Using microalgae to reduce global warming

Residents of Bellary district in Karnataka, India often joke that they experience only two seasons throughout the year—summer and extreme summer.

Temperatures here are so high, and the atmospheric conditions so dry, that very few algal species survive in this region.

And this is precisely what got Prachi Varshney, a researcher with the IITB-Monash Research Academy, interested in Bellary.

The IITB-Monash Research Academy, a Joint Venture between IIT Bombay and Monash University, Melbourne operates a graduate research program in Mumbai. Research is conducted by scholars in both India and Australia, whilst studying for a dually-badged PhD from both organisations.

JSW Steel, one of the Academy's industry partners, has erected India's largest single location integrated steel plant at Toranagallu village, Bellary, and Prachi's project, titled, 'Investigation on CO2 sequestration with microalgae under dry and hot ambient conditions' aims to capture carbon dioxide (CO2) from the flue gases emitted from this plant.

Flue gas is the gas released to the atmosphere via a flue, a pipe that conveys exhaust gases from a furnace. The flue gas at Toranagallu contains a high concentration of CO2, and its temperature can reach 1200C. Carbon dioxide is a major greenhouse gas that contributes to global warming, and it is therefore necessary to capture this gas in order to make the earth clean and green.

Prachi's project also seeks to achieve a significant reduction in the cooling costs of flue gases, and thus her overall objective is to find appropriate algal species and develop an algal cultivation system that can tolerate both high temperatures and high CO2 concentrations.

Fig. 1: mage of flue gas being released at the JSW plant in Toranagallu
(Courtesy: JSW annual report 2011-2012)

"There are numerous technologies available for CO2 capture and fixation such as absorption, adsorption, mineral sequestration, oceanic sequestration, geological sequestration, etc." explains Prachi. "However, they are expensive, energy-consuming and also present several other significant challenges, such as non-renewability of most of the adsorbent materials (e.g. lithium hydroxide), high space requirement for storage, and potential leakage of CO2 over time."

Therefore, biological capture remains the only economically feasible and environmentally sustainable technology which works under limited carbon dioxide concentrations and a wide range of light and temperature conditions.

Though considerable research has already been conducted in this area, admits Prachi, several gaps need to be overcome before microalgal CO2 capture can be deployed at an industrial scale. Some of these are:

  • Most of the studies on algal physiology and biotechnology so far have been based on effects of relatively low CO2 levels (<5%). Few studies have been performed on high CO2 levels up to 15-20%, a typical CO2 concentration in flue gases emitted from combustion sources and their CCM (carbon capture mechanism) functions.
  • A lot of research has been conducted on microalgae cultivation systems based on the use of elevated CO2 alone, however, flue effluent contains a range of other gases. According to the existing literature available, most of the micro-algal species do not require high purity CO2; hence sources such as CO2 from ammonia synthesis plants and flue gases from power stations can be used to improve the overall performance of microalgae-based production systems.
  • Most studies have been done on a "bench" scale and performed under highly controlled conditions, therefore not much is known about the effects of competition with the other microbial species present in the system

Fig. 2: icroalgae cultivation using stack gases in laboratory and large scale open ponds, and usage of biomass produced in energy/food supplements and fertilizer production. (Courtesy:Google and drawn by Prachi )

Says Prof Murali Sastry, CEO, IITB-Monash Research Academy, "Currently 85% of world energy is supplied by fossil fuel thermal power plants including coal, oil and gas. They are the main contributors of increased atmospheric carbon dioxide. Our industry partner JSW Steels emits close to a whopping 40000 tons CO2 per day from its Bellary plant. The system that Prachi develops will hopefully be able to capture CO2 from flue gases directly emitted by power plants, and then transform the biomass produced to carbohydrates, proteins and lipids, so that energy (biofuels), chemicals and food additives can be synthesized from them. This will ensure that there is no requirement of further disposal of the trapped CO2, which is a major drawback in most of the physiochemical processes."

Research scholar: Prachi Varshney, IITB-Monash Research Academy

Project title: Investigation on CO2 sequestration with microalgae under dry and hot ambient conditions

Supervisors: Prof Pramod P Wangikar, Prof John Beardall, Prof Sankar Bhattacharya

Contact details: prachi.varshney.monash.edu

This story was written by Mr Krishna Warrier based on inputs from the research student and IITB-Monash Research Academy. Copyright IITB-Monash Research Academy.