Iron and Manganese Sequestration Facilities Using Sodium Silicate

Abstract

Field studies were conducted at five water systems that used sodium silicate and chlorine to sequester iron and manganese. Sequestering was generally successful in four of the systems but was unsuccessful in one system that was not adding the silicate and chlorine nearly simultaneously. Iron and manganese did precipitate in hot water heaters, with no apparent red water at the tap and few customer complaints. Higher iron concentrations required less than proportionately higher dosages of silicate, and when water was stored in reservoirs for long periods of time, customer complaints seemed to rise. Total yearly chemical costs for silicate and chlorine were $1.25–$1.75 per person in 1985 at the two Canadian systems. Of this cost, $1.03–$1.14 perperson peryear was for silicate. Silicate dosages can be chosen by filtering treated‐water samples through a membrane filter and increasing the dosage upward until the filter paper is not discolored.