a b s t r a c t
Pulp and paper industry generates 30–180 m3 of wastewater per ton of manufactured pulp and 20–70 m3
of wastewater per ton of manufactured paper and paperboard. Coagulation process is widely applied as
a pre-treatment or primary treatment to remove suspended solids from industrial effluent including
pulp and paper mill effluent (PPME). Nevertheless, the excessive use of inorganic coagulants, such as
alum, poses deleterious environmental impacts and risks to living organisms include low biodegradability,
increase of metal content in discharged effluent and generation of toxic sludge. In view of this,
the present study investigated the potential use of natural Cassia obtusifolia seed gum in treatment of
raw and undiluted PPME through coagulation process. Recommended conditions (initial pH 5, 0.75 g/L
dosage, 10 rpm and 10 min slow-mixing, and 1 min settling time) allowed C. obtusifolia gum removed
high total suspended solids and chemical oxygen demand up to 86.9 and 36.2%, respectively. Findings
from the present study showed that the coagulation efficiency using C. obtusifolia gum was comparable
to alum. Also, characterizations showed that C. obtusifolia gum, alum and their flocs possessed distinctive
features. The difference in peak occurrence from Fourier-transform infrared spectroscopy analysis indicated
that the mechanism of floc formation using C. obtusifolia gum and alum differed. Besides, dissimilar
thermal decomposition stages were observed for C. obtusifolia gum and alum through thermogravimetric
analysis. Scanning electron microscope images showed that flocs formed using C. obtusifolia gum was
highly fibrous-like and aggregate, whereas irregularly-shaped and aggregate for alum. In conclusion, C.
obtusifolia gum could be served as a promising alternative to alum as a natural coagulant in treatment of
PPME.