TREATMENT OF SYNTHETIC INDUSTRIAL EFFLUENT AIMING AT THE REMOVAL OF GLYPHOSATE BY MEANS OF ADVANCED OXIDATION

Objective : The purpose of this study was to assess the efficiency of an advanced oxidative process gradually applying different oxidative agents, i. e. UV, TiO 2 and O 3 , to evaluate the removal efficiency of a commercial composition of glyphosate from an aqueous matrix. Theoretical framework: In Brazil, approximately 150 million liters of glyphosate are consumed per year, representing 30% of the total pesticides used, which can contaminate surface water due to aerial or terrestrial spraying, erosion and runoff, improper disposal of commercial packaging and cleaning of contaminated spray tanks. Advanced oxidative processes have emerged as an alternative to the degradation of glyphosate since they have high efficiency in reducing organic contaminants to an acceptable limit with a low operating cost. Method : Experimental consisted of a benchtop-scale system, composed of a batch reactor with a 25W UV lamp inside and a feeding pump in a recirculation reservoir. It was responsible for performing the removal of glyphosate by means of an advanced oxidative process after receiving TiO 2 and O 3 application. Results and conclusion : The photolysis process obtained an efficiency of 24.69%, the photocatalytic oxidation process with TiO 2 obtained 37.78%, and the photocatalytic ozonation with TiO 2 obtained 45.46% efficiency in 60 minutes of reaction. The possible formation of byproducts after one hour of reaction due to the increase in concentration was also observed, since it was not possible to distinguish glyphosate from other compounds in the analysis method applied. Implications of the research : As demonstrated by the results of the experimental assays, the advanced oxidative technique proved to be very efficient to make the removal of a commercial composition of glyphosate from an aqueous matrix. Originality/value : It has been shown that it is possible to remove glyphosate in an efficient way, using a highly efficient fast technique.


INTRODUCTION
Agricultural production in Brazil and in the world has been growing according to the increased demand for food and for agriculture to have high production, and the consumption of pesticides has grown intensely (dos Santos et al 2021). The most commonly used pesticides in agriculture are herbicides for the combat of weeds (Neto, 2009).
However, the use of these pesticides in large areas of cultivation and, most of the time, in quantities larger than necessary has become a major environmental problem (Aranha, 2013).
Among the various herbicides, glyphosate works as an enzyme inhibitor for hundreds of crops and is widely used in world agriculture. In Brazil, 150 million liters are consumed per year, representing 30% of the total pesticides used. The plant does not metabolize glyphosate, so practically all the concentration reaches the soil and water courses (Toni et al, 2006;Huang et al 2021).
Water contamination by herbicides can occur due to aerial or terrestrial spraying; leaching due to erosion and runoff; improper disposal of commercial packaging; and cleaning of contaminated spray tanks (Tapia, et al 2023;Neto, 2009).
Glyphosate has some acute and chronic effects in humans, such as contact dermatitis and toxic syndrome, and toxicological effects, such as liver and kidney damage, after ingestion of high doses. In aquatic environments, toxicity is accentuated with increases in temperature and pH, and fish and invertebrates are the most sensitive to this herbicide. The toxicity of glyphosate in mammals and birds is relatively low, but glyphosate leads to the destruction of natural environments and food sources of some birds and amphibians, leading to a reduction in populations (Amarante Jr et al., 2002, Nerozzi et al 2020. CONAMA Resolution 430 (2011), which provides for the conditions and standards for the discharge of effluents, does not require a maximum concentration of glyphosate in the industrial effluent, but the concentration of glyphosate in the river, after the mixing zone, cannot exceed that established by CONAMA Resolution 357 (2005). The maximum permissible value of glyphosate in Class 1 and Class 2 fresh waters is 65 μg. L -1 and for Class 3 fresh waters, 280 μg.L -1 .
Several treatment processes have been investigated to reduce the concentration of pesticides in the water and minimize the health risks associated with exposure to these products in contaminated water. Traditional techniques such as coagulation, absorption in activated carbon, reserve osmosis and others can usually be used to remove these pollutants; however, these methods are not destructive and have a high price to remove these pollutants posttreatment. Biodegradation reduces these pollutants, but it is not a technique generally used in water treatment since it is complex to maintain biofilms and has other associated problems. In this way, advanced oxidative processes (AOPs) have become the best technology to solve the problem of pesticide contamination during water and sewage treatment.
POAs have high efficiency in reducing organic contaminants to an acceptable limit with a low operating cost. They are oxidation processes that generate hydroxyl radicals in large quantities, causing the degradation of the compounds. These radicals can be formed by various processes, and catalysts such as titanium dioxide and zinc oxide can be used (Teixeira & Jardim, 2004;Tran et al 2021).
The general objective of this work was to evaluate the efficiency of the process of removal of the herbicide glyphosate in synthetic effluent by means of photocatalytic ozonation with titanium dioxide (TiO2) as a catalyst.

MATERIALS AND METHODS
A photocatalytic reactor of useful volume of 2.6 L was built, consisting of a PVC tube of 100 mm in diameter, closed at its ends (with specific caps), with two low-pressure tubular lamps of 15 W, with emission peak of 253 nm, as a source of ultraviolet radiation. The lamps were arranged close to the central axis and connected to a tubular bivolt electronic reactor with the capacity to connect two lamps of up to 20 W.
The reactor also had two connectors of 1.27 cm in diameter to connect the hoses to the reactor to introduce the affluent flow and remove the effluent. They were connected in a recirculation vessel with a capacity of 2 L containing a submersible pump with a maximum flow of 230 L.h -1 to take the affluent flow into the reactor.
For the photocatalytic ozonation tests, an ozone generator with a capacity of 3 to 5.5 g.h -1 and a power of 85 W was coupled to the system, which collected the atmospheric air and transformed it into ozone, which was released into the system by means of an air diffuser disposed in the recirculation vessel. 4 The schematic representation of the longitudinal section of the reactor can be seen in Figure 1, and the system with all its elements is represented in Figure 2. Figure 3 shows a picture of the system as a whole.

5
The reactor was operated in batches in three stages (Table 1) so that before each stage, the system was cleaned with distilled water to remove any remaining substance that could interfere with the results. The first stage was photolysis to verify the efficiency of glyphosate degradation using only ultraviolet light. The second step was photocatalysis using titanium dioxide to verify the efficiency of glyphosate degradation by combining ultraviolet light and the semiconductor TiO2. The third stage was photocatalytic ozonation, in which ozone was added as an auxiliary oxidant along with UV light and TiO2 to verify the efficiency of glyphosate degradation. The first stage lasted 60 min of reaction, and the second and third stages lasted 120 min to verify the degradation behavior over time. The samples were monitored every 10 min, and the samples were collected from the hose that took the effluent to the recirculation container. The samples were then filtered on 47 mm filter paper to remove the remaining titanium dioxide and submitted to the analysis method proposed by Bhaskara and Nagaraja (2006).
The method consists of the transfer of 5 mL of the samples to glass tubes and the addition of 0.5 mL of 5% ninhydrin and 0.5 mL of 5% molybdate, which are then placed in a water bath at a temperature between 85 and 95 °C for 12 minutes. After cooling to room temperature, the absorbance was checked in a spectrophotometer at 570 nm. Through the calibration curve performed for this method, it is possible to determine the concentration of glyphosate remaining in the sample.
The concentration of glyphosate used was 12 mg. L -1 , since it was the maximum concentration of the calibration curve of the analysis method, obtained through Monsanto's commercial product Roundup, which contains 370 g.L -1 glyphosate in its formulation. Titanium dioxide was added in the liquid effluent to obtain a higher process efficiency, with a concentration of 0.05 g.L -1 .
Through the results of the analyses, Cartesian axis graphs were constructed showing the decay of glyphosate concentration over time.
The study of reactions kinetics was performed using the first-order with residual equation (Dotro et al., 2017). This method simply deducts the fraction of background concentration C* from the inlet and outlet concentrations (Eq. 1), where C is the concentration, C* is the residual concentration, Co is the initial concentration, t is time and k is the kinetic constant.

RESULTS AND DICUSSION
The pH of all samples analyzed during the experiments was maintained according to the preparation of the solution, being on average 7.45. Although they were collected, the pH data were not used because a study on the effect of the same on the degradation of glyphosate had not been conducted.
The first stage of the experiment was to test the degradation of glyphosate using photolysis alone. Using a solution of glyphosate with a concentration of 12 mg. L -1 , since it is the maximum concentration of the calibration curve constructed, the experiment was carried out with 60 minutes of reaction collecting the samples every 10 min. After reading the 6 spectrophotometer, a graph was obtained (Figure 4) showing the degradation of glyphosate by reaction time. We can verify that it degraded from 12.09 mg. L -1 to 9.11 mg.L -1 , obtaining an efficiency of 24.69% with one hour of reaction. Prepared by the authors. Direct photolysis is not considered an option in most studies in the literature because it has a low efficiency for most pesticides (Assalin et al., 2010). Therefore, the low efficiency obtained in the photolysis of glyphosate was expected, showing that it is necessary to use other compounds to assist in this degradation, such as the catalyst titanium dioxide and ozone.
The photocatalytic oxidation experiment was performed using titanium dioxide with an initial glyphosate concentration of 12 mg. L -1 and TiO2 with 0.05 g. L -1 for 120 min. Figure 5 shows the degradation of glyphosate using UV and TiO2, in which glyphosate reached a concentration of 7.60 mg. L -1 in 60 min, but the concentration increased in the rest of the experiment, reaching 10.89 mg. L -1 with 120 min of experiment.   The degradation of glyphosate generates the formation of byproducts, such as aminomethylphosphonic acid (AMPA) (Bourgeois, Klinhamer & Prince, 20120). These byproducts can contribute to errors in the analyses, since they have structures similar to glyphosate, and the spectrophotometer does not identify them, leading to increased absorbance over time. In addition, byproducts can compete with glyphosate for hydroxyl radicals, causing the degradation efficiency over the same period of time to be lower compared to other pesticides. For example, oxidation using hydrogen peroxide removed only 50% of glyphosate in 90 min, while other pesticides such as alachlor and atrazine were removed in percentages of 95% and 83%, respectively, in the same time period.
Thus, it can be inferred that the increase in glyphosate concentration after 60 min of reaction in Figure 5 represents the generation of glyphosate byproducts, since the analysis method uses the spectrophotometer and this does not distinguish glyphosate and its byproducts. Therefore, disregarding the interference of the byproducts obtained between 60 and 120 min of reaction, the photocatalytic oxidation using TiO2 degraded approximately 37.78% of glyphosate with one hour of reaction.
In addition, the glyphosate used was not pure, but the commercial product of Monsanto may have caused the formation of byproducts that interfered with the results obtained.
Finally, photocatalytic ozonation with titanium dioxide was performed to degrade glyphosate with a concentration of 12 mg. L -1 , TiO2 at 0.05 g. L -1 for 120 min. In Figure 6, we can see the graph of glyphosate degradation, where it can be observed that with 10 min of reaction, the concentration passed 12.41 mg. L -1 to 7.59 mg. L -1 . After that time, it continued to decay to a concentration of 6.76 mg.L -1 in 60 min of reaction, representing 45.46% efficiency. After one hour of reaction, the concentration of glyphosate increased, as well as in the experiment using photocatalysis with TiO2, representing the formation of byproducts. Ozonation is an effective method of degrading glyphosate through the free radicals that are generated in the process, but there are indications that in some circumstances, the byproduct AMPA may increase the concentration after the ozonation of glyphosate (Hall & Camm, 2013).
The determination of the degree of degradation of pesticides using ozonation with advanced oxidative processes is very difficult due to the complexity of the reactions. The complete disappearance of the compound monitored with liquid chromatography is not enough  8 to prove the disinfection of the solution, since other more toxic compounds may be present or were produced by the treatment (Assalin et al. 2010). Thus, the reason why the concentration of glyphosate increased can be justified by the formation and/or presence of AMPA and other compounds in the glyphosate solution in the ozonation process since these compounds influence the absorbance of light by the spectrophotometer.
The study of the kinetics of the reactions followed the differential method for each of the stages, and the results of the velocity constant, the order of the reaction and the correction factor can be seen in Table 2. The first stage, photolysis, was very slow and had low efficiency in degrading glyphosate, which can be observed with the value of the constant k, which was the lowest among the three stages. In the photocatalytic oxidation in the second stage, the constant was higher than that in the first stage, representing faster degradation, since the titanium dioxide catalyst was added, which accelerated the reaction. In the photocatalytic ozonation, third stage, the study of kinetics was performed in the first 10 minutes because it is where the greatest degradation of glyphosate occurs, the constant was the lowest and the reaction was of the first order. The best correlation factor was in the third stage, followed by the first and finally the second stage. For Stages 2 and 3, the kinetic studies were developed with the data obtained in the first 60 min of exposure to oxidants since in the remining 60 min, the production of byproducts was observed. In stage one, the data of all the 120 in was used since just UV radiation was the oxidative agent. No byproducts presence was observed in this stage.

CONCLUSIONS
Advanced oxidative processes showed good efficiency in the removal of glyphosate in a commercial formulation. The photolysis process obtained an efficiency of 24.69%, the photocatalytic oxidation process with UV/TiO2 obtained 37.78%, and the photocatalytic ozonation with UV/TiO2/O3 obtained 45.46% efficiency in 60 min of reaction. The possible formation of byproducts after one hour of reaction due to the increase in concentration was also observed, since the method of analysis carried out cannot distinguish between glyphosate and the other compounds.
The results obtained indicate that the process tested can remove glyphosate in a commercial formulation in a 60 min hydraulic detention time. This is considered feasible to apply in any wastewater treatment plant as an advanced treatment unit.
It is recommended that future work identify the byproducts generated by the degradation of glyphosate, as well as a study showing which catalyst is the most efficient at degrading glyphosate. Another recommendation is to perform a comparison of glyphosate concentration using the method proposed by Bhaskara & Nagaraja (2006) and using HPLC or other methods to verify which is the most efficient to determine glyphosate without the interference of byproducts.
About ozone, it is recommended that for a better degradation efficiency of the compound, carry out a study determining the exact concentration of the ozone present in the solution and the degradation power, as well as change the shape of the reactor so that the ozone enters directly inside the reactor and not into the recirculation vessel.