Scholarly article on topic 'Wastewater Discharge Impact on Groundwater Quality of Béchar City, Southwestern Algeria: An Anthropogenic Activities Mapping Approach'

Wastewater Discharge Impact on Groundwater Quality of Béchar City, Southwestern Algeria: An Anthropogenic Activities Mapping Approach Academic research paper on "Earth and related environmental sciences"

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Procedia Engineering
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{Bechar / hydrochemistry / "onthropgenic activities" / Groundwater / Wastewater}

Abstract of research paper on Earth and related environmental sciences, author of scientific article — Kabour abdesselem, Heni Azedine, Chebbah Lynda, Sadek Younes

Abstract Southwestern Algeria, where Béchar city is located, crossed along 16 Km by the Béchar wadi from north to south. Very large wastewater outflow is discharging in this river, which has negative impact on groundwater quality. In spite of water supply network coverage estimated by 96% (2007), are solicited for very sensitive daily tasks (irrigation, Turk bath, public bath, washing…). Assessing human activity impact is an approach that is selected in this work to determine the impact of wastewater on groundwater quality. Some elements are selected like NO3, NO2, NH4+, Eh, and O2 as pollution indicators and potential tracers of wastewater.

Academic research paper on topic "Wastewater Discharge Impact on Groundwater Quality of Béchar City, Southwestern Algeria: An Anthropogenic Activities Mapping Approach"

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Procedía Engineering

ELSEVIER

Procedia Engineering 33 (2012!) 242 - 247

www.elsevier.com/Iocate/procedia

ISWEE'll

Wastewater Discharge Impact on Groundwater Quality of Bechar City, Southwestern Algeria: An Anthropogenic Activities Mapping

Approach

Kabour abdesselema*, Heni Azedineb,Chebbah Lyndac, Sadek Younesa

Southwestern Algeria, where Bechar city is located, crossed along 16 Km by the Bechar wadi from north to south. Very large wastewater outflow is discharging in this river, which has negative impact on groundwater quality. In spite of water supply network coverage estimated by 96% (2007), are solicited for very sensitive daily tasks (irrigation, Turk bath, public bath, washing...). Assessing human activity impact is an approach that is selected in this work to determine the impact of wastewater on groundwater quality. Some elements are selected like NO3-, NO2-, NH4+, Eh, and O2 as pollution indicators and potential tracers of wastewater.

© 2012 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ISWEE'11

Keywords: Bechar ; hydrochemistry; onthropgenic activities; Groundwater; Wastewater.

1. Introduction

The Study area is located in the south west of Algeria (Fig. 1), with arid climate and irregular precipitation, with an average of 71.48 mm/year (data collected from 1988-2008). The lowest temperature recorded in January is 4 °C and the highest in July of 40 °C, with an average of 27.16 °C. Evaporation (mean of 305.29 mm) and evapotranspiration exceeds the precipitation, therefore the temperature is warm during the Whole year. [1]

Bechar city suffers a high water demand, proportional to the population increase; growth rate of 3.11%, up to 161 902 of population in 2007 [1].

aFIMAS Lab, University of Bechar, PB. 417 Bechar 08000, Algeria 'Department of Earth Science, University of Annaba, PB 12, Annaba 23000, Algeria c Department of Hydraulic, University of Bechar, PB 417,Bechar 08000, Algeria

Abstract

* Corresponding author.

E-mail address: kabour_abs@yahoo.fr

1877-7058 © 2012 Published by Elsevier Ltd. doi:10.1016/j.proeng.2012.01.1200

Bechar city occupy an area of 160 square kilometers approximately, supplied by a drinking water network (96%), endowment of 139 liter/person/ day, and a satisfaction rate of 71% [2].. However, groundwater plays an important role in daily human activities (irrigation, Turkish bath, washing) [3].

The river of Bechar, has from over 16 Km long north to south of infero-flux, crossing the outcrop of the old Quaternary alluvial formations (variable thickness between 5 and 10 m), Eocene limestone called Barga II (more than 60 m of thickness), The Turonian limestone called Barga I (25 to 45 m thick), inter-bedded limestone, sandstone of Carboniferous Westphalian and finally a lateral contact with the alluvium of Namurian [3,4,5, 6, 7, 8, 9].

2. Results and discussion

The human activity is the main source of groundwater contamination in Bechar city. Water samples were collected in April 2008, with pervasion through the whole study area, of 14 logged water and 6 surface water samples (fig 1). To determine the wastewater impact [10, 11, 12, 13, 14], we used the concentrations of the following elements: NO3-, NO2-, NH4+, Eh and O2.

Polyethylene bottles, with a volume of 1.5 l, are taken and destined to physicochemical analyses; the sampling bottles were transported to the laboratory in a low temperature icebox (4°C). The physical parameters (Eh, O2) have been measured in situ by means of multi-parameter (Consort 861).

At the laboratory, the nitrates dosing method used [15] is the potentiometric method (HI 121) using a specific electrode.

Results of these analysis shown in table 1 indicate varying concentrations, NO2- varies from 1-8 mg / l with an average of 3.7 mg / l, NO3- oscillates between 9.7 and 99.23 mg / l, its average is 45.44 mg / l and NH4+ has a minimum of 0.2 mg / l and maximum of 4.4 mg / l, an average of 0.68 mg / l. Eh values range from -80 to -25 Mv, around an average of -53.57 Mv and dissolved oxygen O2 is 4.14 to 6.89 mg / l with an average value of 5.3 mg / l.

Firstly, to prove the detected contamination [2] and on the other hand to assess the variability of the contribution of wastewater hydrogeological conditions [16], the calculation of the parameter named anthropogenic activity is obtained by using the following formula [17]:

Fig. 1 : Location map of Bechar town (SW Algeria), and sampling network.

Anthropogenic activity (CA) (%) = {([X]effluent - [X] uptake)x100} / [X]effluent

Where: [X]effluent - X element concentration in the effluent (discharge). [X]uptake - X element concentration in the uptake point (closest well).

The results are shown in Table 2, where CA (Anthropogenic activity) of nitrate is -121.07 ± 173.88%, when that of nitrite is 52.94 ± 49.06% and 68.14 ± 51.41% for NH4+ ion. The AC value of Eh is -57.24 ± 90.03%, and finally that of the dissolved oxygen is -58.24 ± 92.70%.

The quantities of absolute CA value exceed 50% for all considered ions, which confirm that the wastewater in the river has a significant contribution in the chemical composition of groundwater of Bechar city.

The interpretation of the spatial distribution maps for the anthropogenic activity values can establish the following findings:

On the map (Fig. 2) of the CA of nitrate (NO3") shows that 42.9% of the wells have a CA between -62 and-65%, divided from north and south of the city, the rest is divided into three almost equal parts, relatively low value of the CA, is located in the center.

On the map (Fig. 3) of the CA of nitrites, where the majority, 64.3% of the wells are belong to the 56 to 95% of the CA, which are distributed over almost the entire area of the city.

On the map (Fig. 4) of the CA of the NH4+, 85.7% of the wells are in the range 56.93 to 97.51%, that CA has spatial distribution ofall the groundwater.

On the map (Fig. 5), CA value of the dissolved O2, we see that the wells that are in the range of -54 to 18% exceeding the 78% is occupying almost the entire area.

CA value for the parameter Eh shown in the map (Fig. 6), can describe, four interval values of CA, which are distributed irregularly from north to south, such as: 35% from -4 to -67%, 28% from 76 to -4%, 21% between -76 and -148%, and finally 14% of values are between -148 and -220% of the CA.

According to these results, some interpretations are needed: - If we classify the different ions by the average value of CA, we will obtain, in descending order; NH4+, NO2-, NO3-, Eh and finally O2. If we focus on nitrogen form when the solution action, and excluding of N2, the most common species are NO2-, nitrite and NH4+ in ammonium form [18].

This will be more easily written:

2 NO3- = 2 NO2- + O2 Moreover, nitrite as ammonium form NH4+ are deducted from

NO2- + 8H + 6e- = NH4+ + 2(H2O) [18].

- The ammonium ion (NH4+) is the most reduced form from nitrogen in fresh water. It has the property to be adsorbed on the mineral surface. The source of ammonia nitrogen are varied, either meteoric water (0.1 to 2 mg / l), the nitrates reduction by the autotrophic bacteria, metal components, or degradation of organic matter [19, 20].

- Although the potential redox (Eh) is relatively low, reflecting a reducing environment and a partial presence of NH4+ [19].

Faced with an aquifer whose content of NO3- decreases in time or space, several hypotheses can be formulated, nitrate assimilation by plants in the root zone, in case of shallow groundwater, the nitrate consumption will be by denitrification.

Negative values of CA indicates the presence of nitrate nitrification, it is probably the matter that can be dismissed as ammonia nitrogen (NH4+), which can be oxidize into NO3- once in the aqueous environment. Also, nitrate content observed in wells (NO3-10 mg/ l) can nonetheless considers that the wastewater in the river impact nitrate contribution in groundwater.

NO3" + 2H+ +2e- = NO- + HO

Fig.2. Spatial distribution of CA for NO3-(%)

Fig.3. Spatial distribution of CA forNOi- (%)

Fig.4. Spatial distribution of CA for NH„+ (%)

Fig.5. Spatial distribution of CA for O2 (%) Fig.6. Spatial distribution of CA for Eh (%)

3. Conclusion

Our objective in this work was to determine the anthropogenic activity for different selected elements (NO3-, NO2-, NH4+, Eh and O2) exiting in the chemical composition of groundwater of Bechar city, as well as their spatial distribution, which reflects irregular and widespread contamination highlighting a variable pollution with the proximity of both solid waste and wastewater in Bechar river, accenting the hydrogeological conditions which is too favourable for the infero-flux aquifer formation, allows infiltration of these elements to groundwater.

The negative effect of urban waste on this aquifer, revealed, and it is important to stop this pollution by adopting the necessary technical solutions. The preservation of this resource requires a comprehensive redevelopment plan based on the location of an adequate wastewater disposal system to reach the wastewater for gathering all the waste into a channel that can deliver downstream, to a purification station that will impact very positively to the environment.

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