Discovering tomorrow

InnoVenton and The Downstream Chemicals Technology Station

There are three Cultivation Theme Project Suggestions for Post Graduate Students to consider:

 

Project 1 - Investigating methods suitable for harvesting microalgae biomass and recycling resultant culture medium (PhD)

Project 2 - Could Microalgae facilitate the removal of organics accumulated in the culture medium during phototrophic cultivation throught the implementation of a heterotrophic cultivation step? (PhD)

Project 3- A comparison between the productivity of an astaxanthin producing microalgae strain in traditional open raceway- and modified raceways ponds (MSc)

 

Project 1 - Investigating methods suitable for harvesting microalgae biomass and recycling resultant culture medium

Problem Statement

The NMMU has designed and implemented an integrated raceway system for the potential large scale cultivation of microalgae.  The system is less expensive than those constructed purely of photo-bioreactors, and is more productive relative to traditional paddle wheel driven open raceway systems.  The system does however need further optimization.  Harvesting and dewatering (as well as nutrient supply) is the most expensive part of tmicroalgae production, constituting between 20 and 30 % of the total operational costs.  The reasons for this is the small size of the unicellular microalgae (typically 10-30 micron) and the low solids loading of the growth media (1-3 g/L).  The mannder in which microalgae are harvested is also dependent upon the intended end-use of teh microalgae biomass.  Also, the culture medium from which the biomass is removed is nutrient rich and needs to be recycled back into the system for re-use.  For this reason, a variety of potential havresting methodologies need to be developed and evaluated, fit for purpose.

Approach

Up to date, microalgae have been harvested throught the natural settleing of cells, but significant variations in the efficiency of this method of harvesting has been observed.  Literature suggests that numerous factors impact harvesting efficiencies when biomass is concentrated throught settling.  Multiple harvesting methods (chemical, biological and/or physical), their efficiencies and the quality of the resultant culture medium be will be investigated.  Also, the ability to re-use the culture medium without negatively impacting productivity is of key interest.  The primary objectives would be to select a method which is easy to implement, scalable, cost effective and suitable for the end use of the harvested biomass.

 

Project 2- Could microalgae facilitate the removal of organics accumulate in the culture medium during phototrophic cultivation through the implementation of a heterotrophic cultivation step?

Problem Statement

Growing microalgae cost effectively and with a small carbon footprint, requires recycling of the cultivation medium both to reduce water requirements and costs associated with purchasing inorganic salts.  With repeated harvest-recycle cycles, organic matter, cellular debris, unsused nutrients and auto-inhibitory substances accumulate.  These organic compounds are introduced to the culture medium by dead or lysed cells and throught the active release and passibe permeatio of extracellular organics from cells.  The accumulatio of these substances is hypothesized to induce decreased productivity and potentially culture collapse.  Furthermore, frequent culture collapse and losses in culture medium could contribute tremendously to the cost of microalgae cultivation when considering the unnecesary losses attributed to nutrient and water replenishment.

 

Approach

This research will focus on cleaning or scrubbing water to be recycled back into the cultivation system.  The idea is to cultivate a mixed culture of Scenedesmus, which is currently grown phototrophically, heterotropically or mixotrohpically.  The efficacy of this cleaning mehtod will be established by measuring the organic load and by testing how well microalage grow/recover in the treated water.

 

Project 3- A comparison between the productivity of an astaxanthin producing microalgae strain in traditional open raceway-and modified raceway ponds.

Problem Statement

Multiple microalgae strains have been identified as potential sources of astaxanthin, a red pigment high in antioxidants.  The most common natural source thereof is the green microalga, Haematococcus pluvialis, whose biomass contains up to 2% astaxanthin on a dry weight basis.  Microalgae capable of producing astaxanthin are grown in a two stage approach.  The first step of the process is to accumulate biomass and is called the 'green' or vegetative phase, while the second phase is usually an aplanospore or 'red' phase.  The latter is brought about by exposing the cuture to increased light intensity and nutrient deprivation (usually N).  However, the cultivation of a pure culture of, for example, Haematococcus, is difficult in open raceway systmes, primarily due to risks associated with contamination from other microalgae that flourish under similar culture conditions.  Other factors hampering the efficient cultivation of H pluvialis in particular, are low cell densities in conjunction with poor growth rates and contamination during the vegetative growth phase.

Approach

Microalgae have been cultivated in a technical demonstration facility at the NMMU for the lawt 6 months and is proving to be highly efficient.  Eventhought Haematococcus pluvialis has been cultivated in open raceway systems in the past they require excellent mixing efficiencies for the establishement of a relatively stable culture.  Open raceway systems are usually paddle wheel driven and has horizontal, but almost no vertical mixing capabilities. Therefore, this research aims to cultivate a stable culture of an astaxanthin producing microalgae strain, such as Haematococcus pluvialis, in an open, modified raceway system in an effort to reduce cost associated with the cultivation of such strains.

 

For more information contact Dr Carla Kampman at carla.kampman@nmmu.ac.za