The Algae Purification Project

The Algae Purification Project

By: Louis, Rosalie & Yasmeen

Licence Frontières du Vivant, Centre de Recherche Interdisciplinaire

Our group was really interested by environnemental issues and wanted to study the abilities of plants to purify water.

We had at our disposal a super eco friendly algae named Egeria densa, it doesn’t have the best reputation because it is responsible for crowding rivers in agricultural areas. Not only E. densas have a rhythm to their name, they are also known to be among the best chemical absorbents. This algae also have a really fast growth rate ! If our idea worked it could have been easy to reproduce for anyone who wanted to get their diy water purifier!

The main chemicals responsible for water pollution are nitrates (NO3-) and ammonium (NH4+). Both those chemicals are residues of fertilizer use in Bretagne, which is known as one of the most water polluted area. Plants absorb the nitrates and ammonium in aqueous form  in order to fill their nitrogen supplies because they cannot fix it when in gaseous form. This supply will be used to produce the amino-acids, helping the development of the plant.

We chose to determine the influence of temperature on nitrate absorption by measuring the a nitrate concentrations of samples at different temperatures. We determined that the normal thermal conditions of Egeria densa are 16 to 28°C, but they can survive up to 33°C. We used two color-changing reagents to determine the nitrate concentration by spectrophotometry. We decided to study samples at 18, 25 and 35°C. We found that there were more variables involved than expected, like the mass of the algae samples or the light exposition. We also found that it was difficult to stay on time for the different measurements.

Here are the graphs of our result. The time is on the x axis, in minutes, and on the y axis, the absorbance (the ability of a medium to capture light beams). The green curve represent the erlenmeyer that contains only the medium and the pink curve represent the erlenmeyer that contain both algae and medium. We will only comment the pink curve, because it is the one of interest.  

Let’s have a look at the 25°C graph. We can see that the absorbance increases between the first and the second dot and then it decreases. We were not suppose to find this result, we imagined that the absorbance would decrease slowly but it’s not that we observed at all.

The second graph represents the second condition of our experiment, the temperature of the medium was at 35°C. We can see that the curve decreases quickly and that was not what we were supposed to observe.

The third graph fit a 18°C temperature and seems to be the best graph we have because the absorbance for only the medium was almost stable and the absorbance of the medium and the algae decreased very rapidly, which is the result we expected.

We concluded from our results that despite some imprecisions, temperature did have an influence on nitrate absorption efficiency in Egeria densa. If we were to repeat this experiment we would paint the glass bottles black, in order to control light exposition better. We would try to more precisely measure the mass of algae per sample. What remains unclear is how long algae can absorb nitrate at 35°C, as it should only live up to 32°C. The next question could be to repeat the experiment for ammonium absorption, because Egeria densa is used to purify water of both nitrate and ammonium.