 We are discussing the air sterilization system that is the second part of the oxygen delivery system. So, as we have seen that the Teflon filters are mostly used on a small scale fermenter, but the sterilization of the inlet and the exit air in large scales bioreactors more than 10,000 litre capacity that can present a major design problems because on a large scale filtration is very expensive process. The filters also have a very expensive material and then they are their other problems. So, it is very difficult to make and the make the filter and then their energy requirement that is very considerable factors while designing, while selecting the filtrate material or a different filter for large scale fermenters. As we know that heat sterilization is an alternative option apart from the filter system heat sterilization system is also used. So, the steam can use to sterilize the air in older style compressors it was possible to use heat generated by the air compression process to sterilize the air because sometimes when the compressor compress the air in that process heat is also produced when that heat is produced. So, that is automatically helped to sterilize the air, but at that time the heat is required and the temperature is required created by that compressor should be that must need the sterilization requirement. But if we say if we use that compressor heat just for the sterilization of the air then before supply to the fermentation vessel then that has to cool down to the required temperature that is needed inside the fermenter. So, that is why before injecting into the fermentation vessel that there should be a multi-device cooled system is required that is attached to the fermentation. So, that is very critical mostly the in a small scale reactors we can see here that these are the small Teflon type, but in case of the high scale large scale this is the mostly the HEPA filters. Before talking about this we are discussing about the sterilization of air through heat either through the dry heat either through the compressor heat, but here I want to talk here about this that on a large scale fermenters that mostly the HEPA filter high efficient particular particulate resistance filters are mostly used. You can see in this slide the arrangement and the packing of that material just to have the pore size of 0.2 micron to 0.45 micron. But this is a small size of HEPA filter that is mostly used in different fermentation and other biomedical equipment, but as we know that we are talking about the air sterilization and then the condenser is needed just that is the simple heat exchanger through which the cool water is passed around the air chambers that just to maintain the temperature. So, in such case there is another problem when the air has to exit from that then there is the volatile substances and then air has to pass through that then there is the fermenter should be attached with the condenser. So, before exit the air outside then that should pass through the condenser and condenser should be linked with the chilled water. So, that is why that minimize there are two role of that condenser one is that reduce the escape of the volatile compounds on other hand that also reduce the evaporation loss through the fermentation. So, the dry the air also prevents the blocking of the air exit air filter with the water. But in problem of using the filter on the exit point because when the air pass through the medium that mostly become wet and that is the more chances of the choking or the blocking of the exit filters. So, in such case we have to be very careful because sometimes when there is a blockage of the air from the outside in an exit point then what happen there is a continuously rise of the pressure. So, in case of the laboratory scale fermenter when the vessel is made up of the glass then there is a chance of burst. So, we have to be very careful while maintaining that the pressure on exit point.