Decrease In Removal Efficiency Research Articles

Minimizing excess sludge production under synergistic effect of diatomite and uncoupling agent 2,4-dinitrophenol: An in-depth study

Excess sludge production is one of the major challenges in the wastewater treatment plants worldwide. The main solution is to reduce the burden of sludge by lowering its production. In this study, the strategies for sludge reduction using uncoupler DNP (2,4-dinitrophenol) with diatomite or diatomaceous earth (natural sedimentary rock) are evaluated for practical application using cost analysis and assessment of environmental impact. There was a decrease in average removal efficiency of chemical oxygen demand (COD), ammonia nitrogen (NH 4 + -N) and total nitrogen (TN) of 7–30%, 20% and 44%, respectively. The sludge volume index (SVI) was 80–120 mL/g while the sludge activity increased by 21%. By cost analysis and comparison of the various parameters, it was determined that the optimal dosage of DNP was 6 mg/L. The problem of poor effluent quality and sludge performance caused by the addition of DNP alone was solved by the collaborative addition of DNP and diatomite. Diatomite can absorb the coupling agent like a carrier to form a compound uncoupling agent. Diatomite easily aggregate and mixed with sludge micelle particles. DNP will slowly release and dissolve into sludge micelles after they are mixed, resulting in higher DNP concentration in sludge micelles. A synergistic effect of DNP and diatomite on sludge reduction showed increase in removal efficiency COD, NH 4 + -N and TN of 13.35%, 18.6% and 26.58%, respectively. SVI was decreased by 13%. A sewage treatment of 1 m 3 can still save sludge treatment cost by $ 0.0084. Comparing the synergistic dose, observed sludge yields (Yobs) decreased by 28.28% (48 mg of DNP with 0.4 g of diatomite; one-time dosage per two-days) and 21% (24 mg of DNP with 0.2 g of diatomite; once a day dosage). The sludge activity also increased. By orthogonal test results, the optimum environmental influence factors for the treatment system are set to 25 °C and pH 7.

A Study on Performance and Reusability of Certified and Uncertified Face Masks

In this study, the performance (particle removal efficiency and breathing resistance) of several commercially available face masks (KF80-certified electrostatic and nanofiber filter masks, and an uncertified mask) was evaluated, along with their filter structure and composition. Also, the effects of the relative humidity (RH) of incoming air, of water and alcohol exposure, and of reuse, on the performance of face masks were examined. Monodisperse and polydisperse sodium chloride particles were used as test aerosols. Except for the uncertified mask filter, PM2.5 removal efficiency was > 90%. The nanofiber filter mask had the highest quality factor due to its low pressure drop and high removal efficiency, and densely packed nanofiber pore structure, and significant amounts of fluorine, carbon and oxygen. The removal efficiency of the KF80-certified mask was barely affected by the higher RH of incoming air. When the mask filters were soaked in water, their removal efficiency decreased. The uncertified mask filter showed the largest decrease in removal efficiency (26%). When the mask was soaked in alcohol, the removal efficiency decreased to a greater degree than when soaked in water. The nanofiber mask filter showed the strongest resistance to alcohol among the tested mask filters. During evaluation of mask reusability, the removal efficiency of certified mask filters decreased by 4% over 5 consecutive days (2 hours per day), and that for the uncertified mask filter decreased significantly, by 30% after 5 days.

Construction of the micro-electrolysis system by Fe0 and clay-carbon derived from oil refining for the removal of ozone disinfection by-products

In this work, the construction of iron-cetyltrimethylammonium chloride modified spent bleaching earth carbon (Fe/CTAC-SBE@C) micro-electrolysis system was first proposed for bromate removal in water. The effects of system parameters including Fe to CTAC-SBE@C mass ratio, CTAC concentration, total dosage, temperature, initial pH and reaction atmosphere were studied. Bromate removal efficiency increased with the decrease of Fe/SBE@C mass ratio from 4/1–3/1, and the further decrease of the mass ratio (from 3/1–1/4) led to the decrease of bromate removal efficiency. CTAC modification could provide the active electron transport paths (SBE@C-CTAC+-BrO3-) theoretically for bromate improved removal, and the optimal CTAC concentration was 25 mmol/L. It was found that pH was a key factor of micro-electrolysis reaction, and bromate removal decreased with the increase of pH, while the removal under neutral (pH=7) and basic (pH=9) conditions still could reach more than 75%. Surprisingly, the coexisting of Cl-, SO42- and NO3- as the electrolytes could penetrate the passivated films on the surface of iron and promote bromate removal; air atmosphere was more favorable to bromate removal than nitrogen atmosphere. In addition, based on product determination and characterization data, the removal mechanism of bromate mainly included CTAC-SBE@C adsorption and electrochemical reduction.

Impact of prefilter dilution on IgG removal in membrane-based therapeutic plasma exchange.

Previous studies have demonstrated that a "one plasma volume exchange" would result in an estimated 63% decline in pretreatment IgG levels. We evaluated the use of prefilter dilution with normal saline as a method to prevent filter failure without decreasing the efficiency of IgG removal. Twenty-one treatment sessions were analyzed and all received prefilter dilution with normal saline. Primary outcome was to determine whether prefilter dilution resulted in decreased treatment efficiency in removing the targeted IgG. Secondary outcome was filter failure in conjunction with the combined use of prefilter heparin and saline infusions. All 21 treatments (100%) received prefilter dilution with saline solution and 19/21 (90.47%) also received prefilter heparin (bolus and/or hourly infusion). We demonstrated a 60%-70% decline in pretreatment IgG levels. Prefilter dilution during membrane-based therapeutic plasma exchange based treatment did not result in a demonstrable decrease in efficiency of IgG removal while maintaining filter patency.

Monitoring of the Operating Membrane Condition Using PZT Based EMI of External Steel Pipe

Membrane systems are increasingly being used for treating water, wastewater, and reused water. However, membrane damage can decrease removal efficiency and hinder downstream applicability. Thus, the operating conditions of the membrane should be monitored. This study monitored the operating conditions of the membrane using lead zirconate titanate (PZT)-based electro-mechanical impedance (EMI) measurements in an external air pipe. Pilot-scale tests were performed to verify the performance of the proposed method. A pressure decay test (PDT) was performed using a PZT-attached air pipe, in which the pressure was measured using PZT, and a pressure gauge was employed to measure the reference pressure. The EMI signals changed according to the variations in the pressure inside the steel air pipe. To index the signal variation, the amplitude of the major peak was extracted and compared with the reference pressure. The amplitude of the major peak was inversely proportional to the pressure change. The pressure estimation equation was derived using a linear regression between the amplitudes of the major peak and the reference pressures. According to the results, the proposed monitoring system that utilizes the EMI of an external steel pipe is a potential solution to improve the sensitivity and speed of the PDT.

Study the Use of Activated Carbon and Bone Char on the Performance of Gravity Sand-Bag Water Filter.

In this study, granulated activated charcoal (GAC) and bio charcoal (BC) is used as a filler in P3 biosand bag filter to study their filtration performance against a range of fluoride impurities from 1–1400 mg/L. A set of experiments are done to analyze the filtration efficiency of the sandbag filter against fluoride impurities after incorporating different amounts (e.g., 0.2, 2 kg) and a combination of GAC and BC. A combination of filler GAC and BC (1 kg each) have exhibited excellent results with 100% fluoride removal efficiency against 5 mg/L fluoride impurities for an entire experimental time of 165 min. It is because of the synergetic effect of adsorption caused by the high surface area (739 m2/g) of GAC and hydroxyapatite groups in BC. The data from remediation experiments using individual GAC and BC are fitted into the Langmuir and Freundlich Isotherm Models to check their adsorption mechanism and determine GAC and BC’s maximum adsorption capacity (Qm). The remediation data for both GAC and BC have shown the better fitting to the Langmuir Isotherm Model with a high R2 value of 0.994 and 0.970, respectively, showing the excellent conformity with monolayer adsorption. While the GAC and BC have presented negative Kf values of −1.08 and −0.72, respectively, for Freundlich Model, showing the non-conformity to multilayer adsorption. The Qm values obtained from Langmuir Model for GAC is 6.23 mg/g, and for BC, it is 9.13 mg/g. The pH study on adsorption efficiency of individual GAC and BC against 5 mg/L of fluoride impurities indicates the decrease in removal efficiency with an increase in pH from 3 to 9. For example, BC has shown removal efficiency of 99.8% at pH 3 and 99.5% at pH 9, while GAC has exhibited removal efficiency of 96.1% at pH 3 and 95.9% at pH 9. Importantly, this study presents the significance of the synergetic application of GAC and BC in the filters, where GAC and BC are different in their origin, functionalities, and surface characteristics.

Regeneration of odorous sulphur compound-exhausted activated carbons using wet peroxide oxidation: The impact of chemical surface characteristics

The efficiency of hydrogen peroxide in the regeneration of dimethyl sulphide (DMS) exhausted-activated carbons (ACs) is assessed in this study. Moreover, the influence of chemical surface composition is evaluated using six ACs (two commercial ACs and four chemically modified ACs) with different surface features. Chemical surface composition of ACs before and after different adsorption-regeneration cycles is assessed by temperature-programmed desorption coupled with mass spectroscopy (TPD-MS) and by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Results reveal that up to a 60% of regeneration efficiency is attained, being more effective in the presence of ACs derived from Filtrasorb 300 AC sample. Experimental findings show that ACs with high content of basic oxygen–containing functional surface groups and mineral fraction are responsible to promote the catalytic decomposition of hydroxide peroxide, leading to a higher formation of hydroxyl radicals and to the observed increase in the regenerative oxidation of adsorbed DMS. However, a decrease in removal efficiency is related to an increase in the amounts of oxygen functionalities mainly in the form of strong acidic surface groups such as carboxylic acid anhydrides and carboxylic acids that shift the reaction mechanism from promoting the initiation of radical chain reactions to termination. Additionally, DRIFTS analyses indicate that after successive adsorption-regeneration cycles the fraction of organic molecules that remains adsorbed limits the access to active surface sites responsible for radical generation, reducing drastically the catalytic activity of ACs.

Synthesis and performance evaluation of diphenylcarbazide functionalized mesoporous silica for selective removal of Cr(VI)

We have successfully synthesized diphenylcarbazide functionalized mesoporous silica (DPC-SBA-15) for the selective removal of chromium (Cr(VI)) from aqueous solution. The structural characteristics and the surface modification of DPC-SBA-15 were investigated by small-angle XRD, SEM, HR-TEM, FTIR, and CHNS elemental analysis techniques. Results showed that the mesoporosity and long-range structural ordering of SBA-15 were well-maintained before and after the functionalization. Adsorption parameters such as pH, contact time, adsorbent dose, and initial concentrations were optimized under given conditions. DPC-SBA-15 revealed fast initial kinetics for Cr(VI) ions. Maximum removal up to 0.85 mmol/g was achieved in a short time of 20 min at pH range 1–3, S: L ratio of 4 g/L at 25 ᵒ C. Adsorption kinetics followed the pseudo-second-order and the adsorption process is mainly driven by chemisorption. Thermodynamic parameters showed the spontaneous and exothermic nature of the adsorption process. DPC-SBA-15 is capable to selectively remove Cr(VI) up to 86.3% from the aqueous system in the presence of alkali, alkaline, transition metal ions. Moreover, only a 5.6% decrease in removal efficiency was observed in a mixture of anionic species like phosphates and sulfates. • Pristine SBA-15 is successfully synthesized and functionalized with diphenylcarbazide (DPC) for the selective removal of Cr(VI). • DPC-SBA-15 showed faster initial and equilibrium adsorption kinetics (20 min) and good adsorption capacity even at low Cr(VI) concentrations. • Thermodynamic parameters showed the spontaneous and exothermic nature of the adsorption process. • DPC-SBA-15 is capable to selectively remove Cr(VI) up to 86.3% from the aqueous system in the presence of alkali, alkaline, and transition metal ions.

Analysis of the influence of rapid filter cycle interruption on filtrate quality

The article presents research carried out on a sand/anthracite filter in a water treatment plant in Cracow in the south of Poland. These studies show that shutting down the filter after only three hours of operation, setting it aside for four hours and restarting without backwashing did not cause any visible deterioration in the quality of the produced filtrate. Stopping the same filter for four hours, however, after 68 h of operation, visible deterioration in the quality of the filtrate can be observed. After a significant initial deterioration, the quality of the filtrate slowly improved and after a few hours, it reached a level comparable to that before the filter was taken out of service. This was probably the result of characteristic changes in shear stress at the boundary of the deposit and flowing water in the capillaries, which accompanied changes of filtration rate. Decrease in the removal efficiency of coarser particles lasted longer and was greater than that of finer particles. Decrease in particle removal efficiency after restarting the dirty filter was difficult to identify by turbidity measurements, but clearly identifiable by measuring suspended solid concentration and the number of coarser particles. Interrupting the operation of a rapid filter shortly after it has been backwashed should not significantly reduce its efficiency, but after prolonged operation, it may adversely affect the quality of the filtrate.

Phytoremediation of Boron using Lemna minor from Synthetic Aqueous Solutions and Real Geothermal Water

In this study, phytoremediation performance of Lemna minor L. on boron removal from synthetic solution and real geothermal water was evaluated. Effects of initial boron concentration, initial pH, water height in cell, and initial humic acid concentration were investigated. The maximum removal efficiency was achieved as 96.7 % with the experimental run with 5 mg L-1 initial boron concentration, pH 8, and 1.5 cm water depth. Increasing the initial boron concentration from 5 to 30 mg L-1 resulted in a drastic decrease in removal efficiency to 36.6 %, due to the toxic effect of high boron content, which was clearly observed from deterioration of plant’s color and structure. SEM, FTIR, and mass balance analyses revealed that the boron removal mechanism was mainly biosorption. Geothermal water experiments indicated L. minor’s applicability with 59.5% removal efficiency, proving high potential in being used for post-treatment of geothermal waters with high boron content.

Increasing salinity concentrations determine the long-term participation of methanogenesis and sulfidogenesis in the biodigestion of sulfate-rich wastewater

The competition between sulfate-reducing bacteria (SRB) and methanogenic archaea (MA) depends on several factors, such as the COD/SO42− ratio, sensitivity to inhibitors and even the length of the operating period in reactors. Among the inhibitors, salinity, a characteristic common to diverse types of industrial effluents, can act as an important factor. This work aimed to evaluate the long-term participation of sulfidogenesis and methanogenesis in the sulfate-rich wastewater process (COD/SO42− = 1.6) in an anaerobic structured-bed reactor (AnSTBR) using sludge not adapted to salinity. The AnSTBR was operated for 580 d under mesophilic temperature (30 °C). Salinity levels were gradually increased from 1.7 to 50 g-NaCl L−1. Up to 35 g-NaCl L−1, MA and SRB equally participated in COD conversion, with a slight predominance of the latter (53 ± 11%). A decrease in COD removal efficiency associated with acetate accumulation was further observed when applying 50 g-NaCl L−1. The sulfidogenic pathway corresponded to 62 ± 17% in this case, indicating the inhibition of MA. Overall, sulfidogenic activity was less sensitive (25%-inhibition) to high salinity levels compared to methanogenesis (100%-inhibition considering the methane yield). The wide spectrum of SRB populations at different salinity levels, namely, the prevalence of Desulfovibrio sp. up to 35 g-NaCl L−1 and the additional participation of the genera Desulfobacca, Desulfatirhabdium, and Desulfotomaculum at 50 g-NaCl−1 explain such patterns. Conversely, the persistence of Methanosaeta genus was not sufficient to sustain methane production. Hence, exploiting SRB populations is imperative to anaerobically remediating saline wastewaters.

A new approach on synergistic effect and chemical stability of graphene oxide-magnetic nanocomposite in the heterogeneous Fenton degradation of caffeine.

Two compositions of graphene oxide-magnetite nanocomposites were studied as catalysts in the heterogeneous Fenton process. Transmission electron microscopy and X-ray diffraction revealed that the graphene oxide sheets were covered with nanoparticles of magnetite, with an average crystallite size of 7 nm. Infrared spectroscopy analysis indicated that the phases interacted through covalent Fe-O-C bonds. The composites presented significantly improved catalytic activity, compared to pure magnetite, with a synergistic effect of up to a factor of 17.1 for the Fenton degradation of caffeine, achieving total removal after 90 min. This synergistic effect was a consequence of the interaction between the phases, resulting in improved mass transfer of caffeine to the catalyst surface, adsorption and efficient degradation, with enhanced HO• generation. The surface reaction constant increased by up to three orders of magnitude, demonstrating the important role of graphene oxide in the degradation kinetics of the heterogeneous Fenton process. The surface-bonded hydroxyl radicals were responsible for caffeine degradation, achieving 9.4 μmol L-1. After five degradation cycles, a loss of Fe-O-C bonds and increase in oxygenated groups were associated with a small decrease of caffeine removal efficiency, from 98 to 82%, without significant iron leaching, in the dark, and with low consumption of hydrogen peroxide.

Formation of Formaldehyde and Other Byproducts by TiO2 Photocatalyst Materials

Photocatalysts promised to control pollution in an environmentally benign manner, inexpensively, and with a low or cheap energy input. However, the limited chemical activity of photocatalysts has prevented their widespread use. This limitation has two important consequences; in addition to limited removal efficiency for pollution, photocatalysts may also generate unwanted byproducts due to incomplete reaction. This study focuses on the byproducts formed in the photocatalytic degradation of dimethyl sulfide (DMS) on titanium dioxide (TiO2), using a continuous flow reactor and detection via proton transfer reaction mass spectrometry. TiO2, activated carbon (AC), TiO2/AC (1:1) and TiO2/AC (1:5) were tested using either a laser-driven light source or LED lamps at 365 nm. The samples were characterized using a N2-BET surface area and pore size distributions, Scanning Electron Microscopy, X-ray Diffraction, and X-ray Photoelectron Spectroscopy, which confirmed that TiO2 was successfully coated on activated carbon without unexpected phases. TiO2 and activated carbon showed different removal mechanisms for DMS. The maximum yield of formaldehyde, 11.4%, was observed for DMS reacting on a TiO2/AC (1:5) composite operating at a DMS removal efficiency of 31.7% at 50 ∘C. In addition to formaldehdye, significant products included acetone and dimethyl disulfide. In all, observed byproducts accounted for over half of the DMS material removed from the airstream. The TiO2/AC (1:5) and TiO2/AC (1:1) composites have a lower removal efficiency than TiO2, but a higher yield of byproducts. Experiments conducted from 20 ∘C to 70 ∘C showed that as temperature increases, the removal efficiency decreases and the production of byproducts increases even more. This is attributed both to decreased surface activity at high temperatures due to increased recombination of reactive species, and to the decreased residence time of volatile compounds on a hot surface. This study shows that potentially dangerous byproducts are formed by photocatalytic reactors because the reaction is incomplete under the conditions generally employed.

Ammonium removal from landfill fresh leachate using zeolite as adsorbent

In this study, the effect of natural zeolite on the ammonium ion removal from landfill fresh leachate (LFL) was investigated. The effect of different parameters such as pH, contact time (CT) and zeolite concentration (ZC) in a batch system were studied to optimize ammonium ion removal from LFL by natural zeolite. Firstly, the effect of variable pH values (5–9) was investigated. In the next step, at the optimal pH condition (7), the effect of ZCs of 10–200 g/L was studied. It is indicated that, from 10 up to 80 g/L, the amount of ammonium ion removed is increased. Meanwhile, increasing of the ZC from 80 until 200 g/L resulted in decreasing removal efficiency. Finally, in the previous optimal conditions, the role of CTs (5–300 min) is inspected. With increasing CT from 5 up to 30 min the amount of removal rate was increased. Following with increasing CT, the intensity of the uptrend decreased and the removal rate reached a steady state. Results of the experiments indicate optimal conditions for ammonium ion removal from LFL (44.49%) occur at pH, 7, ZC of 80 g/L and CT of 30 min. In addition, the adsorption isotherm and kinetics confirmed that the Langmuir isotherm (R2 = 0.9451) was more consistent than the Freundlich isotherm (R2 = 0.9211). This study indicates that clinoptilolite zeolite (CZ) as an inexpensive and suitable adsorbent, has a good potential for removing ammonium ions from LFL solution.

Facilely synthesized porous 3D coral-like Fe-based N-doped carbon composite as effective Fenton catalyst in methylene blue degradation

In this study, a 3D Fe-based and N-doped coral-like carbon composite (Fe-NGLC) was successfully prepared via the simple impregnation of a self-made 3D nitrogen-enriched and porous layered graphene-like support with Fe2(SO4)3 as the precursor. It was characterized through X-ray diffractometry, scanning electron microscopy, X-ray photoelectron spectroscopy, etc.; Fe-NGLC exhibited regular three-dimensional coral-like structures with dense porosity and high of Fe–N species content. As a heterogeneous Fenton catalyst of the methylene blue (MB) degradation, the prepared composite showed impressive activity over a wide pH range (4–10). Almost 100% of the MB could be degraded in 60 min, and the results agreed well with the pseudo-first-order kinetic model. To identify the crucial active sites of MB degradation, the correlation between the rate constant derived from the pseudo-first-order kinetic model and the different Fe species in the catalyst prepared under various conditions was investigated. This revealed the key role of the Fe–N complexes for the heterogeneous Fenton reaction. Moreover, Fe-NGLC exhibited recyclability and only a slight decrease in removal efficiency after five cycles. The excellent performance of Fe-NGLC demonstrates its great potential as a Fenton catalyst for wastewater treatment.

Elemental mercury removal from coal gas by CeMnTi sorbents and their regeneration performance

Ce and Mn modified TiO2 sorbents (CeMnTi) were prepared by a co-precipitation method, and their ability to remove elemental mercury from coal gas in a fixed bed reactor was studied. Based on results of Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS) studies, the modification mechanisms of the CeMnTi sorbents are discussed. Mn doping improved the specific surface area and dispersion of cerium oxides on the sorbent surface, while Ce doping increased the proportion of Mn4+ in manganese oxides by a synergetic effect between manganese oxides and cerium oxides. The effects of the active component, temperature, and coal gas components on the mercury removal performance of the sorbents were investigated. The results showed that the CeMnTi sorbents exhibited high mercury removal efficiency. Ce0.2Mn0.1Ti adsorbed 91.55% elemental mercury from coal gas at 160 °C. H2S and O2 significantly improved the ability of sorbents to remove mercury. Part of the H2S formed stable sulfates or sulfites through a series of oxidation reaction chains on the sorbent surface. HCl also improved the mercury removal performance, but reduced the promotion effect of H2S for mercury removal when coexisting with H2S. CO and H2 had a minor inhibitory effect on mercury adsorption. The recycling performance of the sorbents was investigated by thermal regeneration. The thermal decomposition of the used sorbents indicated that mercury compounds were present mainly in the form of HgO and HgS, and higher temperature was beneficial for regeneration. The formation of sulfates and sulfites in the presence of H2S led to a decrease in mercury removal efficiency.

Behavior of mercury in chemical looping with oxygen uncoupling of coal

Mercury pollution is a critical point in chemical looping with oxygen uncoupling combustion (CLOU) of coal. This work aims to investigate the behavior of mercury and the role of oxygen carrier (OC, CuO@TiO2-Al2O3) in the CLOU of Pingdingshan (PDS) anthracite. The average CO2 yield was 93.9% during the 15 redox cycles. The mercury balance was 119.0% ± 0.49 in the CLOU test (8 min, 4 repeated redox cycles). The distribution of Hg0(g) and Hg2+(g) was 0.033 ± 0.9*10−5 μg and 0.054 μg within the reduction process, respectively. The removal efficiency of Hg0(g) by the OC was 60.71%. Moreover, the Hg(p) was adsorbed on the OC with an adsorption capacity of 0.281 μg/g and was composed of 23.48% and 76.52% for Hg0 and Hg2+. The decreasing removal efficiency of Hg0 was listed as: OC + the complicated atmosphere of CLOU > OC + 5 vol% O2 > the completely oxidized OC > the partially reduced OC. The oxidation of Hg0(g) was promoted by sufficient active sites, absorbed oxygen and lattice oxygen of the OC. A long reduction time in the fuel reactor reduced the mercury released in the air reactor.

Degradation of basic violet 16 dye by electro-activated persulfate process from aqueous solutions and toxicity assessment using microorganisms: determination of by-products, reaction kinetic and optimization using Box–Behnken design

Abstract This study was performed to determine the efficiency of the electro/persulfate process to remove basic violet 16 (BV16) dye and COD from aqueous solutions. The present study was experimentally performed on a laboratory scale. The effect of pH on the process was investigated independently, and after performing the experiments, the effect of voltage (volts), the dose of persulfate (g/L), initial concentration of BV16 dye, and electrolysis time was investigated with the model presented by Box Behnken design, and optimal conditions for BV16 dye removal was obtained. Under optimal conditions, COD removal efficiency and toxicity changes during the process were calculated, and the effect of distance between electrodes and surface of electrodes on process efficiency was investigated. By-products of oxidative degradation were determined with LS-MS. The amount of electrical energy consumed by the process was investigated by voltage changes and then the kinetics of the process was investigated by a pseudo-first-order model. The results showed that the electro/persulfate process in optimal conditions including pH of 5, a voltage of 11.43 V, persulfate dose of 0.09 g/L, initial BV16 concentration of 45 mg/L, and electrolysis time of 48.5 min could provide BV16 dye removal efficiency of 95% and COD removal efficiency of 57.14%. Findings of electrical energy consumption showed that with increasing voltage, the efficiency of the process increased, but the amount of energy consumption also increased. Under optimal conditions, increasing distance between the electrodes was led to a decrease in removal efficiency, but the removal efficiency increased with the increasing surface of the electrodes. Based on the kinetic results, the electro/persulfate process followed pseudo-first-order kinetics with R 2 = 0.9956. The present study showed that the electro/persulfate process as a useful technique has high efficiency in removing BV16 dye and its toxicity from aqueous solutions and can be effective and useful in removing the COD of solution.

Removal of gas-phase arsenic and selenium in flue gas by a new combined spray-and-scattered-bubble technology based on ammonia desulphurization

The integrated control of multiple pollutants is a promising approach for efficient and economical pollution reduction. Inspired by the simultaneous removal of SO2 and NOx by the spray-and-scattered-bubble (SSB) technology, this paper further explores gas phase arsenic and selenium removal ability of this new technology. Ammonia concentration, SO2 concentration, liquid/gas ratio and immersion depth, which are the key operating parameters of SSB technology, are evaluated to determine their effect on arsenic and selenium removal. The experimental results indicate that ammonia concentration and SO2 will facilitate the simultaneous removal of arsenic and selenium by SSB technology. However, the excess ammonia concentration and SO2 should avoided to prevent the decrease in removal efficiency caused by the ammonia escape, increased mass transfer resistance, and mechanical carry-over. The maximum removal efficiency for arsenic can be obtained at the liquid-gas ratio of 10 L/m3, and for selenium, the maximum removal efficiency will be reached at 14 L/m3. For the technology of spray-and-scattered-bubble, chemical reaction and mass transfer jointly play the role in contaminant removal. By changing the immersion depth and measuring the corresponding pressure drop, the weight assigned to the effect of chemical reaction and mass transfer effect could be ascertained to a certain degree. It is speculated that chemical reaction will play a more important role for selenium removal in the bubble zone than the mass transfer. Moreover, for arsenic, mass transfer effect will play a more important role than chemical reaction. The sensitivity analysis for simultaneous removal of arsenic and selenium by SSB technology indicating that the variation of operating conditions will lead to a greater change in arsenic removal as compared with selenium.

Improving removal rate and efficiency of As(V) by sulfide from strongly acidic wastewater in a modified photochemical reactor

ABSTRACT Employing ultraviolet light to enhance the removal of As(V) by sulfide (S(-II)) from strongly acidic wastewater is a potential method. However, we found the arsenic trisulfide (As2S3) and elemental sulfur (S8) particles formed in this method not only vastly hinder light transmission in the wastewater but also undergo light-induced redissolution, leading to a decrease in removal rate and efficiency of As(V). Herein, As(V) removal by sulfide from strongly acidic wastewater was performed in a modified photochemical reactor to weaken the effect of the formed particles on As(V) removal. It was found that in this study, the formed particles could be efficiently removed from the photoreactor by three operations, i.e. circulation-filtration, septum setting, and lamp sleeve cleaning. The removal of As(V) was approximately 11-fold faster than that without three operations, saving 90.9% of the reaction time and 89.4% of energy consumption. The removal efficiency of As(V) also increased through weakening the light-induced redissolution of the formed particles. This study facilitates the practical application of the UV light promoted As(V) removal technology and also provides a new method to lessen the light-blocking effect in the particle-forming photochemical reaction systems.