Evaluation of bio-crude oil through hydrothermal liquefaction of microalgae-bacteria consortium grown in open pond using wastewater

Abstract

The present study demonstrates a promising approach for production of bio-crude oil via hydrothermal liquefaction of microbial biomass grown in large-scale open raceway pond. Three key attributes to achieve process feasibility are co-cultivation of microalgae and bacteria resulting in high biomass titre, utilization of paper industry wastewater as cheap source of nutrients and water, and one-step direct conversion of biomass into bio-crude oil. High biomass titre of 4 g L−1 with 90% of COD removal efficiency was achieved, depicting robust performance of the microalgae-bacteria consortium in industrial wastewater and under fluctuating environmental condition. Statistical optimization resulted in highest bio-crude oil yield of 21.7 (%, w/w) under optimal temperature, biomass loading and reaction time of 299.7 °C, 16.1 (%, w/v) and 65 min, respectively. Bio-crude oil with energy recovery of 43% and heating value of 33.1 MJ kg−1 reflects 81.7% and 73.4% heating value of biodiesel and diesel, respectively. While high percentage of hydrocarbon content in bio-crude oil indicates good oil quality, the presence of significant esters fraction might offer resemblance to biodiesel. Lower H/C ratio and higher O/C ratio in comparison to diesel indicate requirement of upgradation of bio-crude oil before it can be realized at commercial scale.