Removal of glyphosate in neutralization liquor from the glycine-dimethylphosphit process by nanofiltration

Application of Bipolar Membrane Electrodialysis in Environmental Protection and Resource Recovery: A Review

Bipolar membrane electrodialysis (BMED) is a new membrane separation technology composed of electrodialysis (ED) through a bipolar membrane (BPM). Under the action of an electric field, H₂O can be dissociated to H⁺ and OH^-, and the anions and cations in the solution can be recovered as acids and bases, respectively, without adding chemical reagents, which reduces the application cost and carbon footprint, and leads to simple operation and high efficiency. Its application is becoming more widespread and promising, and it has become a research hotspot. This review mainly introduces the application of BMED to recovering salts in the form of acids and bases, CO₂ capture, ammonia nitrogen recovery, and ion removal and recovery from wastewater. Finally, BMED is summarized, and future prospects are discussed.

Treatment technologies and degradation pathways of glyphosate: A critical review

Glyphosate is one of the most widely used post-emergence broad-spectrum herbicides in the world. This molecule has been frequently detected in aqueous environment and can cause adverse effects to plants, animals, microorganisms, and humans. This review offers a comparative assessment of current treatment methods (physical, biological, and advanced oxidation process) for glyphosate wastewaters, considering their advantages and drawbacks. As for other molecules, adsorption does not destroy glyphosate. It can be used before other processes, if glyphosate concentrations are very high, or after, to decrease the final concentration of glyphosate and its by-products. Most of biological and oxidation processes can destroy glyphosate molecules, leading to by-products (the main ones being AMAP and sarcosine) that can be or not affected by these processes. This point is of major importance to control process efficiency. That is the reason why a specific focus on glyphosate degradation pathways by biological treatment or different advanced oxidation processes is proposed. However, one process is usually not efficient enough to reach the required standards. Therefore, the combination of processes (for instance biological and oxidation ones) seems to be high-performance technologies for the treatment of glyphosate-containing wastewater, due to their potential to overcome some drawbacks of each individual process. Finally, this review provides indications for future work for different treatment processes to increase their performances and gives some insights into the treatment of glyphosate or other organic contaminants in wastewater.

Kinetic study of glyphosate degradation in wet air oxidation conditions

Glyphosate is one of the most widely used herbicides in the world against perennial and annual weeds. It has been reported to be a micro pollutant, and its degradation in different wastewater treatment processes must be studied. For that purpose, the kinetics of wet air oxidation of glyphosate was studied in an autoclave reactor at a temperature range of 423-523 K and under a total pressure of 15 MPa. Oxidation reactions obeyed the first-order kinetics with respect to glyphosate concentration. The activation energy for glyphosate oxidation was found to be equal to 68.4 kJ mol-1. Furthermore, the possible reaction intermediates and main end products of glyphosate degradation in the wet air oxidation process were identified and quantified using UV-spectrophotometry and liquid chromatography coupled to high resolution mass spectrometry. A degradation pathway for glyphosate oxidation was proposed.

Adsorption performance and mechanism of magnetic reduced graphene oxide in glyphosate contaminated water

In this study, the magnetic reduced graphene oxide (RGO/Fe3O4), with easy separation and high adsorption performance, was prepared and used to treat glyphosate (GLY) contaminated water. GLY adsorption performance of RGO/Fe3O4 was investigated, and influences of pH, adsorption time, temperature, contaminant concentration, and competing anions were analyzed. Moreover, the adsorption mechanism was discussed in the light of several characterization methods, including scanning electron microscopy (SEM), energy dispersive spectrum (EDS), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The results demonstrated that the RGO/Fe3O4 presented a significant GLY adsorption capacity and acid condition was beneficial for this adsorption. The pseudo-second-order kinetic model and the Langmuir model correlated satisfactorily to the experimental data, indicating that this process was controlled by chemical adsorption and monolayer adsorption. Thermodynamic studies revealed that the adsorption of glyphosate onto RGO/Fe3O4 was spontaneous, endothermic, and feasible process. High temperatures were beneficial to GLY adsorption. The GLY adsorption mechanism of RGO/Fe3O4 was mainly attributed to hydrogen-bond interaction, electrostatic interaction, and coordination. Therefore, the RGO/Fe3O4 investigated in this research may offer an attractive adsorbent candidate for treatment of glyphosate contaminated water and warrant further study as a mechanism for glyphosate efficient removal.

Electrochemical degradation and mineralization of glyphosate herbicide

The presence of herbicide is a concern for both human and ecological health. Glyphosate is occasionally detected as water contaminants in agriculture areas where the herbicide is used extensively. The removal of glyphosate in synthetic solution using advanced oxidation process is a possible approach for remediation of contaminated waters. The ability of electrochemical oxidation for the degradation and mineralization of glyphosate herbicide was investigated using Ti/PbO2 anode. The current intensity, treatment time, initial concentration and pH of solution are the influent parameters on the degradation efficiency. An experimental design methodology was applied to determine the optimal condition (in terms of cost/effectiveness) based on response surface methodology. Glyphosate concentration (C0 = 16.9 mg L-1) decreased up to 0.6 mg L-1 when the optimal conditions were imposed (current intensity of 4.77 A and treatment time of 173 min). The removal efficiencies of glyphosate and total organic carbon were 95 ± 16% and 90.31%, respectively. This work demonstrates that electrochemical oxidation is a promising process for degradation and mineralization of glyphosate.

Feasibility of disposing waste glyphosate neutralization liquor with cement rotary kiln

The waste neutralization liquor generated during the glyphosate production using glycine-dimethylphosphit process is a severe pollution problem due to its high salinity and organic components. The cement rotary kiln was proposed as a zero discharge strategy of disposal. In this work, the waste liquor was calcinated and the mineralogical phases of residue were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). The mineralogical phases and the strength of cement clinker were characterized to evaluate the influence to the products. The burnability of cement raw meal added with waste liquor and the calorific value of waste liquor were tested to evaluate the influence to the thermal state of the kiln system. The results showed that after the addition of this liquor, the differences of the main phases and the strength of cement clinker were negligible, the burnability of raw meal was improved; and the calorific value of this liquor was 6140 J/g, which made it could be considered as an alternative fuel during the actual production.

The use of BMED for glyphosate recovery from glyphosate neutralization liquor in view of zero discharge

Alkaline glyphosate neutralization liquors containing a high salinity pose a severe environmental pollution problem by the pesticide industry. However, there is a high potential for glyphosate recovery due to the high concentration of glyphosate in the neutralization liquors. In the study, a three-compartment bipolar membrane electrodialysis (BMED) process was applied on pilot scale for the recovery of glyphosate and the production of base/acid with high concentration in view of zero discharge of wastewater. The experimental results demonstrate that BMED can remove 99.0% of NaCl from the feed solution and transform this fraction into HCl and NaOH with high concentration and purity. This is recycled for the hydrolysis reaction of the intermediate product generated by the means of the Mannich reaction of paraformaldehyde, glycine and dimethylphosphite catalyzed by triethylamine in the presence of HCl and reclamation of the triethylamine catalyst during the production process of glyphosate. The recovery of glyphosate in the feed solution was over 96%, which is acceptable for industrial production. The current efficiency for producing NaOH with a concentration of 2.0 mol L(-1) is above 67% and the corresponding energy consumption is 2.97 kWh kg(-1) at a current density of 60 mA cm(-2). The current efficiency increases and energy consumption decreases as the current density decreases, to 87.13% and 2.37 kWh kg(-1), respectively, at a current density of 30 mA cm(-2). Thus, BMED has a high potential for desalination of glyphosate neutralization liquor and glyphosate recovery, aiming at zero discharge and resource recycling in industrial application.

Composite hollow fiber nanofiltration membranes for recovery of glyphosate from saline wastewater

A high performance versatile composite hollow fiber nanofiltration (NF) membrane is reported for the separation of glyphosate from saline waste streams. Preparation of SPEEK based on an amorphous poly (ether ether ketone, PEEK) was investigated. The membrane was prepared by coating sulfonated polyether ether ketone (SPEEK) onto a polyethersulfone (PES) ultrafiltration (UF) hollow fiber membrane. The composite membrane was characterized by water permeability, scanning electron microscopy, and rejection toward sodium sulfate (Na₂SO₄), sodium chloride (NaCl), and calcium chloride (CaCl₂). About 90% rejection toward sulfate anions and only 10% rejection for calcium cations were obtained. A water permeability around 10-13 LMHBar and 90% rejection for polyethylene glycol (PEG) with a molecular weight of 4000-6000 Da were observed. In the separation of glyphosate from saline wastewater, the membrane rejected less than 20% of NaCl and higher than 90% of glyphosate at an operating pressure of 5 bars and pH = 11.0. An economic analysis indicated that the cost for recovery of glyphosate was comparably low to the value gained by an increase in the productivity. The results may lead to a new promising low energy solution for the environmental problem faced by the herbicide industry.

Preparation and adsorption performance of MnO2/PAC composite towards aqueous glyphosate

Glyphosate (N-phosphonomethylglycine (PMG)) is the organophosphate herbicide most widely used in the world, and industrial production of PMG generates large quantities of wastewater. A manganese dioxide-coated powdered activated carbon (MnO2/PAC) composite was synthesized and investigated for the adsorption of PMG from wastewater. The results of scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectrometry (EDAX) revealed that MnO2 was formed on the surface of the carbon during the modification process. Batch adsorption results showed that the optimal pH for glyphosate adsorption on MnO2/PAC was 3.0. In the range 0.01(-1) molL(-1), glyphosate removal by MnO2/PAC decreased with an increase in ionic strength. Among the coexistent anions, only phosphate showed significant inhibition of PMG removal due to competitive complexation. Batch studies revealed that MnO2/PAC could reach a maximum PMG adsorption capacity of 283 mg g(-1). The Langmuir equilibrium model was found to be suitable for describing PMG sorption, and kinetic studies revealed that adsorption followed second-order rate kinetics. It was also proved that the adsorbed PMG could be effectively desorbed from MnO2/PAC in 1.0 molL(-1) NaOH. All of these results implied that the MnO2/PAC composite may be used as an effective adsorbent for recycling PMG from wastewater.

Drinking water obtaining by nanofiltration from waters contaminated with glyphosate formulations: process evaluation by means of toxicity tests and studies on operating parameters

Glyphosate formulations toxicity depends on all its components but commercial products only specify the active principle in their label. To treat contaminated waters and to verify if the unknown components which add toxicity have been removed represent a challenge. Nanofiltration and permeate analysis by toxicity tests with fish are an interesting alternative to evaluate the process. Permeates of solutions with concentrations five times above the lethal doses (48 mg/l) did not present toxicity, pointing that all toxic compounds were removed at the same time. Glyphosate rejection over an 80% despite its molecular weight is lower than membrane MWCO, this could be associated to a predominant Donnan exclusion mechanism, combined with dielectric exclusion due to the solute high charge density. Glyphosate concentration did not show any effect over rejection. It increased when pressure was incremented from 2.5 to 4 bar and then remained constant in a 4-10 bar range. Because of dissociation of the glyphosate and the surface charged of the membrane depend on pH value, the rejection increase from 72.5 to 92.5% when pH increase from 4 to 8.5. Studies with river water showed the same behavior with a slight decrease in rejection.

Partial desalination and concentration of glyphosate liquor by nanofiltration

Partial desalination and concentration of glyphosate liquor by nanofiltration under different operation modes were investigated experimentally in this study. These operation modes were direct nanofiltration, diafiltration, dilute-diafiltration and interval washing-nanofiltration. The four different operation modes were evaluated and compared in terms of glyphosate recovery and NaCl removal. Diafiltration and dilute-diafiltration performed better than direct nanofiltration. The glyphosate loss was between 11.5% and 18.8% when the dilution factor varied from 0.4 to 0.8. Interval washing-nanofiltration alleviated the concentration polarization and membrane fouling to a certain extent. Dilute-diafiltration may be the best operation mode in terms of glyphosate recovery, salt removal and cost.