Pure Oxygen Systems
With process efficacy so closely dependent on aeration and the ability to support a high microbial biomass, the use of pure oxygen to enhance the effective levels of the gas dissolved in the effluent has an obvious appeal. The UNOX process, which was developed by the Union Carbide Corporation is probably amongst the best known of the pure oxygen activated sludge systems and Figure 6.6 shows the general layout of the bioreactor vessels.
Pure oxygen obviously gives a better oxygen transfer rate per unit volume of the bioreactor than can be achieved using conventional aeration methods. In turn, this allows a heavier organic loading per unit volume to be treated compared with ordinary air-fed systems, which enables this system to be used to deal with stronger effluents and permits a high throughput where space is restricted. Typically these systems are fed using liquid oxygen tanks.
Despite their clear advantages, pure oxygen systems suffer with some major drawbacks. For one thing, the capital costs involved in installing them in the first place are considerable, as are their running costs and maintenance requirement. The pure oxygen itself represents an explosion risk, thus necessitating intrinsically safe operational procedures and, in addition, leads to accelerated corrosion of the equipment used.
However, for some applications and for certain kinds of effluents, they can prove particularly appropriate.