Abstract
This study investigated the performance of different ionic solvents (NaCl, KNO3, and Na2SO4) in mediating electrolytic decontamination of pesticide-containing wastewaters and established the most suitable ionic solvent that can satisfactorily achieve decontamination of such wastewaters. These were done to find a water-purification technique suitable for the removal of recalcitrant and hazardous trace organic substances from wastewater. Organochlorine pesticide (OCP)-containing wastewaters were constituted according to prescribed modalities. It was observed that complete decontamination of the wastewater was achieved within 2 h of using Na2SO4. The study concluded that the 1.0 M of Na2SO4 solution-mediated electrolytic process was most efficient in decontaminating OCP-containing wastewater.
HIGHLIGHTS
Several investigations on wastewater treatment using an electrolytic method for the removal of contaminants have been carried out, but there is paucity of information on the comparative efficiencies of ionic solvents of different strengths to affect decontamination of pesticide-containing wastewater.
Degradation of organochlorine pesticides (OCPs).
Effects of ionic solution on decontamination of waste water.
INTRODUCTION
The world population has continuously been on the increase. For example, the world witnessed a population increase from 1.5 to 6.9 billion between 1900 and 2000 (Saleh et al. 2020). This increase has led to a corresponding demand for improved crop yields and general healthy living conditions which have come under pressure as a result of a meteoric rise in population figures. Hence, there is widespread use of thousands of tons of pesticides to curb the menace of domestic, industrial, and agricultural pests throughout the world. Without a doubt, such diverse applications of pesticides have generated large volumes of contaminated waste water, whose direct disposal into natural channels causes their accumulation in various environmental compartments (Cabrera 2017; Kim et al. 2017; Ouni et al. 2021). To a large extent, modern agricultural practices rely on pesticides to increase crop yield to an economically profitable level (Kılıç et al. 2020).
Pesticides are chemical substances used for destroying, preventing, mitigating, and repelling any pest; they can also be used as a plant regulator, desiccant, or defoliant (Ouni et al. 2021). According to the Food and Agricultural Organization of the United Nations (FAO), more than 500,000 tonnes of obsolete pesticides are stored worldwide (FAO Pesticide Disposal Series 2011). Agriculture can therefore be considered to be the greatest contributor to both surface and groundwater contamination by pesticides.
In addition to pesticides, pharmaceuticals (hormones, antibiotics, and others), cosmetics, and synthetic dyes are also emerging contaminants of concern in many areas around the world (Gomes et al. 2018). Pesticides can pose a threat when they leach into groundwater and enter into drinking water supplies. Ingestion through prolonged reliance on a source of drinking water contaminated with pesticides can be a major cause of a myriad of health challenges such as birth defects, respiratory failure, biochemical instability, kidney failure, the onset of diabetes, hepatic problems, and cardiac disorder with symptoms that may include nausea, vomiting, tremors, and hypotension (Jayaraj et al. 2016; Bakhsh et al. 2021; Masibi et al. 2021). The frequency of symptoms has been identified to be higher among planters, weeders, and harvesters (Mergia et al. 2021).
Several techniques such as biological processes, filtration, coagulation, adsorption, membrane processes, chemical oxidation, and so on have been employed in the treatment of contaminated wastewater (Rodríguez-Rodríguez et al. 2013; Castro-Gutiérrez et al. 2019; Saleh et al. 2020) but none of these has been found to eliminate the pollutants (Ouni et al. 2021). For instance, chemical oxidation is unable to mineralize the persistent organic pollutants (Rodríguez-Rodríguez et al. 2013; Saleh et al. 2020), coupled with the slow reaction rates and the problem of disposal of sludge, biological treatment lacks efficacy in the presence of non-biodegradable and toxic pollutants (Saleh et al. 2020). To overcome these drawbacks, advanced oxidation methods have been developed allowing the destruction of organic pollutants (Moreira et al. 2017; Ribeiro et al. 2019; Hoang & Holze 2021). Among these methods, electrochemical oxidation has shown a significant efficiency in the destruction of organic pollutants (Moreira et al. 2017; Hoang & Holze 2021). Thus, there is a need to develop methods that could satisfactorily decontaminate wastewater to safe levels.
Some investigations on wastewater treatment using an electrolytic method for the removal of contaminants have been carried out (Rodrigo et al. 2014; Sirés et al. 2014; Martínez-Huitle et al. 2015; Min et al. 2018; Khan et al. 2020; Lourinho & Brito 2021; Santos et al. 2022) but there is a need to further investigate the comparative efficiencies of ionic solvents of different strengths to effect decontamination of pesticide-containing wastewater. Thus, the present study aimed to investigate the performance of various ionic solvents in aiding the electrolytic degradation of some organochlorine pesticides (OCPs) in synthetic wastewater to safe levels.
MATERIALS AND METHODOLOGY
Reagents used and their sources
All chemical reagents used were of analytical grade and they include dichloromethane (DCM) (GFS Chemicals, Coulombus), potassium nitrate (Laboratory Tech Chemicals, Poole England), anhydrous sodium sulfate (Na2SO4) (GFS Chemicals, Coulombus), n-Hexane (GFS Chemicals, Coulombus), sodium chloride (Aldrish Chemical Company, USA), silica gel (Oxford Laboratory Reagents, Mumbai, India), glass wool (Chemei Laboratory, Mumbai, India), and distilled water (from the preparatory room of Department of Chemistry, Obafemi Awolowo University, Ile-Ife).
Decontamination of apparatus
All glassware used (conical flask, beaker, measuring cylinder, volumetric flask, watch glass, and sample bottles) was washed thoroughly with liquid detergents using a brush and rinsed with tap water until no foam was observed. Thereafter, they were rinsed thoroughly first with distilled water followed by analytical grade acetone, and then air dried. The glassware used during the clean-up stage was pre-extracted with DCM to remove organic grits that could interfere with results.
Preparation of solutions and wastewater
Standard solutions (0.3, 0.5, 1.0 M) of NaCl, KNO3, and Na2SO4 were prepared by serial dilution of 1.0 M of each of the salt solutions. Also, for the preparation of synthetic wastewaters, three commercially available pesticides, namely: Paraforce (Paraquat dichloride), Weed off (paraquat isopropyl amine), and Perfect Killer (Chlorpyrifos) were mixed in a ratio of 5:5:20 mL, respectively. These pesticides have been reported to contain some levels of OCPs. The mixture was made up to 2.0 L. From this wastewater, 10 mL was collected and poured into a 250-mL volumetric flask. Thereafter, 40 mL of a standard solution of a given ionic solvent was added and made up to the mark with distilled water. The samples were prepared with the intention of being able to retrieve detectable concentrations without approaching the detection limits. As a control, 10 mL of the pesticide solution was also added to an equal volume of distilled water which had been spiked with a corresponding amount of ionic solvent.
Decontamination procedure
Extraction and clean-up
The wastewater that had been electrolytically decontaminated was subjected to liquid–liquid extraction and the solvent in the extract was allowed to evaporate until the volume remained about 2 mL. The control sample was similarly treated. The clean-up procedure which refers to an extraction in which impurities are extracted from the solvent containing the desired compound was carried out in solid phase extraction (SPE) columns with adsorbents that have different polarities. For each of the uncontaminated and decontaminated extracts, a silica gel SPE column plugged with glass wool was prepared by packing 10 g of silica gel in a glass column with anhydrous sodium sulfate packed on top of the adsorbent in the glass column. The packed column was conditioned with 20 mL of DCM. The extract was applied to the conditioned column and the flow-through was collected in a 50 mL amber-colored glass vial (Bempah & Donkor 2011). The vial was left open for the cleaned-up sample to fully dry under nitrogen. The air-dried sample was reconstituted with 1 mL od n-hexane in readiness for GC-MS analysis.
Instrumental analysis
The determination of OCPs in the extracts was performed by a gas chromatograph (Agilent Model 7890B) coupled with a Pegasus 4D Mass Spectrometer (GC-MS) at the Nigerian Institute of Oceanography and Marine Research, Victoria Island, Lagos, Nigeria. The features and operating conditions were as follows: a GC column Restek Rtx-CL pesticides; two capillary columns of 30 m × 0.25 mm id × 0.25 μm film thickness at 340 °C. The GC operating conditions were splitless injection, injector temperature of 250 °C, helium carrier gas (99.99% purity) at a flow rate of 0.9 mL min−1 with a column head pressure of 7.4 psi; oven temperature was kept at 70 °C for 2 min and then programmed to rise to 130 °C at 25 °C min−1, afterward rise to 220 °C at 2 °C min−1, and then finally set to 280 °C at 10 °C min−1. This temperature was maintained for 4.6 min. The sample (1 μL) was injected in splitless modes. The mass spectrometer was set as follows: electron impact ionization mode with 70 eV of electron energy, scan mass range 100–400 at 0.62 s/cycle, ion source temperature of 230 °C, MS quad temperature 150 °C, EM voltage 1,450, and solvent delay 4 min. The MS system was routinely operated in selective ion monitoring (SIM) mode with electron ionization. The OCP compounds were identified based on a comparison of the retention times of peaks with those of standard OCP compounds. Thereafter, the internal standard method was used for OCP quantification. The chromatogram of the analyzed OCPs can be found in Supplementary material S1.
RESULTS AND DISCUSSION
Levels (μg/mL) of OCPs in wastewater
The freshly prepared wastewater containing various OCPs indicated that out of the 17 OCPs intended for analysis, α-BHC, Endosulfan I, p,p′-DDT, and Endosulfan sulfate were below the detection limit (BDL) or absent. On the other hand, the remaining 13 OCP congeners were detected at levels ranging from 1.35 μg/mL of δ-BHC to 35.92 μg/mL of Endrin as shown in Table 1.
OCP congeners . | R . | NaCl solutions . | KNO3 solutions . | Na2SO4 solutions . | ||||||
---|---|---|---|---|---|---|---|---|---|---|
H . | I . | J . | K . | L . | M . | N . | O . | P . | ||
0.3 M . | 0.5 M . | 1.0 M . | 0.3 M . | 0.5 M . | 1.0 M . | 0.3 M . | 0.5 M . | 1.0 M . | ||
α-BHC | – | – | – | – | – | – | – | – | – | – |
β-BHC | 6.53 | – | – | – | – | – | – | – | – | – |
Heptachlor | 3.56 | – | – | – | – | – | – | – | – | – |
Aldrin | 4.06 | – | – | – | – | – | – | – | – | – |
γ-BHC | 4.07 | – | – | – | – | – | 1.52 | – | 3.16 | – |
δ-BHC | 1.35 | – | – | – | 1.16 | – | – | – | – | – |
Heptachlor Epoxide | 7.54 | – | – | – | – | – | – | – | 5.86 | – |
Endosulfan I | 12.35 | – | – | – | – | – | 3.53 | 9.50 | – | – |
p,p′–DDE | 9.03 | – | – | – | – | – | – | – | – | – |
Dieldrin | 3.29 | – | – | – | – | – | 1.43 | 1.13 | – | – |
Endrin | 35.92 | 2.60 | – | 8.06 | 8.75 | 9.97 | 9.23 | 1.13 | – | – |
p,p′–DDD | 5.31 | – | – | – | – | – | 2.22 | – | – | – |
Endosulfan II | – | – | – | – | – | – | – | – | – | – |
p,p′–DDT | – | – | – | – | – | – | – | – | – | – |
Endrin Aldehyde | 6.92 | – | 4.05 | – | – | – | – | – | – | – |
Endosulfan sulfate | – | – | – | – | – | – | – | – | – | – |
Methoxychlor | 7.06 | – | 1.24 | – | 4.59 | – | 1.37 | – | – | – |
Total remaining | 106.99 | 2.60 | 5.29 | 8.06 | 14.50 | 9.97 | 19.30 | 11.76 | 9.06 | 0.00 |
% Decontamination | – | 97.57 | 95.06 | 92.47 | 86.45 | 90.68 | 81.96 | 89.01 | 91.53 | 100 |
OCP congeners . | R . | NaCl solutions . | KNO3 solutions . | Na2SO4 solutions . | ||||||
---|---|---|---|---|---|---|---|---|---|---|
H . | I . | J . | K . | L . | M . | N . | O . | P . | ||
0.3 M . | 0.5 M . | 1.0 M . | 0.3 M . | 0.5 M . | 1.0 M . | 0.3 M . | 0.5 M . | 1.0 M . | ||
α-BHC | – | – | – | – | – | – | – | – | – | – |
β-BHC | 6.53 | – | – | – | – | – | – | – | – | – |
Heptachlor | 3.56 | – | – | – | – | – | – | – | – | – |
Aldrin | 4.06 | – | – | – | – | – | – | – | – | – |
γ-BHC | 4.07 | – | – | – | – | – | 1.52 | – | 3.16 | – |
δ-BHC | 1.35 | – | – | – | 1.16 | – | – | – | – | – |
Heptachlor Epoxide | 7.54 | – | – | – | – | – | – | – | 5.86 | – |
Endosulfan I | 12.35 | – | – | – | – | – | 3.53 | 9.50 | – | – |
p,p′–DDE | 9.03 | – | – | – | – | – | – | – | – | – |
Dieldrin | 3.29 | – | – | – | – | – | 1.43 | 1.13 | – | – |
Endrin | 35.92 | 2.60 | – | 8.06 | 8.75 | 9.97 | 9.23 | 1.13 | – | – |
p,p′–DDD | 5.31 | – | – | – | – | – | 2.22 | – | – | – |
Endosulfan II | – | – | – | – | – | – | – | – | – | – |
p,p′–DDT | – | – | – | – | – | – | – | – | – | – |
Endrin Aldehyde | 6.92 | – | 4.05 | – | – | – | – | – | – | – |
Endosulfan sulfate | – | – | – | – | – | – | – | – | – | – |
Methoxychlor | 7.06 | – | 1.24 | – | 4.59 | – | 1.37 | – | – | – |
Total remaining | 106.99 | 2.60 | 5.29 | 8.06 | 14.50 | 9.97 | 19.30 | 11.76 | 9.06 | 0.00 |
% Decontamination | – | 97.57 | 95.06 | 92.47 | 86.45 | 90.68 | 81.96 | 89.01 | 91.53 | 100 |
R refers to the values of OCPs in untreated wastewater.
Levels (μg/mL) of OCPs remaining in the decontaminated wastewater
Results obtained indicated that out of the 13 OCP congeners in the various solutions, the decontamination process followed the pattern: P (13 OCPs, 100%) > H, J, L (12 OCPs, 92.31%) > I, O (11 OCPs, 84.62%) > K, N (10 OCPs, 76.92%) > M (7 OCPs, 53.85%). Evaluated in terms of OCPs decontaminated, the percentage efficiency of the solution at effecting decontamination occurred in the order P (100%) > H (97.57%) > I (95.06%) > J (92.47%) > O (91.53%) > L (90.68%) > N (89.01%) > K (86.45%) > M (81.96%). Thus, solution P demonstrated the highest decontamination efficiency and should be considered whenever electrolytic decontamination of OCP-containing wastewater is desirable.
Degradation effects on classes of OCPs
The OCP congeners present in the synthetic wastewater are classified into dichlorodiphenylmetahne (DDT), cyclodienes, and chlorinated benzenes/cyclohexanes. The degree of their decontamination is discussed in the following.
A total of 14.34 μg/mL of DDTs was present in the synthetic wastewater, both NaCl and Na2SO4 caused a significant degradation process in the decontamination of OCP-containing wastewater except 1.0 M of KNO3 that had 2.22 μg/mL of DDTs present in the synthetic wastewater.
A total of 80.70 μg/mL of cyclodienes was present in the synthetic wastewater; NaCl with molar concentrations of 0.3, 0.5, and 1.0 caused a significant degradation process in the decontamination of OCP-containing wastewater, reducing it to 2.60, 5.29, and 8.06 μg/mL, respectively. In the case of KNO3 with molar concentrations of 0.3, 0.5, and 1.0, there was a reduction of the contaminants to 13.34, 9.97, and 15.56 μg/mL , respectively. Furthermore, 0.3 and 0.5 M of Na2SO4 reduced the concentration of the OCPs in the wastewater to 11.76 and 5.86 μg/mL, respectively, while 1.0 M of the Na2SO4 cased a complete reduction of all the OCPs metabolites that were originally present in the wastewater.
For chlorinated benzenes/cyclohexanes, a total of 11.95 μg/mL was present in the synthetic wastewater, all the NaCl solutions, 0.5 M of KNO3, 0.3 and 1.0 M of Na2SO4 caused a significant degradation process in the decontamination of OCP-containing wastewater. However, 0.1 and 0.3 M of KNO3, and 0.5 M of Na2SO4 left 1.16, 1.52, and 3.16 μg/mL, respectively, of chlorinated benzenes/cyclohexanes undegraded from the synthetic wastewaters as can be seen in Table 2.
. | . | R . | NaCl solutions (M) . | KNO3 solutions (M) . | Na2SO4 solutions (M) . | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|
OCP congeners . | 0.3 . | 0.5 . | 1.0 . | 0.3 . | 0.5 . | 1.0 . | 0.3 . | 0.5 . | 1.0 . | ||
DDTs | p,p'-DDE | 9.03 | – | – | – | – | – | – | – | – | – |
p,p′-DDD | 5.31 | – | – | – | – | – | 2.22 | – | – | – | |
p,p'-DDE | – | – | – | – | – | – | – | – | – | – | |
Total | 14.34 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 2.22 | 0.00 | 0.00 | 0.00 | |
Cyclodienes | Heptachlor | 3.56 | – | – | – | – | – | – | – | – | – |
Aldrin | 4.06 | – | – | – | – | – | – | – | – | – | |
Heptachlor Epoxide | 7.54 | – | – | – | – | – | – | – | 5.86 | – | |
Endosulfan I | 12.35 | – | – | – | – | – | 3.53 | 9.50 | – | – | |
Dieldrin | 3.29 | – | – | – | – | – | 1.43 | 1.13 | – | – | |
Endrin | 35.92 | 2.60 | – | 8.06 | 8.75 | 9.97 | 9.23 | 1.13 | – | – | |
Endosulfan II | – | – | – | – | – | – | – | – | – | – | |
Endrin Aldehyde | 6.92 | – | 4.05 | – | – | – | – | – | – | – | |
Endosulfan sulfate | – | – | – | – | – | – | – | – | – | – | |
Methoxychlor | 7.06 | – | 1.24 | – | 4.59 | – | 1.37 | – | – | – | |
Total | 80.70 | 2.60 | 5.29 | 8.06 | 13.34 | 9.97 | 15.56 | 11.76 | 5.86 | 0.00 | |
Chlorinated benzenes/Cyclohexanes | α-BHC | – | – | – | – | – | – | – | – | – | – |
β-BHC | 6.53 | – | – | – | – | – | – | – | – | – | |
γ-BHC | 4.07 | – | – | – | – | – | 1.52 | – | 3.16 | – | |
δ-BHC | 1.35 | – | – | – | 1.16 | – | – | – | – | – | |
Total | 11.95 | 0.00 | 0.00 | 0.00 | 1.16 | 0.00 | 1.52 | 0.00 | 3.16 | 0.00 |
. | . | R . | NaCl solutions (M) . | KNO3 solutions (M) . | Na2SO4 solutions (M) . | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|
OCP congeners . | 0.3 . | 0.5 . | 1.0 . | 0.3 . | 0.5 . | 1.0 . | 0.3 . | 0.5 . | 1.0 . | ||
DDTs | p,p'-DDE | 9.03 | – | – | – | – | – | – | – | – | – |
p,p′-DDD | 5.31 | – | – | – | – | – | 2.22 | – | – | – | |
p,p'-DDE | – | – | – | – | – | – | – | – | – | – | |
Total | 14.34 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 2.22 | 0.00 | 0.00 | 0.00 | |
Cyclodienes | Heptachlor | 3.56 | – | – | – | – | – | – | – | – | – |
Aldrin | 4.06 | – | – | – | – | – | – | – | – | – | |
Heptachlor Epoxide | 7.54 | – | – | – | – | – | – | – | 5.86 | – | |
Endosulfan I | 12.35 | – | – | – | – | – | 3.53 | 9.50 | – | – | |
Dieldrin | 3.29 | – | – | – | – | – | 1.43 | 1.13 | – | – | |
Endrin | 35.92 | 2.60 | – | 8.06 | 8.75 | 9.97 | 9.23 | 1.13 | – | – | |
Endosulfan II | – | – | – | – | – | – | – | – | – | – | |
Endrin Aldehyde | 6.92 | – | 4.05 | – | – | – | – | – | – | – | |
Endosulfan sulfate | – | – | – | – | – | – | – | – | – | – | |
Methoxychlor | 7.06 | – | 1.24 | – | 4.59 | – | 1.37 | – | – | – | |
Total | 80.70 | 2.60 | 5.29 | 8.06 | 13.34 | 9.97 | 15.56 | 11.76 | 5.86 | 0.00 | |
Chlorinated benzenes/Cyclohexanes | α-BHC | – | – | – | – | – | – | – | – | – | – |
β-BHC | 6.53 | – | – | – | – | – | – | – | – | – | |
γ-BHC | 4.07 | – | – | – | – | – | 1.52 | – | 3.16 | – | |
δ-BHC | 1.35 | – | – | – | 1.16 | – | – | – | – | – | |
Total | 11.95 | 0.00 | 0.00 | 0.00 | 1.16 | 0.00 | 1.52 | 0.00 | 3.16 | 0.00 |
R is the amount of pesticides in raw water/synthetic wastewater.
Effect of solution strength
From Figure 3(a), it can be deduced that as the concentration of NaCl increased, the decontamination process decreased, whereas for Na2SO4, as the concentration of the ionic solvent increased, the decontamination process also increased. The concentration of NaCl has an inverse relation with its decontamination process, while that of Na2SO4 has a direct relation with its decontamination process. Nevertheless, there was no regular pattern observed for the KNO3 solution-mediated decontamination process.
Solution strength efficiency
The three sets of freshly prepared salt solutions (NaCl, KNO3, and Na2SO4) used to mediate the decontamination process of wastewater containing various OCPs were grouped into concentrations of 0.3, 0.5, and 1.0 M, respectively.
Effects of NaCl in electrolytic decontamination of wastewater
It was observed that solution H (0.3 M NaCl) caused the decontamination of 12 out of the 13 OCPs (Supplementary material S2), in which 2.60 μg/mL (7.24%) of Endrin remained uncontaminated. The solution I (0.5 M NaCl) caused the decontamination of 11 out of the 13 OCPs, in which 4.05 μg/mL (58.53%) of Endrin Aldehyde and 1.24 μg/mL (17.56%) of Methoxychlor remained uncontaminated. Solution J (1.0 M NaCl) caused the decontamination of 12 out of 13 OCPs, in which 8.06 μg/mL (22.45%) of Endrin remained uncontaminated. Therefore, aside from the role played by Cl− atom in effecting the degradation process, Na+ probably had a significant role to play in the process.
Effects of KNO3 in electrolytic decontamination of wastewater
It was observed that solution K (0.3 M KNO3) caused the decontamination of 10 out of the 13 OCPs (Supplementary material S3), in which 1.16 μg/mL (85.93%) of δ-BHC, 8.75 μg/mL (24.36%) of Endrin, and 4.59 μg/mL (65.01%) of Methoxychlor remained undecontaminated. Solution L (0.5 M KNO3) caused the decontamination of 12 out of the 13 OCPs, in which 9.97 μg/mL (27.76%) of Endrin remained uncontaminated. Solution M (1.0 M KNO3) caused the decontamination of only 8 out of the 13 OCPs, in which 1.52 μg/mL (37.35%) of γ-BHC, 3.53 μg/mL (28.58%) of Endosulfan I, 1.43 μg/mL (43.47%) of Dieldrin, 9.23 μg/mL (25.70%) of Endrin, 2.22 μg/mL (41.81%) of p,p′-DDD, 1.37 μg/mL (19.41%) of methoxychlor remained undecontaminated. In the previous studies conducted in respect of OCPs removal from wastewater, it was reported that more than 82 and 80% of OPCs were eliminated from the water samples by Sahmarani et al. (2021) and Suo et al. (2019), respectively. The present study even recorded better performance in the removal of up to 12 out of 13 (92.3%) OCPs from synthetic wastewater.
Therefore, aside from the role played by ions in achieving the degradation process, K+ probably had little or no significant role to play in the process.
Effects of Na2SO4 in electrolytic decontamination of wastewater
It was observed that solution N (0.3 M Na2SO4) caused the decontamination of 10 out of the 13 OCPs (Supplementary material S4), in which 9.50 μg/mL (76.92%) of Endosulfan I, 1.13 μg/mL (34.35%) of Dieldrin, and 1.13 μg/mL (3.15%) of Endrin remained uncontaminated. Solution O (0.5 M Na2SO4) caused the decontamination of 11 out of the 13 OCPs, in which 3.16 μg/mL (77.64%) of γ-BHC and 5.86 μg/mL (77.72%) of heptachlor epoxide remained uncontaminated. Solution P (1.0 M Na2SO4) caused the decontamination of all 13 OCPs, in which none remained uncontaminated. Therefore, aside from the role played by atom in achieving the degradation process, Na+ probably had a significant role to play in the process as well.
CONCLUSION
This study investigated the effects of various ionic solvents (NaCl, KNO3, and Na2SO4) of different strengths (0.3, 0.5, and 1.0 M) in mediating electrolytic decontamination of pesticide-containing wastewater. It also established the most suitable ionic solvent that could be adopted to affect decontamination of OCP-containing wastewater. The electrolytic decontamination which spanned 2 h in each case indicated that the ranges of decontamination were: 92.47–97.57% OCPs for NaCl, 81.96–90.68% KNO3, and 89.01–100% Na2SO4. It was also observed that as the concentrations of NaCl increased, the decontamination process decreased, whereas for Na2SO4, as the concentration increased, the decontamination process also increased. However, no regular pattern was observed for the performance of KNO3 to the ionic solvent strength. The study concluded that the Na2SO4 solution-mediated electrolytic process was the most efficient at the decontamination of OCPs in wastewater. This study has implications in the area of treatment of industrial effluents containing recalcitrant pesticides such as OCPs. It also forms the basis for future researches that bother on wastewater pollutants evaluation and treatment.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.