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Hydrothermal Liquefaction of Algae Grown on Brackish Dairy Wastewater

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2018 ASABE Annual International Meeting  1801158.(doi:10.13031/aim.201801158)
Authors:   Meshack Audu, Maung Thein Myint, Feng Cheng, Kwonit Mallick, Umakanta Jena, Nagamany Nirmalakhandan, Catherine E Brewer
Keywords:   algae, brackish, biofuels, dairy wastewater treatment, energy recovery, hydrothermal liquefaction.

Abstract. Hydrothermal Liquefaction (HTL) is a thermochemical process that uses subcritical water (270-350 °C and 8-18 MPa both as a solvent and a reaction medium to convert organic biomass constituents into energy-rich bio-crude oil. HTL is most suitable for conversion of wet feedstocks including algae. In this study, we compare the oil yields and energy recoveries from the HTL of a microalgal polyculture used to remove excess nutrients from brackish dairy manure effluent. The biomass was cultured from a sample taken from the U.S. Bureau of Reclamation‘s Brackish Groundwater National Desalination Research Facility (BGNDRF), Alamogordo, NM in a photo bioreactor system. Batch HTL experiments were carried out in a 1.8 L autoclave reactor at reaction temperatures of 310 and 350°C for 30 and 60 minutes. Product yields and the higher heating values (HHV) of the bio-crude oils were measured for different HTL conditions. Prior to HTL, the microalgae biomass was diluted with deionized water to lower the electrical conductivity of the reaction medium to approximately 1000 μS/cm and centrifuged; this pretreatment was used to lower the ash content of the feedstock and to decrease corrosion of the reactor surfaces. The light bio-crude oil (LBO) yield ranged from 9-24 wt. %, heavy bio-crude oil (HBO) yield and char yield were ranged from 3-7 wt. % and 10-26 wt. % respectively. The feedstock was still relatively high in ash and presented low-moderate potential for energy recovery as liquid fuels. Future work will focus on the evaluation of the combined process of brackish dairy effluent wastewater treatment and renewable energy production.

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