Growth potential of mixed microalgae cultivated in domestic wastewater with nutrient supplementation under Malaysian weather conditions
Microalgae are considered to be potential biocatalyst for the production of renewable biofuel along with other valuable products. For sustainable algal production, optimization of the algal growth with cost effective harvesting is crucial. An attempt was made to evaluate the effect of nutrients o...
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| Format: | Thesis |
| Language: | English |
| Published: |
2017
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/68633/1/FS%202018%202%20-%20IR.pdf |
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| Summary: | Microalgae are considered to be potential biocatalyst for the production of renewable
biofuel along with other valuable products. For sustainable algal production,
optimization of the algal growth with cost effective harvesting is crucial. An attempt
was made to evaluate the effect of nutrients on biomass production of photoautotrophic
mixed microalgae using domestic wastewater as feed-stock under varying weather
conditions in open pond system. The objectives were to - i) study the effects of
concentration and ratio of nitrogen and phosphorus on growth and biomass production,
ii) find out the most efficient flocculating agent for effective harvesting, iii) examine
the proximate composition of harvested biomass and iv) evaluate the microalgae
composition and diversity prevailed under nutrient adjustments while culturing
microalgae in wastewater under weather variations. In order to achieve the objectives,
microalgae were collected from wastewater pond and cultured in three different
weather conditions (dry, wet and mixed). Nitrogen and phosphorus treatments in
wastewater were taken in two different ratios (0.77:1 and 5:1) with increasing
concentrations (N and P concentration ranges from 10.30 to 41.20 ppm and 2.06 to
53.12 ppm respectively). Bold Basal Medium (BBM) and original wastewater were
taken as control. Meanwhile, four flocculating agents namely FeCl3, alum, Ca(OH)2
and Aflok® (organic flocculant) were investigated to find out the most efficient one
for harvesting microalgae considering different pH condition, dosage, algal
concentration and sedimentation time. The mixed microalgae diversity under given
treatments and weather variations was also closely observed during the culture periods.
It was found that, the increase of nutrients concentration in the medium increased the
final algal biomass regardless the weather condition. Whereas, significantly higher
biomass (>0.60 g/L) obtained where the N : P ratio was greater (5:1). The results from
harvesting efficiency of flocculants indicated that, FeCl3 and Aflok® at their minimal
dosage (<0.08 g/L and <0.112 g/L respectively) were more effective compared to alum and Ca(OH)2 under wide environmental variations of the medium. In proximate
analysis, it was found that protein content increased with increasing nutrient
concentration but lipid and carbohydrate increased when nutrients are in depleted
condition. The highest protein, lipid and carbohydrate content were found to be
26.89%, 32.07% and 37.47% respectively. In species composition, the Chlorophyta
division was observed to be the largest (62.5% - 90%) microalgae group encountered
both in terms of abundance and frequency occurrence regardless of weather variations.
The genus Chlorella vulgaris was the most dominant species that sustained in all
treatments culture due to their resiliency to the media conditions. The species richness
was observed to be higher in treatments with higher nutrient content than in treatments
with lower value. Meanwhile, diversity indices were found to be lower in both low and
high nutrient treatments. However, higher diversity indices were found in treatments
with comparably moderate nutrients content, which indicated uneven distribution of
microalgae species in lower and higher nutrient treatments. It can be concluded that,
when mixed algae is cultivated in open pond system, both the nutrient concentration
and ratio are dominating factors that can highly influence the microalgae biomass
growth, their biochemical composition as well as their community structure. Therefore,
by regulating the nutrients and applying effective harvesting technique sustainable
microalgae biomass production is possible from mixed algae culture in wastewater. |
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