COAL BIOBENEFICIATION FOR ELIMINATING SULFUR AND ASH BY IRON- AND SULFUR-OXIDIZING MIXOTROPHIC BACTERIA

• Main Author: Ratmi Nurhawaisyah, Sitti
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/37003
• Institution: Institut Teknologi Bandung

The elimination of sulfur and ash from coal has been studied continuously due to the sulfur emissions which causes acid rain that has an unfavorable impact on the environment. The sulfur compound contained in coal is generally divided into two major groups, i.e. inorganic sulfur and organic sulfur, where any form of sulfur has the opportunity to produce SO2 during the combustion process, which further develop an obstacle in the utilization. The organic sulfur in coal is covalently bound to its large complex structure and physical and chemical removal is challenging. Therefore, the biobeneficiation process has begun to be developed. It is based on the bacterial degradation of sulfur compounds which generates safer products and moreover remains the calorific value of coal. In this study, the biobeneficiation process has been optimized using two methods, namely biooxidation and bioflotation using an iron- and sulfur-oxidizing mixotrophic bacteria. The various experimental variable of biooxidation and bioflotation were tested to observe their effect on sulfur and ash elimination. A series of biobeneficiation experiments has been performed at various biooxidation parameters, including inoculum dosage, particle size, pulp density and biooxidation time. Meanwhile, the bioflotation processes including variation in pH of the slurry, inoculum dosage and pulp density. Biooxidation and bioflotation experiments were carried out in Erlenmeyer which were shaken at 180 rpm in a rotary shaker at ambient temperature and using Denver flotation cell, respectively. Proximate analysis, form of sulfur and calorific value were measured in accordance with ASTM D3174 (ash), ASTM D3175 (volatile matter), ASTM D3177 (total sulfur), ASTM D2492 (forms of sulfur) and ASTM D2015 (caloric value) standards. Mineral contents in coal samples were analyzed using XRD (X-Ray Diffraction). in addition, FTIR (Fourier Transform Infra Red) and SEM (Scanning Electron Microscopy) analyses were also conducted to determine the bacteria-coal interaction. The results of biooxidation experiments showed that Citrobacter youngae strain of SKC-4 and Pseudomonas plecoglossicida strain of SKCSH-9 were able to increase the sulfur elimination by 54.16% and 61.17%. Moreover the ash elimination were also increased to 51.75% and 55.37%, respectively. Both bacteria had the capability to eliminate sulfur and ash under biooxidation conditions of 20% (v/v) inoculums, the particle size of -28 + 35 mesh, 10% (w/v) solids and biooxidation time for 28 days. While the results of bioflotation experiments using Citrobacter youngae strain SKC-4 has achieved sulfur and ash elimination by 28.63% and 32.77%, respectively. The optimization processes were conducted at neutral pH (7) with 10% (v/v) inoculum and 10% (w/v) solids. The optimization process has shown a positive result in enhancing the sulfur and ash elimination. This suggested that biobeneficiation process is likely to be a promising method to be applied in larger scale, concerning affordable cost, environmentally friendly, milder condition, yet reduce the chemical reagent consumption.