STUDY THE EFFECT OF DIFFERENT COMPONENTS OF CRUDE GLYCEROL ON HYDROGEN PRODUCTION BY MIXED CULTURE

Abstract

The present study aimed to investigate the impact of various components of biodiesel-derived crude glycerol (i,e. methanol, soap, and glycerol) on hydrogen production using cow dung as the source of mixed microflora through dark fermentation. The main by-product of biodiesel manufacturing is crude glycerol (CG), produced by the transesterification reaction of vegetable oils or animal oils reacting with ethanol or methanol in the presence of a catalyst. Every 100kg of biodiesel generates 10 kilograms of glycerol. Crude glycerol (CG) possesses high energy content, i.e.,25.30MJ/kg, making it an effective carbon source for the bio-production of hydrogen, propane-diol, and ethanol. The purity of Biodiesel derived crude glycerol varies between 55% to 90%, and the rest consists of impurities like methanol, soap, salt, etc. Methanol and soap have been found as the most inhibitory agents in crude glycerol affecting bio production. A total of 17 runs have been performed in batch mode, as determined by the design of experiments. Batch studies for dark fermentation were undertaken in 250 mL Erlenmeyer flasks, having 150 mL as working volume and 100ml as headspace, under the anaerobic condition to study the bio-hydrogen production. The reactor flasks containing nutrient media were fed with glycerol, methanol, and sodium oleate as soap of different concentrations according to the design of experiments(DOE) data. The initial pH of the nutrient media was set to 7 by using 1M HCl and 1M NaOH.Then 20 ml of cow dung slurry was added to the above solution. Before the incubation at 370C, reactors were purged with nitrogen for 2-3 mins to built an anaerobic environment to aid the development of hydrogen-producing microbes. Applying response surface methodology in Design-Expert software, the process variables was optimized for maximum H2 production. The gas was collected by downward water displacement, and Gas Chromatography analyzed the composition of H2 and CO2. A control experiment was also performed with only glycerol of 27g/L (without any impurities) for a comparative study with the 17 experimental runs. According to the ANOVA report, methanol, soap, and glycerol have been significant factors affecting H2 production and yield. Moreover, the 3-D response graph has shown the inhibitory effect of methanol, soap, and glycerol on H2 outcome. The non-linear regression modified Gompertz and Logistic models have established a good fit with the experimental hydrogen production data, having a coefficient of determination (R2) of 0.99 and 0.996, respectively.