Elsevier

Desalination

Volume 253, Issues 1–3, April 2010, Pages 180-187
Desalination

Effect of irrigation with treated wastewater on geochemical properties (saltiness, C, N and heavy metals) of isohumic soils (Zaouit Sousse perimeter, Oriental Tunisia)

https://doi.org/10.1016/j.desal.2009.10.019Get rights and content

Abstract

The use of treated wastewater in irrigation is increasing in Tunisia. However, it is imperative to study the impact of this water category on soil.

Since 1995, the Zaouit Sousse perimeter (Tunisia) has been irrigated by treated wastewater. So, this sector is an excellent case study to evaluate the impact of the use of treated wastewater in irrigation on geochemical properties of isohumic soils.

Treated wastewater is characterized by high salinity. The Cd, Cr, Fe, Zn, Pb, Cu, Ni and Al concentrations of treated water range from 10 to 2510 µg L1.

In Zaouit Sousse, we examine seven irrigated sub-perimeters and seven profiles which differ by soil composition, texture and structure and irrigation periods (from zero to 14 years).

The present results showed that soil salinization is caused by high wastewater salinity and increases in irrigation period. The heavy metal content increases with irrigation period, especially for Pb (1010–1890 µg kg1) and Cd (2–20 µg kg 1). The pH values of the water and soil are slightly basic. The metals' migration will especially depend on the concentration of organic carbon and of the soil nature.

Introduction

Within countries of the southern part of the Mediterranean Sea, natural water resources are limited, whereas their demand is constantly increasing. Therefore, non-conventional water resources became important to satisfy different agricultural needs. In Tunisia, the reuse of treated wastewater (TWW) has been adopted since the 1960s with the planning of many irrigated perimeters.

The primary and secondary wastewater treatments improve distinctly the water quality although the treated wastewater still retains a substantial amount of organic and metallic compounds (e.g. [1], [2]). So, the reuse of the TWW can have important supplementary C, N, P and K which had a favourable effect on the growth of certain crops [3], [4]. It can cause soil quality modification by structure deterioration (salinization splash of clays,…) and soil pollution (mineral, organic, bacteriological pollution, etc) [3], [4]. Therefore, the reuse of this water category will have some serious consequences on natural resources [5], [6], [7], [8]. The total pollutant content of water used for irrigation is not the only parameter of which depends the soil pollution. Indeed, the total pollutants content in soil depends on the physicochemical parameters and the mechanisms that govern their distribution and their transport [9]. So, the nature and the soil composition, the climate and the crops' nature play an important role in fixing and the infiltration (toward the different horizons of our soil) of contaminants and their transfer toward plants and groundwater [5], [6], [7], [8], [10], [11], [12], [13]. The long use will also serve as a parameter of soil pollution.

The Zaouit Sousse sector is an excellent case where you can evaluate the effect of the use of treated wastewater on geochemical properties of sandy to sandy–clay soils as pH, carbon, C/N ratio and major elements. We also aimed to identify the heavy metal content in surface and deeper soil sediments (until 120 cm) and the possible factors (organic matter, sand and clay fractions) which can affect heavy metals' mobility in sandy to sandy–clay soils covered by olive trees, bersim and the sorghum.

Section snippets

Geographical localization

The perimeter of Zaouit Sousse is a part of the Tunisian central Sahel. It is situated in the South of Sousse city (Longitude: 35° 47', Latitude: 10°38' and of altitude: 20 m N.G.T.) (Fig. 1).

The perimeter covers 450 ha, 205 ha of which are currently exploited. Sousse Sebkha and Oued Hamdoun assure the drainage of the perimeter which developed on alluviums of tertiary and quaternary age [14], [15]. Soils present an isohumic characters and are covered by olive trees underneath there is bersim (in

Treated wastewater quality

To give a precise idea about the TWW quality used for Zaouit Sousse irrigated perimeter, we made a statistical survey of physicochemical parameters analyzed by the National Agency for Wastewater Management [20], [21] for 2 years. According to the results and statistical study the treated wastewater composition is slightly the same during the analysed period. The results revealed that the mean EC value is 3.5 mmhos cm1 (Tunisian Standards (TS: 7 mmhos cm1) and slightly alkaline (mean pH value = 7.8).

Conclusion

The BOD and COD concentrations and also the CE and pH values measured in treated wastewater are lower than Tunisian Standards but this water is relatively abnormally rich in Na, Ca, Mg, and K. In spite the Ca and Mg important content, the SAR stays high.

The pH, organic compounds (C and N), salinity, some major elements (Na, Ca, Mg, K) and the soil EC indicates that the extended irrigation with treated wastewater involves, in our case, the increase of its salinity, which is dependent of the

Acknowledgments

This work was supported by CERTE-Borj Céria techno park. The authors also appreciate the support of the national agency for wastewater management (ONAS) for this study. The authors would like thank the referees for their constructive comments. We also thank a second reviewer for effort provided in correcting the English text.

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