Conventional jar tests and on-line size monitoring were used to investigate the effects of slow-mixing intensity and duration on residual turbidity and floc size during charge neutralization coagulation and sweep floc...Conventional jar tests and on-line size monitoring were used to investigate the effects of slow-mixing intensity and duration on residual turbidity and floc size during charge neutralization coagulation and sweep floc- culation with polyaluminum chloride. The compensatory effect of slow-mixing on coagulation performance fol- low!ng inadequate_or excessive rapid-mi_xing was also examined. It is found that slowTmixing intensity has a more marked positive ettect on charge neutralization coas;ulatlon tlaan on sweep tlocculatlon. llle optimal root-mean- square velocity gradient, G, for slow-mixing is 15 s-＇ for both coagulation mechanisms, and charge neutralization coagulation requires a longer slow-mixing duration. The optimal slow-mixing duration, based on residual turbidity,is longer than the time to tbrm the largest mean Ilocs. The optimal product of G and mixing duration, GT, lbr slow-mixing during charge neutralization coagulation （13500） are higher than that during sweep flocculation （4500） and both are less than the range of values recommended by the American Water Works Association （24000-84000）.The optimal GT value under various slow-mixing conditions increases with G. Appropriate extension＇of slow-mixing duration during charge neutralization coagulation can improve coagulation performance after an inadequate or excessive rapid-mixing duration, but during sweep flocculation, appropriate shortening of slow-mixing duration after an excessive rapid-mixing or appropriate extension of slow-mixing duration after an inadequate rapid-mixing is favorable.展开更多
基金Supported by the National High Technology Research and Development Program of China (2009AA063901)the Special Funds for Technological Development of Research Institutes from the Ministry of Science and Technology of China(2010EG111022, 2011EG111307)+1 种基金the Budding Program (2011A-12-L)the Program for Innovative Research Team(IG201204N) of Beijing Academy of Science and Technology
文摘Conventional jar tests and on-line size monitoring were used to investigate the effects of slow-mixing intensity and duration on residual turbidity and floc size during charge neutralization coagulation and sweep floc- culation with polyaluminum chloride. The compensatory effect of slow-mixing on coagulation performance fol- low!ng inadequate_or excessive rapid-mi_xing was also examined. It is found that slowTmixing intensity has a more marked positive ettect on charge neutralization coas;ulatlon tlaan on sweep tlocculatlon. llle optimal root-mean- square velocity gradient, G, for slow-mixing is 15 s-＇ for both coagulation mechanisms, and charge neutralization coagulation requires a longer slow-mixing duration. The optimal slow-mixing duration, based on residual turbidity,is longer than the time to tbrm the largest mean Ilocs. The optimal product of G and mixing duration, GT, lbr slow-mixing during charge neutralization coagulation （13500） are higher than that during sweep flocculation （4500） and both are less than the range of values recommended by the American Water Works Association （24000-84000）.The optimal GT value under various slow-mixing conditions increases with G. Appropriate extension＇of slow-mixing duration during charge neutralization coagulation can improve coagulation performance after an inadequate or excessive rapid-mixing duration, but during sweep flocculation, appropriate shortening of slow-mixing duration after an excessive rapid-mixing or appropriate extension of slow-mixing duration after an inadequate rapid-mixing is favorable.
