Biofuels derived from microalgae have promise as carbon-neutral replacements for petroleum. However, difficulty extracting microalgae-derived lipids and the co-extraction of non-lipid components add major costs that detract from the benefits of microalgae-based biofuel. Selective fermentation could alleviate these problems by managing microbial degradation so that carbohydrates and proteins are hydrolyzed and fermented, but lipids remain intact. We evaluated selective fermentation of Scenedesmus biomass in batch experiments buffered at pH 5.5, 7, or 9. Carbohydrates were fermented up to 45% within the first 6 days, protein fermentation followed after about 20 days, and lipids (measured as fatty acid methyl esters, FAME) were conserved. Fermentation of the non-lipid components generated volatile fatty acids, with acetate, butyrate, and propionate being the dominant products. Selective fermentation of Scenedesmus biomass increased the amount of extractable FAME and the ratio of FAME to crude lipids. It also led to biohydrogenation of unsaturated FAME to more desirable saturated FAME (especially to C16:0 and C18:0), and the degree of saturation was inversely related to the accumulation of hydrogen gas after fermentation. Moreover, the microbial communities after selective fermentation were enriched in bacteria from families known to perform biohydrogenation, i.e., Porphyromonadaceae and Ruminococcaceae. Thus, this study provides proof-of-concept that selective fermentation can improve the quantity and quality of lipids that can be extracted from Scenedesmus.

Scenedesmus

10.1002/bit.25714

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Citations (30)

Effects of light intensity and carbon dioxide on lipids and fatty acids produced by Synechocystis sp. PCC6803 during continuous flow

Algal Research (2015)

Sara P. Cuéllar‐Bermúdez Miguel A. Romero‐Ogawa Raveender Vannela YenJung Sean Lai Bruce E. Rittmann

We studied the effects of light intensity (LI) and CO2 supply on pH and total lipid production and fatty acids by Synechocystis sp. PCC6803 during continuous-flow operation of a photobioreactor having continuous nutrient supply. The temperature was fixed at 30 °C, and the LI pattern mimicked a day/night light cycle from 0 to 1920 μmol/m2 s. The CO2 supply varied from 1 to 5% v/v of total air. The total lipid content increased proportionally to LI, reaching a high content of 14% of dry weight (DW) at the highest LI at 3% CO2. In contrast, LI had no significant influence on the total fatty acid content, which was 3.4% ± 0.5% DW, measured as fatty acid methyl esters (FAMEs). Palmitic acid (C16:0) was the main fatty acid (52% of FAMEs), but γ-linolenic acid (C18:3n6) and linoleic acid (C18:2) were significant at 20% and 14% of total FAMEs, respectively. Also, α-linolenic acid (C18:3n3), oleic acid (C18:1), and palmitoleic acid (C16:1) represented 5%, 4%, and 4% of the total FAMEs, respectively. In case of C16:0, its highest content was achieved at LI of 400 to 1500 μmol/m2 s and pH media values from 7.2 to 8.8 (3% CO2). The highest formation of C16:1 and C18:1 (desirable for biodiesel production) occurred with LI up to 600 μmol/m2 s at pH 9 (3% CO2). Stearic acid (C18:0) and linoleic acid (C18:2) contents did not vary with LI or pH, but α-linolenic acid (C18:3n3) formation occurred with patterns opposite to C18:3n6, C16:0, and C16:1. LI of 400 to 1600 μmol/m2 s and pH range from 7.7 to 8.7 led to the highest values of C18:3n6 (0.8% DW), but C18:3n3 was suppressed by these conditions, supporting a desaturation pathway in Synechocystis. These results point to strategies to optimize LI, CO2, and pH, to enhance the fatty acid production profile for biofuel production.

Stearic acid

Palmitoleic acid

Light intensity

Linolenic acid

10.1016/j.algal.2015.07.018

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Citations (57)

Electron‐acceptor loadings affect chloroform dechlorination in a hydrogen‐based membrane biofilm reactor

Biotechnology and Bioengineering (2019)

YenJung Sean Lai Aura Ontiveros‐Valencia Tamer H. Coskun Chen Zhou Bruce E. Rittmann

Abstract Chloroform (CF) can undergo reductive dechlorination to dichloromethane, chloromethane, and methane. However, competition for hydrogen (H 2 ), the electron‐donor substrate, may cause poor dechlorination when multiple electron acceptors are present. Common acceptors in anaerobic environments are nitrate (NO 3 − ), sulfate (SO 4 2− ), and bicarbonate (HCO 3 − ). We evaluated CF dechlorination in the presence of HCO 3 − at 1.56 e − Eq/m 2 ‐day, then NO 3 − at 0.04–0.15 e − Eq/m 2 ‐day, and finally NO 3 − (0.04 e − Eq/m 2 ‐day) along with SO 4 2− at 0.33 e − Eq/m 2 ‐day in an H 2 ‐based membrane biofilm reactor (MBfR). When the biofilm was initiated with CF‐dechlorination conditions (no NO 3 − or SO 4 2− ), it yielded a CF flux of 0.14 e − Eq/m 2 ‐day and acetate production via homoacetogenesis up to 0.26 e − eq/m 2 ‐day. Subsequent addition of NO 3 − at 0.05 e − Eq/m 2 ‐day maintained full CF dechlorination and homoacetogenesis, but NO 3 − input at 0.15 e − Eq/m 2 ‐day caused CF to remain in the reactor's effluent and led to negligible acetate production. The addition of SO 4 2− did not affect CF reduction, but SO 4 2− reduction significantly altered the microbial community by introducing sulfate‐reducing Desulfovibrio and more sulfur‐oxidizing Arcobacter . Dechloromonas appeared to carry out CF dechlorination and denitrification, whereas Acetobacterium (homoacetogen) may have been involved with hydrolytic dechlorination. Modifications to the electron acceptors fed to the MBfR caused the microbial community to undergo changes in structure that reflected changes in the removal fluxes.

Reductive Dechlorination

Electron acceptor

Electron donor

Desulfovibrio

Dichloromethane

10.1002/bit.26945

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Citations (15)

A two-stage design enhanced biodegradation of high concentrations of a C16-alkyl quaternary ammonium compound in oxygen-based membrane biofilm reactors

Water Research (2023)

Chen-Wei Zheng YenJung Sean Lai Yihao Luo Yuhang Cai Weiyu Wu

Stenotrophomonas maltophilia

Alcaligenes

10.1016/j.watres.2023.120963

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Citations (1)