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•Graphene nanomaterials (pGr, GO, RGO, FLG and MLG) have a different fate in WWTPs.•pGr, FLG and MLG settle down more easily than RGO in the primary clarifier.•GO hinders the ...anaerobic denitrification, but improves the anaerobic NH4+ oxidation.•Various minerals can adsorb GFNs and improve the pretreatment/primary sedimentation.•GO and RGO favoured the formation of disinfection by-products (trihalomethanes).
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.
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 (N
2
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.
In this study, novel cellulose-bead-based biosorbents (CBBAS) were successfully synthesized from almond shell using a simple three-step process: (i) dissolution of bleached almond shell in ionic ...liquid (1-butyl-3-methylimidazolium chloride), (ii) coagulation of cellulose-ionic liquid solution in water and (iii) freeze-drying. Their morphological, structural and physicochemical properties were thoroughly characterized. These biomaterials exhibited a 3D-macroporous structure with interconnected pores, which provided a high number of adsorption sites. It should be noted that CBBAS biosorbents were efficiently employed for the removal of copper (II) ions from aqueous solutions, showing high adsorption capacity: 128.24 mg g
−1
. The biosorption equilibrium data obtained were successfully fitted to the Sips model and the kinetics were suitably described by the pseudo-second-order model. Besides, CBBAS biosorbents can be easily separated from the solution for their subsequent reuse, and thus, they represent a method for the removal of copper (II) from aqueous solutions that is not only eco-friendly but also economical.
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.
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 Co x O y /MgO catalysts. While all three catalyst types enhanced CO2 conversion, Co x O y /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.
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 VO x /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.
The degradation of cyanide was performed in a 1-L semibatch reactor at temperatures between 393 and 473 K and at total pressures in the range of 2.0–8.0 MPa. The initial pH of the solution was set at ...11, whereas initial concentrations ranged from 3.85 to 25 mM, which resemble the typical concentrations of cyanide-containing wastewater. The change with time of cyanide concentration, intermediates, and final products was analyzed in order to elucidate the reaction pathways. The experimental results suggest two parallel pathways of alkaline hydrolysis for the degradation of the pollutant. Formate and ammonia were identified as the final reaction products for one of the pathways, whereas carbon dioxide, nitrogen, and hydrogen were considered to be the final products for the other one. The degradation reaction results were fitted to first-order kinetic equations with respect to cyanide, giving respectively activation energies of 108.2 ± 3.3 and 77.6 ± 3.0 kJ/mol. Consequently, the formation of formate and ammonia is favored at high temperatures, whereas low temperatures favored the pathway leading to the formation of carbon dioxide and nitrogen.
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).
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•High and fast degree of solubilisation initially, with polymers ranging 23–190 kDa.•Oxidation reactions have a screening effect on molecular size of polymers.•Final effluent: 90% of low molecular weight solubilized substances (<35 kDa).•Possible proteins modification by phenylalanine hydroxylation during wet oxidation.•Refractoriness to oxidation: SMP > LB-EPS > TB-EPS > naked cells.
Sewage sludge can be treated by anaerobic processes that frequently are followed by physical separation processes. In this work, a high-throughput sequencing technology, based on variation in the ...bacterial 16S rRNA gene, has been used to characterise the bacterial populations present in samples taken from different points of an industrial anaerobic digestion process fed with sewage sludge. Relative abundances of phyla and classes throughout the biological process and the subsequent separation steps were determined. Results revealed that the Bacteroidetes, Firmicutes and Proteobacteria phyla were the most representative. However, significant changes in relative abundance were detected along treatments, showing the influence of operational parameters on the distribution of microorganisms throughout the process. After anaerobic digestion, phylum Firmicutes doubled its relative abundance, which seems to indicate that the anaerobic conditions and the nutrients favoured its growth, in contrast to other phyla that almost disappeared. After centrifugation, Proteobacteria went preferentially to the solid phase, in contrast to Firmicutes which was the dominant phylum in the liquid phase. After decanting the liquid phase during 45 h, an important growth of Proteobacteria, Spirochaetes and Tenericutes was detected. At class level, only significantly changes were observed for Proteobacteria classes being α-proteobacteria dominant in the digestate, while γ-proteobacteria was the majority since this point to the final steps. To know the changes on the kind and abundance of microbial populations throughout the anaerobic and separation processes is very important to understand how the facilities design and operation conditions can influence over the efficiencies of next biological treatments.
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•Microbiota of the digested sewage sludge and subsequent processes was investigated.•Sequencing of the hypervariable regions of the 16S rRNA gene was performed by PGM.•Firmicutes, Proteobacteria and Bacteroidetes were the most representative phyla.•Firmicutes was the predominant phylum in the digestate after anaerobic digestion.•Decantation process had a significant influence on the distribution of the phyla.
Metal nanoparticles have been reported as effective catalysts for the removal of refractory compounds from industrial wastewaters in advanced oxidation processes. Additionally, hundreds of thousands ...of tons of eggshells are discarded worldwide each year. In this work, this waste has been evaluated as support for the synthesis of nanomaterials by wet impregnation method. Four supported catalysts, with a load of iron or copper of 5% and 15%, were prepared and thoroughly characterized by means of different techniques (elemental analysis, XRF, XRD, FTIR, N2 adsorption-desorption, SEM, TEM and TGA). The catalysts performance was evaluated in wet oxidation tests to degrade humic acids, analyzing the evolution with time of COD, biodegradability index (BOD5/COD), color number and pH. The best results were achieved with 15% Cu and 5% Fe catalysts (COD reduction being 82.3% and 75.1%, respectively), whereas a COD reduction of 58% was obtained employing non-impregnated eggshell. This can be mainly attributed to the metal loading and the good metal distribution on the surface of the support. The BOD5 value of humic acids was initially null and, in all assays, the oxidation treatment enhanced the biodegradability. Therefore, eggshell has proved to be an interesting material to be employed as support in nanoparticles preparation.
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