An assessment of oxygen transfer efficiency in a gas permeable hollow fibre membrane biological reactor
The clean water oxygen transfer efficiency (OTE) of a full scale non-porous hollow fibre gas permeable (GP) membrane (surface area of 500 m2) was evaluated at inlet air pressures of 1.2, 1.4, and 1.8 atm using two established testing methods. To form a basis of comparison with traditional aeration technologies, additional testing was done with conventional aerators (fine bubble and coarse bubble diffusers) replacing the GP membrane. OTE can be established based on the re-aeration of deoxygenated water or by monitoring the catalytic oxidation of a sodium sulphite (Na2SO3) solution. In this study, OTE values determined by sulphite oxidation (SOTES) were consistently higher than those established during re-aeration (SOTER) suggesting that the chemical reaction was enhancing the mass transfer. The chemical reaction was sufficiently fast in the case of the GP membrane, that the gas phase limited the mass transfer. The GP membrane operating at 1.2 atm had a SOTES of 70.6% and a SOTER of 52.2%.
SOTER for the coarse bubble and fine bubble diffusers were 3.8% and 23.6%, respectively. This is comparable to the manufacturer's values, corrected for depth of 3.4% and 18.3%, respectively. Particularly, the derived OTE values were used to evaluate differences in energy consumption for a conventional treatment plant achieving carbon removal and nitrification. This analysis highlights the potential energy efficiency of GP membranes, which could be considered for the design of the membrane modules.
Keywords: energy, gas permeable membrane, non-porous membrane, oxygen transfer efficiency