沙漠研究 22-1, 333 -336 (2012 )"ICAL 1 / DT X"

Journal of Arid Land Studies－Refereed Paper－

Wastewater Treatment for a Possible Water Reuse in Semi-arid Climate Zone
Moncef KHADHRAOUI*1) and Chokri BELAID1)
Abstract: The main objective of this work was to investigate on the possible conjunction of electrochemical processes(electrooxidation and electrocoagulation) for the treatment of dyes bearing wastewater for a possible valorisation in irrigation fields.
The used methods were also tested separately to see the extent of the treatment yield of each technique. Experiments were conductedin laboratory confectioned reactors under different operating conditions. Obtained results under the optimized experimental
conditions show that both electrooxidation and electrocoagulation applied separately exhibited a limited performance towards
suspended matter, chemical oxygen demand, color and turbidity removal. In fact, neither the electrooxidation nor theelecrocoagulation enabled to meet the discharge criteria of wastewater release into the receptor media. It was also noticed that theelectrocoagulation favored the removal of suspended matter (95%) whereas the electrooxydation lead to an efficient color removal(96%). On another hand, conjunction of these processes enabled a high pollution reduction rate reaching nearly 98% in terms ofcolor, chemical oxygen demand and suspended matters. The obtained results also indicate that the combination of the above
mentioned processes reduced significantly the phytotoxicity of the wastewater and enhanced considerably its biodegradability
exhibited through the drop of COD/BOD5 ratio. Based on this, it was suggested that conjunction of electrochemical processes could
be another alternative for the enhancement of pollution removal efficiency from textile wastewaters. Furthermore attempts weremade to reuse the treated wastewater in the irrigation field. The results indicate that electrochemically treated wastewater showed nophytotoxicity and no cytotoxicity toward the tested plants and microorganisms and therefore can be thought about for a possible
exploitation to irrigate certain plants and trees.
Keywords: Irrigation, Reuse, Valorisation, Wastewater treatment

1. Introduction
Treatment and re-use of wastewater is nowadays a major
need all over the world due to the low availability of waterresources, as well as to the negative impact on environment
through the discharge of the un-treated wastewater [1, 2].
This problem is particularly pressing on the Mediterraneancountries among them Tunisia where the shortage of rain isoften encountered and environmental problems are well taken
in consideration. In parallel to this condition, a considerable
volume of an available treated domestic and industrial
wastewater find its way to the receiving water bodies and thebenefit of its exploitation are therefore lost. These waters, if
carefully treated and reused can alleviate the over exploitation of
the currently water resources and reduces environmental impacts.
Among the water consuming industries, textile industries are
known by their huge water consumption as well as by theirwastewater containing recalcitrant compounds affecting thereceptor media once they are discharged insufficiently treated[3, 4]. Conventional physical/chemical methods used todecontaminate such kind of wastewaters are time and energy
consuming and can not guaranty sufficient contaminants
removals enabling water re-use [5, 6]. Within this regard, themain objective of this work was therefore to investigate on thepossible conjunction of electrochemical processes(electrooxidation and electrocoagulation) for the treatment ofdyes bearing wastewater for a possible valorisation in irrigation
fields. Different studies showed that the use of the so-calledadvanced oxidation processes are gaining popularity in term ofwastewater treatment and recycle [7, 8]. The used methods
were also tested separately to see the extent of the treatment
yield of each technique. Furthermore to assess the possible
reuse of the treated wastewater in the irrigation field andalleviate the burden on underground water overexploitation as
well to promote the practice of treated wastewater to irrigate
golf courses and public gardens, phytotoxicyty tests werecarried via irrigation of broad beans by raw and treatedwastewaters.

2. Materials and Methods
Treated samples were obtained from a local factory having
general characteristics exceeding the Tunisian wastewater
quality standards in term of color, chemical oxygen demand,suspended matter etc..(Data not shown). Sketch ofexperimental apparatus for the tested treatment techniques arepresented in Figure 1. The treated volume was about 1 L.

* Corresponding Author: montunisia@yahoo.fr
Route de Soukra Km 3,5 Po. Box 1173, 3038 Sfax, Tunisia1) University of Sfax , Laboratory of Water, Energy and Environment, National School of Engineering of Sfax (ENIS). Postal addressFig. 1. Sketch of the electrocoagulation (upper one) and electroxidation treatment methods.

Runs were conducted under different operating conditions interms of current intensities. Several parameters weremonitored to assess treatment efficiency, such as chemical
oxygen demand, suspended matter, salinity, color etc…
Phytotoxicity tests were conducted to evaluate the possible
reuse of the treated textile water in the irrigation fields. Seriesof pots containing broad bean were thus irrigated with the raw
and the treated water. For comparison, a run using tap water
was also conducted. The effect of the water quality on theplant growth was assessed by studying the modification
morphology of the plant such calculating the germinationindex, measuring the plant high and the number of the leaves.

3. Results and Discussion
Obtained results under the optimized experimental conditionsshow that both electrooxidation and electrocoagulation applied
separately exhibited a limited performance towards suspended
matter, chemical oxygen demand, color and turbidity removals.
Indeed, for the electrocoagulation, the final COD (325 mg/l) andfinal BOD5 (70mg/l) remain larger than the standards. Also,
we noticed there was a residual color in the treated wastewater
as shown in Figure 2. As for the elecroxydation we can saythat the removal efficiency depends also on each parametercharacterising the treated wastewater. However all values
remain higher than those of the standards for wastewater
discharge. Nonetheless there was no residual color. One
advantage of this latter technique, over the electrocoagulationis that it does not generate any secondary pollutants since themain reagent is the electron, a clean reagent, that ‘incinerates’
the organics without giving any sludge. Anyway, and as adeduction for two these tests, it was concluded that neither theelectrooxidation nor the electrocoagulation enabled to meet thedischarge criteria of wastewater release into the receptor media.
Nonetheless, it was also noticed that the electrocoagulation
favored the removal of suspended matter (95%) whereas theelectrooxydation lead to an efficient color removal (96%) (Fig. 3).
On another hand, conjunction of these processes enabled ahigh pollution reduction rate reaching nearly 98% in terms ofcolor, chemical oxygen demand and suspended matters. The
COD removal could be interpreted either due to the adsorptionof dye molecules on oxy-hydroxide or due to interaction ofmetal ions forming insoluble metal-dye precipitate or by bothmechanisms. The obtained results also indicate that thecombination of the above mentioned processes reduced
significantly the phytotoxicity of the wastewater and enhanced
considerably its biodegradability exhibited through the drop ofCOD/BOD5 ratio. Furthermore attempts were made to reuseFig. 2. Color of the different waters before and after treatment (B2: raw wasterwater, EO: electrooxidizezd wastewater; EC: electrocoagulatedwastewater; EC+EO: Coupled process).

Fig. 3. Citotoxycity of the differents kind of waters (Limite: control; B2: raw wasterwater, EO: electrooxidizezd wastewater; EC:electrocoagulated wastewater; EC+EO: Coupled process.

Fig. 4. Germination tests using different kinds of waters (control; B2: raw wasterwater, EO: electrooxidizezd wastewater; EC: electrocoagulatedwastewater; EC+EO: Coupled process.

the treated wastewater in the irrigation field. As shown in
Figures 3 and 4, the results indicate that electrochemicallytreated wastewater showed no phytotoxicity and nocytotoxicity toward the tested plants and microorganisms andtherefore can be thought about for a possible exploitation toirrigate certain plants and trees. In the same way (data notshown), it was found that the morphology of the plants
irrigated with different kind of waters presents almost similar
high and same leaves length and numbers. One exception forthe plant irrigated with the electro-oxidized wastewater which
presented less length and this might be due to some by-productgenerated upon applying this technique which should beconfirmed by further analysis.

4. Conclusion
This paper describes the treatment and reuse of textile
wastewater in the irrigation field. It was concluded that
conjunction of electrochemical processes could be anotheralternative for the enhancement of pollution removal efficiency
from textile wastewaters. Furthermore tests used to exploit
the treated wastewater to irrigate broad beans and to asses its
toxicity toward microorganisms living in irrigated soil. The
results indicate that electrochemically treated wastewater
showed no phytotoxicity and no cytotoxicity toward the tested
plants and microorganisms and therefore can be thought about
for a possible exploitation to irrigate certain plants and trees inarid and semi arid climate zone.

References
Bousselmi L., Ghrabi, A. (2000): A study on textile wastewater(A review). Waste Waste and Environment Research.

Brown M.A., Devito S.C. (1993): Predicting azo dye toxicity.
Critical review in Environmental Science and Technology,
12: 405- 414.
Correa V.M., Stephenson T., Judd S.J. (1994): Characterizationof Textile Wastewaters. Environnemental Technology, 15:917-929.
Khadhraoui M., Trabelsi H., Ksibi M., Bouguerra S., Elleuch B.
(2009): Discoloration and detoxicification of a Congo red
dye solution by means of ozone treatment for a possiblewater reuse. Journal of Hazardous Materials, 161: 974-981.
Lin S.H., Peng C.F. (1994): Treatment of textile wastewaters
by electrochemical method. Water Research, 28: 277-876.
Pagga U., Brown D. (1986): The degradation of dyestuffs part
II: behaviour of dyestuffs in aerobic biodegradation tests.
Chemosphere, 15: 479-491.
Raghavachary C. (1997): Colour removal form industrialeffluents. A comparative review of available technologies.
Chemical Engineering World, 32: 53-54.
Rozzi A., Malpei F., Bonomo L. (1999): Textile Wastewater
Reuse in Northern Italy (COMO), Water Science andTechnology, 39: 5.