Initial Herbicide Concentration Research Articles

Na-alginate, polyaniline and polypyrrole composites with cellulosic biomass for the adsorptive removal of herbicide: Kinetics, equilibrium and thermodynamic studies

This study was designed to prepare the sugarcane bagasse (SB) composite with polyaniline (PAn), polypyrrole (Ppy) and sodium alginate (NaA) and employed as an adsorbent for the adsorptive removal of herbicide (2,4-dicholorophenoxyacetic acid, 2,4-D). Fabricated composites were characterized by SEM and FTIR techniques. The affecting variables, i.e., temperature, contact time, initial herbicide concentration, medium pH and adsorbent dose were studied in batch mode. Different isotherms were employed on the adsorption data and the maximum adsorption capacity of SB was recorded to be 77.75 mg/g at pH 3.0, 150 mg/L 2,4-D initial concentration at 30 °C. The models (pseudo-second-order and Freundlich) best explained the adsorption experimental data with R2 values ≥ 0.90 and ≥ 0.96, respectively. The thermodynamics parameters (ΔG, ΔH, and ΔS) were computed and the herbicide adsorption onto the composites was an exothermic and spontaneous process. Results revealed that sugarcane bagasse composites with PAn, Ppy, and NaA are efficient adsorbents, which could be used for the remediation of 2,4-D in the effluents.

Biodegradation of Herbicide by the Immobilized Microbial Consortium SMC1 in Continuous Packed-Bed Biofilm Reactor

The present study aimed to investigate the treatment of butachlor and other commonly used herbicides by the synthetically formulated microbial consortium SMC1 immobilized on the ceramic raschig rings in a packed-bed bioreactor (PBBR). The PBBR was operated in continuous mode at various flow rates over a period of 70 days to determine the effect of hydraulic retention time (HRT) and initial butachlor concentration on the removal efficiency and elimination capability of the bioreactor. It was observed that the overall operation of the bioreactor changes from being controlled by the mass transfer limitations to the controlled bio-reaction , thus proposing the range of 270–325 mg/L/d to be the optimum operating range for the efficient removal of butachlor by the PBBR. The bioreactor can reduce up to 90% of the initial chemical oxygen demand (COD) value while treating the mixture of herbicides. The operating parameters were optimized using response surface methodology where the feed flow rate of 2.9 ml/min, initial herbicide concentration of 454.63 mg/L, and concentration of an additional nitrogen source at 1.41 g/L was found to yield maximal COD reduction. To date, a continuous study in the field of butachlor biodegradation is yet to be reported. Hence, the study could be used as a model to design a better herbicide biotreatment technology.

Simultaneous monitoring of the photocatalytic degradation process of trifluralin and pendimethalin herbicides by SBA-15/TiO2 nanocomposite

Today, The occurrence of herbicides in environments attitudes a potential hazard to aquatic life and displays development forbidding of human embryonic cells, therefore their elimination from the environment is a vigorous job. In this paper, the SBA-15/TiO2 nanocomposite were synthesized utilizing amorphous nanosilica, which was extracted from stem cane ash (SCA) with 92.56% purity. FESEM and TEM images of pure SBA-15 and SBA-15/TiO2 nanocomposite demonstrates which their mean particle size was under 50 nm. The average particles size of TiO2 anatase calculated to be 27.6 nm using the Scherrer’s equation. The BET surface area, total pore volume and average pore diameter of the SBA-15/TiO2 was obtained to be 279.2 m2 g−1, 0.39 cm3 g−1 and 5.64 nm, respectively. For the first time, this nanocomposite was used as photocatalysts for degradation of trifluralin (Tri) and pendimethalin (Pen) herbicides in the aqueous solution. Partial least squares-1 (PLS-1) regression was used for simultaneous measurement of them in aqueous solutions before and after photocatalytic degradation with SBA-15/TiO2 nanocomposite. The values of some parameters such as R2(0.9951, 0.9872), recovery (101.5, 102.0%) and root mean square error of prediction (0.231, 0.239) for both Tri and Pen were attained by the PLS-1 regression, respectively. The influence of some operational parameters such as initial herbicide concentrations, photocatalyst dosage, irradiation time and pH were also investigated on the photocatalytic performance using the response surface methodology. Conferring to the ANOVA test, the most important factor on the decomposition of herbicides was photocatalyst dosage. The results displayed that the maximum elimination efficiencies under the optimum conditions (pH = 10, photocatalyst dosage 0.2 g L−1, irradiation time 30 min and initial herbicide concentration 60 mg L−1) from the river water for Tri and Pen were attained to be 90% and 82.5%, respectively.

In vitro removal of paraquat and diquat from aqueous media using raw and calcined basil seed

Raw and calcined basil seeds (BS and BS1000, respectively) were evaluated for their ability to remove herbicides such as paraquat and diquat. The physicochemical properties of BS and BS1000 were determined and the effects of contact time and initial concentration on paraquat and diquat adsorption were assessed. After calcination treatment, the number of pores in BS increased, and the specific surface area was increased from 0.265 to 86.902 m2 g−1. The quantity of herbicides adsorbed using BS1000 was greater than that using either BS or medicinal-grade carbon. Additionally, the adsorption quantity increased with the increase in contact time and initial concentration of herbicide. Therefore, BS1000 is a potential resource for the removal of herbicides. Moreover, BS and BS1000 exhibited the capacity for herbicide adsorption in simulated intestinal fluid.

2,4-D and dicamba removal from the surface of plastic mulch using overhead irrigation: analytical analysis and cucurbit bioassay crop response

AbstractGlyphosate and paraquat are effective preplant burndown herbicide options for multicrop vegetable production that uses plastic mulch, but problematic weeds such as wild radish, cutleaf evening primrose, annual morningglory, or horseweed may not be adequately controlled with these herbicides alone. The herbicides 2,4-D and dicamba could help control these troublesome weeds prior to planting if they can be removed from plastic mulch and thus avoid crop damage. Treatments included 2,4-D (1,065 and 2,130 g ae ha−1) and dicamba (560 and 1,120 g ae ha−1) applied broadcast over plastic mulch a day before transplanting. Just before transplanting, treatments received either 0.76 cm of water via overhead irrigation or no irrigation. Plastic mulch samples were collected at application and planting to determine herbicide presence using analytical techniques, and cantaloupe and zucchini squash were subsequently transplanted on the plastic beds. Analytical ultra-high performance liquid chromatography revealed that 88% to 99% of the initial herbicide concentration was present at crop planting when irrigation was not implemented. At most, a 1/50 rate of dicamba and a 1/500 rate of 2,4-D was present at planting when overhead irrigation was applied prior to transplanting. Maximum cantaloupe and squash injury from 2,4-D with irrigation was 10% and did not influence plant growth, biomass, or yield. For dicamba with overhead irrigation, cantaloupe injury was 35%, vine lengths were reduced by 24%, and maturity was delayed, whereas squash injury ranged from 9% to 12%, with no influence on growth or yield. Without irrigation to wash herbicides from the mulch prior to planting, 60% to 100% injury of both crops occurred with both herbicides. Zucchini squash was more tolerant to dicamba than cantaloupe. Results demonstrated that 2,4-D can be adequately removed from the surface of plastic mulch with irrigation, whereas a single irrigation event was not sufficient to remove dicamba.

Photocatalytic degradation of 2,4-dichlorophenoxyacetic acid from aqueous solutions by Ag3PO4/TiO2 nanoparticles under visible light: kinetic and thermodynamic studies.

Between the countless chemical substances applied in agriculture, 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide is considered as a toxic and carcinogenic pollutant which is difficult to remove from water due to its biological and chemical stability and high solubility. The goal of this study was photocatalytic degradation of 2,4-D, using Ag3PO4/TiO2 nanoparticles under visible light. The Ag3PO4/TiO2 nanoparticles were characterized using XRD, FESEM and EDS analysis to investigate its crystal structure and elemental compounds. The effect of operating parameters such as pH, contact time, catalyst dose, and initial concentration of herbicide on the efficiency of the process was studied. Increasing the pH and initial concentration of herbicide led to the reduction of the efficiency of removing the herbicide, while increasing contact time and catalyst dose increased the efficiency. The best result (98.4% removal efficiency) was achieved at pH = 3, 1 g/L catalyst dose, 60 min contact time, and 10 mg/L initial concentration of 2,4-D. According to the results, 2,4-D removal efficiency with Ag3PO4/TiO2 photocatalyst reached 96.1% from 98.4% after 5 cycles of reaction. The pseudo-first-order kinetics was the best fit for the 2,4-D degradation by Ag3PO4/TiO2 with correlation coefficients (R2 = 0.9945). The results demonstrated that the photocatalytic process using Ag3PO4/TiO2 nanoparticles in the presence of visible light had a relatively good efficiency in removing 2,4-D. Moreover, Ag3PO4/TiO2 can be used as a reusable photocatalyst for the degradation of such toxins from polluted water and wastewater.

Organo-Clay as Adsorbent for Removal of Fenoxaprop-p-ethyl from Water Samples; A Statistical Approach

In this study, fuller’s earth (FE) modified with sodium dodecylbenzene sulphonic acid was used for adsorptive removal of fenoxaprop-p-ethyl (FPE) herbicide from water samples and statistical validation of the experimental observations was accomplished. All the adsorption experiments were conducted in batch mode. The effect of pH, agitation time, adsorbent dose and initial herbicide concentration on adsorption process was studied. About 98.5% adsorption efficiency was achieved at initial analyte concentration of 1000 mg L-1 at pH 6 within 60 min at adsorbent dose of 0.1 g. The adsorption kinetics were studied and pseudo-second-order kinetic model was found to follow the adsorption kinetics with R2=0.998. The isotherm studies show that the adsorption data fit well to the Freundlich isotherms. In statistical evaluation, the individual as well as the interaction effect of various factors on adsorption was investigated and it was found that concentration, pH and adsorbent dose are the significant factors with p values of 0.0001, 0.004 and 0.006 respectively, while contact time was found statistically insignificant having p value greater than 0.05. The coefficient of determination (R2=0.930) shows that % adsorption is highly dependent on the studied factors and their interactions. Under the optimized set of conditions, high absorption capacity of 200.22 mg g-1 was achieved.

Organo-Clay as Adsorbent for Removal of Fenoxaprop-p-ethyl from Water Samples; A Statistical Approach

In this study, fuller’s earth (FE) modified with sodium dodecylbenzene sulphonic acid was used for adsorptive removal of fenoxaprop-p-ethyl (FPE) herbicide from water samples and statistical validation of the experimental observations was accomplished. All the adsorption experiments were conducted in batch mode. The effect of pH, agitation time, adsorbent dose and initial herbicide concentration on adsorption process was studied. About 98.5% adsorption efficiency was achieved at initial analyte concentration of 1000 mg L-1 at pH 6 within 60 min at adsorbent dose of 0.1 g. The adsorption kinetics were studied and pseudo-second-order kinetic model was found to follow the adsorption kinetics with R2=0.998. The isotherm studies show that the adsorption data fit well to the Freundlich isotherms. In statistical evaluation, the individual as well as the interaction effect of various factors on adsorption was investigated and it was found that concentration, pH and adsorbent dose are the significant factors with p values of 0.0001, 0.004 and 0.006 respectively, while contact time was found statistically insignificant having p value greater than 0.05. The coefficient of determination (R2=0.930) shows that % adsorption is highly dependent on the studied factors and their interactions. Under the optimized set of conditions, high absorption capacity of 200.22 mg g-1 was achieved.

Batch and packed bed techniques for adsorptive aqueous phase removal of selected phenoxyacetic acid herbicide using sugar industry waste ash

Abstract Batch and packed bed adsorption of 4-chloro-2-methylphenoxyacetic acid (MCPA) herbicide was performed using bagasse fly ash (BFA) as an adsorbent. In batch process, characteristics of adsorbent, and the influence of adsorbent dosage, initial herbicide concentration, time, pH, particle size of adsorbent and temperature on adsorption were studied. Results disclose higher removal of MCPA on bigger particles of BFA owing to higher specific surface area because of greater carbon and lesser silica percentage in bigger particles. Application of isotherm models in present study indicates the best fitting of Langmuir and Temkin isotherms whereas the kinetic models suggest the suitability of pseudo second order and Elovich models. Thermodynamic study specifies the temperature preferred adsorption process. In packed bed technique, the effect of influent concentration, flow rate and bed height were investigated. The deactivation kinetic model which was previously considered only for studies in gas-solid adsorption is applied in this study to solid-liquid adsorption along with conventional packed bed models. In packed bed study, Bohart-Adams and Wolborska models are appropriate to explain the experimental data upto 60% saturation of the column. The deactivation kinetic model is found the best to elucidate the nature of breakthrough curves till the complete saturation of column. Batch capacity and packed bed capacity per m2 specific surface area of BFA is found about two and three times greater than the previously used adsorbents for MCPA respectively.

Bio-Based Polyurethane Foams with Enriched Surfaces of Petroleum Catalyst Residues as Adsorbents of Organic Pollutants in Aqueous Solutions

In this study the surface of bio-based polyurethane foam was enriched with different contents of catalyst residue from the petroleum industry. The foams were prepared with different residue contents, 20, 50, and 80 wt% relative to the total mass of the polyols and were characterized by several techniques, with X-ray diffraction, X-ray fluorescence spectrometry, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, microtomography, Fourier transform infrared spectroscopy and thermogravimetric. To determine the removing process the effects of various operating parameters, pH of the solution (2–12), initial concentration of pesticides (5–50 mg L−1), contact time (15–1440 min), and amount of adsorbent (30–400 mg) were investigated in a batch adsorption technique. The specific surface area of the residue was determined by the BET method as up to 150 m2/g and mean pore diameter of 4.20 ± 0.42 nm (mesopore), which explains the excellent results of the materials in the adsorption process. The high adsorption capacity is probably due to the presence of highly concentrated catalyst residue on the foam surface. Trifluralin pesticide was removed in water using these polyurethane foams with 20.0 mg L−1 initial concentration of herbicide, 30.0 mg adsorbent mass of, 5.0 pH, and 25.0 °C temperature. The chemically prepared foams with 50 wt% residue (PURC50) have higher adsorption capacities (70%) and can be used to remove trifluralin from natural waters effectively. The efficiency of removing the herbicide increased to 83% with the use of 400.0 mg adsorbent mass. The adsorption efficiency of the pure catalyst residue reaches a maximum (95.3%). The established adsorption method was appropriate for adsorption of trifluralin in contaminated waters.

β-Cyclodextrin-chitosan biocomposites for synergistic removal of imazethapyr and imazamox from soils: Fabrication, performance and mechanisms

The present study delineates to develop and explore the possibility of using chitosan-β-cyclodextrin biocomposites as environmentally friendly decontamination agent for removal of imazethapyr and imazamox from soils. The biocomposites were synthesised using ultrasonic assisted technique and characterised by UV–Visible spectrophotometer. The quantification of imazethapyr and imazamox was done using liquid chromatography tandem mass spectrometry. The adsorption capacity for imazethapyr and imazamox ranged from 0.12 to 1.22 and 0.02 to 1.01 μg1−ng−1mLn, respectively in studied soils (p < .05) indicating strong influence of soil properties on adsorption. Desorption studies indicated that distilled water could desorb only 1.23 to 5.48 and 3.11 to 8.63% of adsorbed imazethapyr and imazamox, respectively at high concentrations (1.0 and 10 μg mL−1) whereas herbicides were not desorbed at low concentrations (0.01 and 0.1 μg mL−1). The removal of imazethapyr and imazamox from soils were carried out with β-cyclodextrin, chitosan and their biocomposites and the influence of various parameters such as type and concentration of extractant, contact time, liquid to soil ratio, temperature and sequential extraction cycle was investigated. Under optimum conditions, herbicides were successfully desorbed from studied soils using low molecular weight chitosan-β-cyclodextrin biocomposite (LCD) and removal rate varied from 59.42 to 99.44% at initial herbicide concentration of 0.01 to 10 μg mL−1. The highest removal rate of imazethapyr and imazamox was observed for inceptisol 3 followed by entisol, inceptisol 2, aridisol, inceptisol 1, vertisol and alfisol probably due to differential physico-chemical properties of soil which affected the herbicide-soil interactions. Based on these results, LCD can be regarded as effective and environmentally friendly in situ green extracting agent for remediating soils contaminated with imazethapyr and imazamox.

Investigation of COD Removal for the Glyphosate Herbicide from Aqueous Solution by Electrocoagulation Process

This study investigated the glyphosate adsorption by water treatment residual using the method of indirect Chemical Oxygen Demand (COD) in aqueous solution using the electrocoagulation process. The optimum glyphosate removal was obtained with typical operating conditions: initial pH of 5.8, initial herbicide concentration of 100 mg/L, current density 25 mA/cm2, type of electrolyte, and salt concentration of 1 g/L and temperature of 20oC. The results showed that the COD of glyphosate removal were 89.8% by using iron (Fe) electrodes at 40 min, 89.8% by using stainless steel S-S at 60 min, while were 84.8 % by using aluminum Al electrodes at the 80 min. It was found that the data fitted to Freundlich (R2 = 0.964) model. In glyphosate the electrocoagulation process can be described by a pseudo first order with rate constant (0.0059, 0.0052 and 0.005 min- 1) by using Fe, S-S and Al electrodes respectively. The consumption of electrical energy for glyphosate at optimum conditions as follows: (9.999, 13.9 and 19.0619 KWh/m3) using Fe, S-S and Al electrodes respectively. Keywords: Electrocoagulation; Electrodes; Herbicide; Glyphosate; Adsorption; Kinetics

Carbon nanotube-based magnetic and non-magnetic adsorbents for the high-efficiency removal of diquat dibromide herbicide from water: OMWCNT, OMWCNT-Fe3O4 and OMWCNT-κ-carrageenan-Fe3O4 nanocomposites

In this study, carbon nanotube-based adsorbents, oxidized multi-walled carbon nanotube (OMWCNT) with non-magnetic property and OMWCNT-Fe3O4 and OMWCNT-κ-carrageenan-Fe3O4 nanocomposites with magnetic property, having different structural and surface properties were prepared and their adsorptive properties for the removal of toxic diquat dibromide (DQ) herbicide from water by adsorption were determined in detail. For each adsorption system, the effects of initial DQ concentration, contact time and temperature on the adsorption processes were determined. Equilibrium time was found to be 300 min for DQ solutions. OMWCNT showed faster adsorption and higher maximum adsorption capacity value than magnetic adsorbents. With increasing initial herbicide concentration from 5.43 mg.L−1 to 16.3 mg.L−1, the values of initial sorption rate exhibited a decrease from 29.1 mg.g−1.min−1 to 4.28 mg.g−1.min−1 for OMWCNT-DQ system, from 1.21 mg.g−1.min−1 to 0.823 mg.g−1.min−1 for OMWCNT-Fe3O4-DQ system and from 0.674 mg.g−1.min−1 to 0.612 mg.g−1.min−1 OMWCNT-κ-carrageenan-Fe3O4 system. Maximum adsorption capacity value of OMWCNT was approximately 2.8-fold higher than magnetic OMWCNT-Fe3O4 and 5.4-fold higher than magnetic OMWCNT-κ-carrageenan-Fe3O4 at 25 °C. Adsorption kinetic and isotherm data obtained for all adsorption systems were well-fitted by pseudo second-order and Langmuir models, respectively. Thermodynamic parameters indicated that the adsorption of DQ onto carbon nanotube-based adsorbents was spontaneous and endothermic process. Furthermore, OMWCNT having the highest herbicide adsorption capacity could be regenerated and reused at least five times. This study showed that carbon nanotube-based adsorbents with magnetic and non-magnetic property were of high adsorption performance for the removal of DQ from water and could be promising adsorbent materials for the efficient removal of herbicides from wastewaters.

Factors Influencing Imazapyr Herbicide Removal from Wastewater Using Photocatalytic Ozonation.

This study investigates the degradation of imazapyr herbicide from wastewater by photocatalytic ozonation using TiO2 as a semiconductor. Effects of operational parameters on imazapyr removal efficiency including TiO2 dosing, initial herbicide concentration and pH were also studied. Obtained results showed that more than 90% of removal efficiency representing the disappearance of imazapyr was maintained until 7 µM in the presence of 200 mgL-1of UV100-TiO2. Otherwise, the degradation of imazapyr followed the first-order kinetics with a photocatalytic rate constant of 0.247 min-1, and complete degradation was achieved within 20 min using photocatalytic ozonation for 5 µM of Imazapyr at pH 7.

Catalytic efficiency of laterite-based FeNPs for the mineralization of mixture of herbicides in water

ABSTRACTIn this work, low cost, locally available laterite-based iron nanoparticles were synthesized using Tectona Grandis extract (Teak extract) with an average size of 75 nm. The synthesized FeNPs were applied as a heterogeneous Fenton catalyst for the oxidation of mixture herbicides, namely ametryn, dicamba and 2,4-D in water. The FeNPs were characterized for various analytical methods (field emission scanning electron microscopy-X-ray energy-dispersive spectrophotometer, XRD, FTIR and BET) and the effect of different variables (FeNPs dosage, H2O2, pH) was studied using the responses surface methodology. The initial herbicide concentration was considered as 25, 3.5 and 94 mg L−1 for 2,4-D, ametryn and dicamba, respectively, with the COD value of 172 mg L−1. The 100% degradation and mineralization was achieved in 135 min and >85% in 45 min (optimum dosage: FeNPs = 25.29 mg L−1, H2O2 = 430 mg L−1 and pH = 5). The degradation kinetics were performed for both pseudo-first order and second order, it was observed that first-order kinetics (R2 > 0.85) was well fitted in the treatment process. Recycling of FeNPs in five cycles was performed at optimum conditions and 10–40% of reduction in degradation efficiency was achieved. Finally, the whole treatment process was validated with a contour overlay plot and analysis of variance.

Applicability of electrochemical oxidation using diamond anodes to the treatment of a sulfonylurea herbicide

In this work, the electrolysis of chlorsulfuron (ClSF, a sulfonylurea herbicide) with conductive-diamond anodes is studied. The influences of the nature of the supporting electrolyte (0.05moldm−3 NaCl and Na2SO4), the applied current density (30 and 100mAcm−2) and the initial herbicide concentration (20,50 ad 100mgdm−3) have been evaluated. Total mineralization of the herbicide was attained regardless of the supporting electrolyte medium used, although electrolyte clearly influenced on the efficiency and rate of the oxidation process. Likewise, the process was found to be more efficient at low current densities. Results point out the importance of mediated electrochemical processes in the removal of ClSF. This influence was confirmed by additional tests in which the electrolysis was combined with UV light or ultrasound irradiation: the use of UV irradiation results in a less efficient process, while US improves importantly the rate of the mineralization as compared to the single electrolytic process. The strong oxidation conditions of electrolysis leads to the formation of reaction intermediates (2-amino-4-methoxy-6-methyl-1,3,5-Triazine, 2-chlorobenzenesulfonamida and oxalic acid) in agreement with the mechanisms proposed in the literature for other AOPs.

Optimization of Electrocoagulation (EC)Process for the Purification of Water from 2,4-Dichlorophenoxyacetic Acid (2,4-D) UsingSacrificial Anodes

The present study provides an electrocoagulation process for the adsorption of 2,4 dichlorophenoxyacetic acid (2,4-D) from aqueous solution using sacrificial anodes. The effects of operational parameters such as initial pH, initial concentration, current density, type of electrolyte, salt concentration and temperature on the herbicide and COD removal efficiency have been studied. The optimal operating condition for removal of 2,4-D herbicide were : initial pH of 10, an initial herbicide concentration of 200 mg/L, temperature of 30 oC, current density (62.5, 12.5 and 37.5 mA/cm2) and salt concentration of 1.5g/L by using Fe, S-S and Al respectively. The results showed that the removal percentage for 2,4-D and COD were (88.7% and 71 %), (94.4% and 74.9%) and (93.4 % and 75.3%) by using Fe, S-S and Al electrodes at 60 min respectively. The adsorption equilibriums were analyzed by Langmuir and Freundlich isotherm models. It was found that the data fitted to Langmuir (R2 = 0.9970) better than Freundlich (R2 = 0.9966) model. The removal of 2,4-D exhibited a pseudo second order reaction with rate constant (0.0861, 0.4224 and 0.1903 mol-1dm3 min-1 ) for Fe, S-S and Al electrodes respectively

Photodegradation of herbicides with different chemical natures in aqueous solution by ultraviolet radiation. Effects of operational variables and solution chemistry

Abstract This study evaluated the effectiveness of ultraviolet (UV) radiation on the photodegradation of the herbicides amitrole (AMT), clopyralid (CLP), fluroxypyr (FLX), and diuron (DRN), investigating the influence of operational variables (initial herbicide concentration and pH) and chemical nature of water (ultrapure, tap, and wastewater) on these processes. We also followed the time course of total organic carbon (TOC) during photodegradation of the herbicides and their photodegradation byproducts. The quantum yield ranged between 1.27 × 10 −2 mol Einstein −1 (DRN) and 6.77 × 10 −2 mol Einstein −1 (CLP), rising with the decrease in HOMO–LUMO energy gap of the triplet states of the herbicide molecules. Photodegradation rate constants ranged between 0.013 min −1 (AMT) and 0.220 min −1 (DRN). Herbicide degradation rates followed the order DRN > FLX > CLP ≫ AMT. Comparison of the time course of herbicide photodegradation with that of the corresponding TOC values showed that the four herbicides were initially degraded to lower molecular weight byproducts that then continued to mineralize, degrading to CO 2 , in the presence of UV radiation. The photodegradation process is highly dependent on the medium pH, generally being favored at pH values at which herbicides are in ionic form. With regard to water type, the herbicide photodegradation rate decreased in the order ultrapure > tap > wastewater; thus, rate constants for DRN were 0.220 min −1 , 0.194 min −1 , and 0.114 min −1 , respectively. The organic and inorganic byproducts (NO 3 − , NH 4 + , Cl − ) generated by herbicide photodegradation were determined; the results indicate that the degradation mechanism involves substitution of Cl of the aromatic ring with HO radicals and the formation of byproducts containing OH in the ring.

Optimal performance of COD removal during aqueous treatment of alazine and gesaprim commercial herbicides by direct and inverse neural network

A direct and inverse artificial neural network (ANN and ANNi) approach was developed to predict the chemical oxygen demand (COD) removal during the degradation of alazine and gesaprim commercial herbicides under various experimental conditions. The configuration 9–9–1 (9 inputs, 9 hidden and 1 output neurons) presented an excellent agreement (R 2 = 0.9913) between experimental and simulated COD value considering the hyperbolic tangent sigmoid and linear transfer function in the hidden layer and output layer. The sensitivity analysis showed that all studied input variables (reaction time, pH, herbicide concentration, contaminant, US ultrasound, UV light intensity, [TiO 2] o,[K 2S 2O 8] o, and SR solar radiation) have strong effect on the degradation of the commercial herbicide in terms of COD removal. In addition, reaction time is the most influential parameter with relative importance of 33.49%, followed by initial herbicide concentration. COD optimal performance was carried out by inverting artificial neural network. Now, ANNi could calculate the optimal unknown parameter (reaction time) to obtain a COD required. Very low percentage of error and short computing makes this methodology attractive to be applied to the on-line control of Advanced Oxidation Process (AOP) over the degradation of commercial herbicide.

Glyphosate degradation in water employing the H 2O 2/UVC process

Glyphosate is the organophosphate herbicide most widely used in the world. Any form of spill or discharge, even if unintentional, can be transferred to the water due to its high solubility. The combination of hydrogen peroxide and UV radiation could be a suitable option to decrease glyphosate concentration to acceptable limits. In this work, the effects of initial pH, hydrogen peroxide initial concentration, and incident radiation in glyphosate degradation were studied. The experimental device was a cylinder irradiated with two tubular, germicidal lamps. Conversion of glyphosate increases significantly from pH = 3–7. From this value on, the increase becomes much less noticeable. The reaction rate depends on the initial herbicide concentration and has an optimum plateau of a hydrogen peroxide to glyphosate molar concentration ratio between 7 and 19. The expected non linear dependence on the irradiation rate was observed. The identification of critical reaction intermediaries, and the quantification of the main end products were possible and it led to propose a plausible degradation path. The achieved quantification of the mineralization extent is a positive indicator for the possible application of a rather simple technology for an in situ solution for some of the problems derived from the intensive use of glyphosate.