I started a microalgal culture in wastewater with constant illumination with an initial ph=8.5 and after 10 days the ph was 8.00. Photosynthesis tends to increase pH, so...I think other processes could explain the microalgal growth (maybe heterotrophy?).
PD: Celular density increased after 10 days, but not as I saw in control cultures.
The carbonic gas form bicarbonate to form carbonic acid in water and therefore decreases the pH. Usually the cultivation of microalgae used buffers as Tris-HCl or HEPES, to maintain the pH between 7.5 to 8.5 pH more favorable to the development of this class of mcro-organisms.
The organism is utilizing ammonium as a nitrogen source. Therefore, as it uptakes ammonium it releases a proton to maintain cell neutrality, which acidifies the medium.
Data Growth, nitrogen utilization and biodiesel potential for two...
Did you measure DBO5 on the wastewater before starting your culture? If pH drops is because there is more heterotrophic than autothrphic activity, either by heterotrophic bacteria using the organic carbón present in the wastewater or because of low ilumination/aeration, combined with a high microalgae biomass, makes a big portion of the microalgae to respire instead of photosyntetize.
Just as microbial photosynthesis leads to an increase in pH, respiration leads to a decrease. Waste water will be rich in heterotrophic organisms. If your culture is net respiring, the pH will decrease with time. That is in addition to the process mentioned above.
Many thanks for your comments. I autoclaved the wastewater before to start the culture.
Many microalgal species can grow heterotrophically if they are light-limited and sugars are available… And, was your culture axenic? that is, bacteria-free?
There are organic compounds in the wastewater that i used. As I mentioned before, wastewater was autoclaved. My strain is not axenic. Is it significant a decrease from 8.5 to 8.0 ph?
Consecutive increase in atmosphere or dissolved Co2 results the acidification of soltion
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