Browsing by Author "Chang, IL"

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Expression dewatering of alum-coagulated clay slurries
(1997-05-01)
Chang, IL
;
Chu, CP
;
Lee, DJ
;
Huang, CP
;
環境工程研究所
Filtration followed by expression characteristics of the alum-coagulated clay slurries are first reported in this paper. A strong correlation between alum chemistry and the dewatering efficiency exists. At pH 3, where the positively charged ions are the dominating species, the alum addition has only a minor improvement on dewatering efficiency. At pH 7 and pH 10, where sweep flocs enmeshment play the major role, dewatering performance improves continuously as alum dose increases. At pH 5.2, where a charge reversal regime exists, the dewatering efficiency exhibits a reversal phenomenon as well. The overall dewaterability follows: pH 5.2 > pH 3 > pH 7 > pH 10. A complete test consists of the filtration and expression stages, which are discussed separately. The filtration stage is discussed based on the average specific resistance and the residual moisture in the filtration cake. The expression stage is discussed based on the combined Terzaghi-Voigt rheological model, from which the fraction contributed by the secondary consolidation (B) and the particle creeping factor (eta) are evaluated. For the dewatering sake, a lower B and a higher eta are desired. Both parameters B and eta increase at elevated alum dose and/or lower pH value, while exhibiting a local minimum in charge reversal regime at pH 5.2. The optimal alum dose considering sludge dewaterability is discussed.
Expression dewatering of alum-coagulated clay slurries
(1997-05-01)
Chang, IL
;
Chu, CP
;
Lee, DJ
;
Huang, CP
;
環境工程研究所
Filtration followed by expression characteristics of the alum-coagulated clay slurries are first reported in this paper. A strong correlation between alum chemistry and the dewatering efficiency exists. At pH 3, where the positively charged ions are the dominating species, the alum addition has only a minor improvement on dewatering efficiency. At pH 7 and pH 10, where sweep flocs enmeshment play the major role, dewatering performance improves continuously as alum dose increases. At pH 5.2, where a charge reversal regime exists, the dewatering efficiency exhibits a reversal phenomenon as well. The overall dewaterability follows: pH 5.2 > pH 3 > pH 7 > pH 10. A complete test consists of the filtration and expression stages, which are discussed separately. The filtration stage is discussed based on the average specific resistance and the residual moisture in the filtration cake. The expression stage is discussed based on the combined Terzaghi-Voigt rheological model, from which the fraction contributed by the secondary consolidation (B) and the particle creeping factor (eta) are evaluated. For the dewatering sake, a lower B and a higher eta are desired. Both parameters B and eta increase at elevated alum dose and/or lower pH value, while exhibiting a local minimum in charge reversal regime at pH 5.2. The optimal alum dose considering sludge dewaterability is discussed.
Polymer dose effects on filtration followed by expression of clay slurries
(1997-01-15)
Chang, IL
;
Chu, CP
;
Lee, DJ
;
Huang, C
;
環境工程研究所
Filtration followed by expression characteristics of cationic polymer conditioned clay slurries are reported for the first time in this work. As the polymer dosage increases, the resistance to filtration greatly decreases until a specific dose has been reached, where the zeta potential is close to zero. And further increase in polymer dose conversely raises the resistance. The expression data are interpreted by the Terzaghi-Voigt combined model, from which the model parameters are evaluated. The polymer conditioning has only a mild effect on the primary consolidation process but has, however, a considerable influence on secondary consolidation characteristics. When zeta potential changes from negative to positive, both the easiness of creeping of constituent particles within the sludge cake and the fraction of moisture removal by the secondary consolidation attain a maximum., The optimal polymer dose criterion considering the filtration and expression stages separately, or in combination, is (sic). (C) 1997 Academic Press