Section V: Section V: Water Resources

Title: Investigating phosphate removal from water in Lebanon

Author(s): George M. Ayoub, Houri Kalinian

Address: Department of Civil and Environmental Engineering, American University of Beirut, Beirut, Lebanon | Department of Civil and Environmental Engineering, American University of Beirut, Beirut, Lebanon

Reference: Science,Technology and Sustainability in the Middle East and North Africa pp. 292 - 308

Abstract/Summary: Phosphate discharges from point and diffuse sources into the water environment leads to a number of negative impacts. Extensive research has been ongoing to alleviate these problems and as a result many processes of different efficacy have been introduced by which phosphates may be removed from water. One of the successful studies dealt with the use of dolomite as an adsorbing material which when utilised can achieve a 100% phosphate removal from water. To optimise on process operation, the present study was conducted with the objective of evaluating the effects of a number of parameters such as, system operating mode, adsorbent particle size, rates of flow through the bed, applied phosphate concentration, dolomite on effluent water quality and competing solutes, on the efficiency of the process. To achieve this objective, series of laboratory tests were conducted using different system operating configurations, different sizes of the adsorbing medium ranging from sizes greater than 0.177 to 0.074 mm, different rates of flow 1.7 and 3.4 m3/m2/hr and different phosphate concentrations 0.34–1.113 mg/l. The effect of dolomite on the effluent water quality was determined by measuring concentrations of the chemical constituents pH, conductivity, Total Dissolved Solids TDS, sulphate, phosphate, calcium and magnesium of the water before and after the adsorption tests. The competing effect of dissolved solutes was established by carrying out adsorption tests on water having different chemical characteristics, namely, Distilled Water DW, Tap Water TW, Synthetic Ground Water SGW and secondary treated sewage effluents. The results indicate that the fluidised bed configuration was the most effective mode of operation for the system. The smaller sizes of the dolomite powder less than 0.074 mm were also found to produce better adsorption. Furthermore, adsorption was found to increase with decrease in flow and initial phosphate concentration. The presence of dolomite resulted in an increase in pH of the feed influents and an increase in the calcium and magnesium ion concentration. It was further noted that the presence of some solutes in the influent compete with phosphate on adsorption sites thus hindering the efficiency in phosphate removal.

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