Solid-liquid Separation Research Articles

Solid–Liquid Separation of Dairy Barn by Electrocoagulation with Cationic Polymer Coagulant

High–molecular-weight polymer coagulants are widely used in wastewater treatment combined with traditional inorganic coagulants to improve the solid–liquid separation efficiency. However, it is desirable to keep chemicals used in treatments at minimum levels for economic and safety reasons. This study aimed to increase the efficiency of two-stage electro- and chemical-coagulation treatment with a minimum chemical dosage for the separation of solids and liquid in dairy manure slurry for the safe composting of solids and safe discharge of wastewater. Accordingly, dairy manure slurry was treated with aluminum (Al) coagulants, such as polyaluminum chloride (PAC), aluminum chloride (AlCl3), and aluminum sulfate (Al2(SO4)3), PAC combined with the cationic polyacrylamide (CPAM), and PAC and CPAM combined with electrocoagulation (EC). Results revealed that PAC was the best among the Al coagulants evaluated for the reduction in turbidity in the liquid fraction at a dosage of 100 mg/L. PAC dosage was reduced to 40 mg/L when the treatments were combined with CPAM at a dosage of 40 mg/L, which was further reduced to 30 mg/L when treatments were combined with 5 min EC and 20 mg/L of CPAM dosage.

Efficient and green water softening by integrating electrochemically accelerated precipitation and microfiltration with membrane cleaning by periodically anodic polarization

• An efficient and reagent-free EAPS-MF system was developed for water softening. • A hydrophilic PTFE membrane was used as the separation medium in electrolysis cell. • The Ti microfilter with membrane cleaning by anodic polarization was used for CaCO 3 interception. • CaCO 3 precipitation rate was 349 g h −1 m −2 at 100 A m −2 with energy consumption of 1.88 kWh kg −1 . Although the electrochemical water softening in the divided cell has been proven capable of avoiding the requirement of high working electrode surface area, its industrial application is seriously constrained by the fouling of the ion exchange membrane and the lack of an environmentally friendly liquid–solid separation method. In this study, an energy-efficient and reagent-free electrochemically accelerated precipitation and microfiltration combined system (EAPS-MF) was developed for water softening. In typical operation mode A, the electrolysis cell divided by a polytetrafluoroethylene microfiltration membrane (PMM), allowing for the simultaneous production of alkaline and acidic effluents. The alkaline effluent was fed directly into the crystallizer for the formation of CaCO 3 crystals, which were intercepted by a Ti tubular microfilter. The filtrate was then blended with acidic effluent to further reduce water scaling potential by removing the residual alkalinity. In this system, the precipitation rate raised from 97.5 to 348.8 gCaCO 3 h −1 m −2 by elevating current density from 20 to 100 A m −2 , accompanying the increased specific energy consumption from 0.68 to 1.88 kWh (kgCaCO 3 ) −1 or from 0.044 to 0.44 kWh m −3 water treated. The Ti tubular membrane fouling was mainly caused by the accumulation of CaCO 3 cake on its surface, which existed in the predominant type of calcite and marginal type of vaterite. Interestingly, the fouled Ti tubular membrane could be recovered completely within 5 min just by periodically anodic polarization at a current density of 200 A m −2 without production of wasted cleaning brine. Generally, the established EAPS-MF system exhibited significant prospects in promoting the applications of the electrochemical softening process in diverse industrial areas.

Ex ante Life Cycle Assessment and Environmental Cost-Benefit Analysis of an anaerobic digester in Italy

The end-use valorisation of food waste (FW) and biowaste is currently being focused on biofuels and bioproducts production through different technologies. This study evaluated the implementation of a new eco-industrial system in Italy that incorporates a micro-scale anaerobic digestion (mAD) and a Solid-State Fermentation (SSF) unit to produce renewable energy (e.g., electricity and heat) from AD biogas and high-quality bio-based products (e.g., bio-pesticides) from digestate. Three scenarios (S0, S1, S2) were modelled. S0 and S1 included only a solid-liquid separation of digestate through a centrifuge, assuming a different fate for the solid fraction (composting in S0 and application on farmland in S1). S2 integrated SSF and reverse osmosis technologies for the treatment and valorisation of digestate with nutrient recovery. The Life Cycle Assessment (LCA) and Environmental Cost-Benefit Analysis (eCBA) methodologies were applied to assess the environmental performances and economic feasibility of the project. The pilot system showed solid environmental performances, especially for S1 and S2, in the five impact categories considered. According to LCA results, the eCBA gives a positive outcome for S2. While the financial and economic analysis showed positive Net Present Values for S2, the project's profitability was not achieved for S0 and S1. If AD plants are implemented at a smaller scale they would represent a favourable investment for the local community; particularly when considering the benefits of nutrient recovery through a complete post-treatment of digestate. The valorisation of organic residues could be better supported through introducing alternative market-based policy tools, as well as removing regulatory barriers and encouraging the implementation of financial schemes to support small-scale renewable production systems and the enhancement of market-based instruments for credits certification from renewable energy production. • Biowaste treatment and valorisation had solid performances in Life Cycle Assessment. • Environmental Cost-Benefit Analysis quantified good revenues for bio-based products. • Nutrient recovery by bio-pesticides and organic fertilizers allow economic benefits. • Limited plans, policies and economic instruments characterize the biowaste sector. • Alternative economic tools can promote biowaste reduction & efficient resources use.

Study on Three-Stage Counter-Current Water Washing Desalination Characteristics and Mechanism of High Chlorine Waste Incineration Fly Ash

The high chloride content of municipal solid waste incineration (MSWI) fly ash and hazardous waste incineration (HWI) fly ash has considerably affected their disposal. This study focused on investigating the three-stage counter-current (TSC) water-washing process to reduce the chlorine content efficiently under the premise of low water consumption. The liquid–solid ratio (LSR) and washing time were investigated, a chloride migration model was established, and the characteristics of the water-washing solution (WWS) and washed fly ash were investigated. The results showed that the dechlorination effect of TSC washing could reach more than 99% in a low liquid–solid ratio (LSR) of 2–4 kg/L. The most appropriate LSR and washing time were found to be around 3:1 L/kg and 15 min per stage, respectively. The concentration of Cl− in WWS reached over 90 g/L, which is very high among industrial saline wastewater. Some heavy metals were also contained in the WWS, and lead was the main heavy metal, followed by zinc, copper, and arsenic. The concentration of WWS of different stages was calculated by a model, and the transfer characteristic of chloride was strongly related to the mass balance between the liquid contained in the solid–liquid separation residue (SR) and the separated liquid. After washing, due to the dissolution of soluble salt, the specific surface area of fly ash increased, and thus the absorption ability of the washed fly ash was greater than the raw one. This study provides a washing condition reference for highly chlorinated fly ash, the basic data of WWS, and the chloride migration model that is a preliminary calculation method to improve the water-washing process.

Novel magnetic covalent organic framework for the selective and effective removal of hazardous metal Pb(II) from solution: Synthesis and adsorption characteristics

The removal of lead(II) from wastewater is conducive to reduce the risk of harmful metals to the environment and people. A magnetic organic framework adsorbent (Ni0.6Fe2.4O4-HT-COF) with high selectivity, repeatability and facile solid–liquid separation was devised through the condensation process of hexachlorocyclo-triphosphazene, trithiocyanuric acid and Ni0.6Fe2.4O4. At 298 K and pH = 5.0, the adsorbent showed remarkable Pb(II) adsorption capability. The removal rate reached 95.64 % at 10 min and the maximum adsorption capacity was 411.80 mg/g. The partition coefficient (KQ) of Pb(II) among the seven coexisting ions was 34079 mL/g and the adsorption efficiency was 97.15 %, indicating that the adsorbent can accurately capture Pb(II) from wastewater containing multiple ions. The PSO kinetic and the Langmuir isotherm models agreed with Pb(II) adsorption on Ni0.6Fe2.4O4-HT-COF, demonstrating that Pb(II) was removed by monolayer chemisorption. The adsorption was a spontaneous exothermic process using thermodynamic analysis. In addition, the adsorbent was able to maintain 91.77 % adsorption efficiency for Pb(II) after four adsorption–desorption cycles. Zeta potential and XPS analysis revealed that Ni0.6Fe2.4O4-HT-COF removed Pb(II) by electrostatic attraction and chelation. Density functional theory (DFT) was utilized to simulate the adsorption process, and the effects of different types of atoms on adsorption were discussed. The results demonstrate that the chelation and electrostatic interaction between Ni0.6Fe2.4O4-HT-COF and lead(II) ions were involved in the selective adsorption. The novel magnetic COF has a lot of potential for removing heavy metal Pb(II).

Hierarchically porous polyimide aerogel fibers based on the confinement of Ti3C2Tx flakes for thermal insulation and fire retardancy

Thermally insulating and flame-resistant fibers/textiles have drawn enormous attention attributing to their great application prospects in personal thermal management and protective clothing. Nevertheless, conventional natural fibers and synthetic fibers are insufficient for advanced thermal regulation. Herein, an in-situ polymerization method and wet-spinning technique are employed for the continuous and scalable fabrication of polyimide (PI) aerogel fibers utilizing monolayered Ti3C2Tx flakes as the pore-generating agents. Benefiting from the intimate interfacial interaction between MXene and the macromolecular chains, hierarchical porosity is constructed in the composite aerogel fibers due to the confinement of the interconnected PAA/Ti3C2Tx networks during liquid-solid phase separation. As a result, the PI/Ti3C2Tx aerogel fibers manifest significantly enhanced mechanical properties (tensile strength of 26 MPa), large specific surface area (145 m2 g−1), excellent flame resistance, and remarkable thermal insulation performance (with a low thermal conductivity of 36 mW m−1 K−1), which can be readily weaved into flexible textiles for practical thermal regulating applications. This approach is expected to pave a new way for the fabrication and application of high-performance thermal insulating fibers and textiles.

Study on the characteristics and mechanism of the flocculation behaviour in a novel fluidized bed flocculator

Fluidized bed flocculator is a novel and efficient flocculation reactor. It has an efficiency that directly affected by flow field parameters. However, the structural characteristics of flocs and their influence on subsequent settling performance in fluidized bed flocculators are not clear. In this study, a multi-stage velocity gradient fluidized bed flocculator (MGF) was constructed for the continuous flocculation-sedimentation of kaolinite to investigate the growth and sedimentation behaviour of flocs. Additionally, MGF was compared with traditional mechanical stirring flocculation (MSF). Results showed that MGF achieved a higher removal efficiency (97.6 ± 0.7 %) with less coagulant and flocculant than MSF. Moreover, flocs generated in the MGF yielded a faster settling performance, which can reduce the sedimentation time by 60 times. Comparative analysis of floc structural characteristics, as well as their relationship with the settling velocity, demonstrated that flocs in MGF were more compacted than those in MSFs and thus achieved higher settling velocity. The settling velocity was collaboratively dominated by the size and fractal dimension of flocs. A modified Stokes’ settling velocity equation introducing the structural characteristics of flocs was derived, and verified by actual data to accurately and quantitatively describe the settling velocity of irregular flocs. These results indicated that MGFs have a better flocculation and sedimentation performance than MSFs for solid–liquid separation, and may lay a theoretical foundation for the design of efficient fluidized bed flocculators and popularize their application in practical engineering.

Removal of dimethylarsinate from water by robust NU-1000 aerogels: Impact of the aerogel materials

This study compared the effect of three matrices on the dimethylarsinate (DMA) removal from water to NU-1000 (zirconium-based metal–organic framework, Zr-MOF) hybrid aerogels. The porous MOF hybrid aerogels were prepared by grafting NU-1000 into green matrices, i.e., agarose (AG), sodium alginate (SA), and carboxymethyl cellulose (CMC) sodium salt. The adsorption data of DMA can be well described by the pseudo-second-order kinetic model and the Freundlich isotherm model. The maximum adsorption capacity of the NU-1000@AG hybrid aerogel for DMA (119.63 mg/g) was higher than the other two hybrid aerogels due to the negligible interference of AG on the active adsorption sites in NU-1000. However, the functional groups in NU-1000@CMC hybrid aerogel and NU-1000@SA hybrid aerogel occupied the Zr adsorption sites during the cross-linked process and decreased their adsorption capacities. The NU-1000@AG hybrid aerogel demonstrated application potential for removing DMA in a fixed-column dynamic adsorption process. Furthermore, the NU-1000 hybrid aerogels exhibited excellent regeneration performance and ease of solid–liquid separation. The characteristics of various matrices may offer diversified facile and viable strategies for fabricating a blocky adsorbent with superior stability and solid–liquid separation efficiency for water treatment, overcoming the disadvantages of MOF powder and ensuring maximum effectiveness of adsorbent components.

Balance of total mass and nitrogen fluxes through consecutive digestate processing steps: Two application cases

The high water content and low nutrient concentration of digestate complicate its storage, transportation, and utilization. Subsequent digestate processing can effectively remove water and influence nutrient partitioning among digestate fractions and final products.The current study was carried out to evaluate the performance of two typical digestate processing chains, solid and liquid ones, respectively, and to give practical recommendations for optimization. Two fully operating biogas plants with advanced heat utilization were considered as data sources. The digestate mass flow balance of dry matter (DM), water, total N (TN), and ammonium-N mass flows was performed and the efficiency of the examined processing units was calculated.It was found that solid-liquid separation of raw digestate shifted 73–87% of TN and 60–93% of NH4–N to the liquid phase. Subsequent drying of separated solid fraction removed about 6% of the initial water and required 84% less thermal energy per kg N recovered than the processing of separated liquid. The final product, pellets, contained 14% of initial TN, but only 2% of initial NH4–N as a result of microbial conversion of inorganic N during drying.Vacuum evaporation of separated liquid fraction removed 34% of the initial water and left a DM-rich concentrate. At the same time, an ammonium sulfate solution (ASS) containing 21% of initial TN and 34% of initial NH4–N was produced.Both evaluated processing chains showed specific advantages and challenges. Solid products were characterized by a high share of recalcitrant organic compounds and could serve as a soil improver. Liquid processing concentrated plant-available N in ASS, which could be used as valuable inorganic fertilizer.

Anaerobic Digestion and Microfiltration of the Liquid Fraction of Pig Slurry: N Mineralization, C-CO2 Emissions and Agricultural Value of the Products

Pig slurry contains valuable nutrients and organic matter, although its high water content makes its management and use as a fertilizer more expensive. It is also an interesting bioenergy resource for biogas production. We propose a treatment that consists of solid–liquid separation followed by the anaerobic digestion of liquid fraction of slurry (LFS) while a microfiltration membrane module concentrates the solids in the digester and removes a liquid fraction of the digestate (LFD). The aims of the work were to evaluate the fertilizer value of the LFS, digestate and concentrated digestate and the possibility of reusing the LFD in agriculture. The LFS contained 72% less dry matter than the slurry. The solid–liquid separation mainly removed N and P. Thanks to microfiltration, the remaining solids were partially recirculated to the digester, concentrating there. To do this, the membrane module continuously removed the LFD, which was made up of 99% water with dissolved elements, mainly C, N, K and Na. The concentrated digestate contained less K, similar amounts of N and P, and more dry matter and C than the initial LFS. The entire slurry treatment affected the mineralization dynamics by increasing recalcitrant C and decreasing labile C without modifying N release. The proposed process allowed taking advantage of the nutrients and stabilized organic matter contained in the LFS, producing a concentrated digestate. LFD did not meet the reclaimed water requirements. However, it could be useful as a fertirrigation solution and a post treatment could be enough to comply with the regulations.Graphical

Liquid-liquid and liquid-solid separation in self-assembled chitosan-alginate and chitosan-pectin complexes

The complexation between two oppositely charged polyelectrolytes (PE) can lead liquid-liquid (complex coacervates, CC) or liquid-solid (solid precipitates, SP) phase separations. Herein, the effect of pH (2−11) and ionic strength (I, 0.05–1.0 M KCl) on the associative interactions between chitosan (QL)-alginate (SA) and QL-Pectin (Pec), polysaccharides widely used in biotechnology field, is described. pH and I, exhibited significant effect on the structure and phase transitions by modifying the ionization degree (α), pka, and associative interactions between PE. Onset of binding was established at pHc 9, while continued acidification (pHτ 5.8) led to simultaneous CC and SP exhibiting a maximum turbidity in both systems. At pHδ 4.0, QL-Pec showed preferably CC structures whereas QL-SA maintained the CC and SP structures. At pHω 2, the associative interactions were suppressed due to the low ionization of Pec and SA. I (1.0 M) significantly diminished the interactions in QL-Pec due to charge screening. Molecular weight, second virial coefficient, hydrodynamic size, ionizable groups, and persistence length of polyion, influenced on the phase behavior of QL-Pec and QL-SA systems. Therefore, CC and SP are found simultaneously in both systems, their transitions can be modulated by intrinsic and environmental conditions, expanding the functional properties of complexed polysaccharides.

Dynamic Assembly of Viscoelastic Networks by Aqueous Liquid-Liquid Phase Separation and Liquid-Solid Phase Separation (AqLL-LS PS2 ).

Living cells comprise diverse subcellular structures, such as cytoskeletal networks, which can regulate essential cellular activities through dynamic assembly and synergistic interactions with biomolecular condensates. Despite extensive efforts, reproducing viscoelastic networks for modulating biomolecular condensates in synthetic systems remains challenging. Here, a new aqueous two-phase system (ATPS) is proposed, which consists of poly(N-isopropylacrylamide) (PNIPAM) and dextran (DEX), to construct viscoelastic networks capable of being assembled and dissociated dynamically to regulate the self-assembly of condensates on-demand. Viscoelastic networks are generated using liquid-liquid phase-separated DEX droplets as templates and the following liquid-to-solid transition of the PNIPAM-rich phase. The resulting networks can dissolve liquid fused in sarcoma (FUS) condensates within 5 min. This work demonstrates rich phase-separation behaviors in a single ATPS through incorporating stimuli-responsive polymers. The concept can potentially be applied to other macromolecules through other stimuli to develop materials with rich phase behaviors and hierarchical structures.

Preparation of novel magnetic porous biochar and its adsorption mechanism on cerium in rare earth wastewater

A novel and efficient process for the removal of Ce(IV) from aqueous solutions was sought, and a new magnetic porous biochar (PBC/ZF) was synthesized by loading ZnFe2O4 (ZF) onto porous biochar (PBC) using a one-step hydrothermal method. The SEM observation of the external features showed that the cubic spinel structured ZnFe2O4 (ZF) particles were loaded onto the porous biochar (PBC) surface. This resulted in a composite with superb paramagnetic properties as well as higher adsorption properties. In addition, the microstructure was characterized by FTIR, which demonstrated that the target material was supplied with a large amount of carboxyl groups (-COOH) by citric acid during the synthesis process. The BET showed that the target material had a higher specific surface area than ZnFe2O4 with PBC, confirming the successful preparation of the target material after activation of the biomass using ZnCl2 immersion as well. The effect of different factors on the adsorption effect was investigated experimentally. The results showed that PBC/ZF had a good adsorption effect on Ce(IV) with a short adsorption equilibrium time and a maximum adsorption capacity of 228.9 mg/g at room temperature with lower acidity (pH = 2.5). The adsorption kinetics and isotherm analysis showed that the Ce(IV) adsorption process fitted well with the quasi-secondary kinetic model and Langmuir model. It indicates that the process is a single molecular layer adsorption process. It was demonstrated that PBC/ZF also has high removal rate for high concentration Ce(IV) solution, and it is easy for solid-liquid separation under the action of applied magnetic field after adsorption. It provides a new treatment method and theoretical support for the adsorption treatment technology of Ce (IV) wastewater.

Improving freeze-thaw stability and 3D printing performance of soy protein isolate emulsion gel inks by guar & xanthan gums

Frozen storage of 3D printing inks could increase their shelf life. We improved freeze-thaw stability and 3D printing performance of soy protein isolate (SPI) emulsion gel inks by guar (GG) and xanthan gums (XG). Freeze-thawed inks led to higher storage modulus (G′), lower water holding capability (WHC) and poor printing performance compared to initial inks. An increase in gums content decreased oil droplet aggregation and protein flocculation in all freeze-thawed inks, hence reducing syneresis in the gel structure and preventing solid-liquid separation during 3D printing. The freeze-thaw stability of SPI-XG inks was consistently greater than that of SPI-GG inks at the same concentrations, resulting in superior 3D printing performance. The hardness of cylinders printed with SPI-XG0.5 freeze-thawed inks was lower than that of the cylinders printed by initial inks, in contrast to the results of G'. At the maximum strain amplitude (500%), Lissajous analysis indicated that the SPI-XG0.5 freeze-thawed inks retained less energy than the initial inks, resulting in a weaker gel. Overall, this study demonstrated that freeze-thaw treatment negatively affected the 3D printing performance of SPI emulsion gel inks, but that the 3D printing performance of freeze-thaw inks could be reinforced by modifying the formulation.

Integration of coagulation-flocculation process for improved solid–liquid separation of anaerobically treated textile effluent

ABSTRACT Anaerobic process is a promising technique for textile effluent treatment. However, poor solid–liquid separation and residual chemical oxygen demand (COD) in the treated effluent limit its scope for industrial applications. The study analyzed the nature of suspended microbial biomass in the anaerobically treated effluent and further targeted its feasible separation process. The size of the majority of suspended biomass (82%) particles ranged from 500 to 1000 nm. The suspended biomass showed 37.13% hydrophobicity and −15.4 mV zeta potential. The optimization of the coagulation-flocculation (CF) process showed 93% turbidity removal at 400 mg/L of alum, 8 mg/L of a cationic polymer and acidic pH 4, through one variable at a time approach. The optimized results using Central Composite Design (CCD) were experimentally validated, and 97% turbidity removal was recorded at 400 mg/L alum concentration, 12 mg/L of the cationic polymer, and pH 3.2. The results obtained were statistically significant, with a high regression coefficient (R2 = 0.97) at 95% confidence limits. The final treated effluent after CF showed 67% COD removal (from 862 ± 40 to 280 ± 14 mg/L) with 83% color removal (from 740 to 124 Hazen). Hence, the integration of the CF process with the anaerobic process could be a promising approach for textile effluent treatment.

Preparation of Iron Oxide Adsorbent Modified by Chitosan Biomaterials and Its Adoption in the Adsorption of Heavy Metals

Heavy metals in water leads to many ecological and environmental problems. All kinds of new magnetic adsorbents are used to adsorb the heavy metals in the aqueous solution, which has the advantages of high efficiency, low consumption, simplicity, convenience, and industrialization. Firstly, Fe3O4 is dissolved, and polyethylene glycol (PEG) and anhydrous sodium acetate are added. The dissolved product is placed in the reaction kettle lined with Teflon and reacts at a high temperature to obtain the Fe3O4 magnetic microspheres. The product is dissolved again. After the ultrasonic water bath, 1 mL tetraethyl orthosilicate (TEOS) is added drop by drop to obtain the SiO2/Fe3O4 magnetic microspheres by the ultrasonic and water-bath stirring. The magnetic microspheres are dissolved in 10 mL 3% chitosan solution. Chitosan/SiO2/Fe3O4 (CSF) magnetic adsorbent is obtained after ultrasonic agitation, and chitosan-biomodified iron oxide adsorbent (EDCSF) is obtained by the ethylene diamine tetraacetic acid (EDTA) modification. After the adsorbent is obtained, the biomaterial is characterized, and its performance of adsorbing heavy metals in water is tested as an adsorbent. In the experiment, the Fourier Transform Infrared Spectroscopy (FTIR) is used to verify that EDTA successfully modifies the surface of the CSF magnetic adsorbent. Through the morphology analysis and nitrogen adsorption–desorption test, EDTA cross-linked with the amino group of chitosan through carbodiimide can cause a decrease in the related physical indexes of the material. Thermogravimetric analysis (TGA) and hysteresis loop tests show that although the magnetism of CSF and EDCSF decreases, the solid–liquid separation is achieved in a relatively short time under the action of magnets. In the adsorption test, EDCSF shows an ideal adsorption performance for Cu(II), Cd(II), and Pb(II) in aqueous solution. With pH = 4.7 and at normal temperature, the maximum saturated adsorption capacity of EDCSF for Cu(II), Cd(II), and Pb(II) is 0.696 mmol/g, 0.586 mmol/g, and 0.562 mmol/g, respectively.

Functionalized graphene oxide/sodium alginate beads with ion responsiveness for uranium trapping

Uranium as a strategic and non-renewable resource has been paid close attention to its efficient recovery and reuse from uranium-containing wastewater. Here, a composite bead was prepared by functionalized graphene oxide and sodium alginate (L-Lys-GO/SA) with ion-stimuli responsiveness for achieving U(VI) adsorption. The L-Lys-GO/SA-60 composite beads can selectively adsorb U(VI) with the maximum adsorption capacity (qmax) of 704.22 mg/g. Interestingly, the composite beads will swell under the stimulation of ions, which is more conducive to rapid solid-liquid separation and U(VI) recovery at low energy consumption. More importantly, the composite beads also exhibit high reusability of U(VI) adsorption with excellent life span of 80.11 % adsorption rate after 9 cycles, meaning that the composite beads and technology may be used in extraction and production for U(VI) from uranium-containing wastewater.

Synthesis of magnetic core–shell Fe3O4@MoS2-Ag composite for the efficient photocatalytic reduction of Cr(VI)

An Ag decorated magnetic core–shell Fe3O4@MoS2 composite was synthesized in this work to improve the photocatalytic performance and solid–liquid separation of MoS2 based materials. The composite was evaluated by UV–vis IS-NIR spectrometer, photoluminescence (PL) spectra, XRD, XPS, EDS, EIS and was devoted to reduce the toxicity of wastewater which contains hexavalent chromium(Cr(VI)) for its potential economic value. The results have shown that the core–shell structure effectively inhibits the stack of nanosheets, increases the specific surface area of the material, and exposes more active sites. Besides, loading Ag can effectively promote the migration of photogenerated electrons and improve the photocatalytic performance. On this basis, the better separability and retrievability which got form the magnetic core–shell Fe3O4 may immensely promote the photodegradation technique of hexavalent chromium (Cr (VI)) and provided a new strategy for photocatalytic degradation of industrial industrial wastewater that containing hexavalent chromium (Cr (VI)).

Removal of small elemental sulfur particles by polysulfide formation in a sulfidic reactor

For over 30 years, biological gas desulfurization under halo-alkaline conditions has been studied and optimized. This technology is currently applied in already 270 commercial installations worldwide. Sulfur particle separation, however, remains a challenge; a fraction of sulfur particles is often too small for liquid-solid separation with conventional separation technology. In this article, we report the effects of a novel sulfidic reactor, inserted in the conventional process set-up, on sulfur particle size and morphology. In the sulfidic reactor polysulfide is produced by the reaction of elemental sulfur particles and sulfide, which is again converted to elemental sulfur in a gas-lift reactor. We analyzed sulfur particles produced in continuous, long term lab-scale reactor experiments under various sulfide concentrations and sulfidic retention times. The analyses were performed with laser diffraction particle size analysis and light microscopy. These show that the smallest particles (< 1 µm) have mostly disappeared under the highest sulfide concentration (4.1 mM) and sulfidic retention time (45 min). Under these conditions also agglomeration of sulfur particles was promoted. Model calculations with thermodynamic and previously derived kinetic data on polysulfide formation confirm the experimental data on the removal of the smallest particles. Under the ‘highest sulfidic pressure’, the model predicts that equilibrium conditions are reached between sulfur, sulfide and polysulfide and that 100% of the sulfur particles <1 µm are dissolved by the (autocatalytic) formation of polysulfides. These experiments and modeling results demonstrate that the insertion of a novel sulfidic reactor in the conventional process set-up promotes the removal of the smallest individual sulfur particles and promotes the production of sulfur agglomerates. The novel sulfidic reactor is therefore a promising process addition with the potential to improve process operation, sulfur separation and sulfur recovery.

A novel approach for nature gas hydrate separation: Downhole spiral-cyclone coupled hydraulic in-situ separation

The weakly cemented mixture slurry which is formed by the natural gas hydrate (NGH) solid-state fluidization mining method that is composed of natural gas hydrate, sediment and water. The downhole cyclone of NGH needs to deal with such problems as high viscosity, narrow radial working space, and difficult to adjust the split ratio. Directly using the conventional solid-liquid cyclone structure for downhole sand removal cannot obtain good separation performance. And the conventional separator does not have a tubular structure suitable for solid fluidization exploitation of NGH. Therefore, in order to solve the problem of weak cementation between NGH and sediment due to large sand production during NGH exploitation, this study proposes a new method to separate weakly cemented natural gas hydrate based on the principle of spiral-cyclone coupling. And the model of spiral-cyclone separator was established. This method can break weakly cemented solid-phase particles in the slurry, and the effective separation and removal of ultra-fine sediment with cross-scale and micron size. The research also designs and optimizes the separation device for NGH sand removal. According to numerical simulation and theoretical analysis, the separation efficiency is greater than 60% when the particle size is larger than 5 µm and the inlet velocity is between 2 m/s and 10 m/s. The research results show that the proposed spiral-cyclone separation method has the characteristics of high separation efficiency, strong sand removal, and can break the cementation bond between the sediment and natural gas hydrate, which is a high-efficiency solid-liquid separation technology.