RESUMO
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 m[3] of drinking water. The most common types of sand filters used in them are Italba deep filter. Increasing rate of filtration by using an 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-anthracite, and dual sand/anthracite] was used and the applied filtration rates were 8 m/hr [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 m[3]/m[2], and the percent removal of turbidity and algae. The results revealed that dual filter media [sand/anthracite] achieved the criteria of filter performance at rate of 8, 12, and 15 m/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 rate to 12 m/h to get an increase in water quantity with gross production =528 m[3]/m[2] instead of 384 m[3]/m[2] 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 m[3]/m[2] but filter run was decreased and may need to fix surface wash system and/or to use filter aid to avoid build up of slime growth on filter bed