Introduction

Energy plays a pivotal role in the economic and social development of a region or a nation. The hydrocarbon based fossil fuels with the share of 45% in the total energy needs are the key economic driver in India¹ and  are getting exhausted at alarming rates². Escalating energy prices coupled with the fast dwindling stock has necessitated substitution for fossil fuels. In this context, algal bio-fuels while providing clean energy,  also helps in the mitigation of green house gases (GHG’s) and aptly have become the focus of research in recent times^3,4. Studies reveal that algal species like Chlorella sp.⁵ and Scenedesmus sp.^6,7  have higher growth rates, while Botryococcus brauni ⁸ and  Dunaliella tertiolecta ⁹  are efficient in storing lipids in the form of TAG’s.

Growing algae for biofuel can be one of the sustainable options of harvesting solar energy optimally. Nutrients from wastewaters and atmospheric carbon-dioxide produce useful lipids in algae. These algae aid as an interface between the atmosphere and hydrosphere similar to solar panels in manifesting the incident solar energy into bio-chemical energy, which is stored as lipids³. Addition of nutrients into the water would stimulate the algal growth, but this entails cost for fertilizing the water that would eventually lower the net benefit in terms of cost and also reduce the total energy gain in the system. Wastewaters generated in enormous amounts¹⁰ from human habitations could ensure sustained growth of algae and biofuel generation^11,12. The use of wastewaters for algal biofuel production would ensure sustainability in terms of a) biofuel production b) nutrient removal and remediation of wastewater and c) mitigation of GHG’s. Thus the development of renewable clean algal biofuel fosters sustainability and helps in maintaining the environment quality.

Screening and scrutiny of efficient algal species are necessary for assessing the biofuel prospects of algae¹³. Especially the native or indigenous algal species thriving in the wastewater conditions with high N and P^14,15 conditions would be more beneficial than the commercially available strains which have a narrow range of tolerance. The locally isolated algae easily adapt to the wastewater conditions and are found to grow at higher biomass densities^11,14.  FTIR spectroscopy helps in rapid determination of lipids and identification of target algae by the unique spectral signatures (characteristic of each algal species) and this constitute an easy and accurate method to assess lipid accumulation and quantification¹¹. In the present study growth rate, biomass densities, productivities and lipid content of the select wastewater algae have been investigated.  FTIR spectroscopy was used for the determination of characteristic spectral signatures of each of the algae. The transitions in the proteins, carbohydrates, lipids and phosphates were also monitored across the growth period. Lipids were extracted and FAME profiling was carried out using GC-MS.

The objectives of the present study were

1. to determine the lipid content with fatty acid (FAME) composition and biomass productivities of the algal species grown profusely in wastewater
2. to identify the spectral signatures and study the cellular compositional changes in wastewater grown algae with the culture time
3. to identify the potential algal sp. growing in wastewaters,  suitable for for sustainable biofuel production