The Changing and Distribution Laws of Oxygen Transfer Efficiency in the Full-Scale IFAS Process

The integrated fixed-film activated sludge (IFAS) process has been widely used in the upgrading of wastewater treatment plants (WWTPs). The oxygen transfer efficiency (alpha OTE) is of great significance to the design and operation of the IFAS process. The carrier filling ratio (CFR) and aeration type are two critical factors affecting alpha OTE and standard oxygen transfer efficiency (alpha SOTE). However, the distribution and changing laws of alpha OTE and alpha SOTE in the full-scale IFAS process areunclear. To optimize the operation of a WWTP and to improve the alpha OTE of the aeration systems, several off-gas tests were conducted under different aeration types and different CFRs. The results show that for the aerobic tank investigated (the ratio of length and width was 8:1), the alpha OTE and the alpha SOTE of the middle of the aeration systems were higher than those of the other two sides. However, the reason for the low alpha OTE at the beginning and the end of the tank may be different. Coarse-bubble aeration systems had a lower alpha OTE and almost the same oxygenation capacity (alpha SOTE) as the fine-bubble aeration systems under constant CFR (43%). The average alpha SOTE (18.7-28.9%) of the hybrid aeration systems increased with increasing CFR (7.7-57.7%), and different locations exhibited different degrees of change. The results reveal the distribution and changing law of the alpha OTE of aeration systems in the IFAS process, and attention should be paid to the improvement of the OTE of the plug-flow IFAS process.