沙漠研究 24-1, 117-120 (2014)
Ἃ₍◊✲ 24-1, 117 - 120 (2014)
Journal of Arid Land Studies
Journal of Arid Land Studies－ DT11 Refereed Paper －㸫DT11 Refereed Paper㸫Effect of Detergents from Greywater on Irrigated Plants: Case of Okra
(Abelmoschus esculentus) and Lettuce (Lactuca sativa)
Boukary SAWADOGO*1), Mariam SOU1), Nowaki HIJIKATA1), 2), Drissa SANGARE1),
Amadou Hama MAIGA1) and Naoyuki FUNAMIZU2)
Abstract: Laundry detergent containing anionic surfactants was used to test their effects on plant growth through irrigation water.
Lettuce and okra were cultivated in pot experiment and irrigated with distilled water containing domestic detergent at three different
concentrations: low concentration (LC) of 0.1 g L-1; normal concentration (NC) of 1.0 g L-1 and high concentration (HC) of 5.0 g L-1
and distilled water (DW) used as control. The experiment was conducted during three months from July to October in a green housein Ouagadougou, Burkina Faso. Lettuce leaves, okra fruits and both crops shoots were measured at harvest period as dry and/or freshweights. Soil pH and electrical conductivity (EC) were analyzed to evaluate changes caused by watering. Soil pH and EC tended
to increase with detergent concentration in irrigation solutions. They were no significant difference in okra’s fruit growth (fresh anddry weight) for DW, LC and NC treatments. However plants in HC died 20 days after planting (DAP). Similarly, no significant
difference was noticed in lettuce shoots (dry weight) between LC, NC and DW treatments but lettuce in HC died 12 DAP. Afterharvest, irrigated soils EC for all treatments were significantly increased in contrast to pH where no significant difference wasobtained.The study show that more than 1.0 g L-1 of laundry detergent can inhibit plant growth and application of high concentrate
greywater on detergent can exacerbate soil salinity.
Key Words: Greywater, Irrigation, Laundry detergents, Soil salinity, Surfactants

1. Introduction
Water scarcity is an ever-increasing concern worldwide.
The reasons are manifold including low rainfall and excessive
demand due to the combined effect of increased water
consumption per capita and population growth. Population
has increased at a rate faster than food production and will add
up to 3 billion more people by the middle of the twenty-first
century, mostly in poor and water - short countries (Jury et al.,2007). One important consequence of population growth isthe necessity of wastewater reuse particularly in the Sahelianarea that suffers from the consequences of climate change. In
this context wastewater reuse in agriculture seems to be themost explored strategy in most water management programs asagriculture is by far the leading user of freshwater worldwide,
accounting for almost 85% of global consumption (Jury et al.,2007).
Wastewater reuse in agriculture requires
implementation of good practices and particular attention to theprotection of environment.
Along with the irrigation plans in the urban centers withconventional wastewater treatment systems, greywater (GW)
reuse appears as the right solution for rural and peri-urban areas.
Greywater includes all washing domestic water produced withthe exception of the toilet water. Despite its apparent clarity
these waters should not be used directly on crops without
sufficient treatment as it is often the case (Gross et al., 2007).
Generally greywater is the result of the using of detergents,
vegetable oils, soaps, water and other kitchen and washingresidues. Indeed, grey water is often a source of elevatedlevels of compounds such as surfactants, oils, boron and salt
which can alter soil properties, damage plants and contaminate
groundwater (Travis et al., 2008; Wiel-Shafran et al., 2006).
Detergents are used in several domestic washing activities.
Their efficiency is due to presence of surfactants (surface-active agents) together with components which provide
cleaning and solubilization properties.
Surfactants in
prepared irrigation solutions with detergent water have beenrecognized as a major contributor to the reduction of hydraulicconductivity of soils and as component that can lead to water
repellent soils with adverse impacts on agricultural
productivity and environmental sustainability (Lado andBen-Hur, 2009; Shafran et al., 2005). When untreatedgreywater is used to irrigate plants growing in soil, the fate ofsurfactants in greywater irrigated soil-plant systems is not wellknown (Misra et al., 2012).
Therefore this work aimed to evaluate the impact oflaundry detergents on lettuce (Lactuca sativa) and okra

* Corresponding Author: boukary.sawadogo@2ie-edu.org
01 BP 594, Ouagadougou 01, Burkina Faso
1) International Institute for Water and Environmental Engineering (2iE), Ouagadougou, Burkina Faso
2) Graduate School of Engineering, Hokkaido University, Japan

㸦Received, September 14th, 2013; Accepted, January 3rd, 2014㸧

118

Table 1. Properties of the soil used for experiments.
Properties

Mean value

Sand % (2.0-0.02 mm)
Silt % (0.02-0.002 mm)
Clay % (<0.002 mm)

51.8
28.7
19.5

O
rganic m
at t er %Organicmatter
pH (soil-water ratio 1:2.5)

22.5.56.4-1

EC (µS.cm )Bulk ddensity
ensit y ooff ssoiloil
Bulk
Sodium Adsorption Ration (SAR)

311
11.6.6
3

Table 2. Irrigation solutions selected parameters value.
Wate ringsolutions

DWLCNC

HCpH

6.9

9.1

9.9

10.2

EC (µS.cm -1-1)
EC (µS.cm )

28159

1082

4870

LAS (mg.L-1-1) aand

13.5

135.6678

Ntotal (mg.L-1-1) aa ndCtotal (mg.L-1-1) aa nd

0.01

0.12

6.6

15.3

153765.1

Ptotal (mg.L-1-1) aa

13.2

132.3

661.6

Ptotal (mg.L )ndnd : not detected.
a: concentrations estimated based on the findings of the analyzes of the(Abelmoschus esculentus), two common plants in Sahelian
region. The plants behavior after the application of threedifferent concentrations of detergent was studied and plants
growth was measured and compared.

2. Material and Methods
2.1. Experimental design
The experiment was conducted in a green house on theexperimental agricultural field station of the International
Institute for Water and Environmental Engineering(Ouagadougou, Burkina Faso). The study was conductedwith six (6) liter cultivation pots. Local field sandy-loam soil
has been used for crop cultivation during July to October.
Soil was sieved to reduce aggregate size with a 2 mm porosity
sieve. The properties of soil used for the experiments areshown in Table 1. The pots were perforated and a system ofwick and gravel provided aeration for the bottom and allowed
the collection of drainage.
Lettuce was selected because of its short life cycle and its
sensitivity to environmental conditions (Castillo et al., 2000)
and surfactants (Eriksson et al., 2006). Okra was chosenbecause it is a popular tropical leafy vegetable, well-known
and appreciated in the sub-Saharan area as its fruits can be
harvested and dried for off-season consumption (Nana et al.,2009). Four (4) replicates were conducted for each crop andfor each watering greywater solution. At least 32 cultivation
pots for the experiment were used during around seventy (70)days treatment.
2.2. Irrigation treatments
For the watering of crops, distilled water (DW) and three(3) watering solutions were prepared by dissolving indistilled water respectively 0.1 gram (low concentration, LC), 1gram (normal concentration, NC) and 5 grams (highconcentration, HC) of a commercial laundry detergent (Omo,manufactured by Unilever). Prior to irrigation, each wateringsolution was freshly prepared to assure consistency andrepeatability. Frequency of irrigation varied over time anddetergent used.

crop so as to satisfy the daily water needs of both cultures toavoid any hydric stress (Misra et al., 2012; Nana et al., 2009) :65 ml every day for lettuce and 130 ml every two days forokra.The properties of the watering solution were described in
the Table 2.
2.3. Chemical measurements and statistical analyses
The pH and electrical conductivity (EC) of irrigation water
samples were measured with a pH meter and a
conductivimeter fitted with calibrated electrodes using themanufacturer WTW instructions. For soils, pHw and EC
were determined respectively in a soil-distilled watersuspension of 1-2.5 and 1-5. Total C and Total N in thedetergents were measured by Sumigraph NC-220F (Sumika
Chemical Analysis Service, Japan). Total phosphorus (P),was analysed by ascorbic acid method using a spectrophometerat 880 nm (Hack Lange, DR 5000). Linear alkylbenzene
sulphonate (LAS) which is one of surfactant widely used in theworld (Cirelli, 2008), were assesed by LC/MS (W3100,Waters) following Huelgas and Funamizu (2010) method but
the separation condition of LC/MS was slightly modified toisocratic mode with 60% of 0.2 mM ammonium acetate and40% of acetonitrile. The concentration of Na, Ca and Mg
were determined by atomic absorption spectrometry withflame analyzer (Perkin Elmer; Model Analyst 200).
Plant growth parameters were measured every week. At
harvest, shoots were severed close to the soil surface and sorted
into stems and leaves. The root system of each plant wasremoved from soil after overnight soaking of each pot in tap
water. The whole root system of the plant with some soil
attached to the root system was removed first. The remaining
soil with roots was washed over a sieve with a 2 mm pore size
to reduce root loss during washing. Fresh roots were dried
with a paper towel before drying at 70°C for 48 hours in aconvection oven to determine dry weight. The dry weight ofstems and leaves of all plants was also measured in a similar
way. Statistical analysis was conducted with SPSS statistic

119Fig. 1. Effects of different irrigation waters on okra stem and fruit
length.

Fig. 2. Effects of different treatments on lettuce root and leave dry weight.

21 software (IBM).
Significant difference in eachcomparison group was evaluated with one-way ANOVA andturkey-HSD test (p<0.05) underequal variance (F-test, p>0.05).
In the case of unequal variance, Dunnett test was conducted.
3. Result and Discussion
Higher concentration of detergent led to higher pH and ECof irrigation waters. The pH and EC of MC values werecomparable to those of grey water used in previous studies(Pinto et al., 2010; Wiel-Shafran et al., 2006). The increaseof detergent concentration leads to more salts in irrigationwaters. The salinity of the treatment with 5 grams ofdetergent (HC) was around 1800 µS cm-1. This is very highcompared to the normal salinity level in laundry greywater
given by Anwar Faisal (2011). This means, irrigation with
HC could have negative effect on plant production and health.
Therefore, this can explain the death of plants in all the pots
irrigated with high concentration of detergent. Indeed for theconcentration of 5 g L-1, there was slow growth of plants andthe complete death of plants during the 20th DAP for okra and12th DAP for lettuce. Okra is therefore more resistant to salts
than lettuce.
For okra, the plants irrigated with LC had the best results interm of fruit and stems length (Fig. 1).
The results show an increasing of organic mater andnutrient with the quantity of detergent in the treatment
solutions. This contribution of organic matter and nutrients
through greywater can explains the good behavior of plants inthe pots watered with LC. Increasing the concentration of
surfactants and salts explains the decrease in the length ofstems and fruits when we pass from LC to NC.
Figures 2 and 3 show the effects of the different irrigation
solutions on the shoot and root dry biomass. The results
obtained are in the following order DW > LC > NC > HC bothFig. 3. Effects of different irrigation waters on okra root and shoot
dry weight.
Table 3. Soil pH and EC values before and after cultivation in agreen house during around 70 days.
-1

pH
Initial soil
Distilledwater
Low conc.
Normalconc.
High conc.

EC (µS .cm )lettuce
okra
311±7
311±7

lettuce6.4±0.2

okra
6.4±0.2

8.2±0.2

8.3±0.3149±6178±138.3±0.2

8.3±0.2187±9211±128.3±0.3

8.5±0.3433±17437±26

8.5±0.2

8.7±0.21537±231772±52

conc.: concentration.

for okra and lettuce (Figs. 2 and 3). The statistical analyses
indicate that shoot and root dry biomass were significantly
affected by the irrigation with HC. As reported in previousstudies, the high contents of salts combined to the action ofother pollutants such as surfactants led to the gradualdegradation of soil structure and affected plant health(Wiel-Shafran et al., 2006; Gross et al., 2005).
Table 3 summarized the pH and EC values of cultivatedsoil before and after crops harvest. There was no significant
difference of soil pH for watering solution. Compared toinitial soil, pH values increased from 6.4 to 8.5 and 8.7

120

respectively for lettuce and okra. The same range of increase
has been reported by Anwar Faisal (2011) who reported thathigh pH liquids act as dispersing agents, causing the soil
particles to separate and led to soil structure decline. The
normal pH range for vegetables biological activity is between 5to 9. Finally he concluded that, if pH value reached morethan 9, biological activity would decrease and dissolved
organic material could leach out of soil. On the other hand,
there is a large gap between the DW EC compared to irrigatedsoil. This increase in soil pH and EC after greywater
application has been also noted by Pinto et al. (2010) in asimilar study. This can be explained by a contribution ofnutrients to the soil by irrigation solutions through the detergent(Fig. 2).

4. Conclusions
The use of water with high concentrations of detergent is
not suitable for application in agricultural irrigation, because
they have a very alkaline pH and high electrical conductivity.
Compared to the control, the use of greywater in agriculture
could be a minor source of nutrients for crops but can also
negatively affect plant growth and health if the detergent
content is high. This study confirms the greater sensitivity oflettuce following application of greywater with high saltcontent. After irrigation, there is a significant increase of soil
pH. However the EC increases with increasing detergent
content which in the long term can increase soil salinity andmake it unfavorable for the growth of crops.

References
Al-Jayyousi O.R. (2003): Greywater reuse: towards sustainablewater management. Desalination, 156: 181-192.
Anwar Faisal A.H.M. (2011): Effect of laundry greywater
irrigation on soil properties. Journal of Environmental
Research and Development, 5(4): 863-869.
Castillo G.C., Vila I.C., Neild E. (2000): Ecotoxicity assessmentof metals and wastewater using multitrophic assays.
Environtal Toxicology, 15: 370-375.

Cirelli A.F., Ojeda C., Castro M.J.L., Salgot M. (2008):
Surfactants in sludge-amended agricultural soils: a review.
Environ. Chem. Lett., 6: 135-148.
Eriksson E., Baun A., Henze M., Ledin A. (2006): Phytotoxicityof grey wastewater evaluated bytoxicity tests. Urban Water
Journal, 3(1): 13-20.
Gross A., Shmueli O., Ronen Z., Raveh E. (2007) : Recycled
vertical flow constructed wetland (RVFCW) - a novel methodof recycling greywater for irrigation in small communities andhouseholds. Chemosphere, 66(5): 916-923.
Huelgas A., Funamizu N. (2010): Flat-plate submerged
membrane bioreactor for the treatment of higher-loadgraywater. Desalination, 250(1): 162-166.
Jury W.A., Vaux Jr. H.J. (2007): The emerging global watercrisis: managing scarcity and conflict between water users.
Advances in Agronomy, 95: 1-76.
Lado M., Ben-Hur M. (2009): Treated domestic sewage
irrigation effects on soil hydraulic properties in arid andsemiarid zones: a review. Soil Tillage Res., 106: 152-163.
Misra R.K., Patel J.H., Baxi V.R. (2012): Reuse potential oflaundry greywater for irrigation based on growth, water andnutrient use of tomato. Journal of Hydrology, 386(1-4):
95-102.
Nana R., Zombre G., Tamini Z., Sawadogo M. (2009): Effet durégime hydrique sur les rendements du gombo en culture decontre-saison. Sciences & Natur, 6(2): 107-116.
Pinto U., Maheshwari B.L., Grewal H.S. (2010): Effects ofgreywater on plant growth, water use and soil properties.
Resources, Conserv. and Recy., 54: 429-435.
Shafran A.W., Gross A., Ronen Z., Weisbrod N., Adar E. (2005):
Effects of surfactants originating from reuse of greywater oncapillary rise in the soil. Water Science Technology, 52:157-166.
Travis M.J., Weisbrod N., Gross A. (2008): Accumulation of oil
and grease in soils irrigated with greywater and their potential
role in soil water repellency. Sci Total Enviro., 394: 68-74.
Wiel-Shafran A., Ronen Z., Weisbrod N., Adar E., Gross A.
(2006): Potential changes in soil properties following
irrigation with surfactant-rich greywater. EcologicalEngineering, 26: 348-354.