TY - JOUR
T1 - Assessment and optimization of chemical and physicochemical softening processes
AU - Chao, Peng Fei
AU - Westerhoff, Paul
PY - 2002/1
Y1 - 2002/1
N2 - Hardness removal processes are very pH-dependent, especially for removal of magnesium (Mg) and silica (Si). Bench-scale tests were conducted with a groundwater that was supersaturated with carbon dioxide and contained calcium (Ca), Mg, and Si. The purpose of this work was to assess and optimize several softening processes to reduce chemical use (i.e., sludge production) and improve turbidity removal. Optimal dosing of lime and soda ash (OLSA) removed 79% of Ca and Mg hardness and 23% of Si hardness. Iron salt addition during OLSA improved the rate of turbidity removal, had minimal effect on Ca or Si removal, but decreased Mg removal unless the pH was readjusted to offset the pH decline that resulted from iron hydroxide formation. Sodium aluminate addition during OLSA improved the rate of turbidity removal and increased settled sludge viscosity, but did not affect Ca, Mg, or Si removal. In separate semibatch aeration softening tests (without lime or soda ash addition), Ca removal increased as a function of aeration rates; Mg and Si were not removed. The addition of a nuclei seed increased dissolved Ca removal from 60% without the nuclei seed to > 80% in the presence of 3 g/L of nuclei seed. Results indicate that the aeration softening process would remove hardness, decrease chemical consumption, and reduce sludge production.
AB - Hardness removal processes are very pH-dependent, especially for removal of magnesium (Mg) and silica (Si). Bench-scale tests were conducted with a groundwater that was supersaturated with carbon dioxide and contained calcium (Ca), Mg, and Si. The purpose of this work was to assess and optimize several softening processes to reduce chemical use (i.e., sludge production) and improve turbidity removal. Optimal dosing of lime and soda ash (OLSA) removed 79% of Ca and Mg hardness and 23% of Si hardness. Iron salt addition during OLSA improved the rate of turbidity removal, had minimal effect on Ca or Si removal, but decreased Mg removal unless the pH was readjusted to offset the pH decline that resulted from iron hydroxide formation. Sodium aluminate addition during OLSA improved the rate of turbidity removal and increased settled sludge viscosity, but did not affect Ca, Mg, or Si removal. In separate semibatch aeration softening tests (without lime or soda ash addition), Ca removal increased as a function of aeration rates; Mg and Si were not removed. The addition of a nuclei seed increased dissolved Ca removal from 60% without the nuclei seed to > 80% in the presence of 3 g/L of nuclei seed. Results indicate that the aeration softening process would remove hardness, decrease chemical consumption, and reduce sludge production.
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U2 - 10.1002/j.1551-8833.2002.tb09439.x
DO - 10.1002/j.1551-8833.2002.tb09439.x
M3 - Article
AN - SCOPUS:0036075970
SN - 0003-150X
VL - 94
SP - 109
EP - 119
JO - Journal / American Water Works Association
JF - Journal / American Water Works Association
IS - 1
ER -