Surfactant-polluted surface water treatment with Moringa oleifera seed extract

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Surfactant-polluted surface water treatment with Moringa
oleifera seed extract
J. Sánchez-Martín*, J. Beltrán-Heredia**
*Universidad de Extremadura, Department of Chemical Engineering and Physical Chemistry, Avda. de
Elvas, s/n, 06071 Badajoz, Spain. Tel: +34 924289 300 Ext: 9033 Fax: +34 924289385
E-mail: jsanmar@unex.es
**Universidad de Extremadura, Department of Chemical Engineering and Physical Chemistry, Avda. de
Elvas, s/n, 06071 Badajoz, Spain. E-mail: jbelther@unex.es

Abstract: Moringa oleifera seed extract has been tested in removing surfactants from polluted surface
water. River water has been polluted with sodium lauryl sulphate, a spread surfactant, and Jar-test have
been carried out in order to evaluate the efficiency of this natural coagulant agent inside a real surface
water matrix. Efficiency has demonstrated to be very high (maximum q of about 2.5 mmol·g−1) and a high
surfactant removal is achieved rapidly. Coagulation process may be modelated through Gu and Zhu
adsorption hypothesis, so an acceptable r2coefficient is obtained (0.94).
Keywords: Moringa oleifera, surfactants, coagulation-flocculation, natural flocculants

1 Introduction
Surfactants dumping into the environment has become one of the main concerns in water
treatment. Due to the main role in some of the most important fields of soft chemical
technology (cosmetics, pharmaceuticals, personal care products…) surfactants have achieved a
relevant position in human activity. More than 15 million tonnes per year are used
(Edser, 2008), so surfactant-induced pollution is considered a main task to research on
(Matthijs et al., 1995).
  Surfactant presence into surface water, such as rivers or lakes, may lead to a harmful situation
for aquatic flora and fauna, due to the fact that may interact with oxygen transfer (Wagner and
Pöpel, 1996) by modifying surface tension. Binding ability of these products with other
dangerous substances (such as pharmaceuticals) is another hazardous property that may damage
environmental equilibrium.
  Due to these reasons, removing surfactants from water flows has become a priority of a large
number of researchers. Nowadays, surfactants can be removed by several mechanisms, most of
them imply adsorption on activated carbon, chemical association or chemical degradation.
However, new removal methods should be researched on because surfactants and tensioactives
impact is high enough.
  In this sense, we have been researching on Moringa oleifera as a water treatment agent for
several years. As a tropical multi-purpose tree, Moringa oleifera is very interesting from the
point of view of developing cooperation, as it is a widespread, easy-available water treatment
method. The use of Moringa oleifera as water treatment can imply two different ways: a) One
concerning its usage as a primary source of activated carbon and b) Another one through seed
extraction, whose product works as a coagulant/flocculant agent (Okuda et al., 1999). Last
method is rather more effective and accurate, and it replies better to its application in
developing countries. Its power lays on the fact that it is not technologically difficult to operate
by non-qualified personal, it is easy to work with and it presents not an external dependency of
reagents, as it would happen with other products (Al2(SO4)3, FeCl3...). Because of those
reasons, it has been recommended by the Food and Agricultural Organization (FAO) as a
proper and advisable way for treating water.
  The main aim of the current investigation is to research on the ability of Moringa oleifera in
removing sodium lauryl sulphate (SLS) from a real surface water matrix such as river water.
The structure of this surfactant (m.w. 288.38 g mol−1) is showed in Figure 1. Surfactant
association with turbidity (humic and fulvic substances) may affect the way SLS-Moringa
oleifera coagulation is carried out.

Water Practice & Technology Vol 5 No 1 © IWA Publishing 2010 doi: 10.2166/WPT.2010.001
Figure 1: Chemical structure for sodium lauryl sulphate.

2 Materials and methods
2.1   Surface water
It was taken from Guadiana river, at Badajoz (Southwest of Spain, Extremadura Community) in
winter (year 2008). It is pretended with this decision to study the problem from a real point of
view, avoiding turbid water simulation with different chemical-physical procedure such as
kaolin addition (Ghebremichael, 2004). River water was treated the same day it was collected,
and its average characteristics are showed in Table 1.
Table 1: Raw water characterization data
       Parameter                       Units               Value
            pH                            7.5
      Conductivity                    µS cm−1                400
    Suspended solids                  mg L−1                  15
       Total solids                   mg L−1                 452
        Turbidity                       NTU                 123.3
         Calcium                    Ca mg L−1
                                       2+                    37.7
        Hardness                   CaCO3 mg L−1              152
      Ammonium                       N mg L−1                1.81
         Nitrate                     N mg L−1                1.20
          Nitrite                    N mg L−1               0.033
        Chloride                    Cl‐ mg L−1               40.4
   KMnO4 oxidability                 O2 mg L−1               19.3
       Phosphate                     P mg L−1               0.044
    Total phosphorus                 P mg L−1               0.064
     Total coliforms            Colonies per 100 mL          800
     Fecal coliforms            Colonies per 100 mL          400
   Fecal streptococcus          Colonies per 100 mL          140

2.2   Moringa oleifera seed extraction
Seeds were obtained from SETROPA (Holland). The extraction process was carried out in
the following way: seeds were reduced into powder by a domestic mill. A 1M NaCl
(PANREAC) solution was prepared and 5 g of powder were put into 100 mL of it. The NaCl
solution with powder was stirred for 30 minutes time at room temperature (around 25ºC). No
pH modification was needed, as natural pH 7 was achieved. Then, the extract was filtered
twice: once through commercial filter paper on Büchner funnel and once again through a fine
filtering millipore system (0.45 µm glass fiber). The result is a clear, milky-like liquid. The
average composition of this extract is referred in Table 2.

                                                  2
Table 2: Seed extract characterization.
               Parameter                     Units         Value
     Dry residue (NaCl excluded)             g∙L‐1          3.24
             Ammonium                       N g L‐1         0.06
                Nitrate                     N g L‐1         0.55
                 Nitrite                    N g L‐1           0
          KMnO4 oxidability                 O2 g L‐1        1.08
              Phosphate                     P g L‐1         0.05
           Total phosphorus                 P g L‐1         0.07
         Isoelectric point (pI)a                           10‐11
          Molecular weightb                  kDa           6.5‐14
a
  (Kwaambwa and Maikokera, 2007).
b
  (Ndabigengesere et al., 1995).

2.3   Jar-test procedure
500 mg·L−1 of sodium lauryl sulphate (ALDRICH) stock solution was prepared. Different
volumes of this stock solution were put into recipients, and controlled quantity of coagulant was
added. Final volume was reached with surface water. A soft blade-stirring agitation (30 rpm)
was applied for 1 h in a Jar-test apparatus (JLT4, Velp Scientifica), until equilibrium was
achieved. Kinetic studies of our specific research (Figure 2) and previous studies carried out
(Beltrán-Heredia et al., 2009) reported this period was enough for guarantee equilibrium. Then,
a sample was collected and it was centrifuged. Surfactant removal was determined by visible
spectrophotometry.

Figure 2: Kinetic study of surfactant removal by coagulation with Moringa oleifera.

2.4   Analytical procedures
All analytical measures were made according to American Public Health Association standard
methods (APHA, 1998).
 Anionic surfactants were determined by a method based on methylene blue-anionic
surfactant association (Tôei and Fujii, 1977). 10 mL of clarified sample was put into a
separation funnel. 25 mL of trichloromethane (PANREAC) and 25 mL of methylene blue
solution (PANREAC) were added and funnel was shaken vigorously for 1 min. Organic
                                                3
fraction was taken out and put into another separation funnel, in which 50 mL of cleaning
solution were added. Funnel was shaken again for 1 min, and the resultant organic fraction
was put into a 25 mL-flask. It was filled up to the mark with trichloromethane and surfactant
concentration was determined by visible spectrophotometry at 652 nm, with zero made with
pure trichloromethane by using an HEλIOS spectrophotometer.

2.5   Mathematical and statistical procedures
Linear data adjustments were carried out by using Origin v. 7.0 for Windows. Non-linear
multiparametric data adjustments were carried out by using SPSS 15.0.1 for Windows.

3 Results and discussion
3.1   Moringa oleifera seed extract dosage
Figure 3 depicts the influence of coagulant dosage in surfactant removal. Initial surfactant
concentration of 25 mg·L−1 was treated with increasing doses of Moringa oleifera.
 As it was supposed, the presence of turbidity enhances the rapid removal of SLS through
coagulation, so the maximum average surfactant removal (ca. 75%) is achieved with
intermediate coagulant dosages of 60-100 mg·L−1 so an increment in efficiency is presented if
compared with the same assay in distilled water (Beltrán-Heredia and Sánchez-Martín, 2009).

Figure 3: Influence of coagulant dosage on surfactant removal.

3.2   Initial surfactant concentration
A fixed dose of ca. 100 mg·L−1 of coagulant was applied in a series that varies the initial
surfactant concentration (ISC) between 0.1 and 0.5 mmol·L−1. As it can be appreciated in
Figure 4, the efficiency of surfactant removal tends to increase as ISC goes up, although
percentual surfactant removal undergoes just a little raise.

                                                  4
Figure 4: Influence of initial surfactant concentration on surfactant removal.

3.3    Theoretical modelization
Interaction between surfactants and natural polymers (polysaccharides, proteins, etc.) has been
studied for many years because it is important to succeed in product formulations in many areas
(pharmaceuticals, cosmetics, food processing, etc.). Although the basic mechanisms of
surfactant-polymer interaction are reasonably well understood, researchers still disagree at
molecular level. It is generally accepted that their interactions may occur between individual
surfactant molecules and the polymer chain, or in the form of surfactant-polymer aggregate
complexes (micellar or hemimicellar interactions).
 By combining data series from sections 2 and 3 and new experiments it is possible to look for
a theoretical model that should explain Moringa oleifera-surfactant interaction phenomena.
According to previous studies (Dymaczewski et al., 1997; Okuda et al., 2001; Miller et al.,
2008; Beltrán-Heredia et al., 2009) coagulation-by removal may be assumed to work as an
adsorption-like process.
 Firstly, adsorption capacity (q) has been determined, defined as:

      (C0 − C1 )V
q=                                                                                       (1)
          w

where
C0 is initial surfactant concentration, (mmol· L−1),
Cl is equilibrium surfactant concentration in bulk solution, (mmol· L−1),
V is the volume of solution, (L),
and W is Moringa oleifera extract mass (g).
 The basic forces controlling surfactant-polymer interactions are van der Waals and dispersion
forces, hydrophobic effects, dipolar and acid-base interactions and electrostatic interactions. The
importance of each type will vary with the nature of the surfactant and the polymer.

                                                    5
Figure 5 shows adsorption capacity values versus equilibrium surfactant concentration for
those experiments carried out varying the coagulant dosage and initial surfactant concentration,
at the same temperature (20ºC).
 When a polymer is added to a surfactant solution, it is often observed that processes such
micellization appear to begin at surfactant concentration below the CMC of the surfactant in the
absence of polymer. In many cases, a complex aggregate structure is formed in association with
the polymer at lower concentration of surfactant (Rosen, 2004). This concentration is known as
critical aggregation (or association) concentration (CAC) and varies with the nature of the
polymer. The difference between both concentrations may vary by a factor of 10 - 1000 in some
cases (Myers, 2006).

Figure 5: General equilibrium and adjustment data.

 A simple model that has been used to describe the adsorption of surfactants is the regular
behaviour model (Hildebrand et al., 1970). For dilute solutions, this model simplifies to the
Frumkin-Fowler-Guggenheim (FFG) equation (Fowler and Guggenheim, 1939; Frumkin,
1925).
  θ1
       = c1 ⋅ k12 ⋅ exp(χ12 ⋅ θ1 ).                                                      (2)
1 − θ2

where θ l is the ratio between the adsorption and the maximum adsorption:

       q
θl =      .                                                                              (3)
       q∞

k12 is the adsorption constant, being a measure of the interaction between surfactant and
polymer surface, and and χ12 is the Flory-Huggins parameter (Flory, 1953), defined as:
        NA ⋅ z
χ12 =          .[(ε12 − 0.5(ε11 + ε22 )].                                                (4)
        R ⋅T

                                                 6
where:
NA is the Avogadro’s number,
z is the number of the nearest neighbors to a central surfactant molecule,
and ∈11 , ∈22 and ∈12 are the pairwise interaction potentials.

  In this model k12 and χ12 should be considered as adjustable parameters expressing the affinity
for the surface and the lateral interactions in the adsorbed layer, respectively. Zhu and Gu
(1991) proposed a very simple model for adsorption of surfactant assuming that the adsorbed
layer is composed of surfactant aggregates. A surfactant aggregate is formed on the surface
before stable aggregates are formed in solution. The model considers that these aggregates are
stabilized by the presence of the surface. This model leads to the following equation 5:
  θl             n
       = k g ⋅ Cl .  g
                                                                                              (5)
1 − θl

where ng is the number of monomers in the surfactant aggregate.
 Taking into account the definition of θl (5) becomes
                         n
                    cl g
q = q∞ ⋅ k g ⋅            n
                              .                                                               (6)
                 1 + k g cl g

 This equation is reduced to the Langmuir equation for ng = 1.

 In the equation 6, if the term kg·Clng is much lower than 1, the derived expression is known as
the Freundlich equation 7.
            n
q = k f ⋅ Cl f .                                                                              (7)

 where kf is the Freundlich adsorption constant and its value is given by equation 8;

k f = q∞ ⋅ k g .                                                                              (8)

 Equations 2, 6 and 7 lead to three models that have been studied: Freundlich (F), Frumkin-
Fowler-Guggenheim (FFG) and Gu and Zhu (GZ) models. Table 3 shows different parameters
that have been used in these modelizations. Parameter values and statistics summary for the
three models are shown in table 4.

3.3.1 Freundlich model
As it is observed in Figure 4, Freundlich model does not work very well because it does not
include a saturation region (final part of the curve). That is, this model just explain first part of
adsorption phenomena. Taking this fact in consideration, the Freundlich non linear adjustment
                                      2
gives an adjusted correlation factor r equal to 0.79, while the characteristic parameters kf and nf
                    0.51    0.49
are equal to 4.76 L mmol g-1 and 0.51 respectively. Linear adjustment also corroborate the
validity of the model (Table 4).
3.3.2 Frumkin, Fowler and Guggenheim model
FFG model (Fowler and Guggenheim, 1939) is used when adsorption from dilute solution is
being studied. With this condition, surfactant concentration usually appears far from CMC
(Rosen, 2004). It is considered a simplification from a general model (Hildebrand et al., 1970)
in which several parameters are included. FFG equation is presented in equation 2.

                                                 7
By carrying out a non-linear fit, it is possible to determine values of χ12, k12 and q∞, this last
parameter needed for θl calculation. This non-linear fit conducts to a χ12 value of 2.39, k12 value
of 6.71 L mmol−1 and q∞ value of 3.17 mmol·g−1.
Table 3: Fitting models parameters.
           Parameter                      Model       Symbol            Units              Expression               Reference

   Equilibrium surfactant               F, GZ, FFG      Cl         mmol·L−1
concentration in bulk solution

        Initial surfactant              F, GZ, FFG      C0         mmol·L−1
         concentration
       Adsorbent amount                 F, GZ, FFG      W                 G

        Total volume                    F, GZ, FFG      V            L
      Adsorption capacity               F, GZ, FFG      q          mmol·L−1                (C0 - C1 ) ⋅V       (Freundlich and
                                                                                                                Heller, 1939)
                                                                                                W
 Freundlich adsorption order                 F          nf               none                                  (Freundlich and
                                                                                                                Heller, 1939)
      Freundlich adsorption                  F          kf             Ln                                      (Freundlich and
            constant                                                                                            Heller, 1939)
                                                                  g ⋅ moles n-1
  Limiting adsorption ratio                FFG          θl               none                        q        (Esumi and Ueno,
                                                                                              θ1 =                 2003)
                                                                                                     q∞
  Flory-Huggins interaction                FFG          χ12              none                                   (Rosen, 2004)
         parameter

      Adsorption constant                  FFG          k12        L·mmol−1                                  (Rosen, 2004; Esumi
                                                                                                               and Ueno, 2003)
Limiting adsorbed surfactant             FFG, GZ        q∞          mmol·g−1                                    (Rosen, 2004)
  Gu and Zhu adsorption                      GZ         kg        (mmol·L−1)-ng                                (Gu et al., 1992)
         constant
Gu and Zhu adsorption order                  GZ         ng               none                                  (Gu et al., 1992)

Linear expression of equation 2 allows to correlate data from q and Cl into a linear model.
 As it can be seen in Table 4, r2 determination coefficient is high enough again, so it is possible
to conclude this model fits reasonably well to present situation.
Table 4: Parameter values and statistical summary.

Model                   Expression                   Parameters    r2                   Linearization                    Linear
                                                       values                                                         expression r2
  F                                n
                       q = k f ⋅ Cl f                 kf=4.76     0.79     ln q = n f ⋅ ln Cl + ln k f                    0.75
                                                      nf=0.51
FFG           θl                                      k12=6.71    0.64                 θl                                 0.80
                   = Cl ⋅ k12 .exp(χ12 ⋅ θl )         q∞=3.17
            1 − θl                                    χ12=2.39                       1 − θl
                                                                              ln =            = ln k12 + x12 ⋅ θl
                                                                                      Cl
 GZ                                 n                 q∞=2.49     0.94            q                                       0.80
                                Cl g                                       ln          = ng ⋅ ln Cl + ln k g
               q = q∞ ⋅ k g                           kg=1493
                                        n
                            1 + k g ⋅ Cl g            ng=2.43                   q∞ − q

                                                        8
3.3.3 Gu and Zhu model
Gu et al. (1992) proposed a two-step adsorption model for various types of S-shaped adsorption
non-Langmuir isotherms. First step implies adsorption of surfactant molecules as individual
molecules or ions. Second step leads to an adsorption increasing as surface aggregates form
through interaction of the hydrophobic chains of the surfactant molecules with each other.
 The physical meaning of this theoretical model may be found in the fact that adsorption
process appears accompanied of some kind of flocculation process, as floc formation is
observed in the experimental assay. This may be due to the hemimicellar formation hypothesis
(Myers, 2006; Rosen, 2004).
 Mathematically, GZ model is expressed by equation 6. Figure 4 shows non-linear experimental
data fit and it is possible to observe a very good r2determination coefficient in Table 4 (0.94).

4 Conclusions
This investigation has the following conclusions:
•    Moringa oleifera seed extract has a very interesting behavior in removing anionic
     surfactants from surface water. A very high efficiency is observed in all of the studied
     cases, so it presents a promising future as water treating agent.
•    Regarding the influence of the coagulant dose, it is observed that a maximum surfactant
     removal is achieved with relatively low coagulant amounts (ca. 100 mg L−1).
•    By increasing the initial surfactant concentration, efficiency of the process is enhanced
     dramatically.
•    Coagulation-flocculation process may be modelated as an adsorption process. Different
     adsorption models (Freundlich, Frumkin-Fowler-Guggenheim and Gu-Zhu) have been
     tested and the best fit was presented by Gu and Zhu model.

5 Acknowledgments
This investigation has been supported by the Programa de Iniciación a la Investigación,
Universidad de Extremadura, oriented modality, GESPESA subprogram, by COMISIÓN
INTERMINISTERIAL DE CIENCIA Y TECNOLOGÍA (CICYT) CTQ 2007-
60255/PPQ project as well as by JUNTA DE EXTREMADURA under PRI-07A031
project.

References
APHA: Standard Methods for the Examination of Water and Wastewater, 20th ed. American Public
    Health and American Water Works Association and Water Environment Association, 1998.
BELTRÁN-HEREDIA, J. AND SÁNCHEZ-MARTÍN, J. Removal of sodium lauryl sulphate by
    coagulation/flocculation with Moringa oleifera seed extract. Journal of Hazardous Materials, 2009,
    164(2-3), pp. 713-719.
BELTRÁN-HEREDIA, J; SÁNCHEZ-MARTÍN, J. AND SOLERA-HERNÁNDEZ, C. Anionic surfactants removal
    by natural coagulant/flocculant products. Industrial and Engineering Chemistry Research, 2009,
    48(10), pp. 5085-5092.
DYMACZEWSKI, Z., KEMPA, E.S. AND SOZANSKI, M.M. Coagulation as a structura forming separation
    process in water and wastewater treatment. Water Science and Technology, 1997, 36 (4), pp.
     25-32.
EDSER, C. Status of global surfactant markets. Focus on Surfactants, 2008, 2008(11), pp. 1-2.
ESUMI, K. AND UENO, M. Structure-performance Relationships in Surfactants. Marcel Dekker,
    New York, 2003.
FLORY, P.J. Principles of Polymer Chemistry. Cornwell University Press, New York, 1953.
FOWLER, R. AND GUGGENHEIM, E.A. Statistical Thermodynamics. Cambridge University Press, London,
    1939.
                                                  9
FREUNDLICH, H. AND HELLER, W. The adsorption of cis- and trans-azobenzene. Journal of American
     Chemical Society, 1939, 61(8), pp. 2228-2230.
FRUMKIN, A.N. Electrocapillary curve of higher aliphatic acids and the state equation of the surface layer.
     International Journal of Research in Physical Chemistry and Chemical Physics, 1925, 116, pp.
     466-488.
GHEBREMICHAEL, K.A. Moringa seed and pumice as alternative natural materials for drinking water
     treatment. PhD Thesis, KTH Land and water resources engineering, 2004.
GU, T.; ZHU, B-Y AND RUPPRECHT, H. Advances in colloid structures Progress in Colloid and Polymer
     Science, 1992, 88, p. 74.
HILDEBRAND, J.H.; PRAUSNITZ, J.M. AND SCOTT, R.L. Regular and related solutions: the solubility of
     gases, liquids and solids. Van Nostrand Reinhold, New York, 1970.
KWAAMBWA, H.M. AND MAIKOKERA, R. A fluorescence spectroscopic study of a coagulating protein
     extracted from Moringa oleifera seeds. Colloids and Surfaces B: Biointerfaces, 2007, 60(2), pp.
     213-220.
MATTHIJS, E.; DEBAERE, G.; ITRICH, N.; MASSCHELEYN, P.; ROTTIERS, A.; STALMANS, M. AND FEDERLE,
     T. The fate of detergent surfactants in sewer systems. Water Science and Technology, 1995, 31(7),
     pp. 321-328.
MILLER, S.M.; FUGATE, E.J.; CRAVER, V.O.; SMITH, J.A. AND ZIMMERMAN, J.B. Towards understanding
     the efficacy and mechanism of Opuntia spp as a natural coagulant for potential application in water
     treatment. Environmental Science Technology, 2008, 42 (12), pp. 4274-4279.
MYERS, D. Surfactant Science and Technology. John Wiley and Sons, New Jersey, 2006.
NDABIGENGESERE, A.; NARASIAH, K.S. AND TALBOT, B.G. Active agents and mechanism of coagulation
     of turbid waters using Moringa oleifera. Water Research, 1995, 29(2), pp. 703-710.
OKUDA, T.; BAES, A.U.; NISHIJIMA, W. AND OKADA, M. Improvement of extraction method of
     coagulation active components from Moringa oleifera seed. Water Research, 1999, 33(15), pp.
     3373-3378.
OKUDA, T.; BAES, A.U.; NISHIJIMA, W. AND OKADA, M. Coagulation mechanism of salt solution-
     extracted active component in Moringa oleifera seeds. Water Research, 2001, 35 (3), pp.
     830-834.
ROSEN, M.J. Surfactants and Interfacial Phenomena. John Wiley and Sons, New Jersey, 2004.
TÔEI, K. AND FUJII, H. Spectrophotometric determination of traces of anionic surfactants with methylene
     blue derivatives. Analytical Chimica Acta, 1977, 90, pp. 319-322.
WAGNER, M. AND PÖPEL, H.J. Surface active agents and their influence on oxygen transfer. Water
     Science and Technology, 1996, 34(3-4), pp. 249-256.
ZHU, B.Y. AND GU, T. Surfactant adsorption at solid-liquid interfaces. Advances in Colloid Interface
     Science, 1991, 37(1-2), pp. 1-32.

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