Hydrilla verticella as a carbon capturing plant

Abstract

Global warming is a threatening problem to the entire world. As a proactive measure, scientists are developing new techniques to reduce CO2 emission to the atmosphere. Carbon capture and long time storage is a relatively new concept even though it is not economically feasible. Hence scientists have now focused on CO2 capture technology utilising salt water alga.

In the present study, CO2 capturing rates of salt water algal plants Ulva fasciata, Caulerpa racemosa, Sargassum cervicone, Chaetomorpha spp, Padina spp, Corallina spp and Gracilaria spp. which are found in the ocean surrounding Sri Lanka were measured. However, it is very difficult to mimic the natural physical conditions inside the laboratory. Therefore an attempt was made to capture CO2 using an aquatic plant found in fresh water. Hydrilla verticella is an aquatic, invasive plant to Sri Lanka with a high growth rate. The CO2 capturing rate of Hydrilla verticella was compared with other salt water algal plants.

When carrying out the experiment for salt water algae, the initial pH was reduced to 5 by pumping CO2 in to a fixed volume of salt water and then 30g of the specimen was placed and the variation of pH was measured with time. A Similar procedure was carried out with Hydrilla verticella by pumping CO2 in to distilled water. A control was kept under similar conditions without the specimen for each case. Ulva fasciata showed highest CO2 capture rate and Hydrilla verticella was second best. Hydrilla verticella was chosen as it is easy to manipulate for this study. The graph plotted between pH and time for Hydrilla verticella exhibited a typical photosynthetic pattern found in other plants.

In this research, main parameters that have been investigated were on the salinity of the medium and the photoperiod to enhance the CO2 capture rate of Hydrilla verticella. Different salinity levels were obtained by adding different quantities of NaCl (10, 20, 30 ….70 g) in to one liter of distilled water. Results showed that this plant is adaptable to very different levels of salinity but the optimum salinity range is 10-20 gdm-3. Photoperiod was determined by exposing the samples to sun light over varying periods (0, 4, 8, 12 hrs) of time. Results showed that maximum activity was seen when exposed to 12 hrs of sunlight yet it is interesting to note that it can capture CO2 even under very low light intensities; even during night time when other plants respirate. CO2 capturing rate was the highest when the pH of the medium was in between 5-7.

The concept of carbon credits came into existence as a result of increasing awareness of the need for controlling green house emissions. There are many companies that cell carbon credit to commercial and individual customer who are interested in lowering their carbon foot print on voluntary basis, hence above technique which is economically feasible can be implemented in order to mitigate global warming by reducing CO2 emission.