Evaluation of Mono-Media and Dual Filter Media for Improving Water Quantity and Quality

Abstract

Water is a unique substance and in the coming decades, there will be increasing competition for water supplies worldwide. Alexandria city has eight water treatment plants with an average daily production of 2 million m3 of drinking water. The most common types of sand filters used in them are Italba deep filter. Increasing rates of filtration by using existing deep sand filter, deep mono-anthracite, and dual sand/anthracite media was studied aiming at increasing plant production without deterioration in water quality. Pilot water treatment plant with three pilot filters [mono-sand, mono-anthracite, and dual sand/anthracite] was used and the applied filtration rates were 8 m/hr [current rate], 12 m/hr, and 15 m/hr. Comparison between mono and dual media at the three rates was evaluated according to performance criteria. These criteria are: Filter effluent turbidity =0.2 NTU, head loss =120 cm, Unit filter run volume [UFRV] ≥400 m3/m2, and the percent removal of turbidity and algae. The results revealed that dual filter media [sand/anthracite] achieved the criteria of filter performance at rates of 8, 12, and 15 ml/h at filter runs of 56, 43, and 30 h. Mono-sand and mono-anthracite achieved these criteria after short run time as a result of development of head loss quickly. So, it is recommended to modify an existing mono-sand deep filter into dual media [sand/anthracite] with increasing filtration rates to 12 m/h to get an increase in water quantity with gross production =528 m3/m2 instead of 384 m3/m2 at 8 m/h by mono-sand and the same water quality with turbidity =0.2 NTU. However, by increasing the filtration rate to 15 m/h, the filtered water turbidity was not affected and UFRV=450 m3/m2 but filter run was decreased and may need to fix surface wash system and/or to use filter aid to avoid buildup of slime growth on filter bed.