Enhanced bioenergy recovery from oil‐extracted microalgae residues via two‐step H₂/CH₄ or H₂/butanol anaerobic fermentation

Abstract

Algae-based biodiesel is considered a promising alternative energy; therefore, the treatment of microalgae residues would be necessary. Anaerobic processes can be used for treating oil-extracted microalgae residues (OMR) and at the same time for recovering bioenergy. In this study, anaerobic batch experiments were conducted to evaluate the potential of recovering bioenergy, in the forms of butanol, H2, or CH4, from pretreated OMR. Using pretreated OMR as the only substrate, a butanol yield of 0.086 g/g-carbohydrate was obtained at carbohydrate of 40 g/L. With supplemented butyrate, a highest butanol yield of 0.192 g/g-carbohydrate was achieved at pretreated OMR containing 25 g/L of carbohydrate with 15 g/L of butyrate addition, attaining the highest energy yield of 3.92 kJ/g-OMR and energy generation rate of 0.65 kJ/g-OMR/d. CH4 production from pretreated OMR attained an energy yield of 8.83 kJ/g-OMR, but energy generation rate required further improvement. H2 production alone from pretreated OMR might not be attractive regarding energy yield, but it attained a superb energy generation rate of 0.68 kJ/g-OMR/d by combining H2 production from pretreated OMR and butanol production from pretreated OMR with supplementary butyrate from H2 fermentation supernatant. This study demonstrated an integrated system as an option for treating OMR and recovering bioenergy.

Microalgae: The Future Supply House of Biohydrogen and Biogas

“…Two-step anaerobic fermentation can make full use of the reaction substrate and increase biogas production, shorten overall residence time and increase organic load when compared with one-step anaerobic fermentation under the same processing condition, so as to improve energy conversion efficiency (Lunprom et al, 2019;Ta et al, 2020). Microalgae as raw materials for fermentation were added to the biohydrogen production reactor, and then the biohydrogen producing bacteria were added to produce biohydrogen by continuous flow fermentation; the biohydrogen producing fermentation tail liquid was sent to the methanogenic reactor, and then the anaerobic digestion sludge rich in methanogenic bacteria was added to continuously anaerobic fermentation to produce methane; methane tail liquid was refluxed to biohydrogen production reactor to maintain biohydrogen production reactor pH value, and the residual methane production tail liquid was discharged into biogas treatment system (Cheng et al, 2016). In addition, pretreatment of biomass by enzyme, CO 2 supercritical fluid extraction and acid thermal method can improve the utilization efficiency of biomass and increase the yield of gas fuel (Nobre et al, 2013;Lunprom et al, 2019).…”

Editorial: Recent Progress in Algal Biotechnology

“…This Special issue collects peer‐reviewed articles on topics of algal biotechnology related research from upstream to downstream. The main topics include strain improvement via genetic modifications and metabolic engineering , algal cultivation systems and photobioreactor design , biomass harvesting and downstream processing , conversion of oil‐extracted algae residue into bioenergy , high‐value products from heterotrophic microalgae , and innovative applications of microfluidic tools in algal biotechnology . The diversified topics of the articles collected in this Special issue reflect current hot issues in algae‐based biotechnology and also point out the future directions in this area, which we hope would benefit the readers of this journal.…”