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Journal of Applied Sciences

Year: 2009 | Volume: 9 | Issue: 5 | Page No.: 901-908
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Authors

Ahmed A. Al-Othman

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Research Article

Effect of Treated Domestic Wastewater on Physical and Chemical Characteristics of Soils

Ahmed A. Al-Othman
The study was carried out to determine the effect of treated domestic wastewater (TDW) on physical, chemical and microbial properties of three soils. There was no significant change in the sand, silt and clay fractions after 458 days of TDW irrigation. The parameters included soil pH, which remained within moderately alkaline region after 458 days of TDW irrigation. The SAR of A and B soils changed from 3.27-2.95 and 3.67-2.15, respectively after 200 days of irrigation. But, the decrease in SAR was less in the same soil when irrigated with TDW continuously for 458 days compared to 200 days due to salt leaching to lower soil depths. The concentration of cations (Na+, K+, Ca2+, Mg2+) showed significant (p<0.001, p<0.032) increase after 200 days followed by a significant (p<0.001, p<0.008) decrease after 458 days of TDW irrigation. The concentrations of Na+ in A and B soils decreased with the soil depth except soil C which showed the highest concentration of K as 13.9 meq L-1 than the control sample as 3.2 meq L-1 after 200 days of irrigation and at 150 cm soil depth. The K+ concentration increased from 0.2 to 0.5 meq L-1 and 0.2-0.8 meq L-1 in A and B soils, respectively. However, at 458 days of irrigation, the K+ concentration dropped below, 0.2 meq L-1 in both samples. The electrical conductivity (EC), sodium absorption ratios (SAR), cations (Na+, K+, Ca2+, Mg2+) and anions (CO32¯, HCO3¯, Cl¯, SO42¯) showed similar patterns. But the values of these cations/anions increased after 200 days of irrigation which again dropped below the initial values of soils. The average number of bacteria in soil A, B and C after 200 days and 458 days of TDW irrigation were 99 and 393 cells, 149 and 333 cells and 56 and 559 cells, respectively. In addition to the above, the microbial analysis indicated that E. coli was absent in all the soils irrigated with TDW. The research findings suggest that although the TDW irrigation did not mainly affect the physical and chemical properties of soil under investigation, but is likely to contaminate the groundwater on long term basis in Riyadh region.
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