxidation) were assessed in this work. Ultrasound and thermal hydrolysis gave solubilizations around 47% and 68% respectively. The best results in terms of total COD removal were obtained when wet air oxidation (8 h, 160 C-200 °C and 6.0 MPa) and ozonation (8 h, 25 °C, 12 g/h O3) techniques were employed achieving COD degradations of 71% and 38%, respectively. The pre-treatment of ADL with the four assayed techniques improved considerably the biodegradability (BOD5/COD) of the effluent, with values around 0.3–0.4, depending on the treatment. The experimental data were successfully fitted by kinetic models and the kinetic constants for the solubilization and degradation steps were obtained. Application of the proposed models can be of interest for the optimization and selection of the most suitable techniques and operational conditions, in each particular case.

The advancement of science has facilitated increase in the human lifespan, reflected in economic and population growth, which unfortunately leads to increased exploitation of resources. This situation entails not only depletion of resources, but also increases environmental pollution, mainly due to atmospheric emissions, wastewater effluents, and solid wastes. In this scenario, it is compulsory to adopt a paradigm change, as far as the consumption of resources by the population is concerned, to achieve a circular economy. The recovery and reuse of resources are key points, leading to a decrease in the consumption of raw materials, waste reduction, and improvement of energy efficiency. This is the reason why the concept of the circular economy can be applied in any industrial activity, including the wastewater treatment sector. With this in view, this review manuscript focuses on demonstrating the challenges and opportunities in applying a circular economy in the water sector. For example, reclamation and reuse of wastewater to increase water resources, by paying particular attention to the risks for human health, recovery of nutrients, or highly added-value products (e.g., metals and biomolecules among others), valorisation of sewage sludge, and/or recovery of energy. Being aware of this situation, in the European, Union 18 out of 27 countries are already reusing reclaimed wastewater at some level. Moreover, many wastewater treatment plants have reached energy self-sufficiency, producing up to 150% of their energy requirements. Unfortunately, many of the opportunities presented in this work are far from becoming a reality. Still, the first step is always to become aware of the problem and work on optimizing the solution to make it possible.

In this study, the effect of ageing on the performance and fouling mechanisms in the ultrafiltration of landfill leachates using titania-zirconia (ZrO2-TiO2) tubular membrane was thoroughly studied. Results revealed that the maturation of the leachate has a positive effect on its ultrafiltration, with a twofold higher final permeability compared with the young one. This is the result of the higher organic load, particularly that corresponding to proteins and carbohydrates, of the young leachate. Resistance-in-series analysis demonstrated that the loss of permeability was mainly due to reversible fouling, caused by cake filtration. Either irrecoverable or irreversible fouling were scarce and not conditioned by the stage of maturation of the leachate. Chemical oxygen demand (COD) rejection for the mature leachate varied with volume concentration ratio (VCR) following an approximately sigmoidal shape, from an initial value of 18.5% to a final one of 49.6%, with the faster increase at VCR ranging from 1.2 to 1.7, due to the permeation of fatty acids by the ultrafiltration (UF) membrane. On the other hand, COD rejection remained approximately constant at 48% during the ultrafiltration of the young leachate, which can be attributed to the presence of higher molecular weight compounds in its composition.

In this work, novel magnetic Fe3O4@CeO2@BiOI nanospheres were synthesized for the heterogeneous photocatalytic activation of peroxymonosulfate (PMS) towards sulfamethoxazole (SMX) degradation. The phase purity, morphology, and surface properties of the nanocomposite were fully characterized and confirmed the formation of a heterojunction between the magnetic Fe3O4@CeO2 and BiOI. Low catalyst (0.1 g/L) and PMS addition (0.2 mM) under UVA-LED light irradiation led to high catalytic activity in SMX degradation (97%, kapp = 0.221 min−1) within 15 min. The highest quantum yield (QY) value (5.02 × 10−4 molecules photon−1) was measured for the ternary Fe3O4@CeO2@BiOI nanocomposite, which is 3.54, 3.76, and 4.04 times higher than Fe3O4@CeO2, BiOI, and CeO2 coupled with PMS/UVA, respectively. Furthermore, different experimental conditions, including initial solution pH, catalyst:PMS ratio, water matrix ions on the Fe3O4@CeO2@BiOI/PMS/UVA system, were investigated under the optimum reaction conditions. As deduced from the LC/MS analysis, the possible SMX degradation pathways were proposed. Based on radicals scavenging experiments, SO 4 ∙ - , HO ∙ , and O 2 ∙ - are mainly involved in SMX degradation. Finally, recycling and leaching experiments confirmed a stable material with coherent catalytic performance for the activation of PMS by Fe3O4@CeO2@BiOI catalyst under UVA, with excellent magnetic recovery capabilities. As such, this material has high potential for degradation of organic contaminants and in extension for water treatment processes.

This work demonstrates a highly efficient photocatalytic reduction of Cr(VI) to Cr(III) by using a AgI/CeO2@g-C3N4 nanocomposite, under visible light (Vis) irradiation. The as-prepared samples were characterized by FT-IR, XRD, FE-SEM, TEM, XPS, DRS, PL, PC, and BET. Optimization of the treatment conditions included systematic parameterization, such as initial solution pH, photocatalyst dosage, and Cr(VI) concentration were investigated in the reaction. Compared with pure g-C3N4, CeO2, AgI, and CeO2@g-C3N4 binary nanocomposite, the as-made AgI/CeO2@g-C3N4 ternary nanocomposite showed significantly higher photo-reduction efficiency. The ternary photocatalyst shows a 99.6% reduction efficiency for Cr(VI) (15 mg/L) within 75 min at pH = 3.0. The highest rate constant value (0.058 min−1) was calculated for ternary photocatalyst that is 2.1 times higher than CeO2@g-C3N4/Vis process. The improved activity could be related to the effective electron/hole ( e - / h + ) pairs separation by forming a hetero-junction structure. The XPS analysis of recovered photocatalyst shows the presence only of Cr(III), which indicated a complete photo-reduction of Cr(VI) over AgI/CeO2@g-C3N4 nanocomposite. Moreover, the as-made photocatalyst exhibited more than 91% reduction efficiency after four cycles under the optimum reaction conditions. Based on the radical trapping experiments, photo-generated electrons (e−), and superoxide radicals O 2 ∙ - were the dominant active species in photo-catalytic Cr(VI) removal.

This study deals with the preparation of biopolymer composite from cellulose nanocrystals (CPCNCs) of almond (Prunus dulcis) shell. These composites were obtained through a simple process based on the dissolution of cellulose nanocrystals (CNCs) in green ionic liquid (IL) 1-butyl-3-methylimidazolium chloride (BmimCl). Structural, textural and morphological analyses of CPCNCs were performed using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques, while thermal stability was evaluated by means of thermogravimetric analysis (TGA) measurements. The performance of CPCNCs as adsorbent for Cu2+ ion removal from aqueous solutions was further investigated in batch mode, the maximum experimental adsorption capacity being 131.16 mg g−1. The equilibrium data was successfully fitted to the Dubinin-Radushkevich model. The kinetic studies showed that the adsorption of Cu2+ ions was well described by the Elovich kinetic model, suggesting that the adsorption was mainly attributed to the chemical process onto heterogeneous surface. Various thermodynamic parameters, such as ΔG°, ΔH° and ΔS°, derived from adsorption data over the temperature range 30–60 °C, accounted for an endothermic and spontaneous process. A possible adsorption mechanism implying electrostatic reactions and surface complexation was proposed based on XPS, FTIR, TEM and pH dependence. The CPCNC adsorbent could be regenerated using diluted HCl (0.1 M) solution, showing excellent recyclability: 81% removal of Cu2+ ions after four adsorption-desorption cycles. Therefore, the synthesized biopolymer composite could be considered as promising adsorbent for Cu2+ ion removal from polluted waters.

The direct oxidative dehydrogenation of lactates with molecular oxygen is a “greener” alternative for producing pyruvates. Here we report a one-pot synthesis of mesoporous vanadia–titania (VTN), acting as highly efficient and recyclable catalysts for the conversion of ethyl lactate to ethyl pyruvate. These VTN materials feature high surface areas, large pore volumes, and high densities of isolated vanadium species, which can expose the active sites and facilitate the mass transport. In comparison to homogeneous vanadium complexes and VOx/TiO2 prepared by impregnation, the meso-VTN catalysts showed superior activity, selectivity, and stability in the aerobic oxidation of ethyl lactate to ethyl pyruvate. We also studied the effect of various vanadium precursors, which revealed that the vanadium-induced phase transition of meso-VTN from anatase to rutile depends strongly on the vanadium precursor. NH4VO3 was found to be the optimal vanadium precursor, forming more monomeric vanadium species. V4+ as the major valence state was incorporated into the lattice of the NH4VO3-derived VTN material, yielding more V4+–O–Ti bonds in the anatase-dominant structure. In situ DRIFT spectroscopy and density functional theory calculations show that V4+–O–Ti bonds are responsible for the dissociation of ethyl lactate over VTN catalysts and for further activation of the deprotonation of β-hydrogen. Molecular oxygen can replenish the surface oxygen to regenerate the V4+–O–Ti bonds.

In this paper, wet oxidation was applied to an activated sludge as a potential technique for the recovery of products of industrial value. With this end, the effect of the treatment on the polymeric composition of the sludge was analyzed. To establish differences due to the origin of the biopolymers (extracellular or intracellular), the sludge was separated into fractions: soluble microbial products (SMP), loosely bound extracellular polymeric substances (LB-EPS), tightly bound extracellular polymeric substances (TB-EPS) and naked cells and each was treated at 190 °C and 65 atm. A model that describes the evolution of soluble biopolymers during the wet oxidation of sludge was proposed and successfully fitted to the experimental data. Results showed a rapid solubilization of polymers during the first minutes of reaction, achieving values of 23.1%, 14.7%, 8.3%, 0.9% and 0.5% for proteins, humic acids, carbohydrates, uronic acids and DNA, respectively, with regard to the initial volatile suspended solids con...

Thermal pre-treatments of activated sludge involve the release of a high amount of polymeric substances into the bulk medium. The molecular size of these polymers will largely define the subsequent biological treatment of the liquid effluent generated. In this work, the effects of wet oxidation treatment (WO) on the fingerprints of the polymeric substances which compose the activated sludge, were analysed. For a better understanding of these transformations, the sludge was separated into its main fractions: soluble microbial products (SMP), loosely bound extracellular polymeric substances (LB-EPS), tightly bound extracellular polymeric substances (TB-EPS) and naked cells, and then each one was subjected to WO separately (190 °C and 65 bar), determining the fingerprints evolution by size exclusion technique. Results revealed a fast degradation of larger molecules (over 500 kDa) during the first minutes of treatment (40 min). WO also increases the absorptive properties of proteins (especially for 30 kDa), which is possibly due to the hydroxylation of phenylalanine amino acids in their structure. WO of naked cells involved the formation of molecules between 23 and 190 kDa, which are related to the release of cytoplasmic polymers, and more hydrophobic polymers, probably from the cell membrane. The results allowed to establish a relationship between the location of polymeric material and its facility to become oxidised; thus, the more internal the polymeric material in the cell, the easier its oxidation. When working directly with the raw sludge, hydrolysis mechanisms played a key role during the starting period. Once a high degree of solubilisation was reached, the molecules were rapidly oxidised into other compounds with refractory characteristics. The final effluent after WO showed almost 90% of low molecular weight solubilised substances (0–35 kDa).

Humic acids are highly distributed in aqueous environments. This article examines in depth the advanced oxidation of humic acid aqueous solutions, in order to understand more complex oxidation processes such as those of the sewage sludge or landfill leachate, or the matrix effects triggered by the humic acids of natural organic matter (NOM) in the oxidation of other aqueous compounds as herbicides. Humic acids were efficiently oxidized; higher temperatures (180−220 °C) involved higher mineralization, the formation of intermediates with lower colour and also led to a higher concentration of organic acids at the end of the treatment, particularly acetic and oxalic ones. Nevertheless, humic acid wet oxidation was not sensitive to changes in the pressure, at least in the range tested (65−95 bar), but the initial pH (4–13) was found to be a key factor. Thus, alkaline media accelerated the humic acid removal, but more refractory intermediates were generated, and the organic acids, excepting malic acid, were more stable than in neutral or acidic media. Eventually, a lumped kinetic model was proposed and successfully fitted to the experimental data, including the effect of all the operating variables studied.

The present study assesses, for the first time, the use of the non-lignin residue from Kraft black liquor as a renewable source of carboxylic acids. For this purpose, the liquid fraction obtained after separating the lignin from the black liquor by acid precipitation was subjected to different hydrothermal treatments. It was found that the formation of carboxylic acids can be maximized at 190 °C, 70 bar and under an inert atmosphere, with concentrations after 2 h of 29.0 g/l of oxalic acid, 1.8 g/L of malic acid, 10.0 g/L of lactic acid, 4.1 g/L of formic acid, 11.8 g/L of acetic acid and 3.4 g/L of propionic acid. The presence of an oxidizing atmosphere generated a less concentrated, but more purified, stream of acids than that obtained by thermal hydrolysis, simplifying the subsequent downstream processing.

Three new ionic liquids with different anions and the same cation were synthesized from fatty acids through a metathesis reaction. All the ionic liquids were identified via NMR and FTIR and several properties (density, viscosity, thermal, and environmental) were measured. Traction tests were performed under different entrainment speeds (10–2000 mm/s), at slide-roll ratio (SRR) of 50% and 30 N-load, and at different temperatures (40, 60, 80 and 100 °C) using a mini-traction machine (MTM). Tribofilm formation tests were also made in the MTM at 50 N-load, 150 mm/s of entrainment speed, at SRR of 50% and temperature of 100 °C, for 60 min. This work showed that the alkyl chain length in the anion affects properties such as viscosity, toxicity, biodegradability and lubrication. Viscosity decreased with increasing alkyl chain length but only below 60 °C, at higher temperatures the viscosity values of the ionic liquids converge. The toxicity increases with the alkyl chain length; whereas, biodegradability shows the opposite behavior. These novel ionic liquids are much better from both toxicity and biodegradability points of view than the [N8881][TFSI] ionic liquid, which contains the same cation and anion not coming from fatty acids. The ionic liquids at low temperature (40 °C) performed under elastohydrodynamic lubrication and changed to mixed lubrication at higher temperatures and decreasing speeds, according to the alkyl chain length of each anion. All ionic liquids adsorbed on the steel surfaces, and the tribofilm thickness and the kinetics of formation were different.

The work upon which this paper is based on was co-financed byConsortium for the Management of Solid Wastes of Asturias (Projects FUO-EM-138-15, FUO-139-16), Institute for Economic Development ofthe Principality of Asturias (Project IDE/2015/000245), Spanish Ministryof Economy and Business (Project CTM2015-63864-R) and European Re-gional Development Funds from European Union. Technical assistancefrom the Scientific-Technical Services of the University of Oviedo is grate-fully acknowledged