AWWA JAW56579

Hardness removal processes, especiallyfor removing magnesium (Mg) andsilica (Si), are very pH-dependent. Astudy was undertaken to determine theextent to which aeration could replace chemicaladdition as a means of calcium (Ca)removal. Bench-scale tests were conductedwith a groundwater supersaturated withcarbon dioxide (CO2) and containing Ca,Mg, and Si.Optimal dosing of lime and soda ash(OLSA) resulted in 79% removal of Ca andMg hardness and 23% Si removal. Additionof iron salts during OLSA improved turbidityremoval, had minimal effect on Ca or Siremoval, and decreased Mg removal unlesspH was readjusted. Sodium aluminate additionduring OLSA improved turbidityremoval and increased settled sludge viscositybut did not affect Ca, Mg, or Si removal. Theauthors found that removing Ca from waterdepends on the presence of "seed" particlesonto which calcite minerals precipitate; theaddition of a nuclei seed increased dissolvedCa removal from 60 to > 80%. Addition ofpolymers affects the density of the sludgesthat are produced.On the basis of these experiments, aerationstripping would appear most appropriatefor waters supersaturated with CO2 andcontaining predominating calcium carbonatehardness. For utilities using these sourcewaters, the article offers a better understandingof the effects of calcite chemistryon aeration and softening processes thatshould help them improve Ca removal whileminimizing chemical addition and sludgeproduction. Includes 20 references, tables, figures.

Product Details

Edition:

Vol. 94 - No. 3

Published:

03/01/2002

Number of Pages:

11

File Size:

1 file , 450 KB