Life cycle assessment of biodiesel from estuarine microalgae

Life cycle assessment (LCA) entails the analysis of potential environmental loads and natural resources utilised while manufacturing a product, which helps in sustainable production of biofuel and prudent management of natural resources. A variety of bio resources including microalgae are being explored for its potential as viable alternatives to conventional fossil fuels. This communication presents the lifecycle assessment of biodiesel production from microalgae and valorisation of other value-added products. Comparative assessment of feed-stock cultivation was done by considering varied nutrient inputs - (i) no nutrient input (scenario 1), (ii) wastewater as nutrient input (scenario 2) and (iii) fertiliser input (scenario 3). Two different transesterification techniques followed for converting microalgal oil into biodiesel were i) acid catalyst and ii) biocatalyst. Environmental impacts of different scenarios considered were assessed using OpenLCA v1.10.3, which highlights higher eutrophication and photochemical oxidation related emissions for fertiliser input scenario with acid catalyst based transesterification. However, significant reductions in environmental impacts with minimal GHG footprint was observed with wastewater use for cultivating algae and transesterification through biocatalyst. Life cycle assessment of three different scenarios revealed a fossil energy requirement variation between 3.6 and 5.7 MJ/kg and the greenhouse gas emission (as kg equivalent CO2 emissions) of 0.85-1.46 kg CO2eq.kg(-1) of biodiesel. This highlights a reduction in fossil energy requirement of about 87.3% in the pilot substrate-based microalgal bioreactor. Wastewater - biocatalyst scenario exhibited a highest net energy ratio (NER) of 18.8 with an additional benefit of low cost remediation of wastewater.