Hydrothermal liquefaction of microalgae biomass grown in wastewater for Bio Energy perspectives

Abstract

The global energy crisis and growing environmental concerns has newlineincreased significant interest to search for alternative energy sources that are newlinepotentially carbon neutral. Microalgae are the most promising source of newlinesustainable energy due to high lipid content, faster multiplication and ease of newlinecultivation. Despite their numerous biotechnological applications, the newlineindustrial scale-up of microalgal technology still remains a challenge due to newlinehigh production cost, low biomass yield, excessive demand for water and newlinenutrients, and energy-intensive harvesting and downstream processing. newlineIntegration of waste streams in microalgae cultivation, optimization of growth newlineconditions, use of natural flocculants in biomass harvesting and hydrothermal newlineliquefaction for bio-oil production were prospective strategies to enhance the newlineeconomic viability and sustainability in microalgal biofuel production. newlineThe microalgae growth depends on various environmental factors newlineand it becomes indispensable to optimize these factors in order to accomplish newlinemaximum biomass yield at reduced cost. This study optimized the growth newlineconditions of four different microalgae species; two fresh water strains Nostoc newlineellipsosporum and Euglena gracilis as well as two marine strains Chlorella newlinesalina and Spirulina subsalsa. The effect of variable light intensities (50, 100 newlineand 150 and#956;mol mand#8722;2 sand#8722;1), photoperiods (12:12 h, 16:08 h and 24:00 h), aeration newlinerates (0.05, 0.1 and 0.2 vvm - volume of air per unit volume of medium per newlineminute) and wavelengths (white, red, blue and green) on microalgae growth newlinein respective nutrient media was investigated. The optimization of growth newlineconditions enhanced the biomass yield of different microalgae by 1.68 to 1.89 newlinetimes achieving maximum biomass of 2.85 g L-1 in S. subsalsa followed by newline2.64 g L-1, 2.57 g L-1 and 2.24 g L-1 in N. ellipsosporum, C. salina and newlineE. gracilis, respectively. newline