Turbidity removal from wastewaters of natural stone processing by coagulation/flocculation methods
Abstract
The effectiveness of coagulation (at pH values of 6, 7.5, and 9), flocculation (at pH 9),
and coagulation plus flocculation (at pH 9) on turbidity removal from natural stone
(travertine) processing wastewaters (NSPW) were examined by applying classical sedimentation
tests. FeCl
3
N 6H
2
O, AlCl
3
, and Al
2
(SO
4
)
3
N 16H
O were used as coagulants
and a polyacrylamide based anionic polymer was used as the flocculant. In this way,
it was found that the coagulation method alone was not sufficient to purify NSPW,
whereas flocculation and coagulation plus flocculation methods provided superior
purification. Among the coagulants used, AlCl
3
2
gave the best result in terms of turbidity
removal by coagulation from NSPW at pH 6 and 9, whereas the turbidity removal
performances of the three coagulants were almost identical at pH 7.5. In addition, relatively
low pH (i. e., pH 6) improved the purification performance of all coagulants.
During coagulation of NSPW at pH 6, a charge neutralization mechanism played a
decisive role in turbidity removal. However, in neutral (pH 7.5) and slightly basic (pH
9) media, a sweep coagulation mechanism was predominant. For flocculation of
NSPW, the basic mechanism comprised of polymer bridging.
