Impact of process variables on nutrient removal in slow sand filters

Abstract

This study is a field evaluation of slow sand filtration as a tertiary treatment at pilot scale level. Three slow sand filters were constructed at Al-Khobar STP site and were operated for about 15 months. Four different flow rates of 8, 10, 16 and 20 1/min at three different sand depths of 150, 80 and 50 cms and two different size of sand of 0.5 and 0.3mm were used. The effect of flow rates, sand depth and sand size on percent removal of BOD, SS, turbidity and nitrogen species were investigated. At these operating conditions the results from the pilot scale filters proved slow sand filtration to be an eefective wastewater treatment technology. The average removal efficiencies of BOD, SS, turbidity as well as nitrification, denitrification and nitrogen removal efficiencies ranged from 41.8 to 83.4%, 21.6 to 71.0%, 37.7 to 62.8%, 42.4 to 78.2%, 58.1 to 82.1% and 34.7 to 67.5% respectively. Statistical analysis was performed on the average means using 't-test' on the experimental data. It was confirmed that the removal efficiencies decreased with the increase in flow rate, decrease in sand depth and increase in sand size.