Optimization of methane production from bituminous coal through biogasification

Abstract

To optimize methane production from bituminous coal through use of a well-studied microbial community derived from the same Illinois basin in USA, a total of 12 parameters were first evaluated by setting up 64 reactors following a 2-level factorial design. Among the 12 parameters, temperature, coal loading, particle size and ethanol were found to have statistically significant effects on methane content and yield from coal. Following screening, to identify optimal value for each significant factor, a Box-Behnken design necessitating 29 reactors was adopted. Optimal conditions provided by the Design of Expert software for the highest methane yield were: temperature, 32 o C; coal loading, 201.98 g/L; coal particle size, < 73.99 µm; and ethanol at 300 mM. Under these optimum conditions, the predicted methane yield and content was 2,957.4 ft 3 /ton (83.7 mm 3 /ton) and 74.2%, respectively. To confirm the predicted results, a verification experiment was conducted, where a methane yield of 2,900 ft 3 /ton (82.1 mm 3 /ton)

Evaluating approaches for sustaining methane production from coal through biogasification

“…To study the mechanisms involved in coal bioconversion, a majority of research has been performed in a laboratory environment where in situ temperature and/or pressure may be simulated in a batch process. As reported by different researchers [9,[17][18][19][20][21][22][23][24], a common phenomenon has been observed: methane production (mass of methane per mass of coal) peaked and then either slowed down or stopped increasing after certain period of time. The possible explanations could be: 1) exhaustion of nutrients in the medium and coal used; 2) product inhibition: CH 4 , H 2 S and NH 3 in the headspace may inhibit microbial activities; 3) accumulation of toxic or inhibitory degradation products; and 4) the residual coal was not available to microbial cells [19].…”

“…In this study, the coal loading used was 20.2% (w/v) which was much higher than others reported. This loading was obtained through an optimization study [17] and toxicity from coal at this high content has not been observed for the microbial community used here. Results from the Group 1 reactors also revealed that coal was not the rate-limiting substrate.…”

“…Coal samples used in this study were the same as those described before [17,18,7,25]. Briefly, chunks of high volatile B bituminous coal from Illinois # 6, the Herrin seam were ground first.…”

“…Use of ethanol at this concentration for coal biogasification has been proven to be the optimal condition for maximizing methane yield [17]. To address the question of how much methane could be produced from ethanol and yeast extract and peptone included in the adopted nutrient solution by the target microbial community, three controls without coal were set up as detailed above.…”

“…All bottles were purged with N 2 completely and then incubated at 32°C under static conditions. Starting from day 10, the headspace gas in each bottle was released and measured according to a protocol reported before [17]. Briefly, when a needle was inserted into the headspace, the pressurized gas due to gas production from coal would escape to a 50-mL gas tight syringe connected to the needle.…”