Tertiary Filtration of Wastewater Using Local Sand

Abstract The use of rapid sand-filtration for tertiary treatment of wastewater in Saudi Arabia is expected to increase dramatically with the implementation of the lately approved Saudi code of reclaimed wastewater and reuse. Almost all-existing tertiary wastewater-treatment plants in the Kingdom utilize imported sand for filtration. The objectives of this research project were to search for appropriate local sand, and to assess its performance in tertiary filtration of wastewater by conducting a pilot-scale filtration study. Sand samples with a size range of 1.1–3.3 mm from Riyadh and Hail cities were tested for conformity to AWWA standards for filtering materials. Hail sand was found to meet the requirements of the standards. According to sieve analysis, the effective size and uniformity coefficient of Hail sand averaged 1.8 mm and 1.44, respectively. Results of the pilot study at three filtration rates of 4, 8, and 12 m/hr, have shown that Hail sand is suitable for filtration of settled stone-trickling-filter effluents. At the rates of 4 and 8 m/hr, effluent suspended solids (SS) concentrations and turbidities as high as 9 mg/L and 3.0 NTU were obtained, satisfying the Saudi reuse quality criteria for unrestricted irrigation and recreational purposes. Results of filtration at the rate of 12 m/h showed that the turbidity criterion was exceeded slightly but the SS criterion was met.