Dynamic Behavior Of Bubble In A Bioreactor For Methane Biodegradation

In the process of coal mining,methane present in coal or surrounding rock in a free or attached state will be diluted and drained to ensure safe production.However,this does not only result in a waste of energy,but also exacerbate the greenhouse effect.Methane is the second largest greenhouse gas after carbon dioxide,but methane has the potential to make climate warming 25 to 30 times larger than carbon dioxide.In recent years,with the rapid development of biological engineering and environmental engineering,the use of biochemical transformation technology for coal mine gas control has become a very forward-looking and challenging research field.This work is towards the background of the bio-degradation of methane by methane oxidizing bacteria.Bubble dynamics in methane oxidizing bacteria suspension were studied more deeply.The mass transfer of CH4 and O2 mixed gas and the distribution of methane oxidizing bacteria around the bubbles in the multi-scale bioreactors were also explored.Visualization experiments were carried out in this work to investigate bubble dynamic behaviors during growth,detachment,bubble inrush,coalescence and rising by changing the gas flow rate,cell concentration,capillary inner diameter,angle of inclination,center distance in the multi-scale bioreactors.The experimental results provided a theoretical guide for gas distributer design and bioreactors operation.The main conclusions are as follows.(1)Methane oxidizing bacteria moved and enriched at the higher concentration of CH4 and O2 near the gas-liquid interface.When the mixing ratio of CH4 and O2 was 1:1,the higher the concentration of bacteria in the suspension was,and the smaller the initial volume of the bubble was,it was more conducive to the transmission and degradation of the mixed gas.(2)Bubble inrush resulted in a significant gas-liquid interface fluctuation,enhancing the mass transfer of gas mixture.The equivalent departure diameter and departure volume of the leading bubble were not much different under various gas flow rates.(3)After coalescence,the gas-liquid interface of bubble began to shock because of the reduced overall surface area of the system and the surface energy converted into mechanical energy.In confined space,the leading bubble was in contact with the front and rear walls,and when the shock wave of the leading bubble interface was in contact with the wall,the mechanical energy loss was large.(4)The flow rate of gas and liquid had an important effect on the flow pattern of bubbles in the microchannel,and the flow pattern had an effect on the degradation of the mixed gas by methane oxidizing bacteria.