Algae can be effective and economical in dealing with industrial effluents

To its votaries, tiny organisms known as microalgae could hold answers to some intractable problems. That includes curbing carbon dioxide emissions that are contributing to global warming and reducing the burden of industrial effluents.

“We can change trash into gold” and safeguard human existence on the planet, exclaimed Ji-Won Yang of the Department of Chemical and Biomolecular Engineering at the Korea Advanced Institute of Science and Technology in South Korea.

Microalgae, like plants, are capable of photosynthesis, using the energy from sunlight to turn carbon dioxide and water into sugar.

In a talk at the International Conference on New Horizons in Biotechnology held in Thiruvananthapuram recently, Prof. Yang spoke of his team's efforts at treating municipal wastewater using the single-celled green alga, Chlorella vulgaris.

Such wastewater contained plenty of organic compounds and nutrients to sustain the organism. The oils that then accumulated in the cells could be harvested and turned into biodiesel.

It was found that untreated wastewater gave the best algal growth. Nitrogen-fixing bacteria found in the wastewater could be acting as growth enhancers, he noted.

In Taiwan, a group is seeking reduce emissions from a steel plant by turning the carbon dioxide it belches out into a resource for growing C. vulgaris. The alga could then be turned animal and aquaculture feed.

A mutant strain of the alga had been isolated that could tolerate the elevated temperatures that resulted from bubbling the steel plant's flue gas through the medium in which the organism was growing, according to Jo-Shu Chang, deputy-director of the Centre for Bioscience and Biotechnology at the National Cheng Kung University.

Using the alga in this manner could halve the carbon dioxide in the flue gas. Simultaneously, the levels of nitrogen oxides could also be drastically cut and that of sulphur oxides considerably reduced.

A pilot plant based on the alga had been established at a plant of the China Steel Corporation, he said.

Both Prof. Yang and Prof. Chang, however, pointed out that technological breakthroughs were needed to bring down the cost of harvesting and processing microalgae.

Algae can be a very effective and economical way of dealing with industrial effluents, according to V. Sivasubramanian, Director of the Vivekananda Institute of Algal Technology in Chennai.

He gave the example of a company based in Ranipet in Tamil Nadu that was producing alginate, a compound with a variety of applications from food to textiles. The effluent from the production process was highly acidic. To meet pollution control norms, the effluent was earlier being neutralised with sodium hydroxide. The large quantities of sludge that resulted had then to be disposed in a secured landfill.

It had been possible to engineer a treatment process to efficiently carry out the neutralisation by providing suitable conditions for a blue green alga, Chroococcus turgidus, to grow in the effluent. As the alga grew, it reduced the acidity of the effluent. This algal strain had been isolated from the effluent itself.

The remediation plant had been working well for over five years, producing negligible quantities of sludge and saving money that had earlier been spent on sodium hydroxide.

An added bonus

An added bonus was that the company was able harvest and sell some of the alga as a biofertiliser and aquaculture feed.

In the case of another company in Ranipet, this time producing chemicals used in leather processing, the microalga Chlorella vulgaris had been successfully employed to reduce the load of heavy metals, such as copper, zinc, chromium, nickel, cadmium and lead, in the effluent.

Once again, the strain of C. vulgaris used for this purpose had been isolated from the effluent itself, he said.