Anaerobic digestion of oil production via hydrothermal liquefaction of cyanobacterias

Abstract

Hydrothermal Liquefaction (HTL) is a promising technology for the conversion of wet biomass into biofuels (bio-crude oil - BCO), with algae and cyanobacteria as an excellent feedstock. In the BCO production, a large amount of post-hydrothermal wastewater (PHWW) is also produced, which contains high concentrations of organic matter, nutrients, as well as various toxic compounds. Anaerobic digestion of PHWW is possible; nevertheless, in discontinuous reactors, high retention times and high dilution rates are necessary. The main bottleneck for the implantation of large scale hydrothermal liquefaction processes for oil production is the continuous treatment and reuse of such wastewater. The horizontal anaerobic fixed bed (HAIB) reactor has been researched in the last 20 years, being particularly efficient for the degradation of toxic effluents. The objective of this proposal is to evaluate degradation of hydrothermal liquefaction effluent in a HAIB reactor inoculated with biostimulated and acclimatized biomass immobilized in polyurethane foam. Biostimulation will be performed in reactors operated in sequential batches, fed with substrate based on acetic, propionic, butyric and valeric acids, with methanol. This strategy aims the development of acetogenic and methanogenic microorganisms capable of acting in environments with high concentrations of these acids, and able to perform the valerate conversion, which was previously identified as a possible limiting step of the process. The microorganisms will then be acclimated to the PHWW also in sequential batch regime. The efficiency of the biostimulation and acclimatization processes will be evaluated through inference of kinetic parameters of methane production, molecular biology analyzes and specific methanogenic activity tests. Kinetic parameters of the degradation of organic matter will also be inferred with microorganisms immobilized in polyurethane foam matrices. The intermediates of the anaerobic digestion will be quantified, using gas chromatography, in order to perform the mathematical modeling of the process. For the modeling, two approaches will be used: i) study and understanding of the International Water Association (IWA) anaerobic digestion model # 1 (ADM1), transposing its matrix notation for biochemical and physicochemical equations in the EMSO - Environment for Modeling, Simulation, and Optimization - platform, and ii) simplified kinetic model of irreversible first-order reactions (in series and in parallel) with intermediate products using the Excel Solver® tool. The present proposal is a continuation of a post doctor project developed by the proposer, granted by FAPESP, under supervision of Dr Yuanhui Zhang, professor at the University of Illinois at Urbana-Champaign (UIUC), and China Agricultural University (CAU). During the development of that project, the anaerobic digestion applicability for the PHWW treatment was tested. The development of this project intends to consolidate the partnership between researchers from the University of Sao Paulo with the research fellows from the UIUC and CAU, contributing for large-scale application of cyanobacteria HTL process for bio-crude oil production, since, to the best of our knowledge, no experiences have been reported on the continuous anaerobic treatment of this type of effluent. (AU)