The critical challenges faced by thousands of power plants and other industries worldwide are wastewater treatment and sequestration of carbon dioxide (CO2). In this context, the biological fixation of CO2 by microalgae is gaining importance as CO2 and solar energy are utilized during photosynthesis. They are mostly mixotrophic adapting themselves to grow in different types of wastewaters as well as suited for mass cultivation in the open environmental conditions owing to their high CO2 sequestration capability in a sustained manner.
Among the few microalgal species viz., Botryococcus sp., Chlorella sp., Chlorococcum sp., Chroococcus turgidus, Spirulina platensis and Scenedesmus sp. tested, Scenedesmus sp. was found to thrive well in the sugar mill effluent utilizing CO2. The COD, BOD & TDS was greatly reduced by 80 – 95% and the pH was between 7.2 – 7.4 indicating that it is the best candidate that can be used in bioremediation of industrial wastewaters.
This microalga was successfully employed to treat the sugar mill effluent generated at EID Parry (I) Ltd., Nellikuppam, Cuddalore district, Tamil Nadu. A pilot scale algal cultivation facility has been established where the CO2, the gaseous waste from distillery unit and sugar effluent, the liquid waste from sugar mill are utilized to cultivate this microalga. This facility is still functioning successfully for over 9 years. As the microalga absorb CO2 emitted from the industry, this greenhouse gas was reduced in that vicinity on one hand and the quality of treated effluent improved on the other hand. The algal biomass generated is being utilized for various applications such as biogas production, biochar, organic manure etc.