The production of natural biopolymers as flocculants for water treatment is highly desirable due to their
inherent low toxicity and low environmental footprint. In this study, bio-flocculants were extracted from
Hibiscus/Abelmoschus esculentus (okra) by using a water extraction method, and the extract yield and its
performance in sludge dewatering were evaluated. Single factor experimental design was employed to
obtain the optimum conditions for extraction temperature (25e90 C), time (0.25e5 h), solvent loading
(0.5e5 w/w) and agitation speed (0e225 rpm). Results showed that extraction yield was affected nonlinearly
by all experimental variables, whilst the sludge dewatering ability was only influenced by the
temperature of the extraction process. The optimum extraction conditions were obtained at 70 C, 2 h,
solvent loading of 2.5 w/w and agitation at 200 rpm. Under the optimal conditions, the extract yield was
2.38%, which is comparable to the extraction of other polysaccharides (0.69e3.66%). The bio-flocculants
displayed >98% removal of suspended solids and 68% water recovery during sludge dewatering, and
were shown to be comparable with commercial polyacrylamide flocculants. This work shows that bioflocculants
could offer a feasible alternative to synthetic flocculants for water treatment and sludge
dewatering applications, and can be extracted using only water as a solvent, minimising the environmental
footprint of the extraction process.