267. The period of cleaning of a slow sand filter, is usually
268. Efficiency of removing bacterias from raw water by a slow sand filter, is
269. Slow sand filter is used if maximum turbidity of raw water is less than
270. The yield of a rapid gravity filter as compared to that of slow sand filter, is
271. In a rapid gravity filter
272. Distribution of wash water is provided in
273. A high velocity of wash water is required for
