Using Bicarbonate as Carbon Source for Microalgae Culture
1. Goals and objectives
1.1. Problem (needs) statement – Scientific question(s) to be answered
The scientific question to be answered in this research is if there is some algae species that is
tolerant to high pH and high bicarbonate concentration environment, and what is their regulating
mechanism to become tolerant to this environment.
1.2. A new, specific hypothesis that will lead to new knowledge resulted from the research;
The effect of high concentration of bicarbonate to algae physiology may share the same
mechanism with high concentration of sodium chloride, which is osmotic pressure. If this is true,
halophilic algae species should be able to survive in the high bicarbonate concentration
environment.
1.3. A technological advancement will be developed based on the new knowledge;
If this process is successful, a new algae culture process will be developed, in which bicarbonate
will be used as carbon source, rather than CO2. The pH doesn’t have to be controlled in the
range of neutral. Also, high pH environment will allow much less CO2 escape, and even it can
utilize the CO2 in atmosphere.
1.4. Specific research objectives to test the hypothesis and accomplish the technology
development goal
1) Test 20 algae species from cyanobacteria, green algae, red algae and alkaliphilic algae
screened from local Soap Lake.
2) Screen several algae strains which can tolerant both high pH and high bicarbonate
concentration
3) Compare the effect of sodium chloride and bicarbonate, in terms of glycerol synthesis, ion
exchange across the cell membrane, the expression of salt induced proteins need to
determined, to explain if the high bicarbonate concentration has the same effect as the
sodium chloride, and share the same mechanisms.
4) Determine the effect of pH to glycerol synthesis, ion exchange across cell membrane, and
expression of proteins.
5) Repeat cultures with recharged CO2, to prove the concept of recycle use of the high alkaline
water for CO2 absorption.
2. Anticipated products of the project (journal papers, invention disclosures, reports, etc)
A journal paper
3. Related progress to date
Tested some algae species (synechocystis PCC 6803, chlorella sorokiniana, and algae strain
screened from alkali lake) under different concentration of bicarbonate, and the pH change was
observed.
4. Literature review
Among all carbon capture technologies, some of them convert CO2 into bicarbonate. For
example, UOP’s Benfield TM process use potassium carbonate to absorb CO2, and convert it into
potassium bicarbonate (Plasynski et al., 2009). Also, there are some researchers working on
using ammonium to absorb CO2 and convert it into ammonium bicarbonate (Plasynski et al.,
2009). There are also technologies using carbonic anhydrase to convert CO2 in the flue gas into
bicarbonate (Bao and Trachtenberg, 2005). Besides, traditional method for sodium bicarbonate
production, such as Solvay process and Hou's process, which pumps carbon dioxide and
ammonia into saturated sodium chloride to produce sodium bicarbonate and ammonium chloride,
may be used as a potential method for CO2 capture if cheap ammonium can be produced with
renewable energy.
Benemann (2009) have pointed out several key challenges to capture CO2 produced from
thermal power plant with algae culture. Firstly, piping of flue gas any distance is a major cost
problem, and transfer flue gas CO2 into algae ponds cost very much and may not be economical
viable. For example, among the $40.5/ton’s cost in Kadam’s estimate (1997), $28.72/ton is for
MEA extraction, $8.48/ton for compression and drying, and $3.30 /ton for transportation to an
place 100 km away from the power plant. If the flue gas was pumped directly into the algae pond,
and combined with the cost of compression and drying, the cost was $46.64/ton, with a
$10.58/ton of flue gas transportation cost. The total annualized cost was $57.21/ton. Thus, it is
actually not economically viable to transport flue gas directly. Secondly, CO2 in flue gas cannot
be stored during night time or winter, and supply to algae pond when it is needed in day time or
summer. Thirdly, there is a significant loss of CO2 from outgasing in algae pond. These
problems result in a maximum ratio of only 25% for carbon capture with algae culture. However,
if the CO2 in flue gas is converted into bicarbonate, it can be stored and transported as solids or
water solution. This will significantly reduce the cost of compression and transportation for CO2.
Also, the energy cost for bubbling CO2 into algae pond can be reduced. In addition, converting
CO2 into bicarbonate and be used in high pH environment would lead to much less CO2 loss
during the algae culture process.
There have been tremendous literatures on the research of carbon concentration mechanisms ,
and it was found that most of the examined algae and cyanobacteria can take up both of HCO3and CO2 (Giordano et al., 2005; Price et al., 2008). However, there was no research on how high
concentration of bicarbonate the algae species can survive and growth in. As a matter of fact,
algae can be found in lagoon in volcano area that is hyper alkaline (pH 11) and contains
concentrations of salt five times higher than those of sea water
(http://www.nature.com/news/2010/100402/full/news.2010.161.html?s=news_rss). If the algae
species that can survive in high concentration of bicarbonate screened, it can be used in the algae
culture process for biofuel and bioproducts production.
Theoretically, if the initial bicarbonate concentration is 0.3 mol/L, the pH in the solution will be 9.92
(Table 1).
Table 1. Theoretical pH of difference concentration of sodium bicarbonate
[HCO3-]
NaHCO3
[CO32- ]
OHmol/L
g/L
mol/L
mol/L
0.6
50.4 0.000119 0.000119
0.3
25.2 8.38E-05 8.38E-05
0.2
16.8 6.85E-05 6.85E-05
0.1
8.4 4.84E-05 4.84E-05
0.01
0.84 1.53E-05 1.53E-05
* Pka = 10.3, and Ka = 2.34×10-8,
pH
10.07
9.92
9.84
9.68
9.18
If 0.1 mol/L of HCO3- was consumed in the algae culture process, then 0.1 mol/L of OH- will be produced.
This 0.1 mol/L of OH- will react with another 0.1 mol/L of HCO3- (among the rest 0.2 mol/L of HCO3- ),
and produce 0.1 mol/L of CO32- . Thus, the theoretical pH in the solution can be calculated as:
pH = pKa + log([CO32- ]/[HCO3-] = 10.3 +log(0.1/0.1) = 10.3+ 0 =10.3. Thus, if the initial concentration
is 0.3 mol/L, the consumption of 0.1 mol/L of bicarbonate will lead to pH increase from 9.92 to 10.3,
which is about 0.4. Once the culture finished, the high pH water should be recycled to absorb more CO2,
and used again in the culture.
The algae strains that can tolerant high concentration of bicarbonate were screened at first. Then, they
were tested in the culture system. The productivity of algae biomass dry weight, lipid yield was
determined. Also, the yield of biomass from bicarbonate (g/g) was investigated. Also, the water produced
in this culture was re-charged with CO2, and then used again in the culture with supplementation of
nutrients.
Using saturated bicarbonate solution will significantly reduce the evaporation rate, and this will save a lot
of cost for supplying fresh water to make up the evaporated water.
5. Tasks and methodology
5.1. Procedures to make sure samples are taken correctly
5.2. Sample analysis procedure and measures to assure data quality during sample analysis
5.3. Anticipated results
5.4. Measures to assure the accuracy of data analysis and reporting
6. Team members and external collaborators
7. Time line
8. Needs for facility, equipment, other assistance
9. Budget for materials and supplies
10. Reference list