Bioconversion of sago processing wastewater into biodiesel: Optimization of lipid production by an oleaginous yeast, Candida tropicalis ASY2 and its transesterification process using response surface methodology.

BACKGROUND: Biodiesel is an eco-friendly and renewable energy source and a valuable substitute for petro-diesel. Sago processing wastewater (SWW), a by-product of the cassava processing industry, has starch content ranging from 4 to 7 g L-1 and serves as an outstanding source for producing microbial lipids by the oleaginous microorganisms. In the present study, Candida tropicalis ASY2 was employed to optimize single-cell oil (SCO) production using SWW and subsequent transesterification by response surface methodology. Variables such as starch content, yeast extract, airflow rate, pH, and temperature significantly influenced lipid production in a preliminary study. The lipid production was scaled up to 5 L capacity airlift bioreactor and its optimization was done by response surface methodology. The dried yeast biomass obtained under optimized conditions from 5 L bioreactor was subjected to a direct transesterification process. Biomass: methanol ratio, catalyst concentration, and time were the variables used to attain higher FAME yield in the transesterification optimization process. RESULTS: Under optimized conditions, the highest lipid yield of 2.68 g L-1 was obtained with 15.33 g L-1 of starch content, 0.5 g L-1 of yeast extract, and 5.992 L min-1 of airflow rate in a bioreactor. The optimized direct transesterification process yielded a higher FAME yield of 86.56% at 1:20 biomass: methanol ratio, 0.4 M catalyst concentration, and a time of 6.85 h. CONCLUSIONS: Thus, this optimized process rendered the microbial lipids derived from C. tropicalis ASY2 as potentially alternative oil substitutes for sustainable biodiesel production to meet the rising energy demands.

Simultaneous lipid production for biodiesel feedstock and decontamination of sago processing wastewater using Candida tropicalis ASY2.

BACKGROUND: Without sufficient alternatives to crude oil, as demand continues to rise, the global economy will undergo a drastic decline as oil prices explode. Dependence on crude oil and growing environmental impairment must eventually be overcome by creating a sustainable and profitable alternative based on renewable and accessible feedstock. One of the promising solutions for the current and near-future is the substitution of fossil fuels with sustainable liquid feedstock for biofuel production. Among the different renewable liquid feedstock's studied, wastewater is the least explored one for biodiesel production. Sago wastewater is the byproduct of the cassava processing industry and has starch content ranging from 4 to 7%. The present investigation was aimed to produce microbial lipids from oleaginous yeast, Candida tropicalis ASY2 for use as biodiesel feedstock and simultaneously decontaminate the sago processing wastewater for reuse. Initial screening of oleaginous yeast to find an efficient amylolytic with maximum lipid productivity resulted in a potent oleaginous yeast strain, C. tropicalis ASY2, that utilizes SWW as a substrate. Shake flask experiments are conducted over a fermentation time of 240 h to determine a suitable fatty acid composition using GC-FID for biodiesel production with simultaneous removal of SWW pollutants using ASY2. RESULTS: The maximum biomass of 0.021 g L-1 h-1 and lipid productivity of 0.010 g L-1 h-1 was recorded in SWW with lipid content of 49%. The yeast strain degraded cyanide in SWW (79%) and also removed chemical oxygen demand (COD), biological oxygen demand (BOD), nitrate (NO3), ammoniacal (NH4), and phosphate (PO4) ions (84%, 92%, 100%, 98%, and 85%, respectively). GC-FID analysis of fatty acid methyl esters (FAME) revealed high oleic acid content (41.33%), which is one of the primary fatty acids for biodiesel production. CONCLUSIONS: It is evident that the present study provides an innovative and ecologically sustainable technology that generates valuable fuel, biodiesel using SWW as a substrate and decontaminates for reuse.

Hydrothermal carbonization of arecanut husk biomass: fuel properties and sorption of metals.

In this study, hydrothermal carbonization of arecanut husk and its potential application as an alternate solid fuel and heavy metal sorption (adsorbent) was attempted. Arecanut husk (AH) treated with citric acid for 9 h resulted in the hydrochar yield of 58.7% with increased fixed carbon from 17 to 39.7% and HHV from 16.98 to 21.14 MJ kg-1 compared to the parent biomass. The arecanut husk hydrochar (AHH) had H/C of 1.27, O/C ratio of 0.59 with an energy yield of 72.81%, and energy densification ratio of 1.24, and the values have the similar fuel characteristics of lignite. The pH, zeta potential, and surface of the hydrochar were 5.56, - 22.60 mV, and 0.98 m2 g-1 respectively. Hydrochar with a dosage of 0.1% showed a maximum rate of adsorption for Pb2+ (79.86 mg g-1) at the initial concentration of 100 mg L-1 in the aqueous solution compared to Zn2+, Cr6+, and Ni2+. SEM with EDAX and FT-IR spectroscopy results confirmed the presence of Pb2+ and changes in functional groups in arecanut husk hydrochar after adsorption of heavy metals in the aqueous solution.