Initial Removal Rate Research Articles

Outdoor Cultivation of the Microalga Chlorella vulgaris in a New Photobioreactor Configuration: The Effect of Ultraviolet and Visible Radiation

Microalgae can be a future source of biomass with a wide range of applications, including its use to solve current environmental issues. One of the main variables for microalgal cultivation is the light supply: (i) its intensity that often does not present a uniform spatial distribution inside the culture; (ii) photoperiod; and (iii) spectrum. Therefore, this study aims to evaluate the growth of the microalgae Chlorella vulgaris in a tubular photobioreactor with compound parabolic collectors (CPCs) under outdoor conditions. The effect of ultraviolet and visible radiation on biomass productivity and nutrients (nitrogen and phosphorus) uptake was assessed. The maximum biomass productivity was (5 ± 1) × 10−3 g·L−1·h−1, and the specific growth rates ranged from (1.1 ± 0.3) × 10−2 to (2.0 ± 0.6) × 10−2 h−1. Regarding nutrient uptake, initial removal rates of (0.9 ± 0.4) mg N·L−1·h−1 for nitrogen and (0.17 ± 0.04) mg P·L−1·h−1 for phosphorus were reached. These values increased with visible and ultraviolet irradiance until certain values (143 WVIS·m−2 and 9 WUV·m−2 for biomass productivity; 101 WVIS·m−2 and 6 WUV·m−2 for nutrient removal) and then decreased for higher ones due to the photoinhibition phenomenon. Therefore, the application of CPCs to photobioreactors (PBRs) may be beneficial for microalgal culture in countries with higher latitude (with lower solar irradiance levels).

Development and application of modified lye for treating hydrogen sulphide in coal mine

To improve the absorption efficiency of alkaline liquor treated with hydrogen sulphide in coal mines, a single sodium carbonate lye was taken as the basic raw material to modify the absorption of lye by adding the surfactant sodium dodecyl benzene sulfonate (SDBS) and the oxidant hydrogen peroxide. Respectively, the effects of different concentrations of surfactants and oxidants in sodium carbonate solution on the removal of hydrogen sulphide gas were investigated. The results show that the concentration of sodium carbonate solution is positively correlated with the removal rate of hydrogen sulphide. When the concentration of sodium carbonate solution increases to 2%, the initial removal rate of hydrogen sulphide is close to 100%, however, the problem of secondary dissipation of hydrogen sulphide is more significant after vibration. With the increase of SDBS and hydrogen peroxide concentration, the removal rate of hydrogen sulphide from sodium carbonate solution respectively increases to 93.1% and 86.2%. Finally, through experimental analysis and in situ measurements, the optimal ratio of the modified lye in the hydrogen sulphide treatment of this experiment is as follows: the concentration of sodium carbonate solution is shown to be 2%, the concentration of surfactant is 0.4%, and the concentration of oxidant is 0.6%. On this basis, by comparing the 40,201 working face of Xiaozhuang Coal Mine with the 40,202 working face, it is concluded that the average removal rate of the modified lye is 93.5%, and the treatment effect of removing hydrogen sulphide is significant.

Manganese oxide-based porous electrodes for rapid and selective (electro)catalytic removal and recovery of sulfide from wastewater

Sulfide and its removal is a major concern in wastewater treatment as it represents a threat to human health and the structural integrity of the water distribution system. In this study, we demonstrated for the first time an exceptional performance of manganese oxide-coated graphite felt (GF-MnxOy) electrodes for selective sulfide oxidation to sulfur. Oxidation state, loading, morphology and crystallinity of MnxOy coating was tuned using electrodeposition synthesis method to enable an efficient and selective sulfide oxidation to sulfur. Excellent (electro)catalytic activity of GF-MnxOy yielded up to 25-fold increase in sulfide removal rates compared to pristine GF, both in the open circuit (OC, no applied potential) and under anodic polarization at 0.4 V vs Standard Hydrogen Electrode (SHE). Although anodic polarization did not further enhance sulfide oxidation rate compared to OC, it enabled a continuous re-oxidation of the reduced MnxOy coating after its reaction with sulfide. Thus, restoring of the catalytic properties of MnxOy coating enabled higher sulfide removal rates compared with the OC experiment. The formed elemental sulfur remained at the surface of GF-MnxOy leading to a gradual electrode passivation. The deposited sulfur was successfully dissolved by reversing the polarity of the GF-MnxOy electrode to -0.8 V vs SHE. However, full electrode recovery and restoring of the initial sulfide removal rates could not be achieved as cathodic polarization at -0.8 V vs SHE during longer time (>3 hours) required to remove S0 also caused a partial dissolution of the MnxOy coating. (Electro)catalytic sulfide removal was somewhat decreased in real sewage (2.42 ± 0.02 h-1 vs 0.93 ± 0.15 h-1 in NaNO3 supporting electrolyte and real sewage, respectively). The selectivity of the process towards deposition of elemental sulfur was decreased in real sewage due to partial production of colloidal sulfur, which was presumably caused by diffusion limitation imposed by presence of other ions. Due to lesser extend of GF-Mn2O3 electrode passivation in real sewage, sulfide removal rates remained stable over six subsequent application cycles. In summary, MnxOy-based electrodes demonstrated exceptional (electro)catalytic activity and selectivity for sulfide oxidation to sulfur and thus its complete separation from water. Upscaling of the proposed electrochemical system and its application for the treatment of complex wastewater streams requires further efforts to maintain the selectivity towards deposited sulfur as a final product and allow its complete recovery.

A study on the mechanism of oxidized quinoline removal from acid solutions based on persulfate-iron systems.

Quinoline (Qu) and its derivatives have been widely regarded as hazardous pollutants in the world because of their acute toxicity to humans and animals, and potential carcinogenic risks. In this study, a novel sulfate radical system co-activated by ferrous and ZVI was developed to remove Qu from acidic solutions. The optimal ratio of ferrous and ZVI in the system and the mechanism of Qu removal from acidic solutions are also explored. The ZVI can initiate activation using hydrogen ions, which are released from the reaction of Fe2+, organics and PS in acidic solutions. This may dramatically improve the overall removal efficiency of Qu. The results indicated that the initial removal rate of Qu increases from 85.8% to 92.9%. The cleavage pathway of Qu is speculated by Frontier molecular orbital (FMO) theory and verified by GC/MS analysis.

Comparative study on the degradation of cephalexin by four electrochemical advanced oxidation processes: Evolution of oxidation intermediates and antimicrobial activity

The degradation of the β-lactam antibiotic cephalexin (CEX) was carried out by the following electrochemical advanced oxidation processes (EAOPs): anodic oxidation (AO), Fered-Fenton (EF-Fered), photoassisted anodic oxidation (PAO), and photoassisted Fered-Fenton (PEF-Fered). All experiments were done in a flow reactor incorporating a boron-doped diamond anode, at a low current density; for the PAO and PEF-Fered processes, the solution was irradiated with UVA light. The initial removal of CEX was attained by all EAOPs, but it was much faster by the Fenton-based processes, which thus presented higher initial rates of TOC removal. However, the coupling of the electrolytic and UVA photolytic processes enhanced the mineralization process; as a consequence, significantly greater TOC removals were attained by the PEF-Fered and PAO processes. From the initial oxidation intermediates detected by LC-MS/MS for the PEF-Fered and AO processes, it could be concluded that addition reactions involving the electrophilic HO∙ radicals occurred preferentially in the β-lactam ring; however, due to the higher availability of HO∙ radicals, the Fenton-based process led to a faster rupture of that ring. Thus, the antibacterial activity of the treated CEX solution against Escherichia coli was completely terminated within less than 1 h of treatment by the PEF-Fered process, compared to 8 h by the AO process. The PEF-Fered and PAO processes yielded enhanced degradation performances despite mere use of UVA light.

Photochemical removal of acetaldehyde using 172nm vacuum ultraviolet excimer lamp in N2 or air at atmospheric pressure.

The photochemical removal of acetaldehyde was studied in N2 or air (O2 1-20%) at atmospheric pressure using side-on and head-on types of 172nm Xe2 excimer lamps. When CH3CHO was decomposed in N2 using the head-on lamp (HL), CH4, CO, and CO2 were observed as products in FTIR spectra. The initial removal rate of CH3CHO in N2 was ascertained as 0.37min-1. In air (1-20% O2), HCHO, HCOOH, CO, and CO2 were observed as products in FTIR spectra. The removal rate of CH3CHO in air using the side-on lamp (SL) increased from 3.2 to 18.6min-1 with decreasing O2 concentration from 20 to 1%. It also increased from 2.5 to 3.7min-1 with increasing CH3CHO concentration from 150 to 1000ppm at 20% O2. The best energy efficiency of the CH3CHO removal using the SL in a flow system was 2.8g/kWh at 1% O2. Results show that the contribution of O(1D) and O3 is insignificant in the initial decomposition of CH3CHO. It was inferred that CH3CHO is initially decomposed by the O(3P) + CH3CHO reaction at 5-20% O2, whereas the contribution of direct vacuum ultraviolet (VUV) photolysis increases concomitantly with decreasing O2 pressure at < 5% O2. After initial decomposition of CH3CHO, it was oxidized further by reactions of O(3P), OH, and O3 with various intermediates such as HCHO, HCOOH, and CO, leading to CO2 as a final product.

Effect of solids residence time on dynamic responses in chemical P removal.

The impact of solids residence time (SRT) on the dynamics of phosphorus (P) removal by hydrous ferric oxide (HFO) floc was characterized through experimental and modeling studies. Three abiotic process conditions were considered in systems operated over a range of SRTs (~3 to 27days): uptake in sequencing batch reactors (SBRs) under (a) constant and (b) dynamic P loading conditions, and (c) uptake in batch sorption tests with preformed HFO solids. P removal under all conditions was characterized by an initial period of fast removal followed by a period of slower removal until pseudo-equilibrium was reached. The initial removal rate increased with increasing P concentrations and was attributed to a larger concentration gradient between soluble- and adsorbed-phase concentrations. A kinetic model was developed and found to describe the dynamic behavior of P adsorption onto HFO floc under all conditions tested. A consistent mass transfer rate coefficient (k) was found to describe mass transfer over a range of SRTs for low initial P concentrations. At elevated SRTs (23-27days) and elevated influent P concentrations, k values were found to deviate from those estimated at reduced SRTs. Differences in process mixing conditions were reflected in the estimated rate coefficients (k). Integration of the kinetic model with existing equilibrium models in wastewater process simulators will improve the ability to predict P uptake onto HFO floc under dynamic loading conditions in water resource recovery facilities. Models that consider the kinetics of P uptake will be particularly relevant for facilities that are required to achieve ultralow P concentrations. PRACTITIONER POINTS: This work provides a kinetic model that can be integrated with existing equilibrium models in wastewater process simulators to improve the ability to predict P uptake onto HFO floc under dynamic loading conditions. This research can be used to assist WRRFs to achieve ultralow effluent P requirements.

A marine biofilm flow cell for in situ screening marine fouling control coatings using optical coherence tomography

A novel fouling marine flow cell was designed and fitted with a clear plastic lid to allow real-time imaging of biofilms using optical coherence tomography (OCT). Marine biofilms were grown under controlled shear flow on coupons coated with 6 different biocidal antifouling coatings (SPC1, SPC2, SPC3, SPC4, CDP1 and CDP2, AkzoNobel) and one inert coating which contained no biocidal actives (NB-D) for 8 weeks. One set of coupons coated with NB was statically immersed in sea water during the same time period (NB-S). Biofilm removal was assessed by increasing the flow velocity while OCT simultaneously measured the biofilm cross-sectional area (CSA). The highest initial removal rates were observed for NB-S, NB-D, and SPC2. Percent biofilm cross-sectional area reduction (%CSAred) was higher on SPCs (>60%) compared to CDPs (<50%). SPCs had the highest percent reduction in biofilm surface area coverage (%SACred >60%) compared to the CDPs (<20%). The marine biofilm flow cell combined with OCT can be used to screen for coating-specific differences in biofilm growth and removal in real time rather than traditional before and after surface area coverage measurements. Future testing will focus on how the biofilm-coatings interactions interact with biofilm mechanical and structural properties to produce drag.

Effect of surfactants on the removal of nitrobenzene by Fe-bearing montmorillonite/Fe(II)

Nonionic and anionic surfactants often occur in anaerobic environments, but their roles in the removal of organic contaminants by Fe-bearing mineral/Fe(II) have not been determined. In this study, batch experiments were performed to investigate the effects of a nonionic surfactant (TX-100) and an anionic surfactant (SDBS) on the removal of nitrobenzene (NB) by Fe-bearing montmorillonite (FM)/Fe(II). Mössbauer spectrum and XPS were applied to analyze the edge surface bound Fe(II) and secondary minerals formed on FM. The contribution of surfactant to the enrichment of NB on FM was studied. The results showed that TX-100 and SDBS had opposite effects on the removal of NB by FM/Fe(II) at neutral pH. The presence of TX-100 improved the removal efficiency of NB from 36.4% to 70.0%, and increased the initial removal rate by 1.7 times. This enhancement effect was mainly attributed to the formation of more active edge surface bound Fe(II) that can reduce more NB to aniline. Formation of more magnetite on FM and selective enrichment of NB on the reactive surface also contributed to the removal of NB. In contrast, the presence of SDBS reduced the amount of edge surface bound Fe(II) via formation of SDBS-Fe(II) complex, which decreased the removal efficiency of NB.

Bagasse Cellulose Grafted with an Amino-Terminated Hyperbranched Polymer for the Removal of Cr(VI) from Aqueous Solution.

A novel bio-adsorbent was fabricated via grafting an amino-terminated hyperbranched polymer (HBP-NH2) onto bagasse cellulose. The morphology and microstructure of the HBP-NH2-grafted bagasse cellulose (HBP-g-BC) were characterized and its adsorption capacity for Cr(VI) ions in aqueous solutions was investigated. The rough surface structure of HBP-g-BC that is beneficial for improving the adsorption capacity was observed by scanning electron microscopy (SEM). The grafting reaction was confirmed by Fourier-transform infrared (FT-IR) spectroscopy. The adsorbent performance was shown to be better with a lower pH value, a higher adsorbent dosage, or a higher initial Cr(VI) concentration. Moreover, the kinetics study revealed that the adsorption behavior followed a pseudo-second-order model. The isotherm results showed that the adsorption data could be well-fitted by the Langmuir, Freundlich, or Temkin models. Moreover, HBP-g-BC could maintain 74.4% of the initial removal rate even after five cycles of regeneration. Thus, the high potential of HBP-g-BC as a bio-adsorbent for heavy metal removal has been demonstrated.

Complex biliary stones management: cholangioscopy versus papillary large balloon dilation - a randomized controlled trial.

Background and study aims Endoscopic removal of biliary stones has high success rates, ranging between 85 % to 95 %. Nevertheless, some stones may be challenging and different endoscopic methods have evolved. Papillary large balloon dilation after sphincterotomy is a widely used technique with success rates ranging from 68 to 90 % for stones larger than 15 mm. Cholangioscopy allows performing lithotripsy under direct biliary visualization, either by laser or electrohydraulic waves, which have similar success rate (80 % – 90 %). However, there is no study comparing these 2 techniques. Patients and methods From April 2014 to June 2016, 100 patients were enrolled and randomized in 2 groups, using a non-inferiority hypothesis: cholangioscopy + electrohydraulic lithotripsy (group 1) and endoscopic papillary large balloon dilation (group 2). The main outcome was complete stone removal. Adverse events were documented. Mechanical lithotripsy was not performed. Failure cases had a second session with crossover of the methods. Results The mean age was 56 years. 74 (75.5 %) patients were female. The initial overall complete stone removal rate was 74.5 % (77.1 % in group 1 and 72 % in group 2, P > 0.05). After second session the overall success rate achieved 90.1 %. Procedure time was significantly lower in group 2, – 25.2 min (CI95 % – 12.48 to – 37.91). There were no significant differences regarding technical success rate, radiologic exposure and adverse events. Conclusion Single-operator cholangioscopy-guided lithotripsy and papillary large balloon dilation are effective and safe approaches for removing complex biliary stones.

Abatement of humic acid from aqueous solution using a carbonaceous conjugated microporous polymer derived from waste polystyrene.

Humic acid (HA) is a major constituent of natural organic matter (NOM) found in water systems. Although NOM generally does not have any known harmful effects to humans, it imparts repulsive organoleptic properties to water, reacts with disinfectants to produce toxic products, and interferes with the efficiency of water treatment processes. The removal of NOM and related compounds from water is therefore important to render water potable and suitable for other applications. In this work, a hitherto unreported carbonaceous conjugated microporous polymer (CCMP) prepared through the organic-polymeric-precursor-controlled carbonization of hypercrosslinked post-consumer waste polystyrene (WPS) was evaluated for its capacity to remove HA from synthetic wastewater. This advanced material retained the morphology of the precursor material, while its porosity and chemical integrity were significantly improved. The approach is an environmentally friendly way of handling WPS while at the same time remediating NOM-contaminated water. Overall, with a maximum adsorption capacity of 340mg/g in batch experiments, and a maximum initial removal rate of 95.7% in column experiments, the results showed that CCMP can be used for the remediation of HA-contaminated water at high pH.

Optimization and mechanisms for biodecoloration of a mixture of dyes by Trichosporon akiyoshidainum HP 2023

ABSTRACTTrichosporon akiyoshidainum HP2023 is a basidiomycetous yeast isolated from Las Yungas rainforest (Tucumán, Argentina) and selected based on its outstanding textile-dye-decolorizing ability. In this work, the decolorization process was optimized using Reactive Black 5 as dye model. Lactose and urea were chosen as carbon and nitrogen sources through a one-at-time approach. Afterwards, factorial designs were employed for medium optimization, leading to the formulation of a simpler optimized medium which contains in g L−1: lactose 10, yeast extract 1, urea 0.5, KH2PO4 1 and MgSO4 1. Temperature and agitation conditions were also optimized. The optimized medium and incubation conditions for dye removal were extrapolated to other dyes individually and a mixture of them. Dye removal process happened through both biosorption and biodegradation mechanisms, depending primarily on the dye structure. A positive relation between initial inoculum and dye removal rate and a negative relation between initial dye concentration and final dye removal percentages were found. Under optimized conditions, T. akiyoshidainum HP2023 was able to completely remove a mixture of dyes up to a concentration of 300 mg L−1, a concentration much higher than those expected in real effluents.

Comparison of Scale in a Photosynthetic Reactor System for Algal Remediation of Wastewater

An experimental methodology is presented to compare the performance of two different sized reactors designed for wastewater treatment. In this study, ammonia removal, nitrogen removal and algal growth are compared over an 8-week period in paired sets of small (100 L) and large (1,000 L) reactors designed for algal remediation of landfill wastewater. Contents of the small and large scale reactors were mixed before the beginning of each weekly testing interval to maintain equivalent initial conditions across the two scales. System characteristics, including surface area to volume ratio, retention time, biomass density, and wastewater feed concentrations, can be adjusted to better equalize conditions occurring at both scales. During the short 8-week representative time period, starting ammonia and total nitrogen concentrations ranged from 3.1-14 mg NH3-N/L, and 8.1-20.1 mg N/L, respectively. The performance of the treatment system was evaluated based on its ability to remove ammonia and total nitrogen and to produce algal biomass. Mean ± standard deviation of ammonia removal, total nitrogen removal and biomass growth rates were 0.95±0.3 mg NH3-N/L/day, 0.89±0.3 mg N/L/day, and 0.02±0.03 g biomass/L/day, respectively. All vessels showed a positive relationship between the initial ammonia concentration and ammonia removal rate (R2=0.76). Comparison of process efficiencies and production values measured in reactors of different scale may be useful in determining if lab-scale experimental data is appropriate for prediction of commercial-scale production values.

DETERMINATION OF THIN-LAYER SOLAR DRYING KINETICS OF CASSAVA NOODLES (TAPIOCA)

The aim of this study is to determine the thin-layer drying kinetics of cassava noodles (tapioca) using a solar dryer. To achieve this, an integral type forced convection solar dryer, equipped with rock storage, was developed. Drying kinetics of tapioca were determined using the solar dryer. The treatments in the experiment comprise of air flow velocities (V) of 1.5, 2.5, and 3.5 m/s; and drying layer thicknesses (B) of 0.48 and 0.72 cm. Tapioca samples were dried from an average initial moisture content of 297% (dry basis) to 9.8% (dry basis). Control experiments in the form of open air sun drying of similar quantity of tapioca were also set up and monitored. Graphical plots of moisture content versus drying time, exhibited the characteristic moisture desorption curve, characterized by initial high rate of moisture removal, followed by a slower rate of moisture removal. It was observed from drying rate curves plotted using the drying data, that the drying of the tapioca took place entirely in the falling rate period. The drying rate of the tapioca varied with the different combinations of velocity and drying layer thickness. The drying rate of the tapioca increased with increase in the air flow velocity until velocity of 2.5 m/s; beyond this velocity the drying rate reduced slightly. Also the drying rate of tapioca decreased with increase in drying layer thickness. A maximum drying rate of 39.2%/hr was obtained during the experiment. The maximum system drying efficiency of the dryer was determined as 47.14%, while the maximum dryer pick-up efficiency of 50% was determined during the drying test.

Microbial removal of selected volatile organic compounds from the model landfill gas

Abstract Landfills of municipal waste are an important source of BTEXs in the atmosphere. Biodegrability of these compounds implies that biological methods, such as oxidation in landfill covers, may be an effective way to mitigate emission of these gases. The aim of the study was to evaluate the efficiency of BTEXs removal from landfill gas by biofiltration method and to analyze the influence of methane on BTEXs oxidation rate. The experiments were carried out at laboratory scale continuous flow system (microcosms) and in batch tests. A mixture of municipal waste compost and expanded clay pellets (1:1 of volume) was used as a filter bed material. The model landfill gas (50% vol. of CH4 and 50% vol. of CO2) purged through the microcosms was enriched with toluene (series 1) and all the BTEXs (series 2). The results of 7-month continuous flow experiment showed that removal efficiency of BTEXs in experimental columns ranged from 91 to 100% when the individual trace gases loading rates in model gas were in the range of 0.1-0.2 g m−2d−1. The rate of toluene removal, which followed the first order kinetics, depended on the presence of methane in treated gas. About 2-fold higher values of rate constant and 2.5-fold higher values of initial toluene removal rates were observed when no methane was present in the headspaces inside the vials used in the batch tests.

Nano-Phytotechnological Remediation of Endosulfan Using Zero Valent Iron Nanoparticles

Endosulfan, an organochlorine pesticide, is known for its toxicity and ability to accumulate in the environment. In India endosulfan was banned only in 2011 and hence toxic residues are still persistent in the environment. The abilities of three plant species Chittaratha (Alpinia calcarata), Tulsi (Ocimum sanctum), and Lemongrass (Cymbopogon citratus) to remove endosulfan from soil in the absence and presence of zerovalent iron nanoparticles (nZVIs) (1000 mg/Kg of soil), i.e., by phytoremediation and nano-phytoremediation, were determined. Extracted soil samples from the experimental plot were analyzed using Gas Chromatograph with Electron Capture Detector (GC-ECD) and final dehalogenated product was confirmed by Mass Spectrometer (MS). A. calcarata had the best efficiency compared to the other two plant species and the efficiency decreased in the order A. calcarata > O. sanctum> C. citrates. The initial endosulfan removal rate was high (82% was removed within 7 days) when nano phytoremediation experiments were conducted with A. calcarata but then gradually decreased, probably because the activity of nZVI decreased over time. The nZVI endosulfan degradation mechanism appears to involve hydrogenolysis and sequential dehalogenation which was confirmed by GC-MS analysis. Only small amounts of endosulfan were accumulated in the plants because the added nZVIs might have promoted the reductive dechlorination of endosulfan.

Impact of Film Morphology on Chemical Mechanical Polishing of Tungsten

This study investigated the effects of tungsten (W) film morphology on the chemical mechanical polishing (CMP) of W. Chemical vapor deposited (CVD) W films with two distinctively different grain sizes were used for comparison. During polishing, W film thickness and optical reflectance, friction, and pad temperature were monitored in-situ. It was found that larger-grained W film took longer to pass the initial low removal rate stage. By correlating four different sensor signals, comparing friction dependency on film morphology, in slurry vs. DIW, it was concluded that W CMP comprises three main stages. First is the low rate initiation stage: grain is being partially planarized, reflectance increases, friction decreases. Second is the transition stage: rate is ramping, grain becomes fully planarized, optical reflectance reaches maximum, and friction becomes minimal followed by a significant rise caused by formation of tungsten oxide passivation layer on the planarized W surface. Third is the high and constant rate stage: passivation and removal occur in a repetitive cycle, friction is high and stable, optical reflectance changes as polishing reaches different film depths. In all three stages, pad temperature increases continuously as friction-induced heat dissipates, with the rate of temperature increase following that of friction magnitude.

Influence of Bi-doping on Mn1−xBixFe2O4 catalytic ozonation of di-n-butyl phthalate

Magnetic porous Bi-doping MnFe2O4 (Mn1−xBixFe2O4, x=0, 0.005, 0.01, 0.02, 0.05) were synthesized by a sol–gel method and characterized via multiple techniques. The influence of Bi-doping on catalytic ozonation of catalysts for di-n-butyl phthalate (DBP) decomposition and ozone utilization were investigated in aqueous solutions. Varying Bi-doping amount had little effect on the crystal structure, morphology and magnetism of MnFe2O4. The introduction of Bi into MnFe2O4 enhanced the catalytic DBP degradation. Hydroxyl radicals played a critical role in the Mn1−xBixFe2O4/O3 heterogeneous systems. OH generation was promoted by the surface hydroxyl groups which were regarded as main active sites of catalyst. The extent of Bi-doping had an effect on crystallite size (DXRD) and resulted in increasing surface hydroxyl site concentrations (SHSC) of catalysts. A good linear correlation between the doping amount and SHSC was observed. The initial reaction rate and DBP removal rate mainly depended on the surface hydroxyl groups in catalytic ozonation. The numbers of SHSC and average ozone utilization rate were correlated with initial reaction rates and DBP removal rates, respectively. Bi-doping not only increased the binding sites but also enhanced the tendency of ozone to decompose into OH.

Heterogeneous Fenton-like oxidation of crystal violet using an iron loaded ZSM-5 zeolite

The heterogeneous Fenton-like oxidation of a cationic triphenylmethane dye, crystal violet (CV), dissolved in water was investigated using an iron-loaded ZSM-5 zeolite catalyst. The catalyst was characterized by powder X-ray diffraction patterns, Fourier Transform infrared spectroscopy (FTIR), scanning electron microscope, analysis, and nitrogen adsorption-Brunauer-Emmet-Teller (N2-BET) studies. The effects of temperature, solution pH, H2O2 amount, catalyst amount, and initial dye concentration were investigated using the heterogeneous Fenton-like oxidation of an aqueous CV. The increase in the concentration of H2O2 from 3 to 7.5 mM enhanced the decolorization. Whereas increasing the H2O2 amount from 7.5 to 10 mM led to a decrease in the color removal from 94.1 to 85.5%. An acidic pH of 3.5 was favorable for the decolorization of the dye. The decolorization of the dye decreased with the increase in the initial concentration of CV. Doubling the amount of the catalyst enhanced the decolorization from 94.1 to 99.6% while the chemical oxygen demand (COD) removal changed from 50 to 58.8%. The increase in temperature positively affected the decolorization and the COD reduction of the dye. The stability of the catalyst was maintained even after using the catalyst for three cycles, and a small iron leaching was also proof of the stability of the catalyst. The initial color removal rate of the CV was described as −rCV,o = 7.3 e−14.7/RTCCV,o0.7CH2O2,0 where R = 8.314 J/mol K and CCV,o and CH2O2,0 were in mol/dm3.