Effect Of Temperature Towards Membrane Fouling By Microalgae Algal Organic Matter
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Date
2021-07-01
Authors
Ragupathy, Sukdarsanan
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Marine algae produce algal organic matter (AOM) which were found to be the
cause in membrane fouling. Many studies shown that algae, cause significant releases
of AOM into water extracellularly and intracellularly through cell lysis. Membrane
distillation (MD) is a new thermally-driven technology that has a lot of potential in
desalination, water and wastewater treatment, and other applications. The viability of
MD for various applications has been improved thanks to advancements in membrane
design and the utilisation of alternate energy sources. Fouling of membranes, on the
other hand, is still a key issue that plagues MD's long-term stability. In this study,
AOMs, which are soluble extracellular polymeric substance (sEPS) and bounded EPS
(bEPS) two benthic species (Amphora coffeaeformis and Navicula incerta) were
exposed to a temperature range to stimulate membrane processes and hollow fire PP
membranes were soaked during the heating process to study the effect on the membrane
fouling at high temperatures. The EPS of benthic diatom species were extracted and
were characterized by using colourimetric analysis where for carbohydrate analysis, the
phenol-sulphuric acid method was used to measure the carbohydrate concentration and
for protein analysis, the bicinchoninic acid (BCA) method was used to determine the
protein concentration. The characterization of the EPS was done after the algal were
harvested at room temperature and exposed to temperatures 60℃, 70℃ and 80℃ for 8
hours. Similarly, the membranes were soaked during the heating process and collected
after the heating for characterization. This study will help in determining the
characteristic of EPS released by algal cells at a higher temperature during the MD
processes. When the temperature exposed to the EPS increased from room temperature
to 60℃, the protein concentration in bEPS increased from 340.74 ± 33.10μg/g to 343.27
± 32.03μg/g for N. incerta and 279.75 ± 88.78μg/g to 338.89 ± 119.51μg/g for A.
coffeaeformis. The highest bEPS protein concentration of 375.58 ± 51.58μg/g for N.
incerta was obtained at 80℃ and for A. coffeaeformis highest of 338.89 ± 119.51μg/g
was obtained at 60℃. For sEPS the trends were different between the species with the
increasing temperature where the highest protein concentration of 356.41 ± 185.16μg/g
for A. coffeaeformis was obtained at room temperature and for N. incerta highest of
321.59 ± 68.89μg/g was obtained at 60℃. The carbohydrate concentration in sEPS and
bEPS varies at different temperatures in different species and cannot be generalized for
every algal species. However, the highest carbohydrate concentration in N. incerta for
both sEPS and bEPS were obtained at 70℃ with values 679.30 ± 230.46μg/g and 883.69
± 51.70μg/g respectively. For A. coffeaeformis, the highest carbohydrate concentration
in sEPS and bEPS were 310.194 ± 38.31μg/g at 70℃ and 540.56 ± 232.79μg/g at 28℃
respectively. Moreover, from the membrane analysis, the contact angle reduces as the
temperature increases for EPS of both species. The contact angle for membrane soaked
in sEPS and bEPS of A. coffeaeformis reduced by 17% and 59% respectively when
temperature increased from room temperature to 80℃. For membrane soaked in sEPS
and bEPS of N. incerta, the contact angle reduced by 29% and 72% respectively when
temperature increased from room temperature to 80℃. The comparison between SEM
images showed that bEPS contributes more severe fouling compared to sEPS.
Furthermore, increasing the temperature increases the fouling of the membrane for both
sEPS and bEPS. Overall, the compositions of protein in the soluble EPS and bound EPS
at different temperatures will likely dictate the severity of fouling in MD operations.