Aeration circulating bioreactor is one kind of bioreactor with aerating riser located at letdown area for wastewater treatment

and there often is packing in the down area as carriers for growth of microbes.Hydrodynamics and mass transfer characteristics of the bioreactor were studied by changing flux(Vl)and velocity(Uld)of circulation liquid

and variance of residence time distribution function(σθ2).There is a better power law correlation between Vl and gas flow(Vg)whether there is packing or no packing in the down area and whatever various sectional area ratios of the aerated riser and the bioreactor(Ar/Are).With increase of Ar/Are

Vl and Uld go up first and then down and the extreme values appear at Ar/Are 0.11.Compared with the packing-free bioreactor

for packing bioreactor both Vl and Uld decrease but value of σθ2 increases

so liquid mass transfer is improved.For bioreactor with parking at the conditions of Ar/Are 0.11

liquid influent 0.1 m3·h-1and the gas flow 0.5-3.1 m3·h-1

the flux of circulation liquid flow is 9—28 times larger than that of liquid influent i.e.from 0.9 m3·h-1 to 2.8 m3·h-1 and σθ2 larger than 0.9.Therefore

the aeration circulating bioreactor is of higher liquid mass transfer such as liquid mixing and diluting

and can be directly used for treatment of high concentration wastewater.