Hibiscus rosa-sinensis leaf as coagulant in wastewater and leachate treatments
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Date
2011
Authors
Awang, Nik Azimatolakma
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Abstract
Applications of natural macromolecular coagulants are having a bright future because
of their abundant source, low price, multifunction and its biodegradibility as compared
to conventional chemical-based coagulants. The use of extracts from Hibiscus rosasinensis
leaves as coagulant has not been discussed in literature. This research
determines water (HBaqs) and thioglycollic acid treated (HBpowd) extraction of
carbohydrate coagulants from the leaves of Hibiscus rosa-sinensis. and examines its
chemical characteristics (i.e. isoelectric point (IEP), molecular weight and Fourier
Transform Infrared). Identified as polymers with high molecular weight, HBaqs (183 kDa)
and HBpowd (1 08 kDa) act as anionic coagulants to promote bridging mechanism via main
functional groups, carboxyl (C=O) and hydroxyl (OH). The ability of Hibiscus rosasinensis
leaves extract to act as primary coagulant and coagulants aid in conjunction
with alum was evaluated using the leachate collected from Pulau Burung Landfill Site
(PBLS) as well as the domestic wastewater collected from oxidation pond of treatment
plant in the Engineering Campus of Universiti Sains Malaysia. Leachate from PBLS
could be classified as stabilized leachate by having a high concentraction of ammonia
nitrogen (NH3-N) (2124 mg/L) and chemical oxygen demand (COD) (2736 mg/L).
Whilst, parameters tested in domestic wastewater was generally under the limits set in
Standard B, Environmental Quality Act 1974, Regulation 2009, Malaysia. Jar test
results were analyzed based on the coagulation activity and the removal percentage of
suspended solids (SS), turbidity, iron (Fe3+), NH3-N, COD and colour. In addition,
operating conditions during coagulation, floc strength and sediment percentage
properties were also studied. Results revealed that 20 mg/L HBaqs at pH 12 achieved
the highest removal of all parameters in the domestic wastewater and managed to
suppress alum with 74%, 98%, 35%, 59%, 87% and 92% of SS, Fe3
+, NH3-N, COD,
turbidity and colour removal from its initial values of 38 mg/L, 1.68 mg!L, 8.75 mg!L,
203 mg/L, 63 F AU and 182 PtCo, respectively. In comparison, 20 mg/L alum at pH 6
had removed only 50%, 86%, 12%, 48%, 81% and 40% of SS, Fe3
+, NH3-N, COD,
turbidity and colour, respectively. Generally, HBaqs and HBpowd showed low removal
rates for all parameter tested in leachate as compared to 7000 mg/L alum at pH 6.
However, at 2000 mg/L and pH 10, HBaqs gave highest removal for NH3-N and
turbidity (54% and 76% with initial values of2188 mg/L and 303 FAU, respectively)
as compared to alum (25% and 50% reductions, respectively). A 43% reduction in the
concentration of alum from its optimal dosage with doses of HBaqs and HBpowd
below 1000 mg/L exhibited a synergic effect on Fe3+ (initial value, 2.69 mg/L) removal
and recovery factors (RF). The average removal of Fe3
+ using 7000 and 4000 mg/L
alum as sole coagulant was around 65% and increased to nearly 100% when 1000
mg/L polymer was mixed with 7000 mg/L alum and 500 mg/L polymer was mixed
with 4000 mg/L alum. Besides, floes formed by 4000 mg/L alum mixed with 500 mg/L
HBaqs also showed better ability to resist shear with the higher strength factor (SF) of 114
which was much higher than 87 for alum alone.
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Keywords
Rosa-sinensis