Photosynthetic Oxygenation and Nutrient Utilization by Chlorella vulgaris in a Hybrid Membrane Bioreactor and Algal Membrane Photobioreactor System

  • Yasmeen Hani Kamal Najm

Student thesis: Doctoral Thesis

Abstract

Aerobic activated sludge membrane bioreactors (AS-MBR) in municipal wastewater treatment are compact systems that can efficiently perform biological organic oxidation. However, aerobic processes require mechanical aeration accounting for over 40% of total expenditure of a wastewater facility. Additionally, a global urgency for nutrient (Nitrogen/Phosphorus) removal strategies due to surges of eutrophication events requires complex MBR configurations. An innovative and cost-effective process was developed with a dual income-stream: high-quality treated effluent and value-added microalgal biomass for several applications. The proposed process involved several integrated components; an ultrafiltration AS-MBR for organic oxidation followed by a microalgal membrane photobioreactor (MPBR) to remove nutrients (N/P) through assimilation while simultaneously photosynthetically generating dissolved oxygen effluent that was recirculated back into the AS-MBR, thereby reducing the need for mechanical aeration for oxidation. A lab-scale system was fed with a synthetic medium-strength municipal wastewater. The microalgal species C. vulgaris was initially tested in batch trials as a proof-of-concept study on its potential as a photosynthetic oxygenator for the AS-MBR and identify its nutrient utilization efficiencies. The MPBR and MBR were later constructed for continuous operation, with the aim to identify an optimal process configuration. The unit processes were subsequently isolated, where the AS-MBR was subjected to a modelled algal effluent to assesses the impact of varying influent characteristics and effluent recycle rates. A microbial community analysis was performed by high-throughput sequencing and a statistical data-driven modeling approach to assess treatment performances. The MPBR stage was then subjected to the effluent achieved by the AS-MBR stage under varying operating conditions to assess its treatment performance and the resulting algal biomass biochemical composition to identify its suitability for bioethanol, biodiesel, or animal feed production. The findings of this study ultimately confirmed the ability of C. vulgaris to support the AS-MBR for organic removal and fractional nutrient removal by supplying the oxygen demand, and further achieve an effluent polish stage for nutrient removal. The process configuration also demonstrated the ability to achieve a high microalgal biomass production with the potential of extracting valuable products as an added benefit of the wastewater treatment.
Date of AwardNov 2019
Original languageEnglish (US)
Awarding Institution
  • Biological, Environmental Science and Engineering
SupervisorTorOve Leiknes (Supervisor)

Keywords

  • Microalgae
  • Wastewater
  • Membrane Photobioreactor
  • Nutrient Removal
  • Activated Sludge
  • Biofuels/Biodiesel

Cite this

'