Environmental Impacts of the Sewage Water Site on the Neighboring Area in Buraydah City
I.S. AL-SALAMAH
Dept. of Soil and Water, Faculty of Agriculture and Veterinary Medicine, King Saud University, Al-Qassim Branch, Buraydah, Saudi Arabia
ABSTRACT. A dumping site for Buraydah city sewage water, located east of the city, was chosen for this study. The site soil texture is sandy, that is high permeable for water and solute. For evaluation of this site contamination effects on the neighbor areas, 169 water sam- ples were collected from swamps, shallow wells and deep wells.
Chemical (pH, total soluble solutes (T.S.S.), chloride (Cl) and nitrate concentrations) and microbiological (Escherichia coli and En- terobacteria aeruginosa) characteristics of the water samples were evaluated. Also, soil samples were collected for analysis. The con- centrations of Cl and T.S.S. in the swamps were first increased as the distance from the site increased then decreased with further distance increases. The effective distance of moving the sewage water from the site was approximately 3.3 km. Cl and T.S.S. decreased as the dis- tance from site increased in the shallow wells. T.S.S. and Cl dis- tributions indicated that the wastewater site causes pollution for the neighbor area. The concentration of Cl and T.S.S. in the deep wells in- dicated no drastic changes. Escherichia coli were found in some swamps and the shallow wells. The Escherichia coli may indicate a contamination from septic tanks.
The texture of the collected soil samples was sandy but its per- centage of particle sizes was different. The T.S.S. and Cl concentra- tions in site sewage water were 21952.0 and 16140 ppm, respectively.
This water was applied at the top of a soil column using a 0.015 m constant pressure head. The effluent of each column was collected pe- riodically, and the concentration of T.S.S. in the effluent was meas- ured. The concentration distribution of T.S.S. in the effluent was de- scribed. It is assumed that the predominant anion was Cl. The dispersion coefficient for the chloride (D) and the mean pore water
39
velocity (v) were calculated using the CXTFIT program. Also, the sat- urated hydraulic conductivity was calculated from the effluent data.
The D ranged between 0.072 to 0.209 m2/day for the soil (92.4%
sand) and soil (97.1% sand), respectively. The respective variations in v were 1.113 and 10.025 m/day. It is recommended to select a dump- ing site containing low percentage of sand particles, hence, reducing the migration of sewage water constitutents toward the water re- sources and land resources.
KEY WORDS: Swamps, sewage water, shallow wells, deep wells, Es- cherichia coli, Enterobacteria aeruginosa, pollution, mean pore water velocity, dispersion coefficient.
Introduction
Domestic sewage contains a wide variety of pollutants (dissolved and sus- pended impurities). It amounts to a very small fraction of the sewage by weight, but it is large by volume and contains impurities (pollutants) such as organic materials, disease-causing microbes and harmful chemicals. Major urban areas in the Kingdom of Saudi Arabia suffer from under capacity of sewage treatment facilities and most of the smaller towns have no sewage treatment plants or sew- er networks. Most households in the small cities depend on septic or ground tanks for disposal of sewage. In some urban cities such as Buraydah, (Kingdom of Saudi Arabia), the sewage is collected and accumulated in sites with high permeable soil (City Council of Buraydah (Al-Qassim region, personal com- munication)). A significant portion of the pollutants might enter water streams, lakes, and groundwater. These pollutants degrade the ground water quality which is the main source of water for Buraydah city. Since the Kingdom is suf- fering a water shortage, the sewage water should be treated for several uses to:
(1) avoid its detrimental effect on the other water resources and (2) save other sources for drinking and other uses. The estimated volume of recycled sewage water by year 2023 will be five Gm3 in the Kingdom of Saudi Arabia (Al- Matroud, 2003). The water resources in Al-Qassim region are limited too and the groundwater represents its main source. This source is not enough to supply the agriculture sector. The only available source to be exploited is the sewage water. In a report about water resources management and conservation in Al- Qassim region, Badr (1984) indicated that treated sewage water may make a valuable contribution to the water resources. Abdel Magid and Al-Oud (2000) studied the efficiency of sewage treatment plant in Buraydah city. They evalu- ated the chemical oxygen demand (COD), the biochemical oxygen damand (BOD), total suspended solids (T.S.S.) and total coliforms. They reported that the effluent is unacceptable for irrigation reuse with respect to its mean BOD level (87-99 ppm), COD level (114-161 ppm) mean T.S.S. (98-104 ppm) and
mean alkalinity level (334-365 ppm). Similar finding by Abdel Magid (1996) is reported about the wastewater treatment plant in Unayzah city. Usually, the authorities in any city search for a nearby location to treat or to dispose the sew- age influent. If the soil of location is highly permeable, it will leak the influent which carries dangerous chemicals and microorganisms toward the groundwater resource. People are using and depending on a contaminated groundwater could be infected by dangerous diseases.
The movement of solute in soils depends on its pore geometry as well as physical and chemical interaction of the solute and media during solution flow- ing (Biggar and Nielsen, 1962). Rao et al. (1980) studied the breakthrough curves (BTCs) for 36Cl– and 3H2O in water-saturated columns of aggregated and non-aggregated porous media at pore-water velocities ranged from 2 to 96 cm/hr. These BTCs were used to verify that convective-depressive solute trans- port occurs in the inter-aggregate pore-water region, while the intra-aggregate pore-water behaves as a diffusion sink/source for solute. Equations describing the movement of a solute through a porous medium such as soil have been de- rived and investigated by many researchers. These equations use both analytical and numerical techniques to describe non-interacting and interacting solute transport. For example, van Genuchten and Alves (1982) introduced analytical solutions for the one-dimensional convective-dispersive solute transport equa- tion. Parker and van Genuchten (1984) introduced a computer program based on the analytical solution of solute transport equation. The program called CXTFIT describes a non-linear least-squares inversion method. The program is useful to identify several parameters in a number of theoretical one-dimensional solute transport models.
According to the literature reported, there are limited data about the suit- ability of treated sewage water for irrigation and the ability of the collecting sewage water site in Buraydah city for controlling the movement of water and solute. Therefore, the goals of the present study were to: (1) evaluate the treated sewage water in one site of Buraydah chemically and bacteriologically, (2) in- vestigate leaks some of its water in nearby areas and (3) evaluate solute and water transfer coefficients in the soil site and other three different soil textures using CXTFIT program.
Materials and Methods I – Experiment
Sewage water samples were collected from Buraydah municipal site at Al- Qassim. It is supposed that the site is leaking sewage water into the low neigh- bor areas. Water samples were collected from the neighbor swamps, the shallow
wells, and the deep wells as well. The total collected water samples were 169. In addition, soil samples were collected from three different locations surrounding the waste site. The soil samples were prepared by air-drying, crushing and siev- ing to pass through a 2 mm screen. The sewage water was primarily character- ized chemically and bacteriologically. The characterization of sewage water samples included total soluble salt (T.S.S.), Cl concentration, nitrate concentra- tion and pH, and testing the presence of Escherichia coli and Enterobacteria ae- ruginosa. The T.S.S. were determined using electrical conductivity and the pH was measured using glass electrode. The Cl was determined calorimetrically and the nitrate was measured using Keljdah technique (Jackson, 1967). The Es- cherichia coli test was performed as described by Woomer (1994). The En- terobacteria aeruginosa test was achieved according to Clesceri et al. (1998).
For studying solute leaching, the sieved soils were packed in PVC columns (0.086 m I.D. and 0.208 m long). The soil columns were leached then saturated using the tap water. A 0.015 m constant water pressure head was maintained at the inlet of each soil column for leaching the soil columns. The sewage water was used for leaching the soil columns. Effluents were collected at fixed times (depending on the soil texture) from each soil column separately and analyzed for T.S.S. The chloride, Cl, was the dominant anion in the water. The dispersion coefficient of Cl, average pore velocity and saturated hydraulic conductivity were estimated as described by Al-Salamah and Nassar (2002).
II – Analysis
The T.S.S. and chloride data of swamps were fitted to a third degree poly- nomial as a function of space from the sewage water site. The following equa- tion describes either T.T.S or chloride concentration, C, as:
C = a + bx + cx2 + dx3 (1)
Where C is the concentration of either T.S.S. or chloride, in ppm, x is the dis- tance from the sewage water site in m, and a, b, c and d are constants. Measured C were fitted to the above equation for calculating the constants. The first de- rivative, dC/dx, of Equation (1) was equalized to zero to give maximum point of C. dC/dx can be calculated from the following:
dC / dx = b + 2cx + 3dx2 (2)
Equalizing equation (2) to zero and solving for x, the calculated x represents the effective circle of the sewage water site that reflects the further distance for traveling the sewage water.
The T.S.S. and chloride data of shallow wells were fitted to a first degree polynomial as a function of space from the sewage water site. The following
equation describes either T.T.S. or chloride concentration, C, as:
C = a + bx (3)
Equation (3) was used to show the trend of concentration.
Results and Discussion
Figure (1) shows the map for the sewage water site and the location of water samples. the location of swamps, deep wells and shallow wells are shown. The agriculture lands surround the wells. The map encompassed an area of 10000000 m2 (1000 h). It is obvious that the sewage water site (main lake) pos- sessed the greatest elevation in comparison to the elevation of water samples.
FIG. 1. Map of the main site of sewage.
The measured chloride concentrations and total soluble solute of the swamp water were described using Equation (1) and shown in Figure (2). Equation (1) described reasonably the measured concentrations. The squared R for chloride and T.S.S. are 0.54 and 61.31, respectively. Equation (2) was used for calcula- tion the maximum traveling distance for the sewage water of the main lake.
This distance is 3.3 km. It is obvious that both concentrations increased till 3.3 km then decreased by further distance increase. The maximum concentrations occurred because of the recharge of the swamps from the main lake. During the winter time of the year great amount of sewage moves from the main lake while during the summer time evaporation of water occurs. The evaporation processes cause an increase in the chloride and T.S.S. The results of concentrations in-
dicated that the sewage water site leaks water and its loading toward the neigh- bor areas. This leakage causes pollution for the near soil and water resources.
Also, the leakage of water results in some swamps that spread diseases to the habitants. Escherichia coli were detected in some swamps near the habitants area. In the studied area, some habitants have some septic tanks that could leak sewage water to the swamps. The presence of nitrate in the swamps may be due to agricultural activity in surrounding area of sewage water site. However, the distributions of nitrate in the swamps are not consistent. This inconsistency is due to the different amount of agriculture water carrying nitrate toward the swamps.
FIG. 2. Effect of distance from the main lake on the chloride and soluble solute concentration dis- tribution in swamps.
Distance from the main lake, m Soluble solute concentration, ppmChloride concentration, ppm
Figure (3) shows the T.S.S. and chloride concentrations in shallow wells. The concentrations of chloride and soluble solute decrease as the distance of a well in- creased. So, it is obvious that the sewage water site caused contamination for these wells. The concentration distributions in the wells were described as a function of the distance of the main site using a first order polynomial. The polynomial does not describe well the concentration, however, it shows a decreasing trend in the concentrations. This trend explains the contamination of wells water from the main site of sewage water. Since these wells are closed, no water evaporation oc- curs that leads to low changes in concentration of solute. Therefore, the con- centrations trend of solute in these wells behaved differently from the concentra- tions trend in the swamp. The concentration of nitrate in the shallow wells ranged between 5.5 to 135.5 ppm. The nitrate concentration in these wells is greater than in the main site of sewage water (5.15 ppm). The presence of the nitrate in these wells is an evidence of a non-source pollution (agricultural activity).
FIG. 3. Effect of the distance from the main lake on the chloride and soluble solute distribution in the shallow wells.
Distance from the main lake, m Soluble solute concentration, ppmChloride concentration, ppm
Table (1) shows the compositions of deep wells water. It is obvious that the concentrations of soluble solute and chloride in these wells are very small in comparison with those of the main site sewage water. The soluble solute con- centration in the main lake is approximately 30 folds as the concentration in the deep wells, which ranged from 832 to723 ppm. We conclude that wells are all drilled in the same aquifer. According to these concentrations, the deep wells are confined aquifers. This kind of aquifer is hardly to be contaminated. There is small amount of nitrate but this solute could reach the aquifer from the re- charge place of aquifer. Escherichia coli were observed in one well and En- terobacteria aeruginosa in another well. Bacteria are found in three wells out of eight studied wells.
TABLE 1. Chemical and bacteriological compositions of the main site of sewage water and in near- by deep wells in Buraydah city.
Distance from the Soluble solute, Cl Nitrate
Bacteria type
main lake, m ppm ppm ppm
0.0 (main site) 21952.0 16140 0.5 Entro bacteria
1250 832 439.9 0.0 Nil
2210 729.6 88.8 4.0 Nil
2500 736 88.8 4.6 Entro bacteria 2500 729.6 78.1 2.5 E. coli
4370 723.2 560.9 0.0 Nil
4460 729.6 639.0 0.0 Nil
4500 768 580 0.0 Nil
The CXTFIT program was fitted to the effluent concentration of chloride cal- culated from the data of T.S.S., the mean pore-water velocity, v, and dispersion coefficient, D, from the fitting processes. Also, saturated hydraulic conductiv- ity, K, was measured using the data of effluent. Table (2) shows the particle size distributions, the mean pore-water velocity, dispersion coefficient and saturated hydraulic conductivity for three sandy soil. It is obvious from Table (2) that the sand fraction in the three soils ranged between 92.37 to 97.10%. Although the variations in the sand is small among the three soils, but these variations lead to differences in the saturated hydraulic conductivity, the average-pore velocity and dispersion coefficient.
The average-pore velocity of water and the saturated hydraulic conductivity increased as the sand fraction increases. In the soil with 92.37% sand, K was one eighth of that in the soil with 97.1% sand. Similarly, v was one tenth in the
respective soils. The dispersion coefficient, D, of the Cl anion increased as the sand fraction increased. This increase is due to the mechanical dispersion that is a function of the pore-water velocity (Leij, et al., 1991). Al-Salamah (2003) re- ported that dispersion coefficient of urea in sandy soil is slightly greater than its value for the loamy sand soil under a high bulk density condition. Therefore, in- creasing the sand fraction in a site of wastewater does lead to the high move- ment of water and its loading chemicals to a further distance.
TABLE 2. Pore-water velocity, v, dispersion coefficient, D, and saturated hydraulic conductivity, K, for three soils.
Soil texture
Particle size distribution
V, m/d D, m2 / d K, m/d
Sand Silt Clay
% % %
Sand 92.37 0.62 7.01 1.113 0.0724 0.524
Sand 95.88 0.41 3.17 4.645 0.0262 3.020
Sand 97.10 0.2 2.7 10.025 0.2090 4.050
Conclusion
One hundred sixty-nine water samples were collected from the main site of sewage water in Buraydah city and its near areas. The samples represented three water resources: swamps, shallow wells, and deep wells. The results of total sol- uble solute and chloride concentrations in the swamps and the shallow wells in- dicated contamination by the main site of sewage water. The effect of sewage water site extended for a distance of 3.2 km. Fortunately, the sewage site did not contaminate the deep well which carries the main water resources for the habitants except two wells located at a distance of 2500 m from the main lake.
Presence of microorganisms in the swamps and shallow wells is due to leakage of water from the near septic tanks and the agricultural activity in the area. The dispersion coefficient and the saturated hydraulic conductivity of some soil sur- rounding the site are correlated positively with the sand content. Therefore, using a dumping site with low hydraulic conductivity (low sand content) is pre- ferred for controlling its load toward the groundwater in the shallow and deep wells.
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