| dc.description.abstract | Rapid population growth, urbanization and industrialization have resulted in
increased use of water, discharge of wastewater; massive use of fossil fuels and
depletion of this energy source. Discharge of wastewater into the ocean introduces,
high loads of degradable organic matter, suspended particulate matter and nutrients.
In this study marine microalgae from a eutrophic environment were used to evaluate
and demonstrate their potential in wastewater bioremediation and production of
biodiesel. Nutrients analysis was done using a flow injection analyser, oil was
extracted gravimetrically and biodiesel fatty acid composition was determined using
a GC-MS instrument. The effects of physicochemical parameters on abundance and
distribution of microalgae was determined in the study sites. Microalgae composition
in Mombasa (Tudor and Makupa Creeks) comprised of 97 species while Gazi Bay, a
relatively uncontaminated environment, had 79 species. 10 classes were recorded in
the study sites namely Bacillariophyceae, Dinophyceae, Cyanophyceae, Coscinodiscophyceae,
Mediophyceae, Fragilariophyceae, Euglenophyceae, Chlorophyceae, Dictochophyceae and
Zygnematophyceae. The abundance of microalgae in Mombasa ranged from 905±112.5
to 26442±375 cells/L while in Gazi Bay it ranged from 942±50 to 14990±427 cells/L.
The concentration levels of nutrients in the Mombasa sampling sites were higher
compared to Gazi Bay. In Gazi Bay, the concentration of phosphates and nitrates
ranged beween ranged between 0.19±0.01 to 0.35±0.07 µg/L and 0.22±0.01 to 0.36±0.1
µg/L respectively. In Mombasa concentration of phosphates and nitrates ranged
beween 0.95±0.79 to 406.0±11.91 µg/L and 4.08±0.74 µg/L to 427.32±17.11 µg/L
respectively. Microalgae from Tudor and Makupa Creek were co-cultured in
wastewater in the laboratory so as to establish optimal conditions for effective removal
of nitrates and phosphates, and production of biomass. The dominant genera of
microalgae in the co-cultures were cyanobacteria (Oscillatoria), chlorophyte (Chlorella)
and diatoms (Entomoneis). It was established that the co-cultures dominated by
Oscillatoria thrived well in 20:80 wastewater:seawater (v/v), Chlorella in 40:60
wastewater:seawater (v/v) and Entomoneis had high biomass productivity at 20:80
wastewater:seawater (v/v). The pH range was between 7.83 to 8.34 for all cultures. Co cultures containing Oscillatoria had the highest percentage decrease in the levels of
phosphates with a 93.63% decrease after 14 days and corresponding decrease in
nitrates of 92.70% by the 7th day. Co-cultures dominated by Chlorella had the highest
ammonium removal within the first 7 days (84.67%). The Biomass productivity was
highest in the co-cultures dominated by Oscillatoria (0.155±0.07 gL-1day-1) but was
lowest for those dominated by Entomoneis (0.086±0.05 gL-1day-1). Co-cultures
containing Chlorella had the highest oil content (55.7±2%), however, amount of oil
extracted varied with method of extraction. The biodiesel produced from the
microalgae biomass had a high percentage composition of palmitic acid (C16:0) (51.4-
60%) and stearic acid (C18:0) (17.1-30%). These fatty acids were present in all
xix
microalgae biodiesel samples, an indication of good biodiesel properties. Overall,
biodiesel made from co-cultures containing Oscillatoria and Entomoneis had the best
quality biodiesel in terms of high MUFA and saturated fatty acids, low levels of acid
value and specific gravity. This study has established that marine microalgae are
viable for the bioremediation of nutrients in wastewater and feedstock for production
of biodiesel.
Key word: marine microalgae, wastewater treatment, biodiesel, nutrients
bioremediation | en_US |
