Optimization of water use in a rapid filtration system: a case study

Abstract

The objective of this research was to reduce water use during the operation of anthracite-sand filters used for treating drinking water. The variables that affect the saturation of the filter bed were evaluated, using procedures proposed by the Pan American Center for Sanitary Engineering and Environmental Sciences (CEPIS). The following were evaluated: filtration velocity, initial filtration quality, filtration runs duration, filter bed expansion, duration of the washing process, washing velocity, granulometry, and mud balls. The results obtained were compared with the design parameters recommended by CEPIS. Maximum turbidity of 0.5 NTU was obtained. Filtration runs were in the lower limit of the range indicated by CEPIS. The filter medium expansion in five of the eight filters was lower than recommended by CEPIS. The optimal washing time was 18 min. The washing velocity was low producing little filter bed expansion. The granulometric result indicated that the effective size and the anthracite uniformity coefficient were different between filters. The results also presented significant improvements in the filtration process and the amount of water saved once the filter washing process was optimized. The results also demonstrated that measuring filters performance could improve the filtration system efficiency and ensure the drinking water quality. Keywords: Filtration velocity, Water treatment, Sand and anthracite filter, Head loss, Backwashing, Filter run