Synthesis of CuO x /TiO2 Photocatalysts with Enhanced Photocatalytic Performance.

CuO x /TiO2 co-photocatalysts with various Cu loading contents were synthesized by an impregnation method, and their photocatalytic activities were evaluated by photodegradation of organic pollutants under visible light illumination. The as-prepared CuO x /TiO2 composites exhibited a unique structure, in which CuO x clusters with about 2-3 nm nanocrystals were uniformly distributed on the TiO2 cube. The mesoporous Ti3+/TiO2 substrate with a uniform pore structure greatly improved the uniformity of the loaded Cu, wherein Ti3+ acted as a reducing agent for reducing Cu2+ to Cu+ and Cu0. The reversible process of the Cu species between Cu+ and Cu0 markedly enhanced the photocatalytic activity of the CuO x /TiO2 co-photocatalyst, by promoting the transfer of photogenerated electrons and suppressing the recombination of photogenerated electron and hole pairs. The synergistic effect between CuO x and TiO2 also played an important role in enhancing the photocatalytic activity of the CuO x /TiO2 co-photocatalyst. The results indicated that CuO x /TiO2-1 had the highest photocatalytic efficiency, which was 1.5 times higher than that of the commercial nano-TiO2 P25 under visible light, and demonstrated a good stability even after five recycles. This structural design and the valence control strategy for the Cu atom provide an idea that facilitates the utilization of visible light and the improvement of the photocatalytic activity of TiO2, promoting the practical application of the TiO2 photocatalyst.

Steel slag as a potential adsorbent for efficient removal of Fe(II) from simulated acid mine drainage: adsorption performance and mechanism.

Acid mine drainage is an extraordinarily acidic and highly heavy metal ion-contaminated leachate, seriously threatening the environment. In this work, an industrial solid waste of steel slag is the adsorbent to remediate the simulated acid mine drainage containing a large amount of Fe(II) ions. Due to the excellent physicochemical properties and structures, steel slag exhibited remarkable Fe(II) removal performance. Its maximum removal efficiency was up to 100%. The initial pH, the dosage and particle size of steel slag, and initial concentration of heavy metal ions on Fe(II) removal efficiency were determined. The pseudo-second-order model and Freundlich isotherm model well described the adsorption behavior of steel slag, implying that the adsorption of Fe(II) by steel slag was mainly multilayer chemisorption. The thermodynamic study demonstrated that the adsorption process was endothermic and spontaneous; the enthalpy change was calculated to equal 91.21 kJ/mol. Mechanism study showed that the entire removal process of Fe(II) by steel slag was completed by electrostatic adsorption, chemical precipitation, and surface complexation in cooperation, and the chemical precipitation was the dominant mechanism. Meaningfully, this study provides a valuable strategy and path for engineering applications of AMD remediation by steel slag, which is prospective as an ideal candidate for Fe(II) ions elimination, inspiring the future development of "Treating the wastes with wastes."

Dealkalization and Leaching Behavior of Fe, Al, Ca, and Si of Red Mud by Waste Acid from Titanium White Production.

Dealkalization is the necessary step for the multipurpose use of red mud (RM), and acid leaching is a productive method to realize the dealkalization of RM. Most researches focus on recovering metals from the highly alkaline waste by pure acid leaching or stabilization by dealkalization. In this study, according to the strong alkalinity of RM and strong acidity of the waste acid from titanium dioxide production, the waste acid was used for the dealkalization of RM. The effects of leaching temperature, reaction time, the concentration of waste acid, liquid-solid ratio (L/S), and stirring rate on the dealkalization of RM were investigated, and the main metal ions in the dealkalization solution were analyzed. The results show that the leaching ratio of sodium can reach 92.3591% when the leaching temperature is 30 °C, the reaction time is 10 min, the concentration of waste acid is 0.6238 mol/L, the L/S is 4:1, and the stirring rate is 300 rpm. The residual alkali content in the treated RM is 0.2674%, which is a reduction to less than 1%. The phase analysis results show that the sodalite and cancrinite in RM are dissolved, decomposed, and transformed after acid leaching. Therefore, RM meets the requirements of building materials after dealkalization, which provides further development as building material products.

Mechanism of Acid Mine Drainage Remediation with Steel Slag: A Review.

Technologies for remediation of wastewater by industrial solid waste have recently attracted interest. Acid mine drainage is an extraordinarily acidic and highly heavy metal ions contaminated leachate which posed some challenges for the environment. Nonetheless, steel slag shows significant potential application prospects in wastewater treatment, due to its excellent physicochemical properties and structures. This paper elaborately reviewed the structure, properties, water treatment applications of steel slags, and the mechanism for removing heavy metal ions from acid mine drainage, discussed the problems existing in industrial wastewater treatment by steel slag, and proposed the solutions for future research, aiming to provide theoretical references for the practical application of steel slag in AMD treatment.

Simultaneous Removal of Nitrogen and Refractory Organics from a Biologically Treated Leachate by Pulse Electrochemical Oxidation in a Multi-channel Flow Reactor.

Electrochemical oxidation (EO) is often used in the advanced treatment of refractory wastewater. However, in a conventional EO process of direct-current (DC) power supply, oxide layers often form on the anodes, which not only hinder the oxidation reaction on them but also cause higher energy consumption. In this paper, a biologically treated leachate (BTL) of municipal solid waste (MSW) was comparably treated by EO with DC (DC-EO), monopulse (MP-EO), and double pulse (DP-EO) power source models in a home-made multi-channel flow reactor. The effects of process parameters of current density (I A), superficial liquid velocity (U L), pulse frequency (f P), duty ratio (R D), and so forth on the removal efficiency of chemical oxygen demand (COD) (RECOD), total organic carbon (TOC) (RETOC), and total nitrogen (TN) (RETN) were investigated simultaneously. Average energy consumption () and organic composition of the treated effluent of DC-EO and MP-EO were also compared comprehensively, and a new mechanism of MP-EO has been proposed accordingly. Under optimal conditions, 2 L of BTL was treated by MP-EO for 180 min, and the RECOD, RETOC, and RETN could reach as high as 80, 30, and 80%, respectively. Compared with DC-EO, the of MP-EO is reduced by 69.27%. Besides, the kinds of organic matter in the treated effluent of MP-EO are reduced from 53 in the BTL to 11, which is much less than in the DC-EO process of 29 kinds. Therefore, the MP-EO process exhibits excellent removal performance of organics and TN and economic prospects in the treatment of refractory organic wastewater.

Lattice Thermal Transport in the Homogeneous Cage-Like Compounds Cu3 VSe4 and Cu3 NbSe4 : Interplay between Phonon-Phase Space, Anharmonicity, and Atomic Mass.

Understanding the correlation between crystal structure and thermal conductivity in semiconductors is very important for designing heat-transport-related devices, such as high-performance thermoelectric materials and heat dissipation in micro-nano-scale devices. In this work, the lattice thermal conductivity ( κ L ) of the cage-like compounds Cu3 VSe4 and Cu3 NbSe4 was investigated by experimental measurements and first-principles calculations. The experimental κ L of Cu3 NbSe4 is approximately 25 % lower than that of Cu3 VSe4 at 300 K. The relevant important physical parameters, including the sound velocity, heat capacity, weighted phonon phase space (W), and third-order force constants along with atomic mass were theoretically analyzed. It is found that W is the dominant parameter in determining the κ L , and the other factors only play a minor role. The physical origin is the relatively "soft" lattice of Cu3 NbSe4 with heavier atomic mass. This research provides deep insight into the correlation between the thermal conductivity and crystal structure and paves the way for discovering high-performance thermal management device and thermoelectric materials with intrinsically low κ L .

Simultaneous Desalination and Removal of Recalcitrant Organics from Reverse Osmosis Leachate Concentrate by Electrochemical Oxidation.

Reverse osmosis (RO) concentrate produced in the municipal solid waste (MSW) leachate treatment process is extremely hard to be treated because of its high color, high salt content, and high concentration of recalcitrant organic compounds. A new multichannel flow reactor with electrode gaps of 5 mm was designed to desalinate and remove organics simultaneously from the RO leachate concentrate (ROLC) by electrochemical oxidation process using the RuO2/IrO2-coated titanium plate (RuO2/IrO2-Ti) as the anodes. The effects of the process parameters of current density (I A), superficial circulating velocity (U L), etc. on the removal efficiency (RE) of the chemical oxygen demand (COD) and average energy consumption () were investigated. The results illustrated that after 3 h of treatment, the RE of COD, Cl-, and color could reach as high as 96.5, 96.7, and 99.6%, respectively. Besides, the of the electrochemical oxidation treatment process is as low as 40.98 kWh/(kg COD), and a new mechanism of the simultaneous removal of COD and desalination has been proposed. This work provides an alternative technology for the treatment of MSW leachate RO concentrate.

The effect of composite PHB coating on the biological properties of a magnesium based alloy.

Magnesium alloys have been widely investigated as biodegradable cardiovascular temporal implants due to their better mechanical properties and biocompatibility, but the rapid degradation limited its application. In this study, the anodic oxidation-Cu structure was used to improve the adhesive strength and stability between poly-ß-hydroxybutyrate (PHB) and magnesium alloys, and the effects of anodic oxidation magnesium alloys with copper film and PHB film (MACP) on human umbilical vein endothelial cells (HUVECs), blood compatibility and antibacterial properties were investigated in this research. As the result, the MACP structure had a stable structure and better corrosion resistance, and significant antibacterial properties. The coating would not affect the original excellent biocompatibility of the magnesium alloy. It was indicated that MACP was a potential surface modification strategy for vascular stents candidate material.

Ozonation of biologically-treated municipal solid waste leachate using an integrated process of O3/Ca(OH)2 and microbubble reactor.

The ozonation process was limited by the relatively low solubility in liquid and low transfer mass efficiency. In this work, O3/Ca(OH)2 was adopted to treat biologically-treated municipal solid waste (MSW) leachate in a microbubble gas-liquid reactor. The residual COD concentration is meeting the discharge standard after treatment. The effects of operating parameters such as Ca(OH)2 dosage, external reactor pressure, liquid temperature, inlet ozone concentration and ozone flow rate on COD removal and mineralization (TOC removal) were studied systematically. This process was able to remove 89.86% of COD, 65.35% of TOC and 92.12% of UV-254 under the optimal conditions. And the intensification mechanism of O3/Ca(OH)2 system was explored through analysing the change of UV-254, 3D-EEM and the organic matters present in the leachate.

Leaching of Valuable Elements from the Waste Chromite Ore Processing Residue: A Kinetic Analysis.

The efficacious treatment and resource utilization of the chromite ore processing residue (COPR) is important for chromate salt production. In this study, the leaching of valuable elements from the waste COPR was investigated. X-ray diffraction (XRD) analysis showed that the COPR mainly contained periclase (MgCr2O4), magnesiochromite ((Fe, Mg) (Cr, Fe)2O4), Fe (Cr, Al)2O4, and MgFeAlO4. The optimum parameters for COPR leaching were as follows: mechanical ball-milling time of 120 min, sulfuric acid concentration (w/w % H2SO4) of 60%, reaction temperature (T) of 403 K, liquid-solid ratio (L/S) of 8 mL/g, and reaction time (t) of 6 h. Under these conditions, the valuable components such as Fe, Al, and Cr were extracted with an ideal leaching efficiency of 94.8, 75.1, and 76%, respectively. The results of the leaching kinetics analysis indicated that the leaching of Fe and Cr from the COPR was controlled by a surface chemical reaction, and the leaching of Al was controlled by diffusion through a product layer. The apparent activation energy of the leaching of Fe, Cr, and Al was calculated to be 23.03, 44.15, and 17.54 kJ/mol, respectively. It is believed that this approach has potential applications for the chromate salt industry because of its advantage of ideal leaching efficiency.

Highly efficient reverse osmosis concentrate remediation by microalgae for biolipid production assisted with electrooxidation.

Phytoremediation of reverse osmosis concentrate (ROC) with microalgae can simultaneously achieve multi-functions of ROC treatment, CO2 mitigation and microalgae biolipid production. But the performances are usually inhibited by high free ammonia nitrogen (FAN) concentration and chromaticity of ROC. To offset these negative effects, an integrated technique including electrooxidation pretreatment and Chlorella vulgaris remediation was proposed, in which the ROC was first pretreated with electrooxidation to decrease FAN and chromaticity, and then the oxidized ROC was remediated with microalgae to reclaim nutrients and produce biolipid. Results showed that FAN was sharply reduced from 53.0 mg N/L to 13.9 mg N/L and chromaticity was decreased from 1600 to 100 Pt-Co via electrooxidation. Possible reaction mechanism of nutrients removal was discussed via electron mass balance. Explanation on chromaticity decrease was revealed by analyzing humic acid conversion path with fluorescence characteristics. During microalgae remediation process, nutrients removal rate, microalgae biomass concentration and lipid yield were effectively enhanced in electrooxidized ROC. Energy balance analysis indicated that microalge lipid energy under current density of 3.25 mA/cm2 basically compensated total input energy despite ROC sterilization. This work provided a promising strategy for large-scale ROC treatment and microalgae biolipid production.

Ozonation process intensification of p-nitrophenol by in situ separation of hydroxyl radical scavengers and microbubbles.

The ozonation efficiency for removal of recalcitrant organic pollutants in alkaline wastewater is always low because of the presence of some hydroxyl radical scavengers. To solve this problem, the O3/Ca(OH)2 system was put forward, and p-nitrophenol (PNP) was chosen to explore the mechanism of this system. The effects of key operational parameters were studied respectively; the Ca(OH)2 dosage 3 g/L, ozone inlet flow rate 3.5 L/min, ozone concentration 65 mg/L, reactor pressure 0.25 MPa, and temperature 25 °C were obtained as the optimal operating conditions. After 60 min treatment, the organic matter mineralized completely, which was higher than the sum of the ozonation-alone process (55.63%) and the Ca(OH)2 process (3.53%). It suggests that the calcium hydroxide in the O3/Ca(OH)2 process possessed a paramount role in the removal of PNP. The liquid samples and the precipitated substances were analyzed by gas chromatography mass spectrometry, X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy; it was demonstrated that Ca(OH)2 could accelerate the generation of hydroxyl radical and simultaneously in situ separate partial intermediate products and CO3 2- ions through some precipitation reactions.

Fluid flow signals processing based on fractional Fourier transform in a stirred tank reactor.

The analysis of fluid flow signals and the characterization of fluid flow behavior are of great importance for two-phase flow studies. In this work, the fractional Fourier transform (FRFT), which was based on the optimum order calculated by stepping search method, was proposed to extract the characteristics of fluid flow signals. Meanwhile, the largest Lyapunov exponent (LLE), which is an indication of the chaotic degree of mixing process, was adopted to quantify fluid flow behavior. The maximum amplitude (MA) and LLE value were taken together to inquire into the relationship between the characteristics of fluid flow signals and the characterization of fluid flow behavior. In addition, differences between the two adjacent values (AD) and the maximum differences (MD) are employed to further analyze the differences in behavioral characterization with MA and LLE. The results show that the MA value performs the same increasing trend as the LLE value when the gas flow rate and agitation speed increase. AD and MD values of the MA are one to two orders of magnitude greater than those of the LLE. The eigenvalues (MA) solved by the FRFT method is facilitates capturing small changes owing to changes in external conditions. These findings can provide new ideas for the extraction and characterization of fluid flow behavior.

Microalgal lipids production and nutrients recovery from landfill leachate using membrane photobioreactor.

The aim of this work was to realize high-efficiency nutrients recovery from landfill leachate (LL) for microalgal lipids production. Negative effects of LL on microalgal lipid synthesis was revealed and a scalable membrane-based tubular photobioreactor (SM-PBR) was proposed to offset these negative effects. Microalgal biomass concentration was improved from 0 g/L in the traditional PBR to 2.13 g/L in the SM-PBR. Major operating conditions were optimized to enhance nutrients recovery and lipid productivity. The maximum N recovery efficiency of 74.31% and the maximum daily lipid production of 404.98 mg/d were obtained under the volume ratio of 5:3 (microalgae culture/LL stream) and phosphate feeding concentration of 50 mg/L. The obtained lipid was convinced to have a good combustion and anti-degradation property, with high cetane number (>52%) and low linolenic acid content (<12%). The SM-PBR provided a feasible approach for large-scale microalgal lipid production with LL.

High-efficiency nutrients reclamation from landfill leachate by microalgae Chlorella vulgaris in membrane photobioreactor for bio-lipid production.

Using microalgae to treat landfill leachate is a promising approach due to the effective nutrients reclamation ability and additional profit of bio-lipid production. To offset the negative effect of landfill leachate on microalgae cells, a membrane photobioreactor (m-PBR) was adopted in the study, in which microalgae biomass concentration was improved from 0.66 in traditional photobioreactor (T-PBR) to 0.95 g/L. Nutrients reclamation efficiencies of leachate were analyzed according to elemental balance, and the results showed that nitrogen reclamation efficiency was generally lower than 50% while phosphorus reclamation efficiency was higher than 70% due to elemental availability. The nitrogen and phosphorus reclamation efficiencies in the m-PBR were much higher than that in the T-PBR. Besides, lipid produced from the m-PBR had a high cetane number of 60.96% and low linolenic acid content of 8.32%, which demonstrated good combustion properties of the microalgae-based lipid when using landfill leachate as nutrients source.

Electrochemical oxidation of recalcitrant organic compounds in biologically treated municipal solid waste leachate in a flow reactor.

Biologically-treated municipal solid waste (MSW) leachate still contains many kinds of bio-recalcitrant organic matter. A new plate and frame electrochemical reactor was designed to treat these materials under flow conditions. In the electrochemical oxidation process, NH3 and color could be easily removed by means of electro-generated chlorine/hypochlorite within 20 min. The effects of major process parameters on the removal of organic pollutants were investigated systematically. Under experimental conditions, the optimum operation parameters were current density of 65 mA/cm2, flow velocity of 2.6 cm/sec in electrode gap, and initial chloride ion concentration of 5000 mg/L. The COD in the leachate could be reduced below 100 mg/L after 1 hr of treatment. The kinetics and mechanism of COD removal were investigated by simultaneously monitoring the COD change and chlorine/hypochlorite production. The kinetics of COD removal exhibited a two-stage kinetic model, and the decrease of electro-generated chlorine/hypochlorite production was the major mechanism for the slowing down of the COD removal rate in the second stage. The narrowing of the electrode gap is beneficial for COD removal and energy consumption.

Synergistic degradation of methyl orange in an ultrasound intensified photocatalytic reactor.

An original ultrasound (US) directly intensified photocatalytic reactor was designed to degrade azo dye pollutant methyl orange (MeO) using Degussa TiO(2) as the photocatalyst. The sonolytic, photocatalytic and sonophotocatalytic degradation of MeO in the new reactor and the synergistic effect between sonolysis and photocatalysis were investigated. Effects of operation parameters i.e., US power, TiO(2) dosage, liquid circulation velocity and air flow rate on degradation efficiency were investigated and optimized. The results showed that all parameters have optimal values for the sonophotocatalytic degradation of MeO, and the optimum conditions for the new process are US power 600 W, TiO(2) dosage 3g/L, liquid circulation velocity 4.05×10(-2) m/s and air flow rate 0.2 L/min. Under the optimum conditions, 91.52% MeO had been degraded within 1h, and the combination of sonolysis and TiO(2) photocatalysis exhibited an obvious synergetic effect.

Photocatalytic degradation of bisphenol A using an integrated system of a new gas-liquid-solid circulating fluidized bed reactor and micrometer Gd-doped TiO2 particles.

A new gas-liquid-solid circulating fluidized bed photocatalytic reactor (GLSCFBPR) with internally placed multi-layered UV lamps was developed. Micrometer Gd-TiO2 particles and commercial nanometer P25-TiO2 were chosen as the photocatalysts, and the hazardous substance bisphenol A (BPA) was chosen as the model pollutant to investigate the performance of this new photocatalytic system. The results showed that the photocatalytic degradation efficiency of the micrometer Gd-TiO2 particles was similar to that of the nanometer P-25 particles at their respective optimum dosage but the former could be easily separated out by gravity. After investigating the effects of process parameters on the photocatalytic BPA degradation, the response surface method (RSM) was further used for process optimization. The interactions among process parameters, i.e., TiO2 concentration, superficial gas velocity and superficial liquid velocity were discovered and a related analysis was carried out to explore the underlying mechanism. A quadratic mathematic model was established and performed satisfactorily when used for prediction. The optimum conditions for this new process were as follows: TiO2 concentration 4.5 g/L, superficial gas velocity 7.83 x 10(-3) m/sec and superficial liquid velocity 8.65 x 10(-3) m/sec.

Simultaneous removal of ammonia, P and COD from anaerobically digested piggery wastewater using an integrated process of chemical precipitation and air stripping.

The paper presented an efficient integrated physicochemical process, which consists of chemical precipitation and air stripping, for the simultaneous removal of NH(3)-N, total P and COD from anaerobically digested piggery wastewater. In the integrated process, Ca(OH) (2) was used as the precipitant for NH(4)(+), PO(4)(3-) and organic phosphorous compounds, and as the pH adjuster for the air stripping of residual ammonia. The possibility of the suggested process and the related mechanisms were first investigated through a series of equilibrium tests. Laboratory scale tests were carried out to validate the application possibility of the integrated process using a new-patented water sparged aerocyclone reactor (WSA). The WSA could be effectively used for the simultaneous removal of NH(3)-N, total P and COD. 3g/L of Ca(OH) (2) is a proper dosage for the simultaneous removal. The simultaneous removal of NH(3)-N, total P and COD in the WSA reactor could be easily optimized by selecting a proper air inlet velocity and a proper jet velocity of the liquid phase. In all the cases, the removal efficiencies of the NH(3)-N, total P and COD were over 91%, 99.2% and 52% for NH(3)-N, total P and COD, respectively. The formed precipitates in the process could be easily settled down from the suspension system. Therefore, the integrated process provided an efficient alternative for the simultaneous removal of NH(3)-N, total P and COD from the wastewater.

Air stripping of ammonia in a water-sparged aerocyclone reactor.

Air stripping of ammonia is a widely used process for the pretreatment of wastewater. Scaling and fouling on the packing surface in packed towers and a lower stripping efficiency are the two major problems in this process. New equipment that is suitable for the air stripping of wastewater with suspended solids has been developed. Air stripping of ammonia from water with Ca(OH)2 was performed in the newly designed gas-liquid contactor, a water-sparged aerocyclone (WSA). WSA exhibited a higher air stripping efficiency and an excellent mass transfer performance, it also consumed less air compared with stripping tanks and packed towers. In addition, no scaling and fouling was observed in the inner structure of the WSA. During the stripping process, the stripping efficiency and mass transfer coefficient naturally increases with the liquid phase temperature and air flow rate. There is a critical value for the air flow rate over which stripping efficiency and the mass transfer coefficient increases rapidly. An efficient air stripping of ammonia should be conducted at a higher ambient temperature (>25 degrees C), and a higher air flow rate (>1.4 l/s).