Microalgae under the microscope. Credit: AlgaePARC Wageningen UR

Microalgae under the microscope. Credit: AlgaePARC Wageningen UR

 
 

Microalgae

 

Eat your greens

 
 

Microalgae are microscopic algae which can live in either fresh or saltwater. There are estimated at least 50,000 species documented and between 200,000 and 800,000 expected to exist, but in general, they can range in size from a few micrometers to a few hundred micrometers and all use photosynthesis to grow

 
 
Green algae. Credit: AlgaePARC Wageningen UR

Green algae. Credit: AlgaePARC Wageningen UR

Of all these thousands of kinds of microalgae, there are a handful which have been proven to be able to degrade dyes under certain conditions. These can break down the dye in two different ways. For both of these ways, the first step is these producing an enzyme called ‘azoreductase’, which breaks down the azo bond in the dye. From here, the microalgae can either break down the dye completely, turning into biomass, CO2 and H2O, or it can absorb parts of the molecule into its own structure. Once the dye has been partially broken down, it can turn into aromatic amines. These can be difficult to break down further, especially under the anaerobic conditions necessary for breaking down the first bonds in the dye, but because algae are photosynthetic, they can add oxygen to the environment which helps aerobic microbes turn these chemicals into simple aromatics.

 
 
 

So far, studies have found that Oscillatoria, Chlorella pyrenoidosa, Chlorella vulgaris and Shewanella algae are able to break down azo bonds. Because textile waters can have fairly high salt concentrations, the fact that some of these microalgae are adapted to living in saline conditions is a huge advantage to using them. 

To try and see whether or not a specific kind of microalgae can degrade dyes or not, to a degree, one only has to add dyes to your microalgae mixture and see what happens. In the case of an experiment with Phaeodactylum tricornutum, which hadn’t been found to degrade dyes yet, this meant creating a microalgae culture, adding the dye in different concentrations, giving the mixture light and continuous mixing, and comparing the colour at the start and end. Unfortunately, this microalgae wasn’t found to be useful in degrading dyes, but there are plenty more which are known to be able to break down dyes!

Microalgae species  Oscillatoria princeps  Credit: Aimar Rakko

Microalgae species Oscillatoria princeps Credit: Aimar Rakko

 
Phaeodactylum tricornutum  mixed  with diluted dyes.

Phaeodactylum tricornutum mixed with diluted dyes.

 
 
 
 
Different concentration of ink samples mixed with microalgae after 1.5 weeks cultivation. No evidence of the decolourisation had showed and same results were retrieved after measuring their UV spectrums. 

Different concentration of ink samples mixed with microalgae after 1.5 weeks cultivation. No evidence of the decolourisation had showed and same results were retrieved after measuring their UV spectrums.