Recovery of nitrogen and phosphorus from domestic wastewater using algae cultivation and harvesting systems based on phototaxis

INTERNSHIP OFFER

Master 1/Master 2 (6 months)

Recovery of nitrogen and phosphorus from domestic wastewater using algae cultivation and harvesting systems based on phototaxis

Keywords: Motile microalgae, Chlamydomonas Reinhardtii, motility, phototaxis, nutrient recovery, image processing.

INTRODUCTION

Microalgae possess diverse biotechnological potential: they can harness solar energy and extract the necessary carbon from atmospheric CO₂ to perform certain biotransformations and produce value-added compounds. However, one of the main obstacles to their large-scale use is the cost of harvesting them, with relatively low-density cultures (0.5 to 4.0 g dry matter/L), and sometimes also the operational costs of the cultivation systems.

This internship is part of a project aimed at developing a new biotechnology for the energy-efficient cultivation and harvesting of microalgae. In this technology, mixing and harvesting operations will be carried out by controlling "phototaxis": a phenomenon of locomotion of an organism guided by light stimuli. This physiological characteristic is specific to several species of motile algae, including the alga Chlamydomonas Reinhardtii. This alga, approximately 10 µm in diameter, uses its two flagella and stigma to detect the presence and intensity of light, swim, and modulate its distance from the light source.

Our most recent study [1] suggests that controlling phototactic movement can both (i) provide access to nutrients, particularly dissolved CO₂, and (ii) be used for cell harvesting. This technology could offer several advantages, such as eliminating mechanical agitation and thus reducing energy consumption for mixing and harvesting operations. Indeed, mechanical agitation, or even agitation by aeration in large volumes, such as ponds, can be very costly and poorly controlled.

INTERNSHIP TASKS

The intern's main mission will be to test the application of the concept of "phototaxis-controlled agitation and harvesting" using reconstituted growth media, whose nitrogen and phosphorus inputs will come from domestic wastewater of varying degrees of treatment, such as urine, nitrate loaded discharge from reed-bed filters, or effluent from clarifiers of activated sludge plants.

To this end, the intern will be assigned the following tasks:

• Conduct a literature review on the mechanisms of N and P assimilation in algae, particularly motile algae.
• Prepare axenic algal cultures (single species: C. reinhardtii) using standard growth media.
• Develop a protocol for preparing non-standard culture media using N and P sources from domestic wastewater.
• Verification of the viability of C. Reinhardtii culture using non-standard media at the Erlenmeyer flask scale.
• Preparation of algal cultures in a larger system (1 L) using the principle of agitation and harvesting guided by phototaxis.
• Recording and analyzing the growth and bioconvective dynamics of the algal culture using video capture and image processing tools.