دراسة لتحسين جودة المياه الجوفية لاستخدامات الري في مزرعة فدك. كربلاء

Study to Improve the Quality of Groundwater for Irrigation Use in Faddak Farm. Kerbala

This study aims to evaluate the groundwater quality for irrigation purpose in the Dammam Formation, Faddak farm, located at 19 km western south of Kerbala Governorate center under the south coast of Al-Razzaza lake, Iraq. The site is located between latitudes (43˚ 52ʹ 44ʺN), and longitudes (32˚ 43ʹ 23ʺE) with gross area reached to 2000 dunam. Results have been interpreted by geographical information system (GIS) software package and obtained maps proved that the groundwater can be classified as “slightly brackish water” due to the total dissolved salts concentration which ranged from 1000 to 3000 mg/L. Also, the sulfate and chloride ions have relatively very high values with arrangement of cations of Na+ > Ca2+ > K+ > Mg2+ and anions of SO42- > Cl-> HCO3-> NO3-.. The calculated values of irrigation water quality index (IWQI) were less than 40; so, the groundwater can be identified as “severe restriction, SR”. Therefore, this water cannot be used for irrigation purpose and can be applied only for soil with high hydraulic conductivity which is the case at the study area.
Due to the high concentration of sulfate ions, were very high and exceeding the allowable limit, this parameter was chosen to be the target contaminant in the evaluation of water quality after treatment by application of permeable reactive barrier (PRB) technique. Manufacturing of new sorbent for PRB was required through modification of the activated carbon with Mg and Fe hydroxides nanoparticles that planted on its surface. This sorbent is named “Activated carbon coated with (Mg/Fe)-layered double hydroxide (LDH)” which abbreviated as “AC-(Mg/Fe)-LDH”. The primary results proved that the prepared sorbent can remove 35.5% of sulfate ions; however, mixing 5 g zero valent iron (ZVI) with 5 g of AC-(Mg/Fe)-LDH can increase the removal efficiency to be 59.0% for Mg/Fe ratio of 7.5/2.5.
Batch tests signify that the prepared material has a high reactivity to eliminate sulfate ions from aqueous solution with efficiency reached to 75% for time, dosage, and pH of 1 h, 5 g/50 mL and 5, respectively; for 50 mg/L concentration at 200 rpm. Models of Langmuir and Freundlich are suitable to describe the sorption isotherm measurements where the maximum adsorption capacity of 2.2027 mg/g and affinity constant of 0.0146 L/mg. The chemisorption was the predominant mechanism because sorption kinetic measurements were described in good manner by Pseudo second-order model. Analyses of characterization demonstrated that the plantation of Mg and Fe nanoparticles onto surfaces of activated carbon was achieved through the manufacturing procedure.
For simulated aqueous solution, continuous tests proved that the longevity of prepared composite sorbent was increased with a thicker barrier which can saturate with sulfate ions as a function of the time. However, the longevity can be increased dramatically with decrease of chemical concentration and water flow rate. The obtained outputs demonstrate that the computer solution (COMSOL) Multiphysics software has a good ability to describe the sulfate ions transport in comparison with experimental measurements. The column tests demonstrate the effectiveness of the prepared material in the remediation of real subsurface water with removal efficiency equal to 70% when flow rate=5 mL/min, inlet concentration of sulfate ion=2301 mg/L and height of bed=50 cm.