Abstract:
The onset of the Water Framework Directive (WFD) will challenge water utilities to
further reduce their wastewater phosphorus discharges to < 0.5 mg.L-
1
. Whilst
conventional treatments, such as chemical dosing, are able to meet these new discharge
consents, the strategies are representative of a linear economy model where resources are
unrecovered and disposed.
An alternative solution which can contribute to the aspiration of a circular economy is
microalgae. Microalgae are ubiquitous in wastewater environments and assimilate
phosphorus during their growth, to residual concentrations complementary of the WFD.
Furthermore, microalgal biomass can be anaerobically digested to produce biomethane
offering the potential for an energy neutral approach. However, uptake of microalgal
systems are lacking in the UK through limited knowledge of operation; and the belief that
such solutions are synonymous to large, shallow open ponds with extensive treatment
times. The development of alternative microalgal reactors are increasingly investigated
to overcome these implementation challenges. Of these, immobilised microalgae has
shown great potential; and whilst within its infancy demonstrates the greatest opportunity
for development and optimisation.
This thesis determines the critical operational parameters that influence the remediation
efficacy of immobilised microalgae for tertiary nutrient removal; including species
selection, biomass concentration, treatment period and lighting; with recommendations
for optimal performance. These recommendations are then applied to the design and
operation of an immobilised bioreactor (IBR) to understand the key design and operating
components that influence the overall economic viability. In doing so, the potential for an
IBR to be economically viable, within the next decade, in comparison to traditional
approaches are discussed.
