Arsenic can cause environmental pollution and also affect mineral processing efficiency. To determine the mechanism of separating arsenic from minerals, microwave roasting tests were conducted using Hunan arsenic sulfide gold concentrate as a raw material. The heating behaviour of gold concentrates under microwave irradiation was analysed. The effects of roasting temperature, reaction time, and oxygen content on arsenic removal were investigated. Temperature has the greatest effect on arsenic removal, followed by reaction time and oxygen content. The optimum parameters were determined experimentally. The removal rate of arsenic was 93.16% (gas supply: 4 L min(-1), reaction temperature: 650 degrees C, duration: 15 min). Scanning electron microscopy analysis of the minerals after microwave roasting and conventional roasting showed that there are more cracks on the surface of minerals after microwave roasting, and the specific surface area is larger. The reaction mechanism of arsenic separation from gold concentrate during microwave roasting is discussed.

In this research, ZnFe2O4 was employed as heterogeneous catalyst for the degradation of tetracycline hydrochloride (TCH) by a novel combined microwave-induced (MW-induced) and photocatalytic oxidation. The ZnFe2O4 catalyst was synthesized using co-precipitation method, and characterized by XRD, TEM, BET and UV-Vis DRS. A microwave electrodeless discharge lamp (MEDL) was introduced to this process as a light source. 91.6% of TCH degradation was obtained in MW/MEDL/ZnFe2O4 system in 4 min. ZnFe2O4 catalyst had both microwave-catalytic and visible-light photocatalytic activities. The operation parameters, such as microwave output, catalyst dosage, initial pH and recycle runs, showed different influence on TCH degradation. The analysis of degradation mechanism indicated that h(+) was the main active species for TCH degradation and little O-2 active species generated in MW/MEDL/ZnFe2O4 system. The decomposition intermediates of TCH were identified by LC-MS. (C) 2018 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

P-nitrophenol (PNP) is considered as a priority pollutant due to its toxicity, non-biodegradation and high persistence in the environment. In this work, microwave (MW) acted as an assistant to enhance the degradation efficiency of PNP in MnFe2O4 activated peroxymonosulfate (PMS) catalytic oxidation. The magnetic MnFe2O4 particles were prepared using the co-precipitation method. The performance of PMS/MnFe2O4/MW is evaluated by the degradation efficiencies of PNP under varied conditions. The results showed that the degradation efficiency of PNP was greatly increased by the use of microwave radiation. 97.2% of PNP was degraded in 2 min using PMS/MnFe2O4/MW. The PNP degradation increased with higher PMS concentration, MnFe2O4 dosages and microwave output, while a slight decrease in PNP degradation was observed when the PMS concentration exceeded 2.5 mM. PNP degradation showed no dependence on initial pH, indicating that PMS/MnFe2O4/MW can be conducted at a wide range of pH value. Moreover, MnFe2O4 remained high catalytic activity after five runs. The mechanism of catalytic degradation was investigated by scavenging test and XPS measurement. Using methanol and tertbutanol as radical scavengers, the dominant radicals of the catalytic oxidation in the PNP degradation were identified as sulfate radicals rather than hydroxyl radicals. XPS measurement showed that both Mn(II)/Mn(III) and Fe(III)/Fe(II) were involved in the activation of PMS in this system. Additionally, the mechanism of microwave activation in PMS/MnFe2O4/MW system is also discussed. The enhancement of electron transfer and the increasing of reactants collision numbers are two potential mechanisms for the non-thermal effect of microwave activation. (C) 2015 Elsevier B.V. All rights reserved.

A novel method for removing arsenic (As) from intractable arsenopyrite (FeAsS)-bearing mine tailings was investigated that used a microwave technique. Although the tailings were poor microwave absorbers, absorption was indirectly assisted by adding various microwave-absorbing materials (MAMs), including MnO2 (oxidant), C (reductant), Fe3O4 and Fe2O3. The results revealed that the type of MAM and the microwave runtime significantly affected the efficiency of As-removal from the tailings and the magnetic effects of the reaction residuals. Compared with MnO2 and C, the best As-removal efficiencies of the tailings and the magnetic effects of the reaction residuals were obtained using Fe3O4 (90.12%, 24997.03 x 10(-8) m(3)/kg, in 4 min) and Fe2O3 (92.10%, 19774.73 x 10-8 m3/kg, in 14 min). In addition, their As-removal efficiencies positively contributed to the magnetic effects, which increased with the microwave runtime. The obtained products were characterized by using a variety of analytical techniques (e.g., SEM, EDAX and XRD). Overall, Fe2O3 and Fe3O4 underwent similar As-removal pathways and magnetic products. Arsenic was mainly removed in the form of As (elemental form) and AsS in the oxygen-free atmosphere, and As2O3 was removed in the oxidizing atmosphere. Meanwhile, the arsenopyrite (FeAsS) and pyrite (FeS2) in the tailings, mixed with Fe2O3 or Fe3O4, were mainly converted into valuable pyrrhotite (Fe1-xS and FeS) and magnetite (Fe3O4) in the oxygen-free atmosphere. This study provides a feasible and environmentally friendly method for removing arsenic from tailings (or minerals), regardless of their microwave-absorbing properties. (C) 2015 Elsevier B.V. All rights reserved.

Alumina trihydrate (ATH), one of typical complexes of aluminum (Al), was selected to study its effects on the formation of biofilms settled on inert carriers made of polyethylene terephthalate (PET) filaments. Four identical biological reactors were developed to cultivate biofilms under a series of ATH concentrations. Three-dimensional elastic inert PET carriers were used as the biofilm substrata. The biofilm characteristics including the amounts of total biofilm, extracellular polymeric substances (EPS) productions, active biomass, and microbial activity, were investigated. The impact of Al toxicity on the formation of biofilms was also discussed. The results showed that the colloidal ATH was easily adhered to the inert carriers, and the effects of ATH on the formation of biofilms colonized on the inert carriers were clearly observed. Compared to the biofilm characteristics when ATH was absent, the presence of ATH could increase the amounts of total biofilm production, EPS production, active biomass, and microbial activity: when the ATH concentrations reached 0.1, 0.2, and 0.5 mg/L (as Al3+), the total biofilm amount would increase to 1.44, 2.14, and 2.60 times, respectively, and the EPS production would enhance to 1.21, 1.60, and 1.85 times, respectively. Similar ratios for EPS production were also obtained for the corresponding active biomass and microbial activity. These results suggested that ATH is beneficial to the formation of biofilms settled on inert carriers, and the impact of Al toxicity seems to be insignificant in this study on the colonized microbes and the biofilm formation, probably due to the low ATH concentration (0.5 mg/L as Al3+ in maximum) in the reactors.

A novel magnetic carrier with surface magnetic field of 4 mT was developed for studying the magnetic enhanced bio-effect on nitrification. The bio-effect on nitrificaton induced by the magnetic carrier was studied by comparing the performance of sequencing batch biofilm reactors filled with magnetic (MC) and non-magnetic (NMC) carriers. The result showed that the bioreactor with MC had better performance for nitrification than bioreactor with NMC. During the biofilm culturing period, the time required for nitrification formation in biofilm of the MC reactor was 25% less than that for the NMC reactor. The results also showed that the ammonium oxidation rate of the MC reactor was 1.6-fold faster than that in the NMC reactor at high influent NH4-N concentration, while nitrite oxidation rate was always accelerated regardless of influent NH4-N concentration. The specific oxygen uptake rate analysis revealed that ammonia and nitrite oxidation activities in biofilm of the MC reactor were 1.65 and 1.98 times greater than those of the NMC reactor, respectively.

The change of sludge characteristic and dewaterability was inspected using microwave irradiation in sludge pretreatment.The microwave powers used were 500,750 and 900 W,respectively.Sludge temperature,particle size,extracellular polymeric substance content,soluble chemical oxygen demand,capillary suction time,and specific resistance of filtration were measured and the related mechanism of microwave treatment was also discussed.The results indicate that the proper microwave condition could not only increase sludge particle size,but also improve sludge dewaterability.After irradiated at the microwave energy of 900 W with the contact time of 60 s,the sludge particle size increases by 71.40%.The capillary suction time and specific resistance of filtration decrease by 42.70% and 73.11%,respectively.Increasing the contact time not only consumes more energy but also decreases sludge dewaterability after obtaining optimal microwave condition.

The combined effects of flow rate and light intensity on the characteristics of biofilm grown on three-dimensional elastic carriers were investigated in this study, to assess as well as to provide guidance for in-situ remediation of polluted ground water using biofilm method. Four identical biological reactors were used to cultivate biofilm on the carriers made from polyethylene terephthalate (PET), at varying flow rates (0.2, 0.4 and 0.8 m(3).m(-2).s(-1)) and under artificial lighting (approximately 130 mu mol photons.m(-2).s(-1)) or dark conditions. The results showed that the characteristics of biofilm, including total biomass, extracellular polymeric substances (EPS), active biomass and microbial activity, were all significantly enhanced with increasing flow rate and under light conditions, indicating that the synergistic effect the high flow rates and stronger light on the improvement of biofilm characteristics.

One of the main obstacles to the agricultural use of the sludge produced in wastewater treatment plants are heavy metals that have accumulated. Electrokinetic treatment can be used to remove these heavy metals, but the process is time consuming, sometimes lasting several days. In this study, the effects of different potential gradients were investigated. Electrokinetic experiments were conducted under constant potential gradients (1 V/cm, 3 V/cm, and 5 V/cm) with a treatment time of 16 hours. Results showed that the most efficient removal of metals was achieved at a potential gradient of 5 V/cm. Average removal efficiencies of heavy metals were 30.29% for copper, 43.52% for nickel, and 33.38% for zinc. Accumulation of metals occurred at a distance of 7 cm from the anode at a potential gradient of 1 V/cm. Results of the sequential extraction and sludge pH profiles show that an acidic front generated at the anode reservoir flushed across the sludge chamber and that the higher potential gradient increased the migration velocity, which aided the dissociation and desorption of metals. Furthermore, the use of higher potential gradients made it possible to remove heavy metals from sludge cells in a shorter period of time.

The potential effects of potassium ferrate (K2FeO4) on sludge dewatering under different pH values (between 3 and 8) and the mechanism of its reaction were investigated in this study. Specific resistance of filtration (SRF) was used to evaluate sludge dewaterability. Sludge water distribution was measured by the drying test. Sludge floc structure was observed by microscopic examination. Soluble chemical oxygen demand (SCOD), extracellular polymeric substances (EPSs) content, sludge disintegration degree and sludge particle size were measured to explain the observed changes in sludge dewaterability. The results indicated that the potassium ferrate pretreatment at pH 3 enhanced sludge dewaterability, while potassium ferrate pretreatment caused deterioration of sludge dewaterability at pH values of 4–8. At pH 3, sludge dewaterability increased with the increase of potassium ferrate, then decreased slightly when the dosage of potassium ferrate was greater than 1200 mg/L. The results showed that a potassium ferrate dosage of 1200 mg/L at pH 3 was an ideal condition, yielding maximum sludge dewaterability characteristics by generating sludge with optimal disintegration, and EPSs concentration. However, particle size changed slightly after potassium ferrate pretreatment at pH 3.

7 ultrasonic energy levels ranging from 0~26 000 kJ/kg TS were used to disintegrate excess sludge to investigate the changes in chemical characteristics.Results indicated that ultrasonication process slightly disrupted floc structure and disintegration effect was weak for ultrasound energy dosages lower than 1 000 kJ/kg TS,and destroyed easily floc structure and broke up cell walls for ultrasound energy dosages above 5 000 kJ/kg TS,as evidenced by increases in SCOD,EPS content and inorganic nitrogen.Effects were enhanced at higher applied sonication energies.Correlation analysis showed that many of the changes were directly dependent upon the amount of ultrasonic energy applied.Ultrasonication can significantly change chemical characteristics of sludge.Sonication at the dose of 26 000 kJ/kg TS increased COD disintegration degree of 25.3% only,comparing the untreated sludge.Thus SCOD analysis indicated that an ultrasound energy of 26 000 kJ/kg TS was suboptimal for thoroughly disintegrating sludge,and as this corresponded to the highest energy examined in the study,an optimal value was never identified.

The comparative study on the electro-generation of H2O2 using an activated carbon fiber cathode and graphite cathode was investigated. The effect of the operating parameters on the H2O2 generation concentration and current efficiency, such as the initial pH, current density and electrolyte concentration, was also evaluated. The results revealed that the activated carbon fiber cathode was more effective compared to the graphite cathode. The maximum value of H2O2 concentration could be achieved with pH 3.00, current density 8.89 mA/cm2 and electrolyte concentration 0.05 mol/L. However, due to the formation of competitive electrode reactions, the current efficiency of this electrolysis system is lower than other electrolysis system. In addition, a new kinetic model was established to well describe the electro-generation of H2O2. The experimental data were fitted well using the kinetic model.

BACKGROUND: To extend the working pH range of electro-Fenton, activated carbon fibre cathode (ACF) supported nano-Fe0 catalysts were prepared by electo-deposition and applied to treat a dye effluent in a neutral aqueous medium. The morphology of the Fe0/ACF cathode was characterized by X-ray diffraction and scanning electron microscopy. The experimental conditions, such as the initial pH, dye concentration and current density of the degradation of the dye effluent were investigated. A pseudo-first-order model was used to simulate the experimental results. RESULTS: Compared with Fe2+ and Fe3+, the degradation of Orange II solution by an Fe0/ACF cathode was shown to achieve much better results at neutral pH values. Additionally, the dissolved iron concentration in the solution was also evaluated. The results showed that 0.79 mg L−1 of total iron was present after 120 min reaction time at neutral pH, suggesting that the Fe0/ACF cathode can be used for a long time and is reusable under neutral pH conditions. A complete description of the possible degradation mechanism in solution is provided. CONCLUSION: The high catalytic activity of this cathode is probably due to the efficient electrotransfer at the Fe0/iron oxide interface. All this demonstrates that Fe0/ACF is a good and promising cathode for the neutral electro-Fenton process. Copyright © 2010 Society of Chemical Industry

Seven ultrasonic energy levels ranging from 0 to 26 000 kJ x kg(-1) were used to disintegrate excess sludge to investigate the changes in physical characteristics. The results indicated that the ultrasonication process destroys floc structure, facilitates the transfer of matter into the aqueous phase, and breaks up cell walls, which facilitated the improvement of settleability and biodegradability. Low ultrasonic energies could improve the settleability and supernatant turbidity. When the energy of 1 000 kJ x kg(-1) was applied into the sludge, the maximal settling velocity of sludge at 45 min was increased by 18.58% and the supernatant turbidity at 24 h was decreased by 43.52%, compared to the control. However, high ultrasonic energies deteriorated the characteristics. The maximal settling velocity was reduced by 37.03% and the supernatant turbidity was increased by 10 times in comparison to the control when the energy dose of 26 000 kJ x kg(-1) was applied. With the increases in ultrasonic energies, the particle size was significantly decreased, the soluble solids increased and the floc clusters dispersed. These changes in sludge characteristics were directly dependent upon the amount of ultrasonic energy applied. Furthermore, these characteristics correlated significantly to the ultrasonic energy. 1000 kJ x kg(-1) was the optimal energy that improved the settleability and the supernatant turbidity, and that destructed the floc structure of sludge. On the other hand, particle size was an important factor affecting sludge settleability and supernatant turbidity. The optimal values led to best settleability and turbidity.

This study investigates the physical and chemical characteristics of sludge treated with controlled levels of electric field. The results indicated that the potential gradient and contact time strongly influenced the physical and chemical characteristics of sludge. Based on the settling velocity measurements, a potential gradient of 6V/cm with a treatment time of 10 min is recommended as an optimal condition for improving sludge settling. For sludge disintegration, applying a higher potential gradient and a longer treatment time to the sludge are more efficient than applying lower levels. The results of the experiments presented here show that an electric field not only disintegrates sludge and destroys microbial cells but also removes and solubilizes organic substances. Possible mechanisms of electric field treatment are also discussed. Crown Copyright (C) 2011 Published by Elsevier B.V. on behalf of The Institution of Chemical Engineers. All rights reserved.

This work evaluates the effect of low frequency ultrasonic irradiation on the sonoelectro-Fenton (SEF) oxidation process in an acid aqueous medium. Ultrasonic irradiation significantly increases the H2O2 production rate and reduces the time needed to reach the maximum H2O2 concentration. In addition, ultrasonic irradiation has a considerable effect on the degradation of the cationic red X-GRL in the SEF process. A pseudo-first-order model was used to simulate the experimental results, and this revealed that the decolorization rate increased with the ultrasonic power in the SEF process. Furthermore, both TOC removal efficiency and mineralization current efficiency were greatly promoted in the SEF process compared with the electro-Fenton (EF) process. These results prove that the SEF process is a promising technology in terms of colored wastewater treatment.

In this study, we investigate the physical and chemical properties of waste-activated sludge after treatment with microwave irradiation. The results indicate that microwave energy and contact time strongly influence the physical and chemical properties of sludge. According to the settling velocity and particle size measurements, the microwave energy of 900 W with a contact time of 60s may be the optimal condition for improving the ability of the sludge to settle. Results of the experiments have shown that supernatant turbidity, soluble chemical oxygen demand, volatile suspended solid solubilization, extracellular polymeric substances content, and inorganic nitrogen increase significantly with contact time. Based on these results, we find that the microwave irradiation treatment specified by the contact time not only improves settleability, but also disintegrates sludge and destroys microbial cells. Possible mechanisms of microwave treatment are also discussed.

We reported the study of the degradation of the azo dye cationic red X-GRL by the electro-Fenton process using an activated carbon fiber cathode. The electrogeneration of hydrogen peroxide in solution using different material cathodes fed with air was investigated, and the results revealed that the activated carbon fiber cathode was more effective compared to the graphite cathode. The decolorization and mineralization of cationic red X-GRL were also determined. The effect of the operating parameters, such as the initial Fe2+ concentration, temperature and initial dye concentration, was investigated. The optimum Fe2+ catalyst concentration values for the degradation of cationic red X-GRL was found to be 5mM. The rate of decolorization and mineralization of dye could be accelerated by increasing the temperature. In addition, the decolorization and total organic carbon (TOC) removal efficiency decreased with the increasing initial dye concentration, while the TOC removal increased. Two different transition metal ions (Cu2+ and Mn2+) were applied as substitutes for ferrous sulfate for evaluating catalytic effect. The results indicated that Cu2+ and Mn2+ were more effective than Fe2+ in catalyzing the degradation of the dye.

This study investigated the potential benefits of ultrasound-conditioned sludge dewatering treatments with specific energy dosages from 0 to 35,000 kJ/kg total solids (TS). Capillary suction time (CST) and specific resistance of filtration (SRF) were used to evaluate sludge dewaterability. Sludge water distribution was measured by the drying test and mechanical separation methods. Both extracellular polymeric substance (EPS) content and sludge particle size were determined in an attempt to explain the observed changes in sludge dewaterability. The results indicated that application of low specific energy dosages (<4400 kJ/kg TS) slightly enhanced sludge dewaterability, but larger specific energy dosages (>4400 kJ/kg TS) significantly deteriorated sludge dewaterability. The optimal specific energy to give maximal dewaterability characteristics was found to be 800 kJ/kg TS, which generated sludge with optimal EPS concentration (400–500 mg/l) and particle size distribution (80–90 μm diameter). Subjecting sludge to a combination of cationic polymer and ultrasound pretreatments did not present any clear advantages over polymeric conditioning alone for improving sludge dewaterability. The effects of cationic polymer treatment predominated over those of ultrasound pretreatment when both were used together.

The utility model relates to a cascaded catalytic and electrolytic coupling reactor which is suitable for treating organic wastewater which is difficult to biodegrade. The reactor mainly comprises an iron internal electrolyzing layer, an ultrasonic radiation layer and a three-dimensional electrode oxidation layer that are coupled and connected in series with one another; the traditional water treatment technologies such as internal electrolysis method, and ultrasonic and electro-Fenton method are coupled so that the organic wastewater which is difficult to degrade can be treated, so as to achieve the standard requirement stably; the cascaded catalytic and electrolytic coupling reactor not only can be applicable to the pretreatment of various high-concentration organic wastewater difficult to degrade, greatly reduces the concentration of the organic contamination, and improves the biodegradability of the wastewater, but also can be applicable to a main treatment unit for small-flow wastewater and leads the treated wastewater to achieve the standard and be discharged directly.