Coagulation is effective, simple to operate, and widely used in treatment of industrial effluent. However,
commonly used inorganic coagulants pose detrimental effects on human health and living organisms in
long run, and generate large amount of toxic sludge. Thus, this study investigated the optimized use of
Cassia obtusifolia alone or combination of alum with lower dosages in treatment of industrial effluent.
In this study, raw pulp and paper mill effluent (PPME) was used as a model wastewater in confirming
the potential use of C. obtusifolia seed gum as a plant-based coagulant or coagulant aid together
with the alum. Response surface methodology (RSM) enabled the study of interactive effects between
operating treatment conditions, and to determine the optimal treatment conditions. The analysis of variance
results obtained in the present study reflected significant quadratic models and strong correlations
between operating conditions and treatment performance. In addition, current findings suggested that
the coagulation mechanisms using C. obtusifolia seed gum together with the alum were most likely based
on adsorption with inter-particle bridging and charge neutralization. Floc characterization also showed
distinctive results, indicating the presence of active functional groups and the thermal stability of floc
formed using C. obtusifolia seed gum and alum. Using RSM, optimal dosages of 0.17 and 0.09 g/L of C.
obtusifolia seed gum and alum, respectively were required to achieve maximum total suspended solids
and chemical oxygen demand removals (89.6 and 55.4%, respectively) under natural pH of raw PPME and
slow-mixing time of 3.40 min. By combining the use of both coagulants, coagulant dosages of C. obtusifolia
seed gum and alum could be reduced up to 90.5 and 62.5%, respectively. The present study revealed C.
obtusifolia seed gum could be used as a potential plant-based coagulant or coagulant aid in treatment of
raw and complex industrial effluent together with reduced dosage of alum.