Batch Degradation Experiments Research Articles

Development of halotolerant multi-pesticides degraders for wastewater treatment

The biotreatment performance of high saline wastewater containing multiple pesticides is significantly reduced because the growth and metabolism of activated sludge microbial communities are severely impaired by high osmotic pressure and joint toxicity of multiple pesticides. In this study, Halomonas cupida J9 was metabolically engineered by chromosomal integration of three different pesticide hydrolase genes, to create a halotolerant multi-pesticides degrader. In batch degradation experiments, the finally constructed strain J9U-PVG was able to simultaneously degrade chlorpyrifos (organophosphate), carbaryl (carbamate) and α-cypermethrin (pyrethroid) in mineral salt medium supplemented with 4 g/L glucose and 60 g/L NaCl. Total cell lysate of J9U-PVG showed obvious degradation activity against chlorpyrifos, carbaryl and α-cypermethrin. Moreover, introduced Vitreoscilla hemoglobin (VHb) can enhance oxygen-sequestering capability of J9U-PVG and introduced green fluorescent protein (GFP) can be used as a biomarker to track the activity and movement of J9U-PVG in natural environments. More importantly, J9U-PVG could simultaneously and completely degrade chlorpyrifos, carbaryl and α-cypermethrin in high saline river water. Here, we demonstrate for the first time the successful construction of a halotolerant multi-pesticides degrader. This study underscores the value of H. cupida J9 as a promising chassis for the development of a halotolerant pesticide bioremediation platform. In the future, synthetic biology may serve as a powerful tool for expanding the catalytic repertoire of extremophiles for bioremediation of extreme environments.

Noncondensed aromatic carbon of sludge-derived biochar predominated peroxydisulfate activation mechanism for tetracycline degradation via an electron transfer pathway

ABSTRACT Discrimination of the catalytic ability of heterogeneous biochar components is often challenging. Herein, a sewage sludge-derived biochar (SDBC) was prepared to activate peroxydisulfate (PDS) for tetracycline (TC) degradation. To verify the contribution of different carbon components, SDBC was bleached with NaClO2 and CH3COOH to remove noncondensed aromatic carbon (NAC) contained in biochar, which was confirmed by 13C Nuclear Magnetic Resonance. The batch degradation experiment revealed that NAC removal decreased TC degradation by SDBC from 84.1% to 33.2% within 2 h, indicating its significant role in PDS activation. The quenching and electron paramagnetic resonance experiments suggested a very minor contribution of radical pathway in TC degradation. Instead, the electron transfer pathway predominated TC degradation mechanism as inferred by electrochemical tests. This is likely ascribed to formation of a biochar-PDS metastable complex, facilitating electron transfer from tetracycline-like compounds. An X-ray photoelectron spectroscopy confirmed that the percent of graphitic N in SDBC decreased after the degradation reaction, which suggested graphitic N is an important active site in biochar. Besides, acid-washed SDBC did not change TC degradation behavior excluding significant contribution of minerals in SDBC to PDS activation. Thus, the roles of biochar components in catalyzing PDS were quantified for the first time, proving insight for selection and manipulation of biochar in catalyzing PDS in environmental application.

Effect of Nitrogen-doped − Palm Oil Mill Effluent Sludge-biochar as Peroxydisulfate Activator on the Removal of Methylene Blue Dye as an Environmental-friendly Approach

Introduction: Water pollution caused by dyes is a major problem as it is a toxic chemical that can cause chronic diseases when exposed to humans and aquatic habitats. Sulfate-based advanced oxidation process based on peroxydisulfate (PDS) has received a lot of attention recently for achieving color degradation in wastewater. Transition metal-based homogeneous/heterogeneous catalysts have shown to be a good alternative for the activation of persulfate. Nonetheless, this leads to significant secondary contamination due to metal leaching. Alternatively, nitrogen-doped biochar is a promising non-metal persulfate activator due to its lower cost and more environmentally friendly. Methods: Biochar from Palm Oil Mill Effluent (POME) sludge doped with nitrogen source of urea, ammonium chloride, and melamine was synthesized at a 700°C pyrolysis process and used to activate PDS. The nitrogen content of synthesized POME biochar was altered to ratios of 25:75, 50:50, and 75:25 respectively. Batch degradation experiments were then conducted to determine the feasibility of catalytic removal of methylene blue (MB) dye. Results: Based on experimental results, urea-doped biochar showed a greater MB removal compared to ammonium chloride and melamine-doped biochar. Besides that, higher nitrogen-to-biochar ratio increases the MB degradation significantly. A similar trend was demonstrated when a higher urea-doped biochar dosage was utilized. By utilizing 5.0 g of urea-doped biochar, a 100 ± 0.7% degradation of MB was achieved. Conclusion: This research provides an effective method to produce carbon-based catalysts from sludge recovery for activation of PDS, also enhancing the catalytic performance of biochar on MB dye removal by N-doping.

Nematodes Degrade Extracellular Antibiotic Resistance Genes by Secreting DNase II Encoded by the nuc-1 Gene.

This study investigated the degradation performance and mechanism of extracellular antibiotic resistance genes (eARGs) by nematodes using batch degradation experiments, mutant strain validation, and phylogenetic tree construction. Caenorhabditis elegans, a representative nematode, effectively degraded approximately 99.999% of eARGs (tetM and kan) in 84 h and completely deactivated them within a few hours. Deoxyribonuclease (DNase) II encoded by nuc-1 in the excretory and secretory products of nematodes was the primary mechanism. A neighbor-joining phylogenetic tree indicated the widespread presence of homologs of the NUC-1 protein in other nematodes, such as Caenorhabditis remanei and Caenorhabditis brenneri, whose capabilities of degrading eARGs were then experimentally confirmed. C. elegans remained effective in degrading eARGs under the effects of natural organic matter (5, 10, and 20 mg/L, 5.26-6.22 log degradation), cation (2.0 mM Mg2+ and 2.5 mM Ca2+, 5.02-5.04 log degradation), temperature conditions (1, 20, and 30 °C, 1.21-5.26 log degradation), and in surface water and wastewater samples (4.78 and 3.23 log degradation, respectively). These findings highlight the pervasive but neglected role of nematodes in the natural decay of eARGs and provide novel approaches for antimicrobial resistance mitigation biotechnology by introducing nematodes to wastewater, sludge, and biosolids.

Regulating the electrokinetic delivery of Tween 80 and persulfate for remediating low-permeability phenanthrene contaminated soil: Importance of reducing unproductive consumption

Controllable delivery of persulfate (PS) and the enhancement of oxidative availability of pollutants in in-situ oxidative remediation of low-permeability polycyclic aromatic hydrocarbons (PAHs) contaminated soil are crucial. To tackle the above challenges, the coupling of Tween 80 solubilization enhanced oxidation of phenanthrene (PHE) in low-permeability soil under electrokinetic remediation (EKR) was proposed. Firstly, batch degradation experiments showed that the addition of Tween 80 significantly inhibited the degradation of PHE in soil under thermally activated PS, as the dosage of Tween 80 increased from 0 % to 1 % with the corresponding removal rate declining from 99.19 % to 40.90 %. Accordingly, in-situ electrokinetic delivery of Tween 80 and PS was regulated in further EKR, intending to reduce unproductive consumption. PS was more uniformly delivered to the whole remediation regions from the cathode chamber by electromigration, while Tween 80 was transported into the soil from the anode chamber by electroosmosis, which made Tween 80 solubilization and PS oxidation achieve synergistic effect. And the total removal rate of PHE reached 64.90 % under this strategy, which had increased by 415.90 % and 8.76 %− 130.14 % compared with only EKR or EKR coupling single enhanced technology, respectively. After further thermal activation of transported PS at 50 ℃ by electrical resistance heating, the total removal rate of PHE increased to 71.58 %. EPR spectrum indicated that SO4.- and OH. were responsible for the degradation of PHE.

Role of the surface characteristics of hyper-crosslinked polymers on the transformation of adsorbed trichlorophenol: Implications for understanding the surface reactivity of biochar derived from waste biomass

The surface reactivity of biochar derived from waste biomass has not been well understood due to its complex composition and heterogeneity. Therefore, this study synthesized a series of biochar-like hyper-crosslinked polymers (HCPs) with different amounts of phenolic hydroxyl groups on the surface as an indicative tool to investigate the roles of key surface properties of biochar on transforming pollutants being adsorbed. Characterization of HCPs suggested that electron donating capacity (EDC) of different HCPs was positively correlated with increasing amounts of phenol hydroxyl groups, whereas specific surface area, degree of aromatization and graphitization were negatively correlated. It was found that greater amounts of hydroxyl radicals were produced with increasing amounts of hydroxyl groups on the synthesized HCPs. Batch degradation experiments with trichlorophenols (TCPs) suggested that all HCPs could decompose TCP molecules upon contact. The degree of TCP degradation (~45 %) was highest for HCP made from benzene monomer with the lowest amounts of hydroxyl groups, which was likely driven by its greater specific surface area and reactive sites for TCP degradation. Conversely, the degree of TCP degradation (~25 %) by HCPs with the highest hydroxyl group abundance was the lowest, probably because the lower surface area of HCPs had limited TCP adsorption, which led to lower interaction between HCP surface and TCP molecules. The results concluded from the contact of HCPs and TCP suggested both EDC and adsorption capacity of biochar played critical roles in transforming organic pollutants.

Biodegradation of monocrotophos by Brucella intermedia Msd2 isolated from cotton plant.

Widespread and inadequate use of Monocrotophos has led to several environmental issues. Biodegradation is an ecofriendly method used for detoxification of toxic monocrotophos. In the present study, Msd2 bacterial strain was isolated from the cotton plant growing in contaminated sites of Sahiwal, Pakistan. Msd2 is capable of utilizing the monocrotophos (MCP) organophosphate pesticide as its sole carbon source for growth. Msd2 was identified as Brucella intermedia on the basis of morphology, biochemical characterization and 16S rRNA sequencing. B. intermedia showed tolerance of MCP up to 100ppm. The presence of opd candidate gene for pesticide degradation, gives credence to B. intermedia as an effective bacterium to degrade MCP. Screening of the B. intermedia strain Msd2 for plant growth promoting activities revealed its ability to produce ammonia, exopolysaccharides, catalase, amylase and ACC-deaminase, and phosphorus, zinc and potassium solubilization. The optimization of the growth parameters (temperatures, shaking rpm, and pH level) of the MCP-degrading isolate was carried out in minimal salt broth supplemented with MCP. The optimal pH, temperature, and rpm for Msd2 growth were observed as pH 6, 35 °C, and 120rpm, respectively. Based on optimization results, batch degradation experiment was performed. Biodegradation of MCP by B. intermedia was monitored using HPLC and recorded 78% degradation of MCP at 100ppm concentration within 7days of incubation. Degradation of MCP by Msd2 followed the first order reaction kinetics. Plant growth promoting and multi-stress tolerance ability of Msd2 was confirmed by molecular analysis. It is concluded that Brucella intermedia strain Msd2 could be beneficial as potential biological agent for an effective bioremediation for polluted environments.

Transcriptomic analysis reveals peripheral pathway in 3-phenoxybenzoic acid degradation by Aspergillus oryzae M-4

As a major intermediate metabolite of synthetic pyrethroids, the occurrence of 3-phenoxybenzoic acid hinders the decomposition of the parent pesticide and poses uncertain risks to environmental ecology and living organisms. Strain Aspergillus oryzae M-4 was previously reported to degrade 3-PBA and several substances were identified as downstream transformation products (TPs). But the mechanism underlying the cleavage of ether bond remains largely unclear. Here, we attempted to address such concern through identifying the peripheral TPs and analyzing transcriptomics, coupled with serial batch degradation experiments. Analysis results of chromatographic/mass spectrometry suggested that 3-PBA underwent twice hydroxylation, to yield mono- and dihydroxylated 3-PBA successively. In parallel, a mutual transformation between 3-PBA and 3-phenoxybenzyl alcohol (3-PBOH) also existed. The proposal of peripheral pathway represents an important advance towards fully understanding the whole 3-PBA metabolism in M-4. A specific altered metabolization was found for the first time, that is, resting cells of M-4 skipped the reduction step and initiate hydroxylation directly, by comparison with growing cells. Transcriptome analysis indicated that 3-PBA induced the up-regulation of genes related to energy investment, oxidative stress response, membrane transport and DNA repair. In-depth functional interpretation of differential expression genes suggested that the generation 3-PBOH and hydroxylated 3-PBA may be due to the participation of flavin-dependent monooxygenases (FMOs) and cytochrome P450 (CYP450), respectively. This study provides new insight to reveal the biodegradation mechanism of 3-PBA by A. oryzae M-4.

Boosting activation of molecular oxygen on the surface of fluorine doped g-C3N4 for efficient degradation of tetracycline: Synergistic effect of surface double central atom coordination and photo-Fenton oxidation

Largely limited by the high dissociation energy of the O-O bond, how to effectively promote the activation of molecular oxygen (O2) on the surface of the graphitic carbon nitride (g-C3N4) has always been the key to improving the photocatalytic performance of g-C3N4. In this study, by utilizing the coordination reaction between F-Fe and O-Fe, a complex (ox-Fe-F-g-C3N4) with F and Fe as central atom, oxalate (ox) and g-C3N4 as ligand molecule was successfully constructed. Relevant characterizations and density functional theory (DFT) calculations together verify that the electron transfer of complex was significantly promoted. It not only beneficial to enhance the ability of photogenerated holes (h+) to directly oxidize tetracycline (TC), but also helps to accelerate the activation of O2 to generate reactive oxygen species (ROS). In addition, under the action of photoelectron reduction, a photo-Fenton oxidation platform based on Fe (III) and Fe (II) cycling can be established on the surface of F-g-C3N4. This facilitates the conversion of H2O2 generated by activating O2 into hydroxyl radicals (•OH) with higher oxidative activity. Batch degradation experiments confirmed that under the synergistic promotion of surface coordination and photo-Fenton oxidation, the photocatalytic efficiency of ox-Fe-F-g-C3N4 is nearly 4 times that of pristine g-C3N4.

Microbial properties of the granular sludge in a psychrophilic UASB reactor fed with electronics industry wastewater containing organic chemicals

In this study, a lab-scale upflow anaerobic sludge blanket (UASB) reactor was applied to the treatment of artificial electronics industry wastewater containing tetramethylammonium-hydroxide (TMAH), monoethanolamine (MEA), and isopropyl-alcohol (IPA) in order to evaluate process performance and degradation properties. During 800 days of operation, 96% efficiency of chemical oxygen demand (COD) removal was stably achieved at an organic loading rate of 8.5 kgCOD/m3/day at 18–19 °C. MEA degradation, carried out by acid-forming eubacteria, was confirmed within a week. The physical properties of the retained granular sludge were degraded by feeding with TMAH wastewater, but maintained by feeding with MEA wastewater due to an accumulation of species from the genus Methanosaeta and family Geobacteraceae. Analysis of the microbial community structure via SEM and 16S rRNA genes showed a proliferation of Methanomethylovorans-like cells and Methanosaeta-like cells at the surface and in the core of the granular sludge with TMAH, MEA and IPA acclimation. Furthermore, a batch degradation experiment confirmed that process inhibition due to increasing chemical concentration was relatively stronger for TMAH than for MEA or IPA. Thus, controlling the TMAH concentration of the influent to below 1 gCOD/L will be important for the stable treatment of electronics industry wastewater by UASB technology.

How microbial community composition, sorption and simultaneous application of six pharmaceuticals affect their dissipation in soils

Pharmaceuticals may enter soils due to the application of treated wastewater or biosolids. Their leakage from soils towards the groundwater, and their uptake by plants is largely controlled by sorption and degradation of those compounds in soils. Standard laboratory batch degradation and sorption experiments were performed using soil samples obtained from the top horizons of seven different soil types and 6 pharmaceuticals (carbamazepine, irbesartan, fexofenadine, clindamycin and sulfamethoxazole), which were applied either as single-solute solutions or as mixtures (not for sorption). The highest dissipation half-lives were observed for citalopram (average DT50,S for a single compound of 152 ± 53.5 days) followed by carbamazepine (106.0 ± 17.5 days), irbesartan (24.4 ± 3.5 days), fexofenadine (23.5 ± 20.9 days), clindamycin (10.8 ± 4.2 days) and sulfamethoxazole (9.6 ± 2.0 days). The simultaneous application of all compounds increased the half-lives (DT50,M) of all compounds (particularly carbamazepine, citalopram, fexofenadine and irbesartan), which is likely explained by the negative impact of antibiotics (sulfamethoxazole and clindamycin) on soil microbial community. However, this trend was not consistent in all soils. In several cases, the DT50,S values were even higher than the DT50,M values. Principal component analyses showed that while knowledge of basic soil properties determines grouping of soils according sorption behavior, knowledge of the microbial community structure could be used to group soils according to the dissipation behavior of tested compounds in these soils. The derived multiple linear regression models for estimating dissipation half-lives (DT50,S) for citalopram, clindamycin, fexofenadine, irbesartan and sulfamethoxazole always included at least one microbial factor (either amount of phosphorus in microbial biomass or microbial biomarkers derived from phospholipid fatty acids) that deceased half-lives (i.e., enhanced dissipations). Equations for citalopram, clindamycin, fexofenadine and sulfamethoxazole included the Freundlich sorption coefficient, which likely increased half-lives (i.e., prolonged dissipations).

Oxidative degradation of Bisphenol A in aqueous solution using cobalt ion-activated peroxymonosulfate

The degradation of Bisphenol A (BPA) in aqueous solution by an advanced oxidation process (AOP) involving cobalt ion activation of peroxymonosulfate (PMS) was investigated, in order to optimize the effectiveness of the PMS/Co system for complete mineralization of Bisphenol A in aqueous media. Batch degradation experiments were carried out in a 500 mL capacity quartz reactor under varied conditions of Co2+ ion source, pH, oxidant and catalyst dosage/ratio and time. The effect of humic acid addition on the degradation process was as well assessed. A technique was adapted for monitoring the degradation process by means of high-performance liquid chromatography. Results obtained show clearly that Co-activated PMS was very efficient for the degradation of BPA in water, due to action of strongly oxidizing sulfate radical anion (SO4−) and hydroxyl radical (OH). Both CoSO4 and CoCl2 as catalysts yielded complete degradation of BPA under different conditions. The time interval to complete degradation increased for higher BPA concentrations, whereas the trend of degradation rate with pH was pH 5 > pH 9 > pH 7. The presence of humic acid in water hindered the degradation performance of Co/PMS in a time-dependent manner. Quantum chemical computations performed to assess the local reactivity of the BPA molecule and to identify the reactive regions in terms of radical (F) and electrophilic attack (F−), revealed that radical attack would be initiated on the aromatic ring and olefinic double bonds. The present study has revealed that the PMS/Co2+ oxidation process has the capacity to completely remove and mineralize Bisphenol A from aqueous solution.

Areca nut (Areca catechu) husks and Luffa (Luffa cylindrica) sponge as microbial immobilization matrices for efficient phenol degradation

Immobilization of microorganisms is a widely adopted strategy for the efficient degradation of hazardous organic compounds like phenol. Microorganisms can be immobilized in synthetic or natural matrices. In this work dried areca nut (Areca catechu) husks and luffa (Luffa cylindrica) sponge fibers were used as alternative and inexpensive natural matrices for microbial cell immobilization. The potential of these immobilization systems for the effective bioremediation of phenolic wastewater was explored. A bacterial consortium was isolated by enriching a sludge sample from a petroleum refinery in high phenol concentrations. The mixed bacterial culture was capable of degrading 1000 mg L−1 of phenol in suspension cultures. The bacterial consortium was immobilized on the lignocellulosic matrices. Phenol degradation studies were performed in batches to optimize the physicochemical parameters. Optimum pH and temperature for phenol degradation was found to be 8.0 and 37 °C. At an optimum pH and temperature, the areca nut husk and luffa sponge systems immobilized with the mixed culture could degrade 1000 mg L−1 phenol in 28 h and 30 h respectively. The highest experimental degradation rates in areca nut husk and luffa sponge systems were 0.37 h−1 and 0.21 h−1 respectively at 200 mg L−1 phenol. Degradation kinetic studies were carried out using several inhibition models. Further studies revealed that both matrices with immobilized microbes could be reused for several successive batch degradation experiments and stored at 4 °C for several weeks without any noticeable loss in degradation efficiency.

Activation of Persulfate by Biochars from Valorized Olive Stones for the Degradation of Sulfamethoxazole

Biochars from spent olive stones were tested for the degradation of sulfamethoxazole (SMX) in water matrices. Batch degradation experiments were performed using sodium persulfate (SPS) as the source of radicals in the range 250–1500 mg/L, with biochar as the SPS activator in the range 100–300 mg/L and SMX as the model micro-pollutant in the range 250–2000 μg/L. Ultrapure water (UPW), bottled water (BW), and secondary treated wastewater (WW) were employed as the water matrix. Removal of SMX by adsorption only was moderate and favored at acidic conditions, while SPS alone did not practically oxidize SMX. At these conditions, biochar was capable of activating SPS and, consequently, of degrading SMX, with the pseudo-first order rate increasing with increasing biochar and oxidant concentration and decreasing SMX concentration. Experiments in BW or UPW spiked with various anions showed little or no effect on degradation. Similar experiments in WW resulted in a rate reduction of about 30%, and this was attributed to the competitive consumption of reactive radicals by non-target water constituents. Experiments with methanol and t-butanol at excessive concentrations resulted in partial but generally not complete inhibition of degradation; this indicates that, besides the liquid bulk, reactions may also occur close to or on the biochar surface.

Lab-Scale Biodegradation Study of BTEX under the Unsaturated Condition and Its Effect on Soil Matric Potential

ABSTRACTBenzene, toluene, ethylbenzene, and xylene are collectively known as BTEX which contributes to volatile environmental contaminants. This present study investigates the microbial degradation of BTEX in batch and continuous soil column experiments and its effects on soil matric potential. Batch degradation experiments were performed with different initial concentrations of BTEX using the BTEX tolerant culture isolated from petroleum-contaminated soil. In batch study, the degradation pattern for single substrate showed that xylene was degraded much faster than other compounds followed by ethylbenzene, toluene, and benzene with the highest μmax = 0.140 h−1 during initial substrate concentration of 100 mg L−1. Continuous degradation experiments were performed in a soil column with an inlet concentration of BTEX of about 2000 mg L−1 under unsaturated flow in anaerobic condition. BTEX degradation pattern was studied with time and the matric potential of the soil at different parts along the length of the column were determined at the end of the experiment. In continuous degradation study, BTEX compounds were degraded with different degradation pattern and an increase in soil matric potential was observed with an increase in depth from top to bottom in the column with applied suction head. It was found that column biodegradation contributed to 69.5% of BTEX reduction and the bacterial growth increased the soil matric potential of about 34% on an average along the column height. Therefore, this study proves that it is significant to consider soil matric potential in modeling fate and transport of BTEX in unsaturated soils.

Effective Biodegradation of Mycotoxin Patulin by Porcine Pancreatic Lipase.

Patulin is a common contaminant in fruits and vegetables, which is difficult to remove. In this study, the biodegradation of patulin using porcine pancreatic lipase (PPL) was investigated. The method of HPLC was used to analyze the concentration of patulin. Batch degradation experiments were performed to illustrate the effect of PPL amount, pH, temperature, contact time, and initial concentration. Besides, the degradation product of patulin was characterized by full wavelength scanning and MS technologies. The results showed that the optimum degradation conditions of PPL for patulin was observed at pH 7.5, 40°C for 48 h. The percentage of degradation could reach above 90%. The structure of degradable product of patulin was inferred by the molecular weight 159.0594, named C7H11O4+. It indicated that PPL was effective for the degradation of patulin in fruits and vegetables juice.

Effect of field site hydrogeochemical conditions on the corrosion of milled zerovalent iron particles and their dechlorination efficiency

Milled zerovalent iron (milled ZVI) particles have been recognized as a promising agent for groundwater remediation because of (1) their high reactivity with chlorinated aliphatic hydrocarbons, organochlorine pesticides, organic dyes, and a number of inorganic contaminants, and (2) a possible greater persistance than the more extensively investigated nanoscale zerovalent iron. We have used laboratory-scale batch degradation experiments to investigate the effect that hydrogeochemical conditions have on the corrosion of milled ZVI and on its ability to degrade trichloroethene (TCE). The observed pseudo first-order degradation rate constants indicated that the degradation of TCE by milled ZVI is affected by groundwater chemistry. The apparent corrosion rates of milled ZVI particles were of the same order of magnitude for hydrogeochemical conditions representative for two contaminated field sites (133–140mmolkg−1day−1, indicating a milled ZVI life-time of 128–135days). Sulfate enhances milled ZVI reactivity by removing passivating iron oxides and hydroxides from the Fe0 surface, thus increasing the number of reactive sites available. The organic matter content of 1.69% in the aquifer material tends to suppress the formation of iron corrosion precipitates. Results from scanning electron microscopy, X-ray diffraction, and iron K-edge X-ray adsorption spectroscopy suggest that the corrosion mechanisms involve the partial dissolution of particles followed by the formation and surface precipitation of magnetite and/or maghemite. Numerical corrosion modeling revealed that fitting iron corrosion rates and hydrogen inhibitory terms to hydrogen and pH measurements in batch reactors can reduce the life-time of milled ZVI particles by a factor of 1.2 to 1.7.

PCPF-M model for simulating the fate andtransport of pesticides and their metabolites inrice paddy field.

The PCPF-1 model was improved for forecasting the fate and transport of metabolites in addition to parent compounds in rice paddies. In the new PCPF-M model, metabolites are generated from the dissipation of pesticide applied in rice paddies through hydrolysis, photolysis and biological degradations. The methodology to parameterize the model was illustrated using two scenarios for which uncertainty and sensitivity analyses were also conducted. In a batch degradation experiment, the hourly forecasted concentrations of fipronil and its metabolites in paddy water were very accurate. In a field-scale experiment, the hourly forecasted concentrations of fipronil in paddy water and paddy soil were accurate while the corresponding daily forecasted concentrations of metabolites were adequate. The major contributors to the variation of the forecasted metabolite concentrations in paddy water and paddy soil were the formation fractions of the metabolites. The influence of uncertainty included in input parameters on the forecasted metabolite concentration was high during the peak concentration of metabolite in paddy water. In contrast, in paddy soil, the metabolite concentrations forecasted several days after the initial pesticide application were sensitive to the uncertainty incorporated in the input parameters. The PCPF-M model simultaneously forecasts the concentrations of a parent pesticide and up to three metabolites. The model was validated using fipronil and two of its metabolites in paddy water and paddy soil. The model can be used in the early stage of the pesticide registration process and in risk assessment analysis for the evaluation of pesticide exposure. © 2017 Society of Chemical Industry.

Heterogeneous Photo-Fenton Degradation of Norfloxacin with Fe3O4-Multiwalled Carbon Nanotubes in Aqueous Solution

A catalyst, ferroferric oxide nanoparticles decorated with multiwalled carbon nanotubes was successfully fabricated, and applied for the degradation of norfloxacin in the presence of H2O2 and xenon light. The catalyst was characterized by different techniques i.e., X-ray diffraction, transmission electron microscope, and fourier transform infrared. The effects of initial pH, catalyst dosage, hydrogen peroxide concentration and iron leaching on the degradation of norfloxacin were studied. The multiwalled carbon nanotubes showed higher ability of degradation efficiency of norfloxacin than bare Fe3O4 nanoparticles in the batch degradation experiment. The results showed that the multiwalled carbon nanotubes catalyst demonstrated good performance in the degradation of norfloxacin with optimum operating conditions of multiwalled carbon nanotubes 1.2 g L−1, pH 3.0, H2O2 0.098 mol L−1 and the multiwalled carbon nanotubes catalyst still exhibited good chemical stability after five consecutive degradation cycles. Further, the catalyst showed stable catalytic activity, fairly good mechanic stability and convenient recycling. Negligible iron leaching demonstrated the reused multiwalled carbon nanotubes could withstood the oxidation.

Microwave-assisted catalytic degradation of methyl orange in aqueous solution by ferrihydrite/maghemite nanoparticles

Six-line ferrihydrite was successfully prepared by precipitation method and characterized with XRD, SEM, TEM, BET and FTIR spectroscopy. The as-prepared ferrihydrite was used as catalyst for the degradation of methyl orange (MO) in an artificial dye wastewater without adding any oxidant. It was found that the ferrihydrite nanoparticles with average size of about 90–220nm exhibited a high adsorption capability to MO and the dye molecules obey Langmuir type of adsorption. Batch degradation experiments show that the catalytic degradation of MO could be remarkably improved by coupling with microwave irradiation. The initial pH value of MO solution exerted notable influence on the degradation reaction and the optimal degradation efficiency was obtained under neutral conditions. Radical scavenger measurements indicated that OH radicals could generate during the catalytic process even without adding oxidant. We proposed that the microwave irradiation facilitates the generation of active oxygen species derived from water and/or oxygen dissolved in water, which are responsible to the excellent performance of the MW-assisted catalytic process.