44 research outputs found
Performance of A Membrane-Less Air-Cathode Single Chamber Microbial Fuel Cell in Electricity Generation from Distillery Wastewater
AbstractDistillery wastewater contains high organic compounds and nutrients suitable for microorganisms in biological processes such as microbial fuel cell (MFC) which converts the chemical energy contained in organic matter into electricity by microorganisms. The bioelectricity production during the treatment of the distillery wastewater was studied using the air-cathode SCMFCs. The distillery wastewater varied concentrations in the range of 125 to 3,000mg COD L-1 and operated in fed batch mode at 37°C. The results shows that the voltage and current outputs increased with increases in distillery wastewater concentration (0.005-0.055mA). Greater soluble chemical oxygen demand (CODS) removal (29.5-56.7%) and total solids reduction was obtained up 35%. Indicated that the distillery wastewater can produced bioelectricity and can be treated using the membrane-less, air-cathode SCMFCs
Improvement of Mesophilic Biohydrogen Production from Palm Oil Mill Effluent Using Ozonation Process
AbstractBiological fermentative production of hydrogen from the ozonated palm oil mill effluent (POME) was conducted in batch reactors using an anaerobic sludge as a microbial seed. Fermentation was setup at pH 4.0-6.0, varying POME concentration range of 5,000-37,000mg L-1 under mesophilic condition (37°C). The results showed that pH 6.0 is an optimum pH and the maximum hydrogen yield of 28.3mL g-1 COD was obtained. Comparative results of hydrogen production from the raw POME versus the ozonated POME indicated that the ozone pretreatment of POME (mg COD: mg ozone = 102.8) elevated the biodegradability of the POME constituents and significantly enhanced yield and rate of the hydrogen production. Hydrogen production using ozonated POME concentration of 30,000mg L-1 displayed the maximum yield of 182.3mL g-1 COD, which is 49% higher than that from raw POME. Meanwhile the maximum production rate of 43.1mL h-1 was observed at COD concentration of 25,000mg L-1 ozonated POME. Maximum COD removal was 44% at COD concentration of 15,000mg L-1 ozonated POME. This work demonstrated ozonation of POME significant improved performance of hydrogen production
Optimizing Sulfur Oxidizing Performance of Paracoccus Pantotrophus Isolated from Leather Industry Wastewater
AbstractBiogas has been used as alternatives for renewable energy in many applications. Hydrogen sulfide in the biogas is a significant factor to limit its usages. This research focused on using a pure bacterial strain for hydrogen sulfide removal from the biogas in a biotrickling filter process. The pure bacterial strain was isolated from a full-scale leather industry wastewater treatment plant. 16S rDNA sequence of the isolated bacterium is closely related to Paracoccus pantotrophus. P. pantotrophus is able to use sulfide and thiosulfate as energy sources for growth under aerobic conditions. The optimum concentrations of phosphate buffer (26 - 78mM, pH 8) and thiosulfate concentrations (5 â 20g/L) were evaluated in order to maximize microbial growth and sulfur oxidation activity before applying in the biotrickling filter system. The result showed that 52mM buffer concentration and 10g/L thiosulfate were suitable for growth and sulfur oxidation activity. The research findings suggest that P. pantotrophus has the potential application in the biotrickling filter process of hydrogen sulfide removal for upgrading biogas quality
Kinetics of Bioethanol Production from Glycerol by Enterobacter Aerogenes
AbstractKinetics of ethanol production from glycerol as sole carbon source using Enterobacter aerogenes were evaluated in batch fermentation with initial glycerol range from 10 to 120 g L-1 under 240 hr incubation at 30°C and pH 7. E. aerogenes was able to grow and produce the maximum ethanol concentration of 136.7 mM at the initial glycerol concentration of 20 g L-1. At this glycerol concentration, glycerol was completely utilized after 40 hr fermentation and ethanol yield was 0.7 mol mol-1. Microbial growth appeared to decrease when the initial glycerol concentrations were increased. In the initial glycerol concentration range of 10-45 g L-1, glycerol utilization was approximately 90% after 40 hr fermentation. Minimal amount volatile fatty acids and 1, 3-propanediol were detected
Bioethanol Production from Glycerol by Mixed Culture System
AbstractGlycerol, a by-product from biodiesel industry, is a promising feedstock for subsequent bioconversion to higher-value products. Potential application of a mixed microbial consortium on the fermentative conversion of glycerol to ethanol was demonstrated in this study. Maximum ethanol concentration of 11.1 g l-1 was produced after 72 h fermentation from the initial pure glycerol concentration of 45 g l-1, at 30 ĖC, and pH 7 under anaerobic conditions, corresponding to the ethanol production rate and yield of 0.34 g l-1 h-1, and 0.81 mol ethanolmol-1 glycerol, respectively. The microbial consortium yielded lower ethanol concentration (6.5 g l-1) but similar ethanol yield (0.85 mol ethanol mol-1 glycerol) when crude glycerol of 45 g l-1 was fermented at the same condition. At the optimum fermentative condition of the pure glycerol, phylogenetic analysis of microbial consortium based on 16S rRNA gene sequences indicated that Gammaproteobacteria represented 95% of the microbial diversity in the consortium while the rest belonged to Betaproteobacteria. The consortium was dominated by bacteria closely related to genera Enterobacter and Klebsiella, which could play the role on conversion of glycerol to ethanol in this system
Sustainable Waste-to-Energy Technologies: Bioelectrochemical Systems
The food industry produces a large amount of waste and wastewater, of which most of the constituents are carbohydrates, proteins, lipids, and organic fibers. Therefore food wastes are highly biodegradable and energy rich. Bioelectrochemical systems (BESs) are systems that use microorganisms to biochemically catalyze complex substrates into useful energy products, in which the catalytic reactions take place on electrodes. Microbial fuel cells (MFCs) are a type of bioelectrochemical systems that oxidize substrates and generate electric current. Microbial electrolysis cells (MECs) are another type of bioelectrochemical systems that use an external power source to catalyze the substrate into by-products such as hydrogen gas, methane gas, or hydrogen peroxide. BESs are advantageous due to their ability to achieve a degree of substrate remediation while generating energy. This chapter presents an extensive literature review on the use of MFCs and MECs to remediate and recover energy from food industry waste. These bioelectrochemical systems are still in their infancy state and further research is needed to better understand the systems and optimize their performance. Major challenges and limitations for the use of BESs are summarized and future research needs are identified
āļāļēāļĢāļāļĨāļīāļāđāļāļāđāļēāđāļāļĒāđāļāđāđāļāļĨāļĨāđāđāļāļ·āđāļāđāļāļĨāļīāļāļāļļāļĨāļīāļāļāļĢāļĩāļĒāđāļāļēāļāļāļāļāđāļŠāļĩāļĒāļāļĨāļĩāđāļāļāļĢāļāļĨāđāļĨāļ°āļāđāļģāđāļŠāļĩāļĒāđāļĢāļāļāļēāļāļāļāļāļŦāļāļąāļElectricity Generation in Microbial Fuel Cells from Waste Glycerol and Tannery Wastewater
āļāļāļāļąāļāļĒāđāļ āļāļēāļāļ§āļīāļāļąāļĒāļāļĩāđāļĄāļĩāļ§āļąāļāļāļļāļāļĢāļ°āļŠāļāļāđāđāļāļ·āđāļāđāļāļĢāļĩāļĒāļāđāļāļĩāļĒāļāļāļĢāļ°āļŠāļīāļāļāļīāļ āļēāļ āļāļēāļĢāļāļĨāļīāļāļāļģāļĨāļąāļāđāļāļāđāļēāļāļēāļāļāļāļāđāļŠāļĩāļĒāļāļĨāļļāđāļĄāļāļļāļāļŠāļēāļŦāļāļĢāļĢāļĄāđāļāđāļāļāļĩāđāļāļĨ āļāļ·āļ āļāļāļāđāļŠāļĩāļĒāļāļĨāļĩāđāļāļāļĢāļāļĨ āđāļĨāļ°āļāļļāļāļŠāļēāļŦāļāļĢāļĢāļĄāļāļāļāļŦāļāļąāļ āļāļ·āļ āļāđāļģāđāļŠāļĩāļĒāļāļēāļāđāļĢāļāļāļēāļāļāļāļāļŦāļāļąāļ āđāļāļĒāđāļāđāđāļāļāđāļāđāļĨāļĒāļĩāđāļāļĨāļĨāđāđāļāļ·āđāļāđāļāļĨāļīāļāļāļļāļĨāļīāļāļāļĢāļĩāļĒāđ āļĢāļ§āļĄāđāļāļāļķāļāļāļēāļĢāļāļģāļāļąāļāļāļāļāđāļŠāļĩāļĒāđāļāļĢāļđāļāļāļĩāđāļāļāļĩ āļāļēāļāļāļĨāļāļēāļĢāļ§āļīāļāļąāļĒ āļāļāļ§āđāļē āļāļģāļĨāļąāļāđāļāļāđāļēāļāļēāļāļāļāļāđāļŠāļĩāļĒāļāļĨāļĩāđāļāļāļĢāļāļĨ āļĄāļĩāļāđāļē 0.0018 āļĄāļīāļĨāļĨāļīāļ§āļąāļāļāđāļāđāļāļāļēāļĢāļēāļāđāļĄāļāļĢ āđāļĨāļ°āļāđāļģāđāļŠāļĩāļĒāđāļĢāļāļāļēāļāļāļāļāļŦāļāļąāļ āļŠāļēāļĄāļēāļāļāļĨāļīāļāļāļģāļĨāļąāļāđāļāļāđāļēāđāļāđ Â 6.2 āļĄāļīāļĨāļĨāļīāļ§āļąāļāļāđāļāđāļāļāļēāļĢāļēāļāđāļĄāļāļĢ āđāļāļĨāļĨāđāđāļāļ·āđāļāđāļāļĨāļīāļāļāļļāļĨāļāļĩāļāļŠāļēāļĄāļēāļĢāļāļāļĢāļ°āļŠāļīāļāļāļīāļ āļēāļāļāļēāļĢāļāļģāļāļąāļāļāļāļāđāļŠāļĩāļĒāđāļāļĢāļđāļāļāļĩāđāļāļāļĩāļāļēāļāļāļāļāđāļŠāļĩāļĒāļāļĨāļĩāđāļāļāļĢāļāļĨ āđāļĨāļ°āļāđāļģāđāļŠāļĩāļĒāđāļĢāļāļāļēāļāļāļāļāļŦāļāļąāļāđāļāđ 80 āđāļĨāļ° 90 % āļāļēāļĄāļĨāļģāļāļąāļ āđāļāļŠāđāļ§āļāļāļēāļĢāļāļģāļāļąāļāđāļāđāļāļĢāđāļāļāđāļāļĢāļđāļ TKN (Total Kjeldahl Nitrogen) āļāļĩāđāđāļāđāļāļēāļāļāđāļģāđāļŠāļĩāļĒāđāļĢāļāļāļēāļāļāļāļāļŦāļāļąāļ āļĄāļĩāļāļĢāļ°āļŠāļīāļāļāļīāļ āļēāļāļāļķāļ 50% āļāļāļāļāļēāļāļāļĩāđāļĒāļąāļāļĄāļĩāļāļēāļĢāļēāļĄāļīāđāļāļāļĢāđāļāļĩāđāļāđāļāļāļāļāļāļķāļāļāļāļīāļāļīāļĢāļīāļĒāļēāļāļāļāļāļīāđāļāļāļąāđāļ-āļĢāļĩāļāļąāļāļāļąāđāļ āļāļķāđāļāđāļāđāļāļāļāļīāļāļīāļĢāļīāļĒāļēāļŦāļĨāļąāļāđāļāđāļāļāđāļāđāļĨāļĒāļĩāđāļāļĨāļĨāđāđāļāļ·āđāļāđāļāļĨāļīāļāļāļļāļĨāļīāļāļāļĢāļĩāļĒāđ āļāļ·āļ āđāļāļāļĨāļīāļāđāļ§āļĨāđāļāđāļĄāļāļĢāļĩāđāļŠāļāļāļāļķāļāļāļāļīāļāļīāļĢāļīāļĒāļēāļāļāļāļāļīāđāļāļāļąāđāļ-āļĢāļĩāļāļąāļāļāļąāđāļ āļāļĩāđāđāļāļīāļāļāļķāđāļāđāļāđāļāļāļēāļĢāđāļāļĨāļĩāđāļĒāļāđāļāļĨāļāļāļĩāđāđāļāļīāļāļāļķāđāļāļāļāļāļąāđāļ§āđāļāļāđāļēāļ āļēāļĒāđāļāļĢāļ°āļāļ āđāļĨāļ°āļāļĢāļ°āļŠāļīāļāļāļīāļ āļēāļāļāļđāļĨāļāļĄāļāđ (Coulombic efficiency: CE) āđāļāļĒāļāļāļāđāļŠāļĩāļĒāļāļĨāļĩāđāļāļāļĢāļāļĨ āđāļĨāļ°āļāđāļģāđāļŠāļĩāļĒāđāļĢāļāļāļēāļāļāļāļāļŦāļāļąāļ āļĄāļĩāļāļĢāļ°āļŠāļīāļāļāļīāļ āļēāļāļāļđāļĨāļāļĄāļāđ 7.62 āđāļĨāļ° 15.6 āđāļāļāļĢāđāđāļāđāļāļāđ āļāļēāļĄāļĨāļģāļāļąāļ āđāļŦāļĨāđāļēāļāļĩāđāļāļ·āļāđāļāđāļāļāļēāļĢāļēāļĄāļīāđāļāļāļĢāđāļāļĩāđāđāļŠāļāļāļāļķāļāļāļĢāļ°āļŠāļīāļāļāļīāļ āļēāļāļāļēāļĢāļāļĨāļīāļāļāļĨāļąāļāļāļēāļāđāļāļāđāļēāļāļāļāđāļāļĨāļĨāđāđāļāļ·āđāļāđāļāļĨāļīāļāļāļļāļĨāļīāļāļāļĢāļĩāļĒāđāļāļēāļāļŠāļēāļĢāļāļąāđāļāļāđāļāļāļąāđāļ 2 āļāļāļīāļ āļāļąāļāļāļąāđāļ āļŠāļēāļĄāļēāļĢāļāļŠāļĢāļļāļāđāļāđāļ§āđāļē āļāđāļģāđāļŠāļĩāļĒāđāļĢāļāļāļēāļāļāļāļāļŦāļāļąāļāļŠāļēāļĄāļēāļĢāļāļāļĨāļīāļāļāļģāļĨāļąāļāđāļāļāđāļēāļāļēāļāđāļāļĨāļĨāđāđāļāļ·āđāļāđāļāļĨāļīāļāļāļļāļĨāļīāļāļāļĢāļĩāļĒāđāđāļāđāļĄāļĩāļāļĢāļ°āļŠāļīāļāļāļīāļ āļēāļāļĄāļēāļāļāļ§āđāļēāļāļāļāđāļŠāļĩāļĒāļāļĨāļĩāđāļāļāļĢāļāļĨAbstractThe aims of this research were compared the electricity generation and COD removal between waste glycerol and tannery wastewater with microbial fuel cell technology. The results showed power generation from waste glycerol and tannery waste water were obtained 0.0018 mW m-2 and 6.2 mW m-2, respectively. Â The COD removal efficiency can be obtained from waste glycerol and tannery wastewater 80 and 90%, respectively. The nitrogen removal efficiency from tannery wastewater in form of TKN (Total Kjeldahl Nitrogen) can be obtained 50%. Moreover, there are 2 parameters that indicated to oxidation-reduction reaction, which important reaction for microbial fuel cell are cyclic voltammetry (CV) and coulombic efficiency (CE). Cyclic voltammetry (CV) was showed the oxidation-reduction on electrode. Coulombic efficiency (CE) from waste glycerol and tannery wastewater were 7.62 and 15.6 %, respectively. There are parameters that showed the efficiency of electricity generation with 2 of substrates from microbial fuel cells. Therefore, microbial fuel cell technology that can be electricity generation from tannery wastewater better than waste glycerol. Â
Performance of A Membrane-Less Air-Cathode Single Chamber Microbial Fuel Cell in Electricity Generation from Distillery Wastewater
āļĢāļ°āļāļāđāļāļĐāļāļĢāļāļąāļāļāļĢāļīāļĒāļ°āđāļāļ·āđāļāļāļēāļĢāļāļąāļāļāļēāļĢāļāļēāļāđāļēāļ§āļāļĩāđāđāļāđāļāļĄāļīāļāļĢāļāđāļāļŠāļīāđāļāđāļ§āļāļĨāđāļāļĄ Smart Agriculture System for Paddy Field Environmentally Friendly Management
āļāļēāļāļ§āļīāļāļąāļĒāļāļĩāđāļĄāļĩāļ§āļąāļāļāļļāļāļĢāļ°āļŠāļāļāđāđāļāļ·āđāļāļāļīāļāļāļąāđāļāļĢāļ°āļāļāđāļāļĐāļāļĢāļāļąāļāļāļĢāļīāļĒāļ°āđāļāļāļēāļāđāļēāļ§ āđāļāļ·āđāļāļāļĢāļ§āļāļāļīāļāļāļēāļĄāļāļēāļāļļāļāļēāļŦāļēāļĢāđāļāđāļāļĢāđāļāļ (N) āļāļāļŠāļāļāļĢāļąāļŠ (P) āđāļāđāļāļŠāđāļāļĩāļĒāļĄ (K) āđāļĨāļ°āļāđāļēāļāļ§āļēāļĄāđāļāđāļāļāļĢāļāļāđāļēāļ (pH) āđāļāļāđāļĢāļĩāļĒāļĨāđāļāļĄāđ āļāļēāļāļāļąāđāļāļāļģāļāđāļāļĄāļđāļĨāļĄāļēāļāļģāļāļ§āļāđāļāļ·āđāļāļ§āļēāļāđāļāļāļāļĢāļīāļĄāļēāļāļāļēāļĢāđāļāđāļāļļāđāļĒāđāļāļāļēāļāđāļēāļ§ āđāļĨāļ°āļāļģāļāļ§āļāļāļēāļĢāļĨāļāļāļēāļĢāļāļĨāļāļāļĨāđāļāļĒāļāđāļēāļāđāļĢāļ·āļāļāļāļĢāļ°āļāļāļāļēāļāļāļēāļĢāļāļģāđāļāļīāļāđāļāļĢāļāļāļēāļĢ āļāļĨāļāļēāļĢāļĻāļķāļāļĐāļēāļāļāļ§āđāļē āļāļēāļāđāļāđāļāļāđāļāļĄāļđāļĨāļāđāļēāļāļĢāļ°āļāļāđāļāļĐāļāļĢāļāļąāļāļāļĢāļīāļĒāļ°āđāļāđāļāļĢāļ°āļĒāļ°āđāļ§āļĨāļē 1 āđāļāļ·āļāļ āđāļāđāļāļĢāđāļāļ Â Â āļĄāļĩāļāđāļē 180-200 mg L-1 āļāļāļŠāļāļāļĢāļąāļŠ āļĄāļĩāļāđāļē 200-300 mg L-1 āđāļāđāļāļŠāđāļāļĩāļĒāļĄ āļĄāļĩāļāđāļē 500-800 mg L-1 āđāļĨāļ°āļāđāļēāļāļ§āļēāļĄāđāļāđāļāļāļĢāļāļāđāļēāļ āļĄāļĩāļāđāļē 7.08-7.28 āļāļēāļāļāļąāđāļāļĄāļĩāļāļēāļĢāļ§āļēāļāđāļāļāļāļĢāļīāļĄāļēāļāļāļēāļĢāđāļāđāļāļļāđāļĒāļŠāļđāļāļĢ 46-0-0 āđāļĨāļ° 16-20-0 āđāļāļ·āđāļāļāļ§āļāļāļļāļĄāļāļĢāļīāļĄāļēāļāđāļāđāļāļĢāđāļāļ āļāļāļŠāļāļāļĢāļąāļŠ āđāļĨāļ°āđāļāđāļāļŠāđāļāļĩāļĒāļĄ āđāļŦāđāđāļŦāļĄāļēāļ°āļŠāļĄāļāđāļāļāļēāļĢāđāļāļĢāļīāļāđāļāļīāļāđāļāļāļāļāļāđāļēāļ§ āļāļķāđāļāļāļĨāļāļēāļāđāļāđāļĢāļ°āļāļāđāļāļĐāļāļĢāļāļąāļāļāļĢāļīāļĒāļ°āđāļāļ·āđāļāļāļēāļĢāļāļąāļāļāļēāļĢāļāļēāļāđāļēāļ§ āļāļāļ§āđāļē āļāđāļ§āļĒāļĨāļāļāđāļēāđāļāđāļāđāļēāļĒāļāļēāļāļāļēāļĢāđāļāđāļāļļāđāļĒāđāļāđāļāļķāļāļĢāđāļāļĒāļĨāļ° 50 āļŠāļēāļĄāļēāļĢāļāļāļĢāļąāļāļāļĢāļīāļĄāļēāļāļāļēāļĢāđāļāđāļāļļāđāļĒāđāļāđāļĨāļāļĨāļāļĢāđāļāļĒāļĨāļ° 50 āđāļāļĒāļāļĩāđāļāļĨāļāļĨāļīāļāđāļĄāđāļĨāļāļĨāļ āđāļĨāļ°āļāđāļ§āļĒāļĨāļāļāļēāļĢāļāļĨāđāļāļĒāļāđāļēāļāđāļĢāļ·āļāļāļāļĢāļ°āļāļāļāļēāļāļāļēāļĢāļāļģāđāļāļīāļāđāļāļĢāļāļāļēāļĢ 58 kg CO2 eq āļāļāļāļāļēāļāļāļĩāđāļāļēāļĢāđāļāđāļāļļāđāļĒāđāļāļāļĢāļīāļĄāļēāļāļāļĩāđāđāļŦāļĄāļēāļ°āļŠāļĄāļĒāļąāļāļŠāļēāļĄāļēāļĢāļāļĨāļāļāļēāļĢāļŠāļ°āļŠāļĄāļāļāļāļŠāļēāļĢāđāļāļĄāļĩāđāļāļāļīāļ āļāļĩāđāļāļ°āļŠāđāļāļāļĨāđāļŠāļĩāļĒāļāđāļāļāļļāļĨāļīāļāļāļĢāļĩāļĒāđāđāļāļāļīāļ āđāļĨāļ°āļāļģāđāļŦāđāļāļīāļāļāļēāļāļāļ§āļēāļĄāļāļļāļāļĄāļŠāļĄāļāļđāļĢāļāđāļāļĩāļāļāđāļ§āļĒThe research aims to install a smart agriculture system in paddy field management for real-time monitoring of nitrogen (N), phosphorus (P) potassium (K), and pH. After that, use the information to calculate the amount of fertilizer utilization and reduction of greenhouse gas emissions from the project's implementation. The results showed that data were collected through smart online monitoring for 1 month, it was found that nitrogen was 180-200 mg L-1, phosphorus was 200-300 mg L-1, potassium was 500-800 mg L-1 and pH was 7.08-7.28. After that, planning for the amount of fertilizer utilization formulas 46-0-0 and 16-20-0 to control the ratio of N: P: K to be optimal for rice growth. As a result of the smart agriculture system for paddy field management, it was found that help to save costs by 50%, reduce fertilizer use by 50% without declining yields, and reduce greenhouse gas emissions from this project by 58 kg CO2 eq. Moreover, the proper use of fertilizers can also reduce the accumulation of chemicals in the soil that will negatively affect soil microorganisms and cause soil depletion.Keywords: āļĢāļ°āļāļāđāļāļĐāļāļĢāļāļąāļāļāļĢāļīāļĒāļ°; āļāļēāļāđāļēāļ§; āļāļēāļĢāđāļāđāļāļļāđāļĒāļāļĒāđāļēāļāļāļđāļāļ§āļīāļāļĩāđāļāļāļ·āđāļāļāļĩāđāđāļāļĐāļāļĢ; āļāđāļēāļāđāļĢāļ·āļāļāļāļĢāļ°āļāļ;Â Smart agriculture system; Paddy field; Good fertilization Practice in Agricultural Land; Greenhouse ga
Enhancement of Biohydrogen Yield by Co-digestion of Waste Glycerol and Glucose
AbstractBiological hydrogen production from glycerol waste with glucose as co-substrate was tested in batch reactor at the varying mass ratios of glycerol and glucose. All ratios have equivalent extent of total chemical oxygen demand of 9.13 g L-1.COD. Fermentation was setup in 0.5 L glass bottle, 37o C, and pH 6. Liquid and gas samples were collected to analyze concentrations of volatile fatty acids and glycerol; and gas compositions. The results showed that glycerol/glucose ratio plays an important role on the H2 yield. Maximum H2 yield was obtained at the glycerol/glucose ratio of 75:1. Acetate and butyrate were the main fermentative end products. This work demonstrated glucose can be used as a co-substrate to promote the H2 yield in the fermentation of waste glycerol