Systematic optimization of biochars derived from corn wastes, pineapple leaf, and sugarcane bagasse for Cu(II) adsorption through response surface methodology.

Many industrial wastewaters contain an appreciable amount of toxic copper (Cu(II)) that needs to be properly treated before discharging into receiving water body. Adsorption can effectively remove Cu(II) with optimized parameters. This study investigates the critical pyrolysis parameters of biochar derived from agricultural waste. Optimized biochar showed maximum Cu(II) adsorption capacity of 60.7, 36.8, and 35.5 mg g-1 by PLB, SBB, and CWB at pyrolysis temperatures of 555 ℃, 559 ℃, 507 ℃, respectively, compared with commercial activated carbon (CAC, 40.8 mg g-1). Surface characterization confirmed surface complexation, electrostatic interaction, and cation exchange capacity as Cu(II) removal mechanisms. The presence of humic acid reduced the Cu(II) removal of both CAC and optimized biochars. Optimized PLB displayed high reusability (87% Cu(II) removal efficiency) after five consecutive cycles using pressure cooker regeneration. With excellent Cu(II) adsorption capacity and reusability, the investigated biochars show high applicability potential to Cu(II)-laden wastewater treatment.

Kinetic study and performance comparison of TiO2-mediated visible-light-responsive photocatalysts for the inactivation of Aspergillus niger.

Fungi are highly survived with exceptional resistance to environmental stress. Conventional fungicides are quite efficient, but the increase in use raises severe environmental problems. In this study, environmentally friendly TiO2-mediated visible-light-responsive photocatalysts, namely N-TiO2, N-T-TiO2, C-TiO2, and Pd-C-TiO2, were used to compare the performance of disinfecting a mold fungi Aspergillus niger. Key parameters, including photocatalyst dosage, the initial fungal concentration, and visible-light intensity, affecting the disinfecting process, was investigated. A new developed Light-responsive Modified Hom's (LMH) kinetic model incorporating visible-light intensity and photocatalyst light-absorption coefficient was firstly used to predict such photocatalytic process in fungal inactivation. Among the photocatalysts, Pd-C-TiO2 showed the highest inactivation performance against fungi, followed by C-TiO2, N-T-TiO2, and N-TiO2. In general, inactivation increased with increasing photocatalyst dosage and light intensity while decreased with increasing initial fungal concentration. For kinetic modeling, the LMH model supports the hypothesis that photocatalyst performance toward visible-light-driven fungal inactivation primarily depends on the light-absorption capacity of the photocatalyst. In conclusion, mold fungi Aspergillus niger are effectively disinfected by TiO2-mediated visible-light-responsive photocatalysts, and such fungal inactivation process could be predicted by LMH kinetic model.

Treatability of phenol-production wastewater: Rate constant and pathway of dimethyl phenyl carbinol oxidation by hydroxyl radicals.

Phenol-production wastewater is difficult to treat biologically by aerobic processes to meet the effluent standard COD of 120 mg L-1 because it contains several highly refractory aromatic pollutants, particularly dimethyl phenyl carbinol. Pretreatment revealed that dimethyl phenyl carbinol was slowly oxidized by molecular ozone; however, it readily reacted with hydroxyl radicals to yield acetophenone as a primary product. Acetophenone was further oxidized, first through five different pathways to form benzoic acid, phenyl glyoxalic acid, 4-4'-diacetyl biphenyl, and several hydroxylated aromatic compounds, and later to aliphatic carboxylic acids via ring cleavage. Regardless of system configuration (homogeneous vs heterogeneous), operating mode (batch vs continuous), and chemical concentration, the average intrinsic rate constants were 1.05 × 1010 and 9.29 × 109 M-1 s-1 for dimethyl phenyl carbinol and acetophenone, respectively.

Effect of the iron oxide catalyst on o-toluidine oxidation by the fluidized-bed fenton process.

This study investigates the effects of the Fe2+ concentration and synthetic iron oxide catalysts on o-toluidine degradation using a fluidized-bed Fenton process. The mineralization ofo-toluidine in the synthetic catalyst system is also examined. The H3.5 and H7.3 Fe/SiO2 and A7.8 and A 12.5 Fe/SiO2 catalysts were successfully synthesized by adding H202 and injecting air process, respectively. The optimum initial ferrous ion concentration for degradation of 1 mM o-toluidine was 1 mM. Experimental results reveal that 1 mM o-toluidine can be 100% degraded at 60 and 120 min in the modified fluidized-bed Fenton process with A7.8 Fe/SiO2 and the conventional fluidized-bed Fenton process with SiO2 carrier, respectively, when the optimum conditions of 1mM Fe2+ and 17mM H202 at pH 3 were used. The A7.8 Fe/SiO2 catalyst had a stronger oxidation ability than the H3.5 Fe/SiO2, H7.3 Fe/SiO2 and A12.5 Fe/SiO2 catalysts, and was attributed to the high iron content on the surface of the SiO2 support. The Fenton and Fenton-like reactions occurred in the A7.8 Fe/SiO2 catalyst system. Degradation of o-toluidine in the Fenton-like process follows pseudo-first-order kinetics. The A7.8 Fe/SiO2 catalyst efficiently enhanced o-toluidine oxidation under the pH range of 2-4.

Treatment of TFT-LCD wastewater containing ethanolamine by fluidized-bed Fenton technology.

The objectives of this study are: (1) to determine the effect of pH, initial concentration of Fe(2+) and H(2)O(2) dosage on the removal efficiency of MEA by fluidized-bed Fenton process and Fenton process, (2) to determine the optimal conditions for the degradation of ethanolamine from TFT-LCD wastewater by fluidized-bed Fenton process. In the design of experiment, the Box-Behnken design was used to optimize the operating conditions. A removal efficiency of 98.9% for 5mM MEA was achieved after 2h under optimal conditions of pH3, [Fe(2+)]=5mM and [H(2)O(2)]=60mM.

Degradation of o-toluidine by fluidized-bed Fenton process: statistical and kinetic study.

BACKGROUND, AIM, AND SCOPE: The optimal conditions of o-toluidine degradation by fluidized-bed Fenton process were determined using Box-Behnken designs (BBD). The BBD can be used to find the optimal conditions in multivariable systems. The optimal conditions obtained by the design were further applied in the kinetic analysis of o-toluidine oxidation in fluidized-bed Fenton process. MATERIALS AND METHODS: The 1.35-L fluidized-bed reactor used in all experiments was a cylindrical vessel with an inlet, outlet, and recirculation pump. The o-toluidine was determined by high-performance liquid chromatography. RESULTS AND DISCUSSION: Analytical results indicated that pH, Fe(2+), and H(2)O(2) were significant factors in o-toluidine and chemical oxygen demand (COD) removal, but loading carrier was not. The pH significantly affected not only o-toluidine degradation, but also total iron removal. The predicted conditions for optimal removal of 1 mM of o-toluidine using 100 g of carriers were pH 3 ± 0.5, 1 mM of Fe(2+), and 17 mM of H(2)O(2). Removal of o-toluidine and COD in the actual experiment was higher than predicted, whereas removal of total iron was slightly lower. The kinetic study showed that the initial rate and rate constant (k) of o-toluidine degradation in the fluidized-bed Fenton process correlated Fe(2+) concentration. In the Fe(2+)/H(2)O(2) stage, high concentration of H(2)O(2) produced a scavenging effect. CONCLUSIONS: The predicted removal efficiencies of o-toluidine and COD were 90.2% and 41.4%, respectively. Moreover, the removals of o-toluidine and COD in the actual experiment were 99.8% and 61.8%, respectively.

Comparison of o-toluidine degradation by Fenton, electro-Fenton and photoelectro-Fenton processes.

A Box-Behnken design (BBD) statistical experimental design was used to investigate the degradation of o-toluidine by the electro-Fenton process. This method can be used to determine the optimal conditions in multivariable systems. Fe(2+) concentration (0.2-1.0mM), H(2)O(2) concentration (1-5mM), pH (2-4), and current (1-4A) were selected as independent variables. The removal efficiencies for o-toluidine and chemical oxygen demand (COD) were represented by the response function. Result by 2-level factorial design show that the pH and the Fe(2+) and H(2)O(2) concentrations were the principal parameters. Among the main parameters, the removal efficiencies for o-toluidine and COD were significantly affected by pH and Fe(2+) concentration. From the Box-Behnken design predictions, the optimal conditions in the electro-Fenton process for removing 90.8% of o-toluidine and 40.9% of COD were found to be 1mM of Fe(2+) and 4.85 mM of H(2)O(2) at pH 2. Under these optimal conditions, the experimental data showed that the removal efficiencies for o-toluidine and COD in the electro-Fenton process and the photoelectro-Fenton process were more than 91% and 43%, respectively, after 60 min of reaction. The removal efficiencies for o-toluidine and COD in the Fenton process are 56% and 27%, respectively.

Photocatalytic activity of tungsten-doped TiO2 with hydrothermal treatment under blue light irradiation.

Tungsten doping and hydrothermal treatment were found to significantly improve the visible-light photoactivity of TiO(2) synthesized by the sol-gel method. It was observed that TiO(2) doped with a 0.5% W:Ti mole ratio and treated with 4 h of hydrothermal curing showed photoactivity under blue light irradiation equal to 74% of the commercial Degussa P-25 under UV irradiation, i.e., 0.01 mM 2-chlorophenol was completely removed in 120 and 90 min, respectively. Light absorptivity and photocatalytic activity under blue light irradiation were not dependent on the crystallite structure of the TiO(2). The oxidation kinetics under blue light irradiation can be effectively explained by the Langmuir-Hinshelwood model with an apparent reaction rate constant and a Langmuir constant of 3.60 × 10(-4) mM min(-1) and 206.53 mM(-1), respectively.

Persulfate oxidation for the aniline degradation in aqueous systems.

Ferrous catalyzed persulfate oxidation of dissolved aniline was investigated in aqueous systems under a variety of ferrous ion concentrations and temperature. Result showed that the addition of ferrous ions accelerated the degradation of aniline by persulfate. For the thermally activated persulfate oxidation experiment, the optimum persulfate/aniline concentration ratio at 30˚C was at 5.4 mM or 20/1. This ratio gave the highest aniline removal of 45%. For the ferrous ion catalyzed persulfate oxidation experiment, there was marginal difference in the result for the various ferrous ion/oxidant molar ratios. Thus, another series of experiment was conducted to determine the optimum ratio and a ferrous ion/persulfate molar ratio of 1.25/1 showed the highest removal efficiency.

Iron crystallization in a fluidized-bed Fenton process.

The mechanisms of iron precipitation and crystallization in a fluidized-bed reactor were investigated. Within the typical Fenton's reagent dosage and pH range, ferric ions as a product from ferrous ion oxidation would be supersaturated and would subsequently precipitate out in the form of ferric hydroxide after the initiation of the Fenton reaction. These precipitates would simultaneously crystallize onto solid particles in a fluidized-bed Fenton reactor if the precipitation proceeded toward heterogeneous nucleation. The heterogeneous crystallization rate was controlled by the fluidized material type and the aging/ripening period of the crystallites. Iron crystallization onto the construction sand was faster than onto SiO(2), although the iron removal efficiencies at 180 min, which was principally controlled by iron hydroxide solubility, were comparable. To achieve a high iron removal rate, fluidized materials have to be present at the beginning of the Fenton reaction. Organic intermediates that can form ferro-complexes, particularly volatile fatty acids, can significantly increase ferric ion solubility, hence reducing the crystallization performance. Therefore, the fluidized-bed Fenton process will achieve exceptional performance with respect to both organic pollutant removal and iron removal if it is operated with the goal of complete mineralization. Crystallized iron on the fluidized media could slightly retard the successive crystallization rate; thus, it is necessary to continuously replace a portion of the iron-coated bed with fresh media to maintain iron removal performance. The iron-coated construction sand also had a catalytic property, though was less than those of commercial goethite.

Verification of competitive kinetics technique and oxidation kinetics of 2,6-dimethyl-aniline and o-toluidine by Fenton process.

The competitive kinetics technique is shown to be a useful and reliable tool for determining rate constants. Regardless of the conditions of the reaction and the operation mode, the intrinsic second-order rate constants of 2,6-dimethyl-aniline and hydroxyl radicals were 1.65 × 10(10), 1.60 × 10(10), and 1.71 × 10(10)M(-1)s(-1) in the absence of SiO(2) under complete-mix conditions, in the presence of SiO(2) under complete-mix conditions, and in a fluidized-bed Fenton reactor with SiO(2) as the media, respectively, demonstrating that the rates are comparable under a variety of reaction conditions. The average intrinsic second-order rate constant of o-toluidine and hydroxyl radicals obtained in a homogeneous system under various conditions was 7.36 × 10(9)M(-1)s(-1), indicating that o-toluidine is less susceptible to hydroxyl radicals than 2,6-dimethyl-anilne. Hydroxyl radicals primarily attacked the amine group rather than the methyl group of the o-toluidine to form o-cresol and 2-nitrotoluene, which sequentially transformed to carboxylic acids including acetic, oxalic, lactic, and maleic acids after the collapse of the benzene ring.

Effect of hydrogen peroxide on aniline oxidation by electro-Fenton and fluidized-bed Fenton processes.

In this study, the electro-Fenton and fluidized-bed Fenton processes under the given conditions were used to oxidize aniline. Factors such as feeding mode and concentration of the hydrogen peroxide were explored. Results showed that the feeding mode of H(2)O(2) did not significantly affect the aniline oxidation in the electro-Fenton process. However, the aniline oxidation slightly decreased with the two-step addition of H(2)O(2) in the fluidized-bed Fenton process. Presumably the decline of remaining Fe(2+) led to destitute hydrogen radicals from the Fe(2+)-catalyzed H(2)O(2). In addition, the removal efficiency of aniline was maintained at a maximum as H(2)O(2) concentration was higher than 0.04 M in the electro-Fenton process. Meanwhile, the almost exhausted H(2)O(2) would increase the amount of Fe(2+) in the solution for the electro-Fenton process. This is because the Fe(2+) is regenerated through the reduction of Fe(3+) on the cathode. The electro-Fenton process has a stronger oxidative ability with regard to the production of the oxalic acid than fluidized-bed Fenton process which was attributed to a higher consumption of H(2)O(2). Therefore, in the aspect of H(2)O(2) depletion, the mineralization efficiency of the fluidized-bed Fenton process was higher than that of the electro-Fenton process.

Hexachlorobenzene dechlorination by indigenous sediment microorganisms.

Indigenous microbes from the sediments, whether contaminated with hexachlorobenzene (HCB) or not, could dechlorinate HCB effectively without any acclimation and supplemental nourishment. Temperature seriously affected the HCB-dechlorination: within the measured 15-45 degrees C span, the optimum range was between 30 and 35 degrees C. Sulfate-reducing bacteria (SRB), denitrifiers, and acetogens might not be directly involved in the HCB dechlorination. However, the SRB retarded subsequent dechlorination of pentachlorobenzene to tetra- and trichlorobenzenes. Some vancomycin-resistant gram-positive bacteria and methanogens were most likely to be the HCB-dechlorinators. The dechlorination followed the Michaelis-Menten behavior with the k'(m) and K(HCB) between 0.45-0.73 mg L(-1)day(-1) and 3.2-17.2 mg L(-1), respectively. These findings suggest a potential HCB treatment and cleanup for wastewater and contaminated site.

Kinetics and mechanism of 2,6-dimethyl-aniline degradation by hydroxyl radicals.

This research investigated the intrinsic second-order rate constant between 2,6-dimethyl-aniline (2,6-DMA) and hydroxyl radicals (OH) using Fenton's reactions under both batch and continuous operations. The competitive kinetics technique with aniline as a reference compound was employed. In the batch study under various conditions, the second-order rate constants of 2,6-DMA with OH were between 1.59 x 10(10) and 1.80 x 10(10)M(-1)s(-1) with a mean of 1.71 x 10(10)M(-1)s(-1) which equals the average value obtained from the continuous study as well. The concentrations of OH at the steady state under the continuous mode were estimated to be between 4.85 x 10(-10) and 6.82 x 10(-10)mM. 2,6-dimethyl-nitrobenzene, 2,6-dimethyl-phenol, 2,6-dimethyl-nitrophenol, 2,6-dimethyl-hydroquinone, 2,6-dimethyl-p-benzoquinone, and 2,6-dimethyl-3-hydroxy-p-benzoquinone were identified as the aromatic by-products indicating that the methyl group on the aromatic ring was not susceptible to OH attack. Maleic, lactic, oxalic, acetic, and formic acids were found as generated carboxylic acids. An oxidation pathway of 2,6-DMA by OH is also proposed.

Kinetics of nitrobenzene oxidation and iron crystallization in fluidized-bed Fenton process.

This research investigated the nitrobenzene oxidation and iron removal by fluidized-bed Fenton process using metal oxide as the carriers. It was found that the removal efficiency of nitrobenzene was not affected in the presence of metal oxide. However, metal oxide could retard the degradation rate of nitrobenzene with Fenton process due to ferrous adsorption/complexation onto its surface leaving insufficient free Fe(2+) to catalyze the decomposition of H(2)O(2). Nonetheless, as the free Fe(2+) was sufficient, nitrobenzene was oxidized at the same rate as that by the conventional Fenton process. Fenton's reagent and nitrobenzene concentrations have an impact on nitrobenzene oxidation rate. The empirical kinetic equation for nitrobenzene oxidation by the fluidized-bed Fenton process under the conditions of 0.667-5mM of Fe(2+), 10-50mM of H(2)O(2), 5-12.5mM of nitrobenzene, 76.9 g/l of metal oxide, and pH 2.8+/-0.2, can be described as: [see formula text] Considering on iron removal performance, it was found that the fluidized-bed Fenton process could remove 30-65% of iron via iron crystallization onto the carriers' surface which could lead to a significant reduction in ferric hydroxide sludge production. H(2)O(2) played an important role in iron crystallization and once it was exhausted, the re-dissolution of iron occurred. In addition, it was found that the metal oxide could be repeatedly used up to 5 cycles without any significant deterioration in its surface activity. Hence, it implies that the metal oxide can be used successfully in the fluidized-bed Fenton process operated under a continuous mode.

Estimation of intracellular phosphorus content of phosphorus-accumulating organisms at different P:COD feeding ratios.

The intracellular phosphorus content of phosphorus-accumulating organisms (PAO) was determined based on a stoichiometric equation and phosphorus balance for an enhanced biological phosphorus removal system fed with different P:COD ratios. The data indicated that a higher P:COD feeding ratio could significantly promote the growth of PAO. As the P:COD feeding ratio increased from 0.02:1 to 0.04:1 and 0.16:1, the phosphorus in the sludge increased considerably from 0.053 to 0.084 and 0.205 mg P (mg VSS(aerobic))(-1), respectively, indicating a dynamic condition in the microbial population. From the calculations, the mass fractions of the PAO, glycogen-accumulating organisms, and ordinary heterotrophs changed from 0.10-0.15, 0.83-0.88, and 0.02 at 0.02:1 to 0.19-0.28, 0.70-0.79, and 0.02 at 0.04:1 and to 0.478-0.71, 0.26-0.50, 0.03 at 0.16:1 P:COD feeding ratios, respectively. Despite the variation in microbial diversity, the calculated phosphorus contents of the PAO at all P:COD feeding ratios were consistent between 0.241 and 0.378 mg P (mg VSS(PAO))(-1). The initial specific phosphorus release and uptake rates were 84.7-167.9 mg P (g VSS(PAO))(-1)h(-1) and 52.8-90.0 mgP (g VSS(total))(-1)h(-1), respectively.

Integrated treatment scheme for rubber thread wastewater: sulfide precipitation and biological processes.

In this study, acidic latex wastewater containing high average zinc and acetic contents of 816mgL(-1) and 20,862mgCODL(-1), respectively, was treated successfully by a series of chemical and biological processes without any addition of acid or base for pH adjustment. Total dissolved solids of the treated effluent increased by only 1.1-fold on average for sulfide precipitation as compared to 2.8-fold for the hydroxide strategy. The oxidation-reduction potential (ORP) value of 0mV was used successfully as an indicator for optimum sulfide addition which consistently provided an appreciable reduction in effluent concentrations to less than 1 and 2mgL(-1) for zinc and residual sulfide, respectively. The anaerobic filter was very stable in handling the chemically treated wastewater up to the organic loading rate of 11.8gCODL(-1)day(-1) with an average efficiency of 92%. Methane production and biomass yield were 0.32L(gCOD(removed))(-1) and 0.014gVSS (gCOD(removed))(-1), respectively. For the activated sludge process, the optimum sludge age and hydraulic retention time were 30 and 0.8 days, respectively, which are equivalent to the organic loading rates of 2.50gCODL(-1)day(-1) or 2.13gBODL(-1)day(-1). Under these optimum conditions, average removal efficiencies for COD and BOD were 96.6 and 99.4%. Average soluble COD, BOD and suspended solids in the effluent were 71, 11 and 38mgL(-1), respectively. This integrated treatment scheme was proven to be an effective approach for highly polluted and toxic rubber thread wastewater.

Oxidation and detoxification of pentachlorophenol in aqueous phase by ozonation.

The degradation and detoxification performance of ozonation in treating pentachlorophenol (PCP) contaminated wastewater was determined. All experiments were conducted in a bench scale glass column equipped with ceramic diffuser and a lab-scale ozone generator under ambient temperature and pH 7. The decomposition rate of PCP in this study was primarily controlled by the ozone mass transfer rate from gas to liquid phases. Principal intermediates found were 2,3,4,6- and 2,3,5,6-tetrachlorophenols (TeCP) and phenol. PCP seems to be more vulnerable to ozone than its intermediates. A bioluminescence technique was used to evaluate the toxicity of PCP with Vibrio fisheri NRRL B-11177 as the test bacterium, and the EC(50) of PCP was found to be 1.0 mg l(-1). Detoxification occurred as the PCP and TeCP reacted with ozone and decomposed to less chlorinated congeners and phenol.

Kinetics of aniline degradation by Fenton and electro-Fenton processes.

Aniline degradation at pH 2 by Fenton and electro-Fenton processes was kinetically investigated in this study. Electro-Fenton process was found to be superior to ordinary Fenton process with the current impacts of 1.2 to 3.1 for removal efficiency and 1.2 to 5.8 for degradation rate depending on initial Fe2+ concentration. This is mainly due to the rapid electrochemical regeneration of Fe2+. Overall rate equations for aniline degradation by Fenton and electro-Fenton processes (in units of molar and minute) are: [EQUATION: SEE TEXT]. With current application, aniline degradation rate seems to be autonomous from Fenton's reagent concentrations and approaching a half order with respect to aniline. In addition, for complete removal of 0.01 M aniline, the delay in current supply at the initial stage could save up to one-third of the total energy required by the ordinary electro-Fenton process. As a result, significant reduction in energy consumption and operating cost could be obtained by the current-delay operating mode.

Effects of water characteristics on nitrate reduction by the Fe0/CO2 process.

In this study, CO2 was bubbled into Fe0-contained solution to create an acidic environment favorable to reduction of aqueous nitrate under various water qualities. Results showed that nitrate of 30 mg l(-1) could be removed from solutions almost completely within 30 min under the conditions of 2 g Fe0 l(-1) and CO2 bubbling flow rate of 200 ml min(-1). It was observed from the Fe0/CO2 system that one mole of nitrate reduced by Fe0 led to the formation of 6.6 mol of ferrous ions. The removal of nitrate increases with increasing Fe0 dosage, however, the removal makes no difference as the Fe0 is applied at a relatively higher dosage. In the system with various water qualities, nitrate removal was inhibited significantly in the presence of humic acid. Calcium ions strongly retard nitrate removal, whereas chloride ions promote the reduction of nitrate in a significant way. Sodium ions impose only slight inhibitive effect on nitrate removal. Water molecule in the studied system can be of significance due to its competitive capability of electrons released from Fe0.