Mixotrophic cultivation of microalgae

Project

Mixotrophic cultivation of microalgae

In mixotrophic cultivation of microalgae, carbon dioxide, and organic carbons are simultaneously assimilated and both a chemoheterotrophic and photoautotrophic metabolism operates concurrently.

This process will be studied experimentally and analysed with mathematical models: metabolic reaction models for balance analyses, kinetic growth models for photobioreactor control, techno-economic model to evaluate the economic feasibility.

Introduction

Microalgae do not require arable land or freshwater supply and can be harvested nearly all-year-round, which makes them attractive for commercial exploitation. Microalgae are commercially exploited for production of health-food and specialty chemicals, and they are applied for wastewater treatment. Microalgae are envisioned to be a future source of animal and fish feed, bulk chemicals, and possibly biofuel. To accomplish this a significant decrease on production price and energy requirement is needed. To this goal, this research project intends to optimize mixotrophic cultivation of microalgae. In this cultivation strategy, light and organic carbons are simultaneously exploited and both chemoheterotrophic and photoautotrophic metabolism operate concurrently.

This process has the potential to significantly decrease the production cost and energy requirement, which is related  to three factors:

  1. Productivity: the simultaneous presence of two energy sources (light and organic carbon) significantly increases biomass productivity in state-of-the-art cultivation systems (i.e. photobioreactors).
  2. Harvesting: because of the addition of a heterotrophic route a higher biomass concentration can be reached in comparison to solely photoautotrophic cultivation. Consequently, a significant reduction on downstream processing costs can be achieved.
  3. assing: Energy demanding gassing can be omitted because the oxygen required by aerobic chemoheterotrophic growth can be completely covered by oxygenic photosynthesis. Vice versa, the carbon dioxide needed to carry on the photosynthesis, can be provided by the chemoheterotrophic metabolism.

Despite encouraging results, mixotrophic cultivation was not investigated in great detail and studies on the relationship between organic carbon assimilation and photosynthesis are scarce, predominantly empirical, and sometimes contradictory. On the one hand, several studies indicated that the two processes proceed non-competitively and that overall growth is the sum of the two metabolic processes. On the other hand, other studies report a wide range of interactions. Mixotrophic cultivation may decrease the pigment content, specific photosynthetic reactions, and photosynthesis as a whole. A better understanding of the effects of organic substrates on photosynthesis will lead to optimize this cultivation strategy. 

Aim

The objective of this project is to study the interaction between organic carbon assimilation and light energy utilization occurring during mixotrophic cultivation. Firstly, the project aims to design an innovative mixotrophic cultivation strategy that requires minimal gas transfer, or no gas transfer at all. Secondly, the possible interaction between photoautotrophic and chemoorganotrophic metabolism will be elucidated. Finally, once the potential of this cultivation technique is  assessed, the project will focus on the challenges related to large scale application of a mixotrophic cultivation strategy. The competition for organic carbon between microalgae and bacteria will be investigated, as well as the control of organic carbon supply in a day/night cycle.

Approach

Mixotrophic cultivation of microalgae will be investigated in bench-scale photobioreactors, where the supply of light and organic carbon can be tightly controlled. As such, outdoor production conditions can be simulated in the laboratory.  The process will be analysed based on mass and energy balances requiring that all relevant process parameters are measured. The microalgae growth process will be analysed and simulated with mathematical models: metabolic reaction models for balance analyses and kinetic growth models for photobioreactor control.

Thesis project

Within this project there are various possibilities for doing a BSc or MSc thesis. Synergies and contributions from different research areas (process engineering, microbiology, environmental technology) are highly appreciated, as well the will of working in a team.

If you are interested in doing an internship or a BSc/MSc thesis, feel free to contact me.