Abstract

This work is part of the context of wastewater management in developing countries. The objective is to set up a simple and less expensive treatment process for soap and cosmetic wastewater. The wastewater from a soap and cosmetics industry in the Abidjan-sud zone was studied. The chemical oxidation method using potassium permanganate is used for the degradation of this raw wastewater at room temperature and basic pH. Indirect volumetric dosage by manganometry and the linear regression method are used to determine the overall order and kinetic parameters of the degradation reaction of oxidizable materials in the wastewater. It appears from this study that permanganate oxidizes the wastewater from the soap and cosmetics unit. All of the materials oxidizable by potassium permanganate (MOPP) with a normality of 2.5.10^-3 degrade after approximately 90 minutes. This MOPP degradation reaction follows kinetics of order 1 with a correlation coefficient. MOPPs behave like a single species and are essentially made up of organic pollutants. The oxidation reaction of MOPP by at room temperature and basic pH is slow with an apparent rate constant

1. Introduction

The recurrent problem of industrial wastewater management is one of the environmental concerns of the State of Ivory Coast. Despite the efforts made by the Ivorian authorities in terms of environmental protection, very few industries comply with the rules and recommendations ^{1, 2}. As a result, effluents are a burden for the State of Ivory Coast, which is unable to treat its wastewater due to lack of technical facilities ^{3, 4}. In Ivory Coast, as in other developing countries, wastewater is discharged into the environment without prior treatment ^{5, 6}.The detergent and cosmetics industry represents an industry of prime importance for developing countries ⁷. Because it makes it possible to satisfy an increasingly growing demand for detergent and cosmetic products ⁸. In Ivory Coast, these industries are in continuous expansion, where several units are installed in the different industrial zones of the Abidjan District ⁹. These industrial units contribute significantly to the growth of the Ivorian economy ⁹. This strong contribution requires significant production activities, thus generating volumes of effluent linked to the use of water in the process ¹⁰. Moreover, these industries use various formulation raw materials (surfactant, fatty acids, organic and inorganic dyes, adjuvants, etc.) whose toxicities on biodiversity have been proven ^{11, 12}. Studies on industrial liquid effluents from soap factories in the Abidjan area have shown that these effluents present certain pollution indicators for aquatic biodiversity ^{13, 14}. They are sources of organic, nutrient, and anionic surfactant pollution. Other studies have also revealed that these detergent and cosmetic effluents are sources of pollution from Trace Metal Elements (ETMs), including chromium ¹⁵. These effluents, which are difficult to biodegrade, are unfortunately discharged into the Ebrié lagoon without prior treatment. In this context, the problem of degradation of detergent and cosmetic effluents is more than necessary.

Several processes (Fenton process, sonication process, etc.) and oxidants (sodium persulfate, potassium dichromate, etc.) have been used for this purpose in order to effectively treat these micropollutants ^{16, 17, 18, 19, 20, 21, 22}. Unfortunately, these processes are very expensive and costly. Potassium permanganate, used as an oxidant, then appears as a palliative to these processes. It is a powerful oxidant, easily used in aqueous media because it is a colored self-indicator. It has been the subject of several studies ^{23, 24, 25, 26, 27}. This simple, rapid and less expensive process is used in this study. Indirect volumetric dosage by manganimetry is used for this purpose. The general objective of this work is therefore to propose a simple and less expensive treatment mechanism for soap and cosmetic effluents. Specifically, it involves carrying out, at ambient temperature and pH of the effluent medium, a kinetic study by determining the overall order and the kinetic parameters of the degradation reaction of the oxidizable materials in the effluent by potassium permanganate. The content of these oxidizable materials in the effluent must be determined.

2. Study Materials and Methodology

The effluent from a soap factory located in the port area of southern Abidjan is the study material. This coded unit (P16) is recognized for its manufacturing of detergent and cosmetic products (Figure 1).

The technical equipment consists of an opaque oxidation reactor and a volumetric dosing device. The commercial reagents used are Potassium permanganate (, Prolabo product), mohr salt (, purity 99%, Prolabo product) and sulfuric acid (, Panreac product).

The samples were taken over a period of four weeks in the month of October corresponding to periods of intense activity of the unit. These effluent samples collected are sent directly to the laboratory for dosage. The degradation of these effluent samples by permanganate (MOPP) is carried out in an opaque oxidation reactor coupled with a volumetric dosing device. The different solutions are prepared with distilled water and the aforementioned reagents, acidified with a sulfuric acid solution. Potassium permanganate solutions are prepared in a volumetric flask by dissolving an appropriate mass of in distilled water. Two solutions of of different concentrations were prepared. This is a solution denoted of permanganate of normality obtained by dissolving a mass in a volumetric flask and a solution denoted of permanganate of normality obtained by dissolving a mass in a volumetric flask. Finally the iron (II) solution with normality is prepared by dissolving a mass of ) (morh salt) in a volumetric flask. For each series of experiments, a volume taken at raw effluent temperature and is poured into the oxidation reactor. A volume of a permanganate solution with indicated normality ( or )taken using a pipette is added. A magnetic stirrer homogenizes the reaction medium continuously. Test samples of volume are taken with a pipette in the reaction medium at different times . The test portion taken at time t is poured into an Erlenmeyer flask, initially containing ice to slow down the reaction and of the prepared acid solution. This test portion is then dosed with the iron (II) titrant solution prepared for measuring the residual potassium permanganate content at time t. The end of the dosage, reflecting the total consumption of residual permanganate ions in the test portion at time t, is marked by the change from purple to colorless of the permanganate. The volume of the iron (II) titrating solution poured at the equivalence V_eq is marked and read on the burette. Each experiment linked to the initial concentration is repeated three times to check the reproducibility of the results. The effluent solution is diluted twice in order to have two different concentrations of MOPP. Knowing the remaining content, the residual content of materials oxidizable by permanganate (MOPP) is determined.

The test portion having been acidified, the redox couples and are used in the context of this study ²⁸. The redox half-equations of the two couples as well as the redox equation are:

(Eq 1)

(Eq 2)

(Eq 3)

The acronym MOPP (Materials Oxidizable by Potassium Permanganate) used throughout this work designates materials, which react in the presence of the oxidant by oxidizing. This oxidation action therefore constitutes a degradation of all of these MOPPs whose balance equation is:

(Eq 4)

As MOPPs are complex and their identity is unknown, it is preferable to always reason in normality rather than molarity. At any time t in the reactor, we have:

Quantity of MOPP material consumed = Quantity of material consumed.

All the species being in the same volume V of solution, we can write:

(1)

The residual normality of is determined at the equivalence of the dosage:

Relation (1) then becomes:

(2)

Thus for the solution S1 of , we have

Relation (2) then becomes:

(3)

Furthermore, for solution S₂ of , we have:

Relation (2) then becomes:

(4)

Thus, although neither knows the initial concentration, nor the residual concentration; we can access the difference . The reaction being assumed to be complete, when all the have been consumed, then we have . The graph then reaches a bearing whose projection on the ordinate axis corresponds to . Once is determined, the normality of the remaining () at time , is deduced from the relation (5 ) below :

(5)

The normality and the molarity of a species are linked by an integer corresponding to the number of particles brought into play by this species in a half-equation such as . Therefore, the concentration and normality of are linked by the following relationship:

(6)

The rate law can therefore be written with normalities instead of molar concentrations.

(7)

The overall order as well as the apparent speed constant will be determined by the linear regression method by comparing the different correlation coefficients , according to the order hypotheses set. Hypotheses of order 1 and 2 are proposed. The order maintained will be the one with the highest correlation coefficient .

3. Results and Discussion

The average values of the volumes at the dosage equivalence, obtained after three tests for each of the three experiments carried out, are recorded in the following table 1.

From the results of Table 1 (Experiments 1, 2 and 3) and expressions (3) and (4), the normalities of the consumed over time are calculated. The values of these normalities are recorded in the following table 2.

Table 2 shows that the normality of in the soap factory effluent is . Its degradation by potassium permanganate takes place after 90 minutes. Experiment 3, with a 2-fold dilution of the effluent from experiment 1, corroborates this result by giving . Moreover, for the same effluent (experiments 1 and 2), the normality of the oxidant of experiment 2 ( ) is higher than that of experiment 1 (. It appears from these two experiments that the degradation of the same MOPP contents occurs quickly after 60 minutes when the normality of the oxidant is higher. In order to determine the kinetic quantities of the degradation reaction with potassium permanganate, the normalities of the remaining at date were determined from relation (5). The different values are recorded in table 3.

The temporal evolutions of the remaining MOPP contents during the degradation of MOPP by permanganate under the different experimental conditions are illustrated in Figure 2.

The graphs ( et )on the ordinate axis at give the content of MOPP in the soap effluent which is . In addition, the curve of experiment 3 gives the value . This third experience consolidates the first two experiences. In fact, the normality of MOPP in soap factory waste water diluted twice is . This value is equal to half of that obtained for experiments 1 and 2 (initial raw effluent) which is .

The kinetic quantities of degradation of oxidizable materials in soap and cosmetic effluent were determined. To do this, hypotheses of order 1 and 2 are formulated. Experiment 1 with raw effluent is retained for this study. The first order hypothesis leads to the kinetic law:

(8)

(9)

With and which are respectively the rate constants of reactions of order 1 and 2. They are expressed in .

The linear regression correlation graph of the degradation reaction of order 1 is illustrated in Figure 3 with a correlation coefficient . Figure 4 gives that of the hypothesis of order 2 with a correlation coefficient

Analysis of the correlation coefficient values shows that . The degradation reaction of MOPP from soap and cosmetic effluent by potassium permanganate at room temperature and basic pH is of order 1 with an apparent rate constant

The variation in the residual concentration of over time shows that permanganate has an oxidative action on the raw soapmaking effluent at the temperature and studied. This oxidative action depends on the concentration of the oxidant. The more concentrated the permanganate, the faster the content consumed increases. In addition, the action of permanganate on is slow (at least 1 hour reaction time). These results are in agreement with those obtained during the work of S. GUERGAZI, and S. ACHOUR ^{29, 30}. Indeed, the study of the oxidative action of permanganate on surface water has shown that oxidation is favored for high levels of oxidant, a basic and a fairly long time (approximately 1 hour) [29,30 ]. The pH could then strongly condition the oxidation mechanisms, depending on the nature of the redox couple present ^{30, 31, 32}. Moreover, the potassium permanganate solution being acidified, the redox couples with strong oxidizing power are and . These higher potential couples would react concurrently with the MOPPs. This last parallel reaction could slow down the main reaction considered with the redox couple . Also, the slow reactivity of permanganate would be due to the presence of free radicals in the reaction medium ³² generated by the different redox couples of permanganate ^{33, 34, 35}. These radicals would generate parasitic reactions thus blocking the main reaction of degradation of the effluent by potassium permanganate ^{33, 34, 35}. However, the degradation kinetics of follows a reaction of order 1 with a rate constant and a correlation coefficient R2 greater than that of order 2. This shows proportionality with the concentration of the effluent, because the higher the concentration of the latter, the higher the rate of degradation of MOPP. The first order kinetics of the degradation reaction of in soap and cosmetics effluent by potassium permanganate confirms that these contain mainly organic pollutants ^{36, 37, 38}. This result is in agreement with several kinetic studies carried out on the kinetics of degradation of organic pollutants ^{36, 37, 38}. It is important to indicate that despite the slow nature of this process, it turns out to be faster than other processes which have remained at the laboratory stage, because they are very complex and their implementation turns out to be expensive ^{39, 40}. This process has the advantage of being simpler, being able to be carried out in situ, with a less expensive reagent.

4. Conclusion

The degradation of Oxidizable Materials by Potassium Permanganate is part of the depollution of industrial effluents. The chemical oxidation process using potassium permanganate and the indirect volumetric dosage by manganimetry used in this work provided interesting and consistent results. The degradation reaction of MOPP by follows kinetics of global order 1 with a rate constant at room temperature and basic pH. It is remarkable that MOPPs, although made up of several oxidizable compounds, behave according to the kinetic law, as a single, predominantly organic species. However, the oxidation reaction of by at room temperature and at basic pH is slow, because all of the degrade after approximately 90 minutes. An improvement of this work is possible by taking into account other kinetic parameters such as pH, temperature, etc. Modeling this degradation reaction is possible for in situ treatment of soap and cosmetic effluents.

ACKNOWLEDGMENT

We would like to thank the authorities of NANGUI ABROGOUA University as well as the Director of the Laboratory of Thermodynamics and Physico-Chemistry of the Environment (LTPCM), of the said University. Furthermore, our sincere thanks go to our various collaborators from the Theoretical Chemistry and Modeling (CTM) and Catalysis and Environment (CE) research teams from the Laboratory of Thermodynamics and Physico-Chemistry of the Middle of the Unit. of Fundamental and Applied Sciences Research Training (UFR SFA) from the NANGUI ABROGOUA University as well as that of the UFR Biological Sciences, from the PELEFORO GON COULIBALY University. Finally, many thanks to the soap making study unit for their invaluable technical and material support.

References