Liquid hydrocarbon production from microalgal biomass cultivated from wastewater

Abstract

The emerging fuel crisis necessitates a shift in focus towards alternative renewable forms, so that sustainable development can be achieved. Bio-oil is a promising alternative renewable source of energy which is a third generation bio-fuel. Algae are a popular candidate for bio-fuel production due to their high lipid contents, ease of cultivation and rapid growth rate. In this study, initially the removal efficiency of organic contaminants by microalgae (Chlorella vulgaris and Scenedesmus obliquus) cultivated using photo bio-reactor (PBR) from municipal wastewater was studied. Microalgae were acclimatized into wastewater to reveal its wastewater contaminants removal efficiency and biomass productivity. A 5-L PBR equipped with white light of 200 W/m2 and 0.2 vvm CO2 (2.5%) was used for biomass production. The wastewater parameters like chemical oxygen demand (COD), ammonia (NH3), phosphate (PO4) and nitrate (NO3) after microalgae cultivation were estimated. C. vulgaris removed 84.3% of COD, 89.1% of NH3, 82.6% of NO3 and 85.3% of PO4 from wastewater. While S. obliquus removed 76.5% of COD, 91.8% of NH3, 89.8% of NO3 and 95.3% of PO4 from wastewater. Microalgae cultivation using PBR resulted in 3.7 and 3.8 g/L of C. vulgaris and S. obliquus respectively. Hydrothermal liquefaction (HTL) was carried out to produce biooil from cultivated microalgal biomass. The bio-oil extraction was carried out separately for C. vulgaris and S. obliquus biomasses. Different biomass to water ratios (0.025, 0.05, 0.075 and 0.1 g/mL) were liquefied at diverse temperatures ranging from 200 to 340°C under 5 MPa N2 gas atmosphere. Experiments were carried out without catalyst initially and then diversecatalyst loadings of NaOH (2.5 % wt, 5% wt, 8% wt) and nano ZnO (1-5 wt %). Bio-oil was analysed using Gas Chromatography Mass Spectroscopy (GC-MS) and Fourier Transform Infrared Spectroscopy (FTIR). Bio-oil yield was 29.37% wt and 27.2 % wt at 300 °C, 60 min, at 15 g/ 200 mL biomass loading rate with 3% wt nano ZnO catalyst loading for C.