|dc.description.abstract||An increase in anthropogenic activity has led to the heightened levels of pollution entering
aquatic systems. These excessive concentrations of heavy metals, nitrogen (N), and
phosphorus (P) in water bodies can lead to several adverse impacts, such as eutrophication
and human health risks. Therefore, the removal of pollutants from wastewaters, prior to
their discharge into the natural environment, is of paramount importance. However,
conventional wastewater treatment (WWT) technologies have their limitations; for
instance, large capital/operational costs, and incomplete removal of contaminants.
Therefore, innovative and more effective treatment technologies are required.
Macro-algae typically have high growth and solar energy conversion rates, and are able to
sequester nutrients, utilise CO2, and adsorb metals from aquatic environments. Therefore,
algae may have potential applications in WWT. Furthermore, costs could be negated by the
production of renewable algal biomass which may have a variety of commercially
exploitable applications. However, issues such as poor selection of species or cultivation
systems, and a lack of understanding of the influence of biological, chemical and physical
factors, particularly in a highly dynamic wastewater environments, has led to varied results
and prevented algal WWT becoming a widespread reality.
In this thesis the algae Cladophora coelothrix and Cladophora parriaudii were studied as
potential organisms for implementation into WWT. In addition to the features mentioned
above, Cladophora was selected due to its ubiquity, filamentous morphology, which
minimises harvesting costs, as well as their natural dominance and bloom forming
behaviour in nutrient-rich environments. The influence of dewatering techniques,
environmental factors, and nutrient regime upon the growth, nutrient/metal removal, and
biochemical composition of the biomass were assessed.
The first aspect of the thesis was an abiotic screening process, in order to investigate the
robustness of Cladophora and its suitability for WWT applications on a fundamental level.
Good rates of growth (4-13.3% d-1) and nutrient removal (45.2-99.9%) were observed
throughout the screening process, except under the most extreme of conditions, e.g. pH 3.
This indicated that Cladophora are potentially suitable for treating a broad range of
wastewaters and merit further research to improve its potential applicability for WWT
applications and commercial realisation. For instance, developing a reliable and accurate
method for fresh weight (FW) assessment and hence productivity estimation.
The determination of growth rate via FW measurement is one of the most basic aspects of
algal biology, yet no standardised method exists for filamentous macro-algae. A variety of
FW methods were systematically assessed in terms of accuracy and physiological impact.
Methods involving mechanical pressing to dewater the biomass resulted in >25% reduction
in the final biomass yield, compared to control cultures. The best method for FW
determination employed a reticulated spinner, which was rapid, reliable, and easily
standardised. Furthermore, this approach ensured accurate growth estimation with
minimal physiological impact, measured as growth, maintenance of structural integrity and
nutrient removal. This indicates that the method developed has the potential for
widespread application in macro-algal cultivation, as such the method was employed
throughout this thesis.
The influence of nutrient regime on growth, biochemical composition, and bioremediation
capacity was studied for both species of Cladophora. The nutrient regimes tested,
representative of a broad variety of wastewaters, included four different N/P ratios, four N
sources (ammonium, nitrate, nitrite and urea), and six different equimolar N source
combinations provided at two N/P ratios. There were clear differences in performance
between the two species, with higher rates of growth observed in all instances by C.
parriaudii (4.75-11.2% d-1 vs. 3.98-7.37% d-1). Furthermore, ammonium was removed
preferentially, whereas urea was removed secondarily. However, the presence of urea in
the medium enhanced growth and uptake of the other co-existing N-forms, and yielded a
carbohydrate-rich biomass (37.6-54% DW). These findings demonstrate that algal strain
selection is important for treating wastewaters with specific nutrient profiles. In addition,
results from this study suggest that nutrient regimes can be tailored to produce biomass
with certain properties or characteristics, which make it suitable for further, potentially
commercially viable, applications, such as metal biosorption.
Since the biochemical characteristics of algal biomass were shown to be affected by
nutrient regime, the final chapter describes research investigating the influence of
nutritional history on metal biosorption. C. parriaudii was cultivated under different
nutrient regimes to produce biomass of varying biochemical composition. This biomass was
then used for metal removal, with maximum removal rates ranging from 1.08-2.35 mmol g1, 0.3-0.62 mmol g-1, 0.22-0.48 mmol g-1, and 0.43-0.61 mmol g-1 for Al2+, Cu2+, Mn2+, and
Pb2+, respectively. Observations from this work indicate that metal removal is achieved by
various mechanisms including adsorption, ion exchange, complexation and micro-precipitation,
and that the biosorption efficacy is dependent upon the number and type of
functional groups present, which are in turn influenced by the cultures nutrient regime.
Overall, this study demonstrates the inter-relatedness of biological, chemical, and physical
factors on algal growth, nutrient removal, biochemical composition, and metal biosorption.
Results from this work have highlighted the need for standardisation in protocols, increased
understanding of the influence of algal selection and nutrient characteristics in
bioremediation, and highlighted the importance of considering biological aspects,
specifically nutritional history, in biosorption studies.||en